Symposium Organizers
Srikar Vengallatore McGill University
S. Mark Spearing University of Southampton
Joerg Bagdahn Fraunhofer Institute for Mechanics of Materials
Norman Sheppard MicroCHIPS, Inc.
GG1: Materials and Processes for MEMS
Session Chairs
Monday PM, December 01, 2008
Room 306 (Hynes)
9:30 AM - **GG1.1
Commercial MEMS Case Studies:The Impact of Changing Materials, Processes and Designs.
Jack Martin 1
1 Micromachined Products Div., Analog Devices, Inc., Cambridge, Massachusetts, United States
Show AbstractMinimizing risk is an important factor in new product planning because high volume breakthrough products require tens of millions of dollars to develop and bring to market. Sometimes risk can be minimized by following the IC model: build new devices on an existing process – just change the mask set. This approach obviously has limits. By adopting new materials and processes, we can greatly expand the horizon for “disruptive” products. This talk uses a case study approach to examine how changes in masks, materials and unit processes were used, and will continue to be used, to produce MEMS products for high volume applications.
10:00 AM - GG1.2
Nucleation, Growth, and Processing of Oriented Diamond Films for MEMS Applications.
Thomas Friedmann 1 , John Sullivan 1 , Subhash Shinde 1 , Ed Piekos 1
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractChemical vapor deposition (CVD) diamond films can be patterned and processed into simple microelectromechanical machines (MEMS) using standard micromachining techniques. Recently, improved nucleation of diamond on (100) oriented Iridium surfaces has led to the development of higher crystalline quality oriented diamond films. These films should have improved mechanical, electrical, and thermal properties over more conventional CVD grown films.The focus of this presentation will be on growth and processing of diamond films into simple MEMS devices suitable for simple mechanical and thermal property measurements. In particular, control of stress and stress gradients is important for successful device fabrication, and an in situ technique has been employed to measure the stress during nucleation and deposition. The magnitude of in-plane biaxial stress can be changed by altering the growth temperature and the methane to hydrogen ratio. Stress gradients through the film thickness can be caused by the evolution of the columnar grain structure that can be influenced by the nucleation conditions. ‡ Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
10:15 AM - GG1.3
Temperature Dependence of Mechanical Stiffness and Dissipation in Ultrananocrystalline Diamond Resonators.
Vivekananda Adiga 1 , Anirudha Sumant 2 , Sampath Suresh 4 , Chris Gudeman 4 , Orlando Auciello 6 , John Carlisle 3 , Robert Carpick 5 1
1 Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States, 4 , Innovative Micro Technology, santa barbara, California, United States, 6 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 , Advanced Diamond Technologies, Romeoville, Illinois, United States, 5 Mechanical Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractUltrananocrystalline diamond (UNCD®)films are promising for MEMS and NEMS applications, including RF-MEMS resonators, due to the superior physical properties of diamond such as high Young’s modulus, quality factor and stable surface chemistry 1 . This, together with the ability to grow smooth films uniformly over large areas at low temperatures has now enabled the co-integration of CMOS with UNCD devices. We have characterized UNCD films grown on silicon using hot filament chemical vapor deposition (HFCVD). Films are grown at 680 °C and have very little sp2 content revealed by near edge x-ray absorption fine structure spectroscopy. UNCD fixed free (cantilever) resonator structures designed for the resonant frequencies in the kHz range have been fabricated using conventional microfabrication techniques and are wet released. Resonant excitation and ring down measurements were conducted under ultra high vacuum (UHV) conditions in a decoupled UHV AFM to determine the Young’s Modulus and dissipation (quality factor) in these UNCD cantilever structures. The Young’s Modulus was found to be about 800 ± 50 GPa after adjusting for the overhang of the levers. The temperature dependence of Young’s modulus of these cantilevers revealed the characteristic Wachtman’s empirical relation whereby the Young’s modulus increased by about 3 % as the temperature was reduced from 300 °K to 135 °K. From this measurement the Debye temperature was estimated to be ≈ 1460 °K, (Debye temperature for single crystal diamond is 1860 °K). This is the first such measurement for UNCD and suggests that the nanostructure plays a significant role in modifying the thermo-mechanical response of the material. The quality factor of these resonators varied from 8000 to 15000 and showed a moderate increase as the cantilevers were cooled from 300 °K to 135 °K. The results suggest that surface and bulk defects significantly contribute to the observed dissipation in UNCD resonators. We do not observe dissipation peaks that would correspond to defect relaxations in the temperature range studied. Nonetheless, some reduction in dissipation is observed when the UNCD surface is treated with atomic hydrogen. This treatment removes contaminants, oxides, and non-diamond (sp2) carbon bonds, leaving an ideal UNCD surface with a predominantly monohydride termination and demonstrates the sensitivity of the quality factor to the surface chemistry. This hydrophobic but stable surface results in the reproducible quality factors even after the exposure to air unlike the silicon resonators. 1. “Are diamond MEMS’ best friend ?”, Auciello. O et al, IEEE Microwave Magazine, vol. 8, pp 61-75, 2007.
10:30 AM - GG1.4
Gold-Tantalum Nanocomposites as Structural Material for Nanomechanical Sensors.
N. Nelson-Fitzpatrick 1 , C. Ophus 2 , E. Luber 2 , Z. Lee 3 , V. Radmilovic 3 , D. Mitlin 2 , S. Evoy 3
1 Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada, 3 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show Abstract10:45 AM - GG1.5
A Novel Gap Narrowing Process for Creating High Aspect Ratio Transduction Gaps for MEM HF Resonators.
Steve Stoffels 1 2 , George Bryce 1 , Rita Van Hoof 1 , Du Bois Bert 1 , Robert Mertens 1 2 , Robert Puers 2 , Harrie A.C. Tilmans 1 , Ann Witvrouw 1
1 , IMEC, Leuven Belgium, 2 ESAT, K.U.Leuven, Leuven Belgium
Show AbstractMotivation and innovation: Microelectromechanical (MEM) High Frequency (HF) Resonators are a promising replacement for existing reference (quartz) resonators and filters due to their tiny size, integration capability, high quality factor and wide frequency range from tens of MHz to several GHz. However, for capacitively transduced MEM resonators, an efficient conversion between electrical and mechanical energy can only be achieved for air gaps in the range of 50-100nm. In this work, a novel process to create nanometer sized air gaps for HF mechanical resonators will be presented and tested in a poly-SiGe based technology. Our technology differs from existing methods as the electrode and resonator are patterned in a single processing step with initially relatively wide air gaps. The required operational width of the gaps is reached by a controlled narrowing of the wide air gaps. The novelty of this technique is that it enables the creation of narrow high-aspect ratio air gaps (e.g., 100nm gaps in 10 micron thick layers) without the need for complex lithography or high aspect ratio etching. Moreover poly-SiGe, chosen as the structural layer, can be deposited at low temperatures (<450C). This temperature is compatible with CMOS processing and therefore allows the fabrication of MEM resonators above CMOS. Concept: The trench narrowing process starts from relatively wide (~ 0.5 micron) transduction gaps, which are formed in the structural layer by normal i-line or DUV lithography and etch. The actual gap-narrowing is achieved by deposition of a second conformal layer. Two different processes are possible in case of a SiGe MEMS technology. The first process uses a boron doped (B-doped) (LP)CVD SiGe layer, which deposits conformally over the entire wafer. This layer is thus also deposited on the bottom of the gap, where it should be removed to avoid short-circuiting the electrode and resonator. The removal can be done using a DRIE etch with sidewall passivation, which is specially tuned to leave the sidewalls intact. The second process uses also a SiGe layer, but with an incubation time (e.g. undoped (LP)CVD SiGe) for growing on oxides, but not on conductive layers. So, this layer will preferentially deposit on the SiGe gap sidewalls and not on the bottom (sacrificial oxide) or top (oxide hard mask). The need for performing an etch after deposition is therefore eliminated. An extra, preferably CMOS-compatible, curing step to diffuse Boron atoms from the structural layer into the CVD deposited SiGe layer and to activate them (e.g. 30’ at 450C for 89% of Ge) may be needed if the selective layer is undoped.Results & Conclusion: We developed and successfully applied a trench narrowing technology to a SiGe based technology for integrated HF-MEM resonators. Current results with the conformal CVD layer show an improvement of the transduction gap aspect ratio (ASR) from 8:1 to 20:1. Using thicker conformal layers could further improve the ASR.
11:30 AM - GG1.6
A Double Polymeric Layer Encapsulation Process for Transplanting Assembly of Carbon Nanotubes into MEMS.
Soohyung Kim 1 , Hyung Woo Lee 1 , Sang-Gook Kim 1
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThis paper presents a novel assembly method of the individual carbon nanotubes (CNTs) for fabricating CNT atomic force microscopy (AFM) probes. The key idea is to grow individual CNTs on a separate substrate and to transplant a well grown CNT to a target location through encapsulation into a MEMS carrier. One of the essential steps in transplant assembly is to encapsulate the individual CNTs into double polymeric layers. We focus on the design, materials selection, and physicochemical interactions of single CNTs with polymers and etchants for transplanting assembly.An array of vertically aligned CNTs was grown by plasma enhanced chemical vapor deposition (PECVD) on the nickel catalytic dots defined on silicon substrates using electron-beam lithography followed by metal deposition and lift-off processes. We used a double polymeric layer encapsulation process with SU8 (top) and polymethylglutarimide (PMGI: bottom): the top SU8 forms the body of the carrier while the bottom PMGI layer holds the carrier until its release from the substrate and determines the length of the CNT tip. An analytic model using fluid and solid mechanics was developed to predict interactions of individual CNTs with liquid polymers during spin-coating processes. After each CNT was embedded into a MEMS scale polymer block which serves as a CNT carrier, transfer of a polymer block to the end of a tipless AFM cantilever forms a CNT AFM probe. No laborious weeding, trimming or welding process was required, and the transplanting assembly technique enabled reliable assembly of CNT tips on various AFM cantilevers. The wall structures of CNTs were characterized by transmission electron microscopy and Raman spectroscopy to confirm negligible effects of the polymers and etchants on the CNT tips. The length of exposed CNT tips corresponds to the thickness of the bottom PMGI layer (1.5µm). The effective radius of the CNT tips is 15nm resulting from the stacked cone shaped internal wall structures of CNTs grown by PECVD.The scanning experiment over a grating (3µm in period and 100nm in depth) shows that our CNT AFM probes scan the vertical trenches close to their vertical walls. The scanning on a biological sample (filament actins) demonstrates the potential of a CNT AFM probe to soft biological samples. The CNT AFM probe will work as a nanoscanning platform for biological samples. Handling and assembling individual nanostructures have been the biggest challenge in their integration into MEMS. The transplanting assembly method can open up the massive parallel assembly of nanostructures in a deterministic manner with high productivity.
11:45 AM - GG1.7
Bottom Up Microsystem Construction Strategies Built Upon3D Directed Self-Assembly of Metallic and Polymeric Nanostructures.
Robert Cohn 1
1 ElectroOptics Research Institute and Nanotechnology Center, University of Louisville, Louisville, Kentucky, United States
Show AbstractRecently our group has developed two distinct methods of directed self-assembly of extremely high aspect ratio nanostructures. In one method a periodic micromachined array of vertical pillars is hand-brushed with a liquid polymer or nanomaterial-polymer composite leading to the spontaneous formation of two-point suspended nanofibers air-bridges and trampoline–like membranes (S. A. Harfenist et al., Nano Lett. 2004, S. Pabba et al., ACS Nano 2007). In some cases fibers as small as 10 nm diameter and exceeding 100:1 aspect ratios have been made with these crude methods of application that are then driven to make precise structures through capillary force driven thinning and self-assembly. In a second method, surfaces patterned with thin films of silver, when dipped into gallium at it melting point, which is near room temperature, can spontaneously grow Ag2Ga nanowires of constant diameter on the order of 100 nm diameter and up to at least 110 μm in length (M. M. Yazdanpanah et al., J. Appl. Phys. 2005). The process is remarkable in that these freestanding needles can be grown individually at selected locations and with a desired orientation with respect to the surface. Additionally the needles are extremely flexible, tough and ruggedly attached to the surface (V. V. Dobrokhotov et al., Nanotechnol. 2008). These approaches enable the rapid, often one step addition, of true third-dimensional complexity to substrates, that after initial micromachining, are at best 2.5 dimensional.Following a brief review of these two methods of directed self assembly, this paper will consider several ways to add increased functionality to the nanostructures through standard additive and subtractive processing. Because the nanostructures already set the limit of resolution, these subsequent processing steps are not critically dependent on extreme resolution patterning systems, which simplify microsystem prototype development. Both the fabrication development of functional elements (e.g. elastomeric and electrostatic actuators, capillaries, optical guides, mechanical and electrochemical sensors) and their planned incorporation into complete biomicrosystems (e.g. microfluidic cell sorters, cell-based biosensors and complete single cell probe and manipulation stations built into a microscope cover slip) will be presented. A final example will describe plans for performing fabrication of point-to-point drawing of nanofibers air-bridges in a rather arbitrary 3D interconnection space, which uses actuated arrays of nanoneedles as a smart brush to draw the polymer fibers.
12:00 PM - GG1.8
Magnetostrictive Fe1-xGax Thin Films via Sputtering and Electrochemistry for MEMS and NEMS.
David Agyeman-Budu 1 , Patrick McGary 1 , Rajneeta Basantkumar 1 , Bethanie Stadler 1
1 , U Minnesota, Minneapolis , Minnesota, United States
Show Abstract12:15 PM - GG1.9
Dicing of Fragile MEMS Structures.
Peter Lange 1 , Norman Marenco 1 , Sven Gruenzig 1 , Stephan Warnat 1 , Thilo Semperowitsch 2
1 Microsystem Technology, Fraunhofer ISIT, Itzehoe Germany, 2 , Accretech GmbH, Munich Germany
Show AbstractConventional singulation of MEMS (Micro Electro Mechanical System) devices is carried out after protection of the fragile structure. Particles generated during dicing can block mechanical movements, mechanical load or vibration can deteriorate hyperfragile structures and, for example for bio-MEMS, cutting fluid can interact with sensitive layers. Protection is mostly done either by a capping process or by a resist, both on a wafer level. Membrane sensors for flow and pressure are usually protected by a temporarily layer, which is removed afterwards. However, this proceedure can cause yield loss. Inertial sensors, micromirrors and rf-MEMS are permanently protected by a capping layer initially for functional reasons. Devices which have open structures on both sides, generally afford new techniques since sensitive structures cannot be enclosed completely, since it could hinder functionality. Maho IR laser technology for (stealth) dicing is claiming to be the ultimate seperation technology for open and fragile structures. Seperation takes place by generating a polycrystalline area within the wafer along the dicing line and subsequent tape expansion thereby avoiding any particle generation. Typical examples are microphones as well as ink jet printheads, which are already fabricated in mass-production. Recently a chip to wafer assembly has been proposed in the European project DAVID (Downscaled Assembly of Vertically Interconnected Devices), in which a sensor chip is bonded face down on top of an ASIC wafer (3-D integration of MEMS and ASIC). Therefore it is needed to singulate before the MEMS is placed on the ASIC structure. This MEMS is a surface micromachined resonator structure with minimum linewidth of 1 µm in a comb structure which features the ISIT thick epipoly-Si process with a height of 11 µm. This device with an aspect ratio of 1:11 is extraordinarily sensitive to any particle contamination and thus appropriate for evaluation purpose. For a characterization of the dicing process with respect to particle generation, chipping occurrence and environmental conditions, the complete process flow has to be taken in mind: the dicing and the seperation of chips by expansion has to carried out in environments with at least a cleanroom class 100. The further transport to the pick and place tool and the die placement has to be done also under controlled conditions. The operating mode of the stealth dicing will be explained. The DAVID project is taken as a reference to evaluate the advantages and limitations of this new dicing method. The preconditions for successful singulations will be discussed. Optical and SEM inspection results will be presented as well as a yield estimation.
GG2: Microdevices and Micro/Nanofluidics
Session Chairs
Monday PM, December 01, 2008
Room 306 (Hynes)
2:30 PM - **GG2.1
BioMEMS Technologies for Regenerative Medicine.
Jeffrey Borenstein 1
1 Biomedical Engineering, Draper Laboratory, Cambridge, Massachusetts, United States
Show AbstractThe emergence of BioMEMS fabrication technologies such as soft lithography, micromolding and assembly of 3D structures , and biodegradable microfluidics, are already having making significant contributions to the field of regenerative medicine. Over the past decade, BioMEMS systems have evolved from early silicon laboratory devices to polymer-based structures and even biodegradable constructs suitable for a range of ex vivo and in vivo applications. These systems are still in the early stages of development, but the long-term potential of the technology promises to enable breakthroughs in health care challenges ranging from the systemic toxicity of drugs to the organ shortage. Ex vivo systems for organ assist applications are emerging for the liver, kidney and lung, and the precision and scalability of BioMEMS fabrication techniques offer the promise of dramatic improvements in device performance and patient outcomes.Ultimately, the greatest benefit from BioMEMS technologies will be realized in applications for implantable devices and systems. Principal advantages include the extreme levels of achievable miniaturization, integration of multiple functions such as delivery, sensing and closed loop control, and the ability of precision microscale and nanoscale machining to reproduce the cellular microenvironment to sustain long-term functionality of engineered tissues. Drug delivery systems based on BioMEMS technologies are enabling local, programmable control over drug concentrations and pharmacokinetics for a broad spectrum of conditions and target organs. BioMEMS fabrication methods are also being applied to the development of engineered tissues for applications such as wound healing, microvascular networks and bioartificial organs. Here we review recent progress in BioMEMS-based drug delivery systems, engineered tissue constructs and organ assist devices for a range of ex vivo and in vivo applications in regenerative medicine.
3:00 PM - **GG2.2
Nanofluidic Transport through Emerging Materials.
Narayana Aluru 1
1 Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractWater and ion transport in nanometer scale channels and pores - referred to as nanofluidic transport - plays an important role in determining the functional characteristics of many biological and engineering devices. In nanofluidic channels, the critical dimension of the channel can become comparable to the size of the fluid molecule, the surface-to-volume ratio can be high, the Debye length characterizing the length scale of ionic interactions can be comparable to the critical channel dimension, the composition of the channel wall as well as its roughness can effect the fluid/ion flow, and macroscopic definitions and assumptions for transport properties may not be accurate. For nanochannels with a critical dimension ranging from a few Angstroms to several tens of Angstroms, the fluid molecules can be geometrically confined and molecular phenomena such as the discreteness of the fluid (e.g. water) and fluid-surface interactions can become important. In this talk, we will present results discussing unique nanofluidic transport in carbon nanotubes and boron nitride nanotubes. In addition, when the fluid is under strong confinement a continuum (or classical) description of the fluid is not valid. We will also present results towards the development of a multiscale theory where atomistic physics is seamlessly integrated into classical continuum theories.
3:30 PM - GG2.3
High Pressure High Temperature Microfluidics for the Synthesis of Nanomaterials.
Samuel Marre 1 , Jongnam Park 2 , Moungi Bawendi 2 , Klavs Jensen 1
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractContinuous synthesis of nanomaterials in microfluidic devices offers several advantages over conventional macroscale chemical processes including enhancement of mass and heat transfer, reproducibility, potential for sensor integration for in situ reaction monitoring, rapid screening of parameters, and low reagent consumption during optimization. The synthesis of inorganic nanostructures generally requires high temperatures to decompose metal organic precursors and to generate nucleation followed by further growth. However, limitations on the number of compatible chemistries and the limited number of available high boiling point solvents have been a major obstacle in the rapid adoption of microreactors as a universal platform for nanomaterials synthesis. One way of improving syntheses in microreactors is to perform experiments at high pressure. Indeed, at sufficiently high pressure, virtually any common solvent, precursor, and ligands will remain either liquid or become supercritical (sc) at the temperatures required for the syntheses. In this context, we have developed high pressure high temperature continuous-flow Silicon-Pyrex microreactors for the synthesis of several nanomaterials. The microreactor consisted of a mixing zone maintained at room temperature and a reaction zone heated up to 400°C. The two zones are separated by a thermally isolating halo etch that allowed for a temperature gradient of over 250°C/cm. High pressure modular compression fluidic connections were realized by compressing the microreactor between two stainless steel parts using viton O-rings. In this configuration, the set-up allows reaching high pressure (up to 25 MPa) and temperature (up to 400 °C in the heated section). Model nanomaterials (semiconductors quantum dots - QDs, metal nanoparticles) were synthesized to demonstrate the process under pressure, while tuning several parameters: Solvent, temperature, residence time or concentration. In the case of QDs, we demonstrate that the use of supercritical fluids, in particular, shows strong influence on both the concentration of the QDs and on their size distribution, leading to small Full Width at Half Maximum (FWHM) of the emission peak. The use of high pressure high temperature microreactors demonstrated in this work opens new routes for nanomaterials synthesis in microfluidic devices by enlarging the set of solvents and phases (liquid, gas, supercritical) available.
3:45 PM - GG2.4
Design of Surfaces with Minimum Water Interaction for MEMS: Optimum Roll-off and Impact Resistance.
Tao Deng 1 , Kripa Varanasi 1 , Ming Hsu 1 , Nitin Bhate 1 , Judy Stein 1
1 Nano Advanced Technology, GE Global Research Center, Niskayuna, New York, United States
Show AbstractMany MEMS devices and systems involve interaction between solid surfaces and liquid, especially water. This presentation will discuss the interaction of both static water droplets and moving water droplets at different velocity with various surfaces as a function of surface texture and surface energy. A general guideline of designing surfaces that minimize the surface-water interaction will be presented. For the static water droplets, we found three different liquid wetting states: equilibrium Cassie, equilibrium Wenzel, and an intermediate state. The minimum-wetting hysteresis happened at the intermediate state, whose internal Laplace pressure was insufficient to overcome the energy barrier required to homogeneously wet the surface. The water droplet roll-off on textured surfaces can be related to a product of the length of contact line in contact with the surface with a “pinning parameter” that can be obtained from roll-off measurements on a smooth surface. The intermediate state had a short contact line and thus the roll-off performance was the best among all three states. In the case of moving water droplets, a simple pressure-based model was used to compare the water hammer and Bernoulli pressures with the capillary pressure. Experiments with moving water droplets showed very good agreement with the model prediction. This study offers general rules to optimize texture design for minimizing liquid-surface interaction, which will reduce the impact of the liquid to the surface and prolong the life of the devices.
4:30 PM - **GG2.5
MEMS and Nanotechnology to Test and Mimic Cell Function.
David LaVan 1 , Feng Yi 1 , Jian Xu 2 , Warren Ruder 3 , Philip Leduc 3
1 Functional Properties Group, Ceramics Division, NIST, Gaithersburg, Maryland, United States, 2 , Yale University, New Haven, Connecticut, United States, 3 Mechanical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania, United States
Show AbstractSmall scale devices produced using MEMS and nanotechnology enable the interrogation of cell behavior at a fine scale and the production of devices that mimic natural cell function. These technologies have been applied to study cell biomechanics; we have found that detailed analysis requires a detailed non-linear solution. The production of closely packed arrays of polydimethylsiloxane (PDMS) posts to measure basolateral cell forces has been developed, yet studies have shown that the relationship between force and displacement must include shear strain and large-deflection contributions. Likewise, electromagnet needles to apply tractions to cells can be simply produced, but these devices violate far-field assumptions and generally held rules-of-thumb. A detailed analysis including non-linear magnetic properties for the electromagnet core and particles yielded optimized designs that provide significantly more force per unit heat than previous devices or even optical tweezers. Tractions applied to cells have been used to activate stretch-activated channels that affect Ca2+ dynamics.Mimicking cell membrane function is another area where MEMS and nanotechnology open new opportunities. Natural cell membranes are normally supported on the actin cytoskeleton. Artificial planar bilayers are necessary to study transmembrane protein function and to create membrane protein dependent devices. Planar bilayers can be formed by painting, folding or vesicle fusion; however the bilayers formed by these methods do not resemble the natural membrane environment and are not very stable. Silica coated polymer nanofibers can be used to create a cytoskeleton-like scaffold to support lipid bilayers in a biomimetic manner. Similarly, lipid bilayers can be assembled around mesoporous silica cores to form an artificial cell that closely resembles natural cell structure and has been shown to support natural membrane protein function.
5:00 PM - GG2.6
High Resolution Nanopillar Scanning Electrochemical Microscopy-Atomic Force Microscopy Probes.
D. Comstock 1 , J. Elam 2 , M. Pellin 2 , M. Hersam 1
1 , Northwestern University, Evanston, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractAs electrochemical and biological systems are reduced to nanoscale dimensions, it becomes increasingly important to probe these systems at nanometer length scales. Scanning electrochemical microscopy-atomic force microscopy (SECM-AFM) provides for such high resolution imaging by integrating a nanoscale electrode into a conventional AFM tip and cantilever. These SECM-AFM probes allow for concurrent imaging of sample topography via conventional AFM feedback and electrochemical or biological activity via the integrated nanoelectrode.In this work, we demonstrate the fabrication of a new type of SECM-AFM probe utilizing a nanopillar geometry. Probe fabrication begins with a conventional AFM probe that is focused ion beam (FIB) milled to form a small platform at the apex. Onto this platform, a 40 nm diameter nanopillar as tall as 1-2 μm is deposited by electron beam induced deposition (EBID). This nanopillar serves as a template for the remainder of the probe fabrication. The electrode is then formed by evaporating a thin conductive film onto the nanopillar. The entire probe is then encapsulated by a thin insulating film of Al2O3 deposited by atomic layer deposition (ALD). ALD is ideally suited to this fabrication procedure as it provides a highly conformal, pin-hole free film, with excellent control over thickness. This allows for a high quality conformal insulating film on the high aspect ratio nanopillar, while also minimizing the overall dimensions of the probe by controlling the film thickness. Lastly, the probe is completed by FIB milling the nanopillar in cross-section to expose the conductive film as a nanoscale electrode at the probe apex.The fabrication procedure itself provides a number of advantages. First, the electrode dimensions are highly reproducible, as they are controlled solely by the nanopillar diameter and conductive film thickness. Second, the FIB milling procedures do not require high precision. Specifically, the final milling and exposure of the nanoelectrode can occur anywhere along the length of the nanopillar with the same resultant electrode dimensions. As a result, the fabrication procedure is very forgiving and reproducible.Prior to use in SECM-AFM imaging, the probes are characterized by cyclic voltammetry to determine electrode geometry and dimensions. Diffusion-limited currents reveal ring electrodes of 40 nm inner and 60 nm outer diameter, which is consistent with the nanopillar diameter and conductive film thickness from the fabrication procedure. Additionally, the SECM-AFM imaging capabilities of the probes have been demonstrated by imaging a number of model substrates.
5:15 PM - GG2.7
A MEMs Differential Scanning Calorimeter for Characterizing Interfacial Reactions and Hydrogen Storage and Release.
Richard Cavicchi 1 , L. Cook 1 , C. Montgomery 1 , W. Wong-Ng 1 , W. Egelhoff 1 , I. Levin 1 , S. Eustis 1 , U. Kattner 1
1 , National Institute of Standards & Technology, Gaithersburg, Maryland, United States
Show Abstract5:30 PM - GG2.8
Nanocalorimeter with a Layer of Mono-crystalline Silicon.
Yonathan Anahory 1 , Philippe Vasseur 2 , Rachid Karmouch 1 , Matthieu Guihard 1 , Leslie Allen 3 , Francois Schiettekatte 1
1 Département de physique, Université de Montréal, Montréal, Quebec, Canada, 2 Département de génie physique, École polytechique de Montréal, Montréal, Quebec, Canada, 3 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractGG3: Poster Session
Session Chairs
Joerg Bagdahn
Srikar Vengallatore
Tuesday AM, December 02, 2008
Exhibition Hall D (Hynes)
9:00 PM - GG3.1
Design and Fabrication of MEMS Piezoelectric Rotational Actuators.
Danny Gee 1 , Luke Currano 1 , Wayne Churaman 1
1 , U.S. Army Research Laboratory, Adelphi, Maryland, United States
Show AbstractMicrodevices have traditionally relied on translational motion for simplicity, which contrasts with the rotational movements that are predominant in nature (e.g. human joints). As Micro Electro Mechanical Systems (MEMS) continue to mature and increase in design complexity, the need to exploit and integrate rotation in MEMS devices has become more apparent, particularly for biologically-inspired and locomotive mechanisms. Previous studies have demonstrated electrothermal bent-beam rotary actuators that generate large displacements and large forces but suffer from high power consumption. In this work, an in-plane piezoelectric rotational actuator is proposed that provides free deflections on the order of 2.25° with applied bias voltages of <15V and significantly reduced current draw of ~0.2nA. The resulting power consumption is four orders of magnitude less than present rotational designs. The actuator utilizes the low-power, high-force characteristics of lead zirconate titanate (PZT) and a compact, offset-beam design to provide either a purely rotational or near-linear translational displacement. The device structure is comprised of a piezoelectric stack, a 1μm PZT layer placed between Pt electrodes, fabricated on a 2μm SOI wafer. The actuator consists of two parallel beams that are offset along a respective axis and are coupled together by a central yoke. When an electric field is applied to the stack, the transverse piezoelectric effect causes the beams to contract, thereby creating a torque about the center of the yoke. A free beam, normal to the offset beams, is extended from the yoke to amplify the rotational actuation, and measurements are taken using an integrated Vernier scale. In this paper we present the fabrication process for the actuator and provide test data that is consistent with a finite element model.
9:00 PM - GG3.10
Filling the Terahertz gap: Development of MEMS-based Active Metamaterial Structures and Devices at Terahertz Frequencies.
Hu Tao 1 , Kebin Fan 1 , Andrew Strikwerda 2 , Willie Padilla 3 , Richard Averitt 2 , Xin Zhang 1
1 Manufacturing Engineering, Boston University, Brookline, Massachusetts, United States, 2 Department of Physics, Boston University, Boston, Massachusetts, United States, 3 Department of Physics, Boston College, Boston, Massachusetts, United States
Show Abstract9:00 PM - GG3.11
Fabrication and Characterization of High-textured (002) AlN Piezoelectric Film and Its Application for 2.4 GHz FBAR Device.
Jiun-Yi Tseng 1 , Chao-Jen Ho 1 , Ming-Yi Yang 1 , Pin-Chou Li 1 , Hsin-Hung Pan 1 , Chih-Hsiang Chang 1
1 Material and Chemical Research Laboratories, Idustrial Technology Research Institute, Hsinchu Taiwan
Show AbstractAlN piezoelectric films have attracted considerable interest in recent years for the fabrication of FBAR and FSAR devices operating in the microwave region. It is well-known that the degree of c-axis orientation of the AlN films correlates directly with the electro-mechanical coupling. In this research, the AlN films were grown at different sputtering pressure of 1 ~ 10 mtorr with a constant dc-pulsed power of 600 W, nitrogen concentration of 75 %, and substrate temperature of 350 oC. The change of preferred orientation and microstructure of the AlN film have been investigated using x-ray diffraction, field-emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). AlN films with a preferred orientation of (002) have been successfully deposited on Pt (111) / Ti bottom electrode in an Ar-N2 gas mixture. The optimum FWHM of AlN (002) was about 1.5 ~ 1.6 degrees. As shown in the plane view image of SEM, the average grain size was estimated about 40 nm; the cross-sectional view revealed the highly aligned columnar structure of AlN. Smooth interfaces and surfaces of all the individual layer in a resonator are important for the FBAR devices. According to the AFM image, the average surface roughness (Ra) of AlN thick film is about 2.3 nm, which indicated a very uniform growth condition for FBAR fabrication. Finally, the FBAR device was manufactured and analyzed by integrating several core techniques, which included piezoelectric thick film deposition of AlN, dry etching of AlN, and XeF2 etching process, etc. The central frequency of the FBAR filter is about 2.48 GHz with an extremely low loss of energy (~ -3.7 dB).
9:00 PM - GG3.12
Very High Cycle-Fatigue Study of Polysilicon Films in Harsh Environments.
Michael Budnitzki 1 , Olivier Pierron 1
1 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractPrevious studies on very high-cycle fatigue behavior of thin silicon films suggest an environmental dependence of the degradation mechanism, the precise nature of which is still subject to debate. However, to the author’s knowledge no data for harsh environments is available in the literature. In the present study, 2-micron-thick polycrystalline silicon notched cantilever beam structures are used to investigate fatigue degradation in a high-temperature (80°C), high-humidity (90% RH) environment. The specimens are subjected to fully reversed sinusoidal loading at resonance (~40 kHz) with stress amplitudes ranging from 2.1 to 2.3 GPa, resulting in life-spans between 10^6 and 10^9 cycles. The degree and rate of degradation are assessed by monitoring the change in resonant frequency resulting from a change in compliance of the structure. Comparison to a reference set of S-N data obtained at moderate environmental conditions (30°C and 50% RH) reveals a strong tendency for faster degradation with increasing temperature and humidity. Specifically, the reference samples did not fail before 10^10 cycles at the stress levels specified above. The damage accumulation rate in the 80°C, 90% RH environment exceeds the reference by two orders of magnitude and tends to increase towards failure, as opposed to decreasing rates at 30°C, 50%RH. In an attempt to further the understanding of the underlying mechanism, a 3D finite element model incorporating semi-elliptical surface cracks and highly localized oxidation is being developed. In order to relate the simulations to experimental data, SEM fractography as well as transmission electron microscopy (TEM) of electron transparent, vertical through-thickness slices, will be used. The TEM analysis is expected to assess the presence and degree of localization along the specimen’s thickness of both nanometer-scale cracks and oxide thickening.
9:00 PM - GG3.13
Low-Cycle Fatigue Study of Single-Crystal Silicon Films.
Pierre-Olivier Theillet 1 , Olivier Pierron 1
1 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractUnderstanding the mechanisms for fatigue crack initiation and propagation in micron-scale silicon (Si) is of great importance to assess and improve MEMS reliability in harsh environments (e.g., high-g shocks, high temperature / high humidity environments). Accordingly, this investigation studies the low-cycle fatigue properties of single-crystal Si films using kHz-frequency resonating structures. The influence of resonant frequency (4 vs. 40 kHz), environment (30°C / 50%RH vs. 80°C / 90%RH), and film thickness (10 vs. 25 micron), on the resulting S-N curves and resonant frequency evolution is closely monitored. During each low-cycle fatigue test, consisting of successive bursts of cycles at large stresses, the resonant frequency is precisely measured (0.01Hz resolution) at very low stress between bursts. Fatigue lives as low as 500-1000 cycles can be accurately measured with this testing technique.We observe a continuous, monotonic decrease in resonant frequency for each fatigue test, indicating damage accumulation from the very first burst of cycles. In the 30°C / 50%RH environment, the average damage accumulation rate is larger for shorter fatigue lives, ranging from 10^-8 Hz/cycle (Nf~10^7 cycles) to 10^-6 Hz/cycle (Nf~10^4-10^5 cycles). However, the damage accumulation rates do not appear to correlate with applied stress (~2.6-3.4 GPa). This behavior may be explained on account of the inherent scatter in initial surface flaws in a brittle material like Si, resulting in different initial stress intensity factors for different specimens with the same nominal applied stress. The damage accumulation rates do not appear to be significantly influenced by the environment (30°C / 50%RH vs. 80°C / 90%RH) for fatigue lives shorter than 10^7 cycles, although they clearly are for longer fatigue lives. However, the S-N curve appears to be slightly shifted downward in the 80°C / 90%RH environment. The underlying mechanism for the low-cycle fatigue behavior of single-crystal Si films is discussed in light of these experimental data and scanning electron microscopy fracture surface evaluation.
9:00 PM - GG3.14
Stress Relaxation in Gold Films and its Influence on the Operation of MEMS RF Capacitance Switches.
Walter Brown 1 , Richard Vinci 1 , Xiaojun Yan 1 , Yuan Li 2 , John Papapolymerou 2
1 Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, United States, 2 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractAn RF MEMS capacitance switch is typically closed by using an applied electrostatic voltage to pull down a metal beam. Re-opening the switch relies on the stress in the deflected structure to provide the restoring force when the voltage is switched off. Because there is often trapped charge in the dielectric covering the bottom electrode of these switches, a force tending to keep the switch closed exists even when the actuating voltage is removed. If the stress in the film which is acting to open the switch decreases with time, the tendency of the switch to remain closed is exacerbated. Stress relaxation with time constants extending from seconds to days has been measured in micron-thick electroplated gold films. Both plastic (creep) and anelastic (viscoelastic) contributions to this relaxation have been identified and separated. The anelastic contribution has been shown to be well represented by a time dependent modulus of elasticity. Time dependent stress has been measured in response to single step changes in strain with strain maintained constant for hours and even days after the step. The single step measurements provide the time dependent modulus function. Time dependent stress has also been measured under cyclic strain conditions, as might be encountered in an operating MEMS switch. Applying linear response theory to simulation of the stress behavior under cyclic straining conditions, the measured stress is well accounted for. The consequences of this stress relaxation on the time dependent force available for switch opening has been calculated for two generic switch designs. The calculated available force is reduced as much as 20% over a switch operating time of 72 hours at room temperature.
9:00 PM - GG3.15
Nanomechanical Resonators for Specific Detection of Proteins.
Csaba Guthy 1 2 , Lee Fischer 1 2 , Vincent Wright 3 2 , Amit Singh 1 2 , Jillian Buriak 3 2 , Stephane Evoy 1 2
1 Department of Electrical and Computer Engineering, University of Alberta, Edmonton, Alberta, Canada, 2 , National Institute for Nanotechnology, Edmonton, Alberta, Canada, 3 Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
Show Abstract9:00 PM - GG3.16
Characterization and Simulation of MEMS Silicon Corrosion by Electrochemical Analysis and Finite Element Method.
Collin Becker 1 , David Miller 1 , Conrad Stoldt 1
1 , University of Colorado, Boulder, Colorado, United States
Show AbstractRecent studies from our group and others reveal that galvanic corrosion of polycrystalline silicon (polySi) and single crystalline silicon (SCS) during chemical post-processing results in porous silicon formation and highly detrimental mechanical and electrical effects in Micro-Electro-Mechanical Systems (MEMS). PolySi and gold have different electrochemical potentials, and once they are placed in a hydrofluoric acid (HF) solution that acts as the electrolyte, a galvanic cell forms. Various analytical techniques reveal and quantify the damage, but limited work exists to characterize the influence of electrolyte compositions, device geometry, and exposed silicon and gold surface areas during corrosion. In this work, we use electrochemical data from polarization characterization to validate corrosion test structures and model corrosion using the finite element method (FEM).Prior research from our group utilized micromachined test structures consisting of phosphorous doped polySi in contact with a gold metallization layer. By analyzing the test structures, the corrosion current density can be determined and compared against electrochemical characterization. In our electrochemical analysis, different responses were attained for varying electrolyte concentrations and makeup, types of silicon, lighting conditions, and cathode types. In addition, the surface area ratio of metal to silicon and geometry of test structures yield different current densities and structure damage. Predicting the extent and geometry of damage to a device is important in both device design and fabrication, allowing performance to be prescribed and damage to be mitigated. In the literature, others have used a heat transfer analogy governed by the Laplace equation, allowing a FEM based representation to model corrosion and electrochemical problems. In our own numerical analysis, the Butler-Volmer equation is used to describe the electrolyte-electrode interface. We determine the Butler-Volmer parameters directly from our electrochemical studies on several silicon types and electrolyte composition. Our FEM model shows excellent agreement with the test structures and the electrochemical polarization characterization. The literature shows that porous silicon formation is possible according to a galvanic corrosion process, but there is limited work related to MEMS specific systems. Our novel study of corrosion specific to microsystems adds an important contribution to the existing library of porous silicon research. We show that the damage to a MEMS device can be analyzed and predicted. That is, unique aspects of corrosion specific to microsystems, such as their three-dimensional nature and finite size, are accounted for in our analysis approach. Therefore, by manipulating the design geometry and surface area ratio of metal to silicon, damage can be predicted and minimized or cast upon select regions/structures.
9:00 PM - GG3.17
Resonant Fatigue Testing of Cantilever Specimens Prepared from Thin Films.
Kwangsik Kwak 1 , Masaaki Otsu 1 , Kazuki Takashima 1
1 Dept. Materials Science & Engineering, Kumamoto University, Kumamoto Japan
Show AbstractFatigue properties of thin film materials are extremely important to design durable and reliable MEMS devices. However, it is rather difficult to apply conventional fatigue testing method of bulk materials to thin films. Therefore, a fatigue testing method fitted to thin film materials is required. In this investigation, we have developed a fatigue testing method that uses a resonance of cantilever type specimen prepared from thin films. Cantilever specimens with dimensions of 1(W) x 3(L) x 0.01(t) mm3 were prepared from Ni-P thin films and Au foils. These specimens were fixed to a holder that is connected to an audio speaker acted as an actuator, and were resonated in bending mode. In order to check the validity of this testing method, Young’s moduli of these specimens were measured from resonant frequencies. The average Young’s modulus of Ni-P was 108 GPa and that of Au specimen was 63 GPa, and these values were comparable with those measured by other techniques. This indicates that the resonance occurred theoretically and this testing method is valid for measuring the fatigue properties of thin films. Resonant fatigue tests were carried out for these specimens by changing amplitude of resonance, and S-N curves were successfully obtained for Ni-P amorphous alloy thin films and Au foils.
9:00 PM - GG3.18
Bending of Pd-based Thin Film Metallic Glasses by Laser Forming Process.
Yuki Ide 1 , Masaaki Otsu 1 , Junpei Sakurai 2 , Seiichi Hata 2 , Kazuki Takashima 1
1 Dept. Materials Science & Engineering, Kumamoto University, Kumamoto Japan, 2 P&I laboratory, Tokyo Institute of Technology, Yokohama Japan
Show AbstractTo reduce size of MEMS devices and improve their performance, it is necessary to fabricate them with not only two-dimensional but also three-dimensional structure in micrometer order. On the other hand, metallic glasses have received considerable attention for MEMS devices materials. Metallic glasses are isotropic and homogeneous because of free from defects originated from the crystal structure. But they are brittle and difficult to deform plastically at room temperature. In the present study, laser forming was employed for bending Pd-based thin film metallic glasses. Working conditions such as laser power, scanning velocity were changed, and thin film metallic glasses were formed into three-dimensional structure. Thin films of Pd77Cu6Si17 having 0.028 mm thick, 10 mm long, and 1.45 mm wide, and thin films of Pd40Ni40P20 having 0.017 mm thick, 10 mm long, and 1.45 mm wide were used for specimens. A 50 W YAG laser was employed for forming. Bending angle was measured by a line scan type laser displacement sensor. From the experimental results, when scanning velocity was v=40mm/s and scanning number was N=80, bending angle of Pd77Cu6Si17 was θ=89.0° and the maximum at the laser power of P=3.0W. In the case of Pd40Ni40P20, the maximum bending angle was θ=86.5° when laser power was P=1.5W, scanning velocity was v=40 mm/s and scanning number was N=80. XRD analysis was carried out after laser forming and both materials did not crystallize. Comparing bending angle of thin films of Pd-Cu-Si with that of Pd-Ni-P, Pd-Ni-P films was much bent. But calculating from the rule that bending angle is proportion to laser power and inversely proportion to square of film thickness, bending angles of both materials were almost equal.
9:00 PM - GG3.19
Droplet Formation at Microfluidic T-junctions
Yu Xiang 2 , David LaVan 1
2 , Yale University, New Haven, Connecticut, United States, 1 Functional Properties Group, Ceramics Division, NIST, Gaithersburg, Maryland, United States
Show AbstractAnalysis of droplet formation in microfluidic systems is important to understand the operation of these devices, and to permit optimal design and process control. Droplet formation in microfluidic T-junction devices was studied using experimental and numerical methods. The simulations agree well with experimental data from PDMS devices; they show that droplet pinch-off is controlled not by viscous stress, but rather caused by pressure buildup after channel blocking due to the second phase. The period of droplet formation is dependent on velocity of the flow, but not viscosity or interface tension of the fluids. Analysis using dimensionless period, which is equivalent to dimensionless droplet length, shows that dimensionless period is controlled primarily by water fraction but is also dependent on velocity following a power-law relationship. Higher values of capillary number tend to extend the distance for droplet pinch-off. Droplet length does depend on flow velocity at low velocities, but reaches a relatively constant length at higher flow velocities. The coefficient of variation of droplet volume/length increases with increasing capillary number.
9:00 PM - GG3.2
Electrostatic Manipulation of a Dielectric Micro-particle Considering the Surface Conductivity by a Single Probe.
Atsushi Yamashima 1 , Shigeki Saito 1
1 Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, Tokyo Japan
Show AbstractIn this study, we have developed the technique of electrostatic manipulation of a dielectric micro-particle by a single probe. The manipulation system consists of three objects: a conductive probe as a manipulating tool, a conductive plate as a substrate, and a dielectric particle that dubs as a micro-particle. In manipulating 60-micrometer-in-diameter particles of polystyrene, when the probe-substrate voltage was applied just as a constant, we observed a phenomenon of the particle going up and down repeatedly between the substrate and the probe tip like a “micro-dribble”. In order to understand the mechanism of the phenomenon, we have proposed a physical model with resistance-capacitance (RC) circuit considering the surface conductivity of the dielectric particle. The model explains the phenomenon clearly in terms of the time required for a particle to be charged; the frequency of “micro-dribble” in experiment was in good agreement with the frequency predicted by the model. By the voltage sequence designed on the basis of the model,we experimentally demonstrated the electrostatic micromanipulation. Although the success rate, which was forty-two percent, still requires further improvement, the experimental result indicates the feasibility of the technique, which can be applied to future technology for micro-device packaging or assembly.
9:00 PM - GG3.20
Controlling the Wrinkling of the Bilayer Thin Films Electrothermally.
Shravan Chintapatla 1 , John Muth 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show AbstractWrinkling of thin films under strain is a universal phenomenon. The amplitude and period of the wrinkles thus formed in these thin films clamped at both ends are dependent on its strain and material parameters. In our study, wrinkling is observed in microscale for the double clamped thin films (L>W>>t) consisting of 200nm deposited low stress silicon nitride bridges fabricated by bulk micromachining under a critical strain. A bilayer system is formed with 30nm aluminum evaporated on to these bridges. At room temperature the bridges are essentially flat as the aluminum releases the stress in the thin film, however as electrical current passes through the aluminum layer electrothermal heating causes wrinkling of the bilayer. In addition the amplitude and the number of wrinkles can be varied in a controllable manner, allowing the material properties of the bilayer at various dimensions of the bridges to be investigated. A theory for the wrinkling for this system has also been developed.
9:00 PM - GG3.21
Degradation of Electrowetting Systems Utilizing Polymer Dielectric Layers.
Nathan Crane 1 , Alex Volinsky 1 , Du Ke 1 , Pradeep Mishra 1
1 Mechanical Engineering, University of South Florida, Tampa, Florida, United States
Show Abstract Electrowetting is the decrease in the apparent liquid/solid surface energy in an applied electric field. In most electrowetting applications, a potential difference is applied between the fluid and the electrode. A dielectric coating is typically applied to the interface to reduce electrochemical interactions. Electrowetting has shown great promise in many fluid manipulation applications, but the electric field can increase degradation of the dielectric coatings. The degradation must be characterized to enable design of reliable electrowetting systems but the mechanisms are poorly understood. This work reports on preliminary investigations of the degradation processes using a novel force measurement method. Typically, the electrowetting effect is measured by the change in contact angles. However, these methods are subject to hysteresis and require visual access for observation. In this work, electrowetting response is assessed by measuring the force applied to a fluid drop. These force measurements are used to measure the properties of a dielectric layer and detect degradation of the dielectric with time. This work addresses the impact of voltage polarity, salt concentration, and time on the degradation processes.
9:00 PM - GG3.22
Thermal Bubble Nucleation in Nanochannels: Simulations and Strategies for Nanobubble Nucleation and Sensing.
Manoj Sridhar 1 , Dongyan Xu 2 , Anthony Hmelo 1 , Deyu Li 2 , Leonard Feldman 3 1
1 Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, United States, 2 Mechanical Engineering, Vanderbilt University, Nashville, Tennessee, United States, 3 Physics and Astronomy, Rutgers University, New Brunswick, New Jersey, United States
Show AbstractNano-scale fluidic devices are ultimately limited by fundamental considerations, possibly different than those of other electronic systems. One unique example is the possibility of spontaneous bubble formation. Progress in the state of the art of nanofabrication now allows devices that may enable the experimental sensing of bubble nucleation in nanochannels, and the direct measurement of the bubble nucleation rate in water and other fluids. We report on two aspects in achieving this goal: 1) new molecular dynamics simulations of nano-bubble formation and 2) more sensitive nano-fluidic device structures potentially able to detect such bubble formation.We report the results of molecular dynamics simulations of thermal bubble nucleation in nano-confined argon and water systems using an isothermal-isobaric (NPT) ensemble to determine the conditions under which nanobubble nucleation may be expected. No bubbles were observed for either system under an external pressure of 0.01 - 0.1 MPa, even for temperatures much higher than the boiling temperature of the respective liquids at 0.1 MPa. To explain these observations, we hypothesize that bubble nucleation induces a pressure disturbance, which travels to the channel wall and reflects back to the nucleation site suppressing bubble nucleation. Simple estimates indicate that the characteristic pressure wave travel time is much shorter than the nucleation time. Our simulation results suggest limits on the nanochannel length scale and conditions under which nanobubble nucleation can be expected. Experimental sensing of bubble nucleation in a nanochannel reactor requires an advanced detection scheme. We report on the development of a new ultrasensitive sensor that has been used to detect the translocation of small particles through a sensing microchannel(1). The device connects a fluidic circuit coupled to the gate of a MOSFET that detects particles by monitoring the MOSFET drain current modulation instead of the modulation in the ionic current through the sensing channel. The minimum volume ratio of the particle to the sensing channel detected is 0.006%, about ten times smaller than the lowest detected volume ratio previously reported in the literature. The device sensitivity has been characterized as a function of the MOSFET gate potential indicating maximum sensitivity when the MOSFET is operating below its threshold gate voltage. In addition, the device sensitivity linearly increases with the applied electrical bias across the fluidic circuit. We demonstrate the application of the device concept as a particle sensor for polystyrene and glass beads on a variety of length scales, and extrapolate its use for the observation of spontaneous bubble detection.The authors acknowledge the financial support of the NSF Award Nos. CTS-0507903 and CBET-0643583, NIH Grant No. 5R01HG002647, and DARPA Grant No. W911NF-07-1-0046.References (1) M. Sridhar, et al., J. Appl. Phys, 103, 104701, (2008).
9:00 PM - GG3.23
Incorporation of Crack-Free Nanoporous Gold Films into MEMS-Based Sensors.
Oya Okman 1 , Jeffrey Kysar 1
1 Department of Mechanical Engineering, Columbia University, New York, New York, United States
Show AbstractThe nanoporous gold films have been a point of interest over the past decade in regard to their high surface area to volume ratio and the related potential applications such as biological and chemical sensors. Nanoporous materials are typically prepared by selectively removing the less noble component of an alloy, in a process called dealloying. In this study, a robust technique for fabrication of nanoporous gold is introduced, which leads to crackless, uniform nanoporous films over areas as large as 25 mm2. The two main fabrication steps, namely, the sputter deposition of the Au-Ag alloy film and the electrochemical dealloying, are presented. A simple prototype of a sensor is also fabricated, in which the device surface is coated with the nanoporous Au film. The process parameters that are critical in terms of tailoring the porosity and thus the effectiveness of a sensor are discussed.
9:00 PM - GG3.24
Atomic Layer Deposited and Molecular Layer Deposited Coatings: Film Properties and Device Performance.
David Miller 1 4 , Shih-Hui Jen 2 4 , Jacob Bertrand 2 4 , Dragos Seghete 2 4 , Shawn Cunningham 3 , Arthur Morris 3 , Yung-Chen Lee 1 4 , Steven George 2 4 , Martin Dunn 1 4
1 Mechanical Engineering, Univeristy of Colorado, Boulder, Colorado, United States, 4 DARPA Center for Integrated Micro/Nano-Electromechanical Transducers (iMINT), University of Colorado, Boulder, Colorado, United States, 2 Chemistry & Biochemistry, University of Colorado, Boulder, Colorado, United States, 3 , WiSpry, Inc., Irvine, California, United States
Show AbstractFilms grown using the atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques are being explored for the purpose of creating high integrity, minimally thick coatings. Applications include encapsulation of MEMS, nano-materials, and microelectronics for improved hermeticity, charge dissipation, and/or improved tribological performance. For example, diagnostic MEMS structures demonstrate a greatly reduced leakage current following ALD/MLD coating. Further, the performance characteristics of actuatable diagnostic structures are examined before and after coating. To meet the intended applications, knowledge of the mechanical properties of the coatings is required to facilitate design and to ensure reliability. In this work, the properties of elastic modulus, hardness, fracture toughness, and critical interfacial shear were characterized. Materials studied include ALD alumina as well as polymer-like MLD aluminum alkoxide (“alucone”) films. Properties of both homobifunctional (“AB”) and heterobifunctional (“ABC”) alucone films are reported here for the first time. The modulus and hardness of ALD alumina was found to be 199.9±10.0 and 10.5±1.2 GPa, respectively, using instrumented indentation The current study incorporates the effects of substrate compliance using a coupled finite element analysis (FEA) procedure [1]. The modulus of the alucone films are roughly 40.2±7.4 and 22.8±3.3 GPa, respectively. As at least moderate stress is expected to be present in the ALD and MLD films, the influence of stress on the measured properties was explored using FEA. Film toughness was examined using a cube-corner tip (radial corner cracking [2]), which is compared against toughness measurements obtained via tensile characterization using polymer substrates (channel cracking of brittle films [3]). Toughness may be estimated from tensile tests at the applied critical strain required to produce steady state crack propagation. Lastly, the critical interfacial shear between the films and a substrate is determined from the channel crack saturation density, according to a shear lag approximation. Several of the material properties measured are notably different than bulk materials, owing to the growth technique utilized, e.g. ALD produces amorphous alumina. References:1.J.A. Knapp, D.M. Follstaedt, S.M Meyers, J.C. Barbour, and T.A. Friedmann, “Finite-element Modeling of Nanoindentation”, J. Appl. Phys., 85 (3), 1999, pp. 1460-1474.2.J. Thurn, and R.F. Cook, “Mechanical and Thermal Properties of Physical Vapour Deposited Alumina Films: Part II Elastic, Plastic, Fracture, and Adhesive Behaviour”, J. Mat. Sci, 39, 2004, pp. 4809-4819.3.J.L. Beuth, “Cracking of Thin Bonded Films in Residual Tension”. Int. J. Solids Structures, 29, 1992, pp. 657-1675.
9:00 PM - GG3.25
Rapid Cell Manipulation by Rotating the Nanowires.
Hansong Zeng 1 , Joshua Ebel 1 , Yi Zhao 1
1 Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
Show AbstractOne-dimensional magnetic nanowires provide a powerful tool for investigating biological systems because such nanomaterials possess unique magnetic properties, which allow effective manipulation of cellular and subcellular objects. In this work, we report the rotational maneuver of ferromagnetic nanowires and their applications in cell manipulation. Ferromagnetic nanowires were fabricated using template-electrodeposition method. The porous permeable membranes (PPM) allowed magnetic nanowires growth in the pores of the membrane under an electrical bias. The electrodeposition process was driven by a DC voltage of 1.5 V. The resulting nanowires were about 200nm in diameter. The length of the nanowires was controlled by changing the electrodeposition time. Two types of rotational maneuvers are studied under different suspending conditions. The out-of-plane rotation of nanowires in the fluid is analyzed using Stroke flow assumption. The experimental results show that when the nanowires develop contacts with the bottom surfaces, the rotational maneuver under a modest external magnetic field can generate rapid lateral motion. The floating nanowires, on the other hand, do not exhibit substantial lateral displacements. Cell manipulation using skeletal myoblasts C2C12 showed that the living cells can be manipulated efficiently on the bottom surface by the rotational maneuver of the attached nanowires. Furthermore, the clustering of nanowires and nanowire-cell couples was demonstrated. Due to the intrinsic ferromagnetic properties, the nanowires interconnect when approaching to each other during the rotation. This can be utilized to build cell-cell pair or cell aggregation, which may help the fundamental study of cellular interaction and tissue engineering. This work is expected to add to the knowledge of nanowire-based cell manipulation and complement a full spectrum of controlling strategies for efficient use of nanowires in micro-total-analytical-systems. It will facilitate the mechanobiological studies at the cellular level, and provide useful insights for development of three-dimensional in-vivo like multicellular models for various applications in tissue engineering.
9:00 PM - GG3.26
Time Dependent Stress and Strain Behavior of Al Thin Films.
Seungmin Hyun 1 , Jungmin Park 1 , Hak Joo Lee 1 , Walter Brown 2 , Richard Vinci 2
1 , Korea Institute of Machinery & Materials, Daejeon Korea (the Republic of), 2 , Lehigh University, Bethlehem, Pennsylvania, United States
Show AbstractMetal films often play an important role as essential components in MEMS and semiconductor devices. A study of mechanical properties in metal thin films has been explored to understand the behavior that is different from it’s bulk counter parts. The accurate measurements of mechanical properties in thin films are very important for a design of the devices that often are operated under various conditions. In this study, we have used capacitance bulge system to investigate time dependent stress behavior of Al thin films under different strain rates. The thin films were prepared by e-beam evaporation of high purity Al onto 2 or 3mm ×12 mm rectangular silicon nitride membrane windows in silicon frames. N2 gas was used to pressurize to deform the rectangular membranes. The deformation of bulge height was measured based on changes of capacitance between the membrane and a fixed, closely spaced electrode. The strain rates result in the modulus changes of Al film. Modulus in the film is sensitive to the deformation rates of thin film. The modulus of Al films are in the range of 68GPa to 60GPa at the strain rates from 10-4 to 10-7. We have shown that time dependent stress changes are related to the viscoelastic behavior of thin films. The stress-strain calculation of Al films based on the linear viscoelastic behavior of thin films is presented to describe the strain rates effect on stress changes in the film.
9:00 PM - GG3.27
Screening Effect of Charge Carriers to the Piezoelectric Potential in a Bent ZnO Nanowire.
Yifan Gao 1 , Zhonglin Wang 1
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractWe applied a macroscopic-statistical theory to calculate how the free electrons screen the piezoelectric field in a bent ZnO nanowire. For a ZnO nanowire with non-negligible donor concentration, the tradition Lippman theory of piezoelectricity cannot be directly used because the conduction band electrons are free to travel all over the material. The redistribution of free electrons will give rise to two effects: on one hand, the carrier redistribution will decrease the piezoelectric potential as observed in piezoelectric nano-generators; on the other hand, such redistribution could create a carrier depletion region or an accumulation region as utilized in GaN/AlGaN HFETs. By considering the statistics of electrons along with the phenomenological thermal dynamics, we can understand how the existence of free electrons affect the piezoelectric voltage. The results show that for a typical ZnO nanowire with diameter 50nm, length 600nm and a typical donor concentration of the order of ~1×1017cm-3,electrons accumulate at the tensile side of the nanowire while the compressed side of the nanowire is partially depleted. Although the piezoelectric voltage will be reduced due to the free electrons, it can never be totally neutralized due to the statistics of electrons. Theoretical results also show that the positive side is always more significantly screened than the negative side. This means that the piezoelectric potential, which is generated by the non-mobile ionic charges, still exist even there are free carriers (electrons) exist in ZnO nanowires. This is consistent with the principle established for piezoelectric nanogenerators and piezoelectric FETs [1]. The theoretical results also reconfirm the experimental observation that the performance of piezoelectric nanogererators sensitively depends on the free electron concentration in ZnO nanowires.
[1] Z.L. Wang and J.H. Song “Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays”, Science , 312 (2006) 242-246.
9:00 PM - GG3.28
Development of Micro Methanol Concentration Sensor using Multi-wall Carbon Nanotube Films.
Dae Seok Na 1 2 , James Jungho Pak 2 , Jai Kyeong Kim 1
1 Center for Energy Materials Research, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Electrical Engineering, Korea University, Seoul Korea (the Republic of)
Show AbstractDirect methanol fuel cells have been the subject of considerable research in the last decade.Performance levels realized in cells, stacks, and systems show that this technology is a promising power source for a wide range of portable applications. A direct methanol fuel cell (DMFC) operates directly on a methanol fuel stream typically supplied as a methanol/water vapour or as an aqueous methanol solution in liquid feed DMFCs. The fuel streams in DMFCs are usually recirculated in order to remove carbon dioxide and to re-use the diluent and any unreacted fuel in the depleted fuel stream exiting the DMFC. The concentration of methanol in the fuel circulation loop is an important operating parameter because it determines the electrical performance and efficiency of the direct methanol fuel cell system. The methanol concentration in the circulating fuel stream is usually measured continuously with a suitable sensor, and fresh methanol is admitted in accordance with the signal from the sensor. There are many factors to consider in developing a methanol sensor suitable for DMFCs. These factors include sensitivity, cost, size, simplicity, reliability, longevity, concentration range, and dynamic response. In particular, reliability and low cost should be addressed. Methanol concentration sensors measure methanol concentration by means of detecting the variations of chemical roperties of the solution.In this work, a new interdigit-type micro methanol concentration sensor was designed and fabricated for measurement of methanol concentration in real time during DMFC system operation. The designed sensor operates based on the change of the dielectric constant and electrical conductivity. In order to improve sensor performance, methanol concentration sensor was fabricated using MEMS technology and multi-wall carbon nanotube film. The experiment was performed with various methanol concentrations. Capacitance changes were measured according to methanol concentrations and the sensors performance was improved. These results show that the proposed sensor could measure the degree of various methanol concentration with a high sensitivity and it is applicable to other DMFC systems.
9:00 PM - GG3.29
Fabrication of a Dualcore Gas Sensor using Single Walled Carbon Nanotubes and Semiconductor Nanowires Integrated into One Microplatform.
Myungho Chung 1 , Ki-Young Dong 1 , Youngmin Park 1 , Jinwoo Lee 1 , Jongheun Lee 2 , Seongdong Kim 3 , Byeong-Kwon Ju 1
1 Department of Electrical Engineering, Korea University, Seoul Korea (the Republic of), 2 Department of Materials Science, Korea University, Seoul Korea (the Republic of), 3 Semiconductor and Display Division, Korea Electronics Technology Institute, Seoul Korea (the Republic of)
Show Abstract9:00 PM - GG3.30
Local Growth of Carbon Nanotubes at the Tip of MEMS Heater.
Yung-Ching Chu 1 , Chia-Pao Hsu 2 , Cheng-Te Lin 1 , Chi-Young Lee 1 , Weileun Fang 2 , Tsung-Shune Chin 3
1 Materials Science and Engineering, National Tsin Hua University, Hsinchu Taiwan, 2 Power Mechanical Engineering, National Tsin Hua University, Hsinchu Taiwan, 3 Materials Science and Engineering, Feng Chia University, Taichung Taiwan
Show AbstractA MEMS device with a microheater and an electrothermal microactuator on SOI wafer was designed for locally growing nanomaterials and measuring their properties. The temperature of microheater is raised from 70 to above 1000 °C by Joule heating with a current of 4 − 45 mA. And the area with effective reaction temperature can be restricted to be ~ 10 μm2 in vicinity of heating tip. Using self-heating of microheater, a thin Fe layer could be deposited at the very tip of it by decomposing vaporized ferrocene, and then carbon nanotubes were catalytically grown by conventional CVD technique. The morphology of nanotubes was identified to be around 60 nm in diameter and 5 μm in length. The gap size between microheater with nanomaterials and conducting microactuator can be changed from 10 µm to contact by electrothermal stress with a current of 4 − 11 mA for measuring their properties. Such a device is expected to provide a platform for fabricating nanomaterials at the localized area and directly measuring their physical characteristics on the same die.
9:00 PM - GG3.31
A Novel Technique to Determine Elastic Constants of Thin Films.
Keckes Jozef 1 , Klaus Martischitz 1 , Matthias Bartosik 1
1 Department of Materials Physics, Univeristy of Leoben, Leoben Austria
Show AbstractA determination of elastic constants of thin films with the thickness in the nm range represents a serious difficulty. The purpose of this contribution is to introduce a novel self-consistent diffraction technique that allows for a rapid experimental determination of in-plane Young’s modulus and Poisson’s number of thin films by X-ray diffraction. The mechanical elastic constants are extrapolated from thin film X-ray elastic constants considering specific sample anisotropy. The X-ray elastic constants can be determined by a simultaneous application of sin2ψ and X-ray diffraction substrate curvature techniques. The basic idea resides in the fact to use a monocrystalline substrate with known mechanical properties as an internal standard to determine the relationship between the measured X-ray elastic strains and the macroscopic stress. The macroscopic stress imposed on a film which is deposited on a mono-crystalline substrate can be calculated from the substrate curvature using Stoney’s formula. The curvature is determined by the measurement of rocking curves on the substrate symmetrical reflections at different sample positions. This gives an opportunity to characterize the X-ray elastic strains for different hkl reflections and also the curvature of the substrate in one XRD system without remounting the sample. The knowledge of the macroscopic stress and the elastic strains can then be used to quantify X-ray elastic constants for different hkl reflections. In order to extrapolate mechanical elastic constants from X-ray elastic constants, however, it is necessary to consider the preferred orientation in the thin film. One of the main goals of this contribution is to demonstrate for which hkl reflection (and the value of the anisotropic factor Γ) the X-ray elastic constants are equal to their mechanical counterparts. This analysis is made by comparing calculated mechanical and X-ray elastic constants of thin films possessing various orientation distribution function f(g). The new approach is demonstrated on a variety of thin film systems like textured Cu, Al and CrN deposited on Si(100) wafers and measured using laboratory and synchrotron sources.This work was supported by Austrian NANO Initiative within the project "StressDesign - Development of Fundamentals for Residual Stress Design in Coated Surfaces”.
9:00 PM - GG3.32
Surface Modificated PDMS by UV-Vis Light for Microfluidic Device
Seisuke Kano 1 , Sohei Matsumoto 1 , Naoki Ichikawa 1
1 AMRI, AIST, Tsukuba, Ibaraki, Japan
Show Abstract9:00 PM - GG3.33
Metal Wafer Bonding for MEMS Applications.
Viorel Dragoi 1 , Gerald Mittendorfer 1 , Franz Murauer 1 , Erkan Cakmak 2 , Eric Pabo 2
1 Technology Development, EV Group, St. Florian/Inn Austria, 2 Technology Development, EV Group Inc., Tempe, Arizona, United States
Show AbstractWafer bonding developed during last decade as a powerful technique for Micro-Electro-Mechanical Systems (MEMS) manufacturing. Due to the large variety of MEMS types subsequently the requirements for the wafer bonding technology cover a wide range.Starting with the basic requirement of strong mechanical connection between two substrates, wafer bonding technology is nowadays developing into directions as providing simultaneously mechanical and electrical interconnection between substrates, mechanical connection and good thermal transfer between substrates, mechanical connection and sealing against various agents (moisture, vacuum sealing) or mechanical connection and optically transparent bonded interface.One particular area of interest is the use of metal layers as bonding layers. One may distinguish between two different types of processes: eutectic wafer bonding (based on formation of an eutectic alloy as bonding layer) and metal diffusion wafer bonding (known also as thermo-compression wafer bonding – based on a metal bond formation).The two types of processes are not only based on different principles but have also important influence on process conditions, equipment capabilities and finally on device performance.This work is presenting a short overview of the most important metal systems used in metal wafer bonding illustrated with examples of processes used for MEMS applications. Low temperature eutectic wafer bonding processes (<300°C) will be reviewed (Au-Sn, Au-In, Cu-Sn), as well as metal-metal bonding systems (Au-Au, Cu-Cu, Al-Al).A special emphasis will be allocated to wafer bonding process selection criteria depending on the application type.
9:00 PM - GG3.34
Nanocalorimetry: Calorimetry of novel materials of ultra-small volumes using micro and nanoelectomechanical devices.
Ozlem Senlik 1 , Hasan Guner 1 , Mecit Yaman 1 , Mehmet Bayindir 1 2 , Aykutlu Dana 1
1 Institute of Materials Science and Nanotechnology, Bilkent University, Ankara Turkey, 2 Department of Physics, Bilkent University, Ankara Turkey
Show AbstractCalorimetry holds an important place in chemistry and materials science, since thermodynamical properties of bulk materials such as phase transition temperatures and enthalpies can be obtained using calorimetry. However, conventional differential scanning calorimeters require large sample mass to acquire data with reasonable signal to noise ratio. It is also known that, nanoscale particles and materials show distinctly different thermodynamical properties than their bulk counterparts due to surface and interfacial effects, negligible in bulk material, become dominant at small scales where the total fraction of atoms at the surface is significant. It is therefore desirable to have a means of studying thermodynamical properties of small volume samples, ultimately a single nanoparticle. In this work, we propose and demonstrate an alternative approach for measurement of changes in heat capacity, elastic modulus and viscosity of small volumes (order of attoliters) of materials during thermal transitions using micro and nanoelectromechanical systems. A resistive heater placed on a mechanical platform that holds the sample to be studied is heated by applying a time varying external voltage. Both DC heating and small signal periodic heating are applied simultaneously. The micromechanical structure vibrates near its resonant frequency by electrothermal excitations. It is also demonstrated that measurement can be done simultaneously at multiple frequencies and mechanical resonant modes. During heating, DC deflection, amplitude and phase of the displacement of the mechanical device at the frequency of applied voltage is monitored. Effects of heat capacity, elastic modulus and thermal expansion coefficient variations at the thermal transitions such as glass transition, melting and evaporation on measured quantities are observed. Using analytical and numerical techniques, the behavior of the system can be modelled and quantitative thermodynamical information about the material properties can be obtained. Applications to thin films of As2S3 and Ge15As25Se15Te45 (GAST) chalcogenide glasses are demonstared. Limits of the technique are discussed.
9:00 PM - GG3.35
Microstructural Characterization of Frit Bonded Interfaces in MEMS Wafer Level Packages.
S. Sridharan 1 , V. Dragoi 3 , E. Pabo 4 , C. Erkan 4 , T. Tang 4 , D. Gnizak 1 , J. Henry 2 , B. Gardner 2 , K. Mason 2
1 Electronic Materials Division, Ferro Corporation, Independence, Ohio, United States, 3 , EV Group - Austria, Florian Austria, 4 , EV Group - US, Tempe, Arizona, United States, 2 Electronic Materials Systems, Ferro Corporation, Vista, California, United States
Show Abstract9:00 PM - GG3.37
Charging Processes in Silicon Nitride Films for RF-MEMS Capacitive Switches: The Effect of Deposition Method and Film Thickness.
Usama Zaghloul 1 , Aissa Abelarni 1 , Fabio Coccetti 1 , George Papaioannou 1 2 , Robert Plana 1 , Patrick Pons 1
1 LAAS, CNRS, Toulouse France, 2 Physics, University of Athens, Athens Greece
Show AbstractThe dielectric charging mechanisms occurring in MEMS based capacitive switches originate from the simultaneous contribution of various physical mechanisms among which the most important are the dipolar polarization, the space charge polarization extrinsic origin and the interfacial polarization. The contribution of trapping centers and dipoles depends strongly on the material deposition method. Additionally in the case of thin dielectric films the effect of the substrate roughness cannot be overruled.Up to now, the assessment of dielectric charging has been performed through current measurements in Metal-Insulator-Metal (MIM) capacitors and capacitance and/or voltage measurements in MEMS capacitive switches. These methods, although extremely useful, lead to results that depend strongly on the nature the device under test. The differences arising from these different experimental procedures allow the accurate determination of the contribution of dipole orientation to the dielectric charging. On the other hand the contribution of injected and trapped charges is determined with a reduced accuracy since only part of the injected charges is collected from the top electrode.This paper presents a systematic investigation of dielectric charging in silicon nitride thin films for RF-MEMS capacitive switches. The investigation took the advantage of Kelvin probe/EFM method to determine the surface potential induced at the SiNx surface by injected charges and simulate the charge injection through asperities. Both, the potential distribution and decay time constants have been investigated for charging induced by applying positive or negative bias to the EFM tip. The effect of charging has been investigated on dielectric films that have been deposited on silicon wafers and on gold, which have been evaporated on a silicon wafers. The later introduced additional roughness to the dielectric film surface. Finally, the effect of dielectric film thickness has been studied by depositing films with different thicknesses (100nm to 500nm).The SiNx films were deposited at 200C with high frequency and low frequency PECVD method. MIM capacitors have been fabricated to assess the dielectric films leakage and Metal-Insulator-Semiconductor (MIS) capacitors to determine the effect of space charge region on the EFM results.The experimental results revealed that the charging process is asymmetric, with time constants ranging from 150sec to 350sec and 400sec to 600sec when the tip injects negative or “positive” charges respectively. This is related to non uniform distribution of charge trapping centers. Finally, the present work points out that the discharging processes depend on the dielectric film thickness, which is caused from the contribution of the space charge polarization mechanism.
9:00 PM - GG3.38
Multi-Beam Cantilever Energy Harvesting Device for High Power and Broad Bandwidth.
Jung-Hyun Park 1 , Dongna Shen 1 , Song-Yul Choe 2 , Dong-Joo Kim 1
1 Material Engineering, Auburn Univerity, Auburn University, Alabama, United States, 2 Mechnical engineering, Auburn University, Auburn, Alabama, United States
Show AbstractA micro power generator using a piezoelectric micro-electro-mechanical system (pMEMS) was developed with a design of multi-beam array cantilevers. Although the MEMS piezoelectric energy harvesting device showed a promising demonstration, the device consisting of single cantilever is limited by its low output power (<3 µW) and narrow bandwidth due to a high quality factor. The MEMS device in this study is aimed at converting vehicle vibrations of low ambient frequency (~100 Hz) and high acceleration (~2-g) conditions. As a piezoelectric material in this device, highly piezoelectric Pb(Zr,Ti)O3 was used due to its high piezoelectric and electromechanical coefficient. PZT film was deposited on 4” silicon-on-insulator (SOI) wafer by a chemical solution deposition method. The silicon proof mass was integrated at the end of tip of cantilever after dry etching (DRIE), which reduces the resonant frequency and enhances the deflection for power conversion. This study addresses the development of MEMS fabrication and structural design related to the properties of the piezoelectric film stress and active mode (33 and 31) for robust cantilever arrays. The output signal of an energy harvester consisting of five cantilevers under 1-g vibration conditions were current (120 µA) and power (12 µW) from parallel connections in phase when cantilevers were connected with 10 KΩ load and parallel circuits. The output power was approximately four times higher than that of single cantilever devices. Other factors, such as structure design and circuit optimization, are discussed. Within the authors’ knowledge, this MEMS device is the first demonstration of a robust microfabricated array structure for an energy harvesting device.
9:00 PM - GG3.39
Enhancing Surface Porosity and Roughness on C-MEMS Based 3D Electrodes for Micro Biofuel Cells.
Varun Penmatsa 1 , Yan Yu 1 , Majid Beidaghi 1 , Chunlei Wang 1
1 , Florida International University, Miami, Florida, United States
Show Abstract Bio-fuel cell is a promising power source for implantable devices such as pacemakers, defibrillators, insulin pumps, drug delivery systems, etc. C-MEMS offer us the flexibility to fabricate high aspect ratio three dimensional (3D) structures. These 3D carbon arrays immobilized with enzymes can be used as electrodes in the biofuel cell. Our goal is increasing the surface area of carbon electrodes to improve immobilization of enzyme which could result in high sensitivity and output.In this work we developed higher surface area carbon electrodes by introducing porosity and activated the surface for immobilizing the enzyme. Treating the carbon post samples with oxygen plasma can both create surface roughness and activate the surface. Copolymer (F127) was mixed with SU-8 and evaporated during pyrolysis step inorder to create microporous structures. We observed surface micro/nano porosity by these techniques which may help in increasing the effective surface area for enzyme immobilization and retention. By varying the processing conditions in the oxygen plasma etching we could see the different surface morphologies. DSC and TGA were performed to investigate and understand the phase transformation effectS during the carbonization cycle. Detailed morphology and surface characterization will be presented at the meeting. This work is supported by NSF Project 0709085
9:00 PM - GG3.4
Measurement and Analysis of Structural Damping in Electrostatically-Actuated Silicon Carbide Microresonators.
Sairam Prabhakar 1 , Frederic Nabki 1 , Mourad El-Gamal 1 , Srikar Vengallatore 1
1 , McGill University, Montreal, Quebec, Canada
Show AbstractThe design of microresonators with low structural damping is a critical requirement for microelectromechanical systems (MEMS) used for applications in sensing, communications, imaging, and energy harvesting. Here we report the measurement and analysis of damping in metallized SiC microresonators that were fabricated using a low-stress, low-temperature (< 300 C), CMOS-compatible, surface-micromachining process developed at McGill University. The structural layer in this process is a 2 micron thick amorphous film of silicon carbide doped with 6 wt% graphitic carbon. The SiC layer is coated with a bilayer of chromium and aluminum; the former acts as an etch stop, and the latter serves as the metallization to enable signal routing and electrostatic actuation. A set of doubly-clamped flexural-mode beam resonators were microfabricated with natural frequencies ranging from 4 MHz to 22 MHz. The quality factors of these electrostatically-actuated microresonators were measured at low pressures of 1 mTorr in a vacuum chamber, and range from 400 to 1000 at room temperature. As the first step in identifying the dominant mechanisms of structural damping, we have performed a detailed analysis of thermoelastic damping in these multilayered structures. Thermoelastic damping is caused by irreversible heat conduction across thermoelastic temperature gradients in flexural resonators, and establishes an absolute lower bound on structural damping. We have developed an exact analytical model to compute the magnitude of thermoelastic damping in these SiC/Cr/Al resonators. An expression for thermoelastic damping is obtained in the form of an infinite series that is a function of material properties and beam geometry. No free parameters appear in this expression. A detailed comparison between theory and measurements suggests that thermoelastic damping is responsible for ~50% of the measured structural damping in these resonators. The role of other damping mechanisms (especially, anchor losses and internal friction due to crystallographic defects), and implications for the design of low-loss SiC-based microresonators, will be discussed.
9:00 PM - GG3.40
Measurement of Photonic Forces in Coupled Nanoplasmonic Structures.
Ozlem Senlik 1 , Hasan Guner 1 , Kemal Gurel 1 , Ozgur Oktel 2 1 , Aykutlu Dana 1 , Mehmet Bayindir 1 2
1 Institute of Materials Science and Nanotechnology, Bilkent University, Ankara Turkey, 2 Department of Physics, Bilkent University, Ankara Turkey
Show AbstractWe study theoretically and experimentally plasmonically enhanced optically induced forces in micromechanical structures. Surface plasmon-polaritons are electromagnetic waves propagating at the metal-insulator interfaces, confined evanescently in the perpendicular direction. In this work, we examine excitation of surface plasmons in MI and MIM systems and pressures induced at the metal surfaces due to these excitations both analytically and numerically. In the MIM systems the insulator is air and the top metal layer is 300 nm thick which can be considered as infinite. In the MI case, we observe a single resonance frequency at which reflection curve has its minima. At this structure the system supports only one plasmonic mode. However, in the MIM case due to two metal-insulator interface this single resonance frequency splits into two resonance peaks at a gap thicknesses in the range of approximately 1 μm. The resonances correspond to symmetric and antisymmetric modes of the system respectively. We calculate symmetric and antisymmetric electric field distributons along the insulator corresponding to the modes. The symmetric/antisymmetric electric field distributions generate attractive/repulsive forces between metal surfaces. In order to measure the photonic forces in coupled plasmonic systems, we fabricate metallic microbridges. We excite the surface plasmon resonances on air/silver interface by ATR prism coupling method. For determination of the resonances, we observe the reflection spectrum of incident light for a specified angle of incidence. Fabricated microbridges consist of 50 nm Ag film as bottom metal layer, 900 nm air gap, 300 nm Ag film as membrane (top) metal layer and 600-900 nm α-Si as support layer deposited on glass substrate. For the fabricated microbridge geometry, induced attractive force is calculated as 1μN/W. We propose to measure this force by monitoring microbridge deflection using interferometry and alternatively by monitoring changes in the reflected intensity of the beam exciting the plasmon. The measurement scheme is carefully designed considering spurious effects such as the effect of thermally induced stress and bending. Preliminary experimental results are presented.
9:00 PM - GG3.41
Electrical Readout of Graphene Mechanical Resonators with Controllable Geometry.
Changyao Chen 1 , Sami Rosenblatt 2 , Kirill Bolotin 3 , Horst Stormer 3 4 5 , Philip Kim 3 , Tony Heinz 2 3 , James Hone 1
1 Mechanical Engineering, Columbia University, New York, New York, United States, 2 Electrical Enginnering, Columbia University, New York, New York, United States, 3 Physics, Columbia University, New York, New York, United States, 4 Applied Physics and Applied Mathematics, Columbia University, New York, New York, United States, 5 Bell Labs, Alcatel-Lucent Technologies, Murray Hill, New Jersey, United States
Show AbstractWe demonstrate electrical actuation and detection of graphene-based electromechanical resonators. Single-layer graphene sheets were suspended and clamped at opposite ends by metal electrodes patterned with separations between 500 nm and 2 microns,and driven by gate voltage modulation. The high transconductance of graphene enabled readout by frequency down-mixing, resulting in low-noise currents with large signal-to-background ratios. Fundamental modes were observed between 10 and 100 MHz, scaling inversely with device length. The resonances were tunable over a 20 MHz range by means of a static gate voltage. These findings suggest the application as wideband variable frequency oscillators that can be integrated into existing CMOS.
9:00 PM - GG3.42
A Perturbation-Based Method for Extracting Elastic Properties during Spherical Indentation of an Elastic Film/Substrate Bilayer.
Jae Hun Kim 2 , Chad Korach 2 , Andrew Gouldstone 1
2 , SUNY Stony Brook, Stony Brook, New York, United States, 1 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
Show AbstractAccurate mechanical property measurement of films on substrates by instrumented indentation requires a solution describing the effective modulus of the film/substrate system. Here, a first-order elastic perturbation solution for spherical punch indentation on a film/substrate system is presented. Finite element method (FEM) simulations were conducted for comparison with the analytic solution. FEM results indicate that the new solution is valid for a practical range of modulus mismatch, especially for a stiff film on a compliant substrate. It also shows that effective modulus curves for the spherical punch deviates from those of the flat punch when the thickness is comparable to contact size.
9:00 PM - GG3.43
Microfabrication of Si/SiO2–Spherical Shells as a Path to Sub-mm3 Autonomous Robotic Systems.
Vladimir Vasilyev 1 , James Reid 1 , Richard Webster 1
1 , Air Force Research Laboratory, Hanscom AFB, Massachusetts, United States
Show AbstractA process for forming thin (1-3 micrometer) stacks of Si/SiO2 or SiO2/Si/SiO2 layers into spherical shells 0.5-3.0 mm in diameter is demonstrated as the base line for realizing sub-mm3 micro-robots. The fabrication process combines bulk and thin-film micromachining, design of novel masks, and multistage wet and dry etching to release the layers from the substrate. The released layers curl up, self assembling into a spherical shell. The radius of curvature of the released stack is a function of the type, thickness, and residual stresses in the layers. The diameter of the resulting shells is calculated using a mechanical model of the multi-layer stacks. This calculation is compared with measurements of fabricated spheres. The fabrication process is fully compatible with CMOS circuitry and future work will focus on realizing spheres with embedded CMOS circuits. When combined with a solar cell to provide a power source and an embedded capacitor for energy storage this will result in a functional micro-robot. Preliminary tests of electrostatic actuation have been performed. When fully realized, these micro-robots will have wide ranging applications.
9:00 PM - GG3.44
Transport of Charged Species Across Solid-State Nanopores.
Eyup Akdemir 1 , Michael Vitarelli 2 , Shaurya Prakash 1
1 Department of Mechanical and Aerospace Engineering, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States, 2 Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, Piscataway, New Jersey, United States
Show AbstractNanofluidic systems have generated tremendous interest due to the promise of revolutionary new technologies for separations, proteomics, and water purification. Here, we present transport studies across solid-state nanopores for simple ions, organic dyes, and proteins as a function of surface charge, pore size, and the electric double layer (EDL) thickness. The main goal is to establish a relation between wall-analyte interactions to determine nanopore transport characteristics. Solid-state polymeric nanopores with diameters 10nm-800nm with membrane thickness from 6-10μm were used. Therefore, the pores can have aspect ratios of ~1000 making the role of pore-walls critical. The experimental set-up consists of a permeation cell with nanopores separating two chambers with electrolyte solutions. A multi-technique electrochemical and optical characterization method is used to quantify transport. Nanopore wall charge density is manipulated by changing the bulk electrolyte pH, and the thickness of the EDL is manipulated by changing the bulk electrolyte concentration. Simple ions (potassium, phosphate, sodium, chloride), methylene blue (MB, positive charge at pH 7), and a protein mixture (Melittin, Apamin, Adolapin, Phospholipase A2, and Hyaluronidase) were evaluated for transport across the nanopores. Transport studies show that simple ions follow, as expected, Fickian diffusion for concentration gradients across the solid-state nanopores. However, when an electrical bias is applied across the solid-state nanopores, it was found that an AC bias enhances ionic flux to the permeate side by over 2 times as compared to a DC bias of similar magnitude. This enhanced transport is likely due to lower power factor losses in an AC field; however, further investigation is required. In comparing transport of macromolecules it was found that surface charge can play an important role in determining flux of larger molecules. For example, of the 5 proteins in the mixture only Hyaluronidase (positive charge, pH 7) was detected on the permeate side for a negatively charged 10nm pore diameter. However, no significant enhancement of protein transport was observed with an applied electric field. Further, no protein transport was detected without the surfactant SDS suggesting that the proteins must be linearized for transport through solid-state nanopores. For MB, it was found that by changing the bulk solution pH and hence the relative dissociation of MB the flux can be enhanced in the pH range from 5-9 suggesting that increased dissociation and a higher positive charge encourages transport across negatively charged solid-state nanopores. These results suggest the importance of not only surface charge but also of analyte species in transport processes. Further experiments to alter surface charge density through chemical modifications are expected to provide quantitative information about the role of surface charge. Such experiments are currently being pursued.
9:00 PM - GG3.45
Fabrication and Piezoelectric Characterization of AlN Mesa Structures.
R. Farrell 1 , A. Kabulski 1 , S. Yeldandi 1 , X. Cao 1 , P. Famouri 1 , J. Hensel 2 , D. Korakakis 1
1 Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, West Virginia, United States, 2 , National Energy Technology Laboratory, Morgantown, West Virginia, United States
Show AbstractAluminum nitride (AlN) films have been explored for piezoelectric and high temperature microelectromechanical systems (MEMS) applications but few device geometries have been explored in depth. One of the main advantages of using AlN as an active material is its ability to retain piezoelectric properties at high temperatures (>300°C). Typically, a metal layer covering the entire AlN film is used as a top electrode in d33 measurements [1]. In this work, circular AlN mesa structures, consisting of an AlN layer, with thicknesses between 200-1000nm, between two ~200nm metal layers, have been created. By decreasing the contact size and limiting the surface area of the AlN film, clamping effects will be reduced. This configuration also minimizes non-normal electric field lines between the top and bottom contacts and further isolates the d33 piezoelectric coefficient. The devices are constructed using two different fabrication methods and the piezoelectric and electrical properties have been studied. The first fabrication method is a bottom-up photolithography fabrication process. AlN films and a thin metal contact layer are reactively sputtered onto a patterned photoresist layer. Varying types of metal contacts were used to study the behavior of the metal-AlN interface. The second fabrication method is a top-down approach that is useful for creating structures using higher quality sputtered films as well as crystalline MOVPE-grown AlN films. Dry etch of AlN was performed using an Inductively Coupled Plasma (ICP) system with Cl2/BCl3 chemistry. The top-down fabrication method allows for more controllable, rapid, anisotropic etching, creating mesa structures with nearly vertical sidewalls.The aluminum nitride mesa structures exhibit a piezoelectric coefficient (d33) typical for aluminum nitride (4-6 pm/V) but can be further controlled (and even increased above 6 pm/V) depending on the thickness of the film, the diameter of the mesa, and the types of metals used for the electrical contacts. In order to further optimize the piezoelectric effect, multiple AlN and metal layers are used to create a mesa stack actuator and the piezoelectric and electrical behavior of these devices has been studied.The piezoelectric coefficient (d33) of AlN mesa structures will be measured at high temperatures, and the effects of oxidation on film quality and d33 of the mesa structures will be presented and discussed.Reference:[1] Kazuhiko Kano, Kazuki Arakawa, Yukihiro Takeuchi, Morito Akiyama, Naohiro Ueno, Nobuaki Kawahara. “Temperature dependence of piezoelectric properties of sputtered AlN on silicon substrate”. Sensors and Actuators A 130-131 (2006) 397-402
9:00 PM - GG3.46
Investigating the Stress and Crystal Quality of AlN Air-Bridges through Micro-Raman Scattering.
Sridhar Kuchibhatla 1 , Lee.E Rodak 1 , Dimitris Korakakis 1
1 Lane Department of Computer Science and Elelctrical Engineering, West Virginia University, Morgantown, West Virginia, United States
Show AbstractAlN thin films are being widely researched due to their high chemical, mechanical stability under harsh conditions in addition to exhibiting piezoelectric properties at elevated temperatures. The application of surface micromachining techniques is the only possible way to achieve sensors and actuators on substrates like sapphire and GaN/sapphire[1]. To fabricate heteroepitaxial nitride based system selective etching technique of group III nitride systems are currently being investigated [1]. SiO2 is a typically used sacrificial layer in Si MEMS technology. But epitaxial growth on SiO2 leads to polycrystalline growth. However it has been shown in our previous results that MOVPE growth of AlN on Si (111) using SiO2 as a sacrificial layer yielded robust and chemically stable bridges [2]. AlN bridges were also demonstrated on sapphire and GaN/sapphire templates.It was also shown that the micro-Raman scattering techniques can be used to determine the residual stress in the AlN bridges. Preliminary results based on the FWHM measurements of the E2 (high) phonon spectra, an indirect measure of the crystal quality, indicate that the substrate influences the crystal quality of the bridge. This work while building up on the preliminary results investigates the origin of the residual stress in the bridges and the corresponding crystal quality of the bridges. The research focuses towards mapping the stress profile by tracking the shift of the E2 (high) phonon mode and at the same time extracting the crystal quality of the bridge through the FWHM of the E2 (high) phonon mode across the width of the bridge using micro-Raman scattering before and after the removal of the sacrificial layer. Micro-Raman scattering measurements, AFM, SEM and optical images will be presented.[1] V.Cimalla, J.Pezoldt, O.Ambacher J.Phys.D: Appl.Phys., Vol 40, 2007, 6386–6434,.[2] L. E. Rodak, Sridhar Kuchibhatla, P. Famouri, Ting Liu, D. Korakakis, Mater. Res. Soc. Symp. Proc., Vol.1040, 2008.
9:00 PM - GG3.47
Aluminum Nitride Thin Film Based Surface Acoustic Wave Sensors.
A. Kabulski 1 , R. Burda 2 , V. Pagan 1 , D. Cortes 2 , O. Mukdadi 2 3 , D. Korakakis 1
1 Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, West Virginia, United States, 2 Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia, United States, 3 Center for Interdisciplinary Research in Cardiovascular Sciences, West Virginia University, Morgantown, West Virginia, United States
Show Abstract9:00 PM - GG3.48
Active Field Effect Capacitive Sensor Array for High-Throughput Biomolecular Screening.
Teena James 1 2 , Manu Sebastian Mannoor 1 2 , Dentcho Ivanov 1 2 , Bill Braunlin 3 , Les Beadling 3
1 Microelectronics Research Center, New Jersey Institute of Technology, Newark, New Jersey, United States, 2 Dept. of Biomedical Engineering, New Jersey Institute of Technology, Newark, New Jersey, United States, 3 , Rational Affinity Devices LLC., Newark, New Jersey, United States
Show AbstractMicro array devices represent a synergistic combination of microelectronics technology and molecular biology, which holds the promise of improving, the way many important molecular analysis are performed. In this work we introduce an active Field effect capacitive sensor with Metal-Oxide-Semiconductor (MOS) structure, for fast, massively parallel and highly selective nucleic acid analysis. Arrays of 50-100 Si-SiO2-Au sensing areas were fabricated using standard Si fabrication techniques. Multiple SS DNA probe sequences were immobilized on the Au electrodes using alkyl thiol linkages. The immobilization and hybridization events were monitored by measuring the Capacitance-Voltage (C-V) characteristics across the sensing elements. Due to the intrinsic negative charge of the DNA molecules, the immobilization of the single stranded probe sequences on the metal gate (Au), will effectively alter the distribution of charge carriers in the semiconducting region (Si) and produces a measurable shift in the C-V characteristics of the sensor. The presence of an additional layer of negatively charged DNA molecules due to hybridization with complimentary targets enhances this effect. The Depletion region of the C-V characteristics is found to be more informative for biosensing applications. Our experiments demonstrate that the rate and selectivity of hybridization reaction can be drastically improved by the application of an external electric field. Since oligomers in solution carry a net negative charge they can be transported towards the probe molecules immobilized on the sensor surface (Au) by application of a positive bias on the Au surface with respect to an electrode in solution. This electric field assisted transport of oligomers towards the immobilized probes will drastically enhance the rate of hybridization event. The movement of the target nucleotide molecules toward the immobilized probe sequences, facilitated by electric field can result in a concentrating effect of the target molecules near the surface enabling the binding of probe and target sequences at a much higher rate.The electric field induced transport of nucleotide molecules is also used for enhancing the selectivity of the sensing process. The sensor selectivity depends on the specificity of the binding between the target and probe sequences. The unhybridized target molecules which stay non-specifically bound on the sensor surface (Au electrode) will also contribute to the sensing signal. By applying an appropriate negative bias on the Gold (Au) surface these nonspecific target nucleotide molecules is released and repelled away from the sensing area, thereby eliminating their effect on the sensing signal.By adjusting the electric field to an appropriate level, selective dehybridization of the target-probe pair is also demonstrated, which is promising for single nucleotide polymorphism (SNP) analysis. This result is confirmed by the use for fluorescently labeled target sequences.
9:00 PM - GG3.49
3D Microsupercapacitor Based on C-MEMS with Improved Electrode Design.
Majid Beidaghi 1 , Varun Penmatsa 1 , Yan Yu 1 , Chunlei Wang 1
1 Mechanical and Materials Engineering, Florida International University, Miami, Florida, United States
Show AbstractWith the miniaturization of portable electronic devices, there is a demand of micro-power source which can be integrated on the semiconductor chips. Carbon-Microelectromechanical systems (C-MEMS) provide a possible way to fulfill this goal. C-MEMS is a simple two step process where patterned photoresist is pyrolyzed to carbon under inert atmosphere. The high aspect ratio three dimensional (3D) Carbon electrodes give us high effective surface area within a small footprint. It was found that a variety of surface structures and material properties can be obtained by changing the lithography conditions, baking time, temperature as well as pyrolysis environment. Now, our attention is focused on improving our three dimensional design and thus improve our microsupercapacitor’s performance. In our previous microsupercapacitor design anode and cathode arrays on two separate substrates were assembled to test the capacity. This time we have employed an improved electrode design by placing both anode and cathode on a cross finger like current collector on a single substrate. The capacity and cycle performance of the microsupercapacitor will be tested by AC impedance, cyclic voltammetry (CV) methods on the potentiostat and the surface morphology by FESEM. It is expected that the new design of carbon-carbon microsupercapacitor will possess higher capacity than our previously designed microsupercapacitor due to the decrease in the distance between cathode and anode arrays. This work was supported by DARPA grant (Number: HR0011-08-0036).
9:00 PM - GG3.5
Fabrication and Hot Switching Behavior of Electroplated Gallium Spheres for MEMS.
Yoonkap Kim 1 , David Bahr 1
1 School of Mechanical and Materials Engineering, Washington State University, Pullman, Washington, United States
Show Abstract Liquid metal microscale switches, often using mercury are sometimes used in place of solid-solid contact switches because of the ability to minimize damage from switching and the ability to make good contacts for electrical and thermal conductivity. However, mercury has potential health and safety problems, and is difficult to use at high frequency (kHz) operation due to poor adhesion between the liquid-solid contacts. One alternative to the mechanical and chemical problems of a liquid mercury switch is using soft metals, such as gallium (Ga) or tin (Sn), as solid metal sphere for switches that can melt at moderate temperature. Ga micro-spheres for switching operations were deposited on a substrate consisting of photolithographically patterned tungsten (W) films on SiO2 and Si substrates by electroplating, and the applicability for use in a microscale switch was investigated by characterizing the macro structure, hardness, and electrical performance of the switches in MEMS structures. The measured resistivity of the electroplated Ga droplets was similar to the theoretical value for pure Ga, and suggests that the electrodeposited Ga will be suitable for a solid MEMS switch. The hardness of the Ga sphere was 5.7 MPa. This suggests a maximum of 77+(-)15 μN can be applied to each 50μm radius Ga contact in the current configuration for switching applications. When the Ga spheres were investigated for electrical performance during hot switching, the resistance increased over six switching cycles, but the original lower resistivity was recovered after a 393 K thermal reflow process.
9:00 PM - GG3.50
Fabrication and Mechanical Testing of Monolayer Graphene Films via Nanoindentation.
Xiaoding Wei 1 , Changgu Lee 1 , Jefferey Kysar 1 , James Hone 1
1 Mechanical Engineering, Columbia University, New York, New York, United States
Show AbstractThe mechanical properties of monolayer graphene are measured via nanoindentation with an atomic force microscope. In this talk, we will concentrate on the details of the specimen preparation process and the mechanical testing regimen. The monolayer graphene films were suspended above circular wells that were fabricated into the surface of a silicon wafer using nanoimprint lithography and reactive ion etching (RIE). The graphene was exfoliated from a Kish graphite source using transparent tape and thinned by folding repeatedly. The thinned graphite was pushed down onto the patterned substrate, rubbed gently, and then the tape was detached. The deposited flakes were examined with an optical microscope to identify candidate graphene flakes with very few atomic layers. The number of graphene layers was confirmed using Raman spectroscopy. The details of the nanoindentation and the subsequent analysis of the force-displacement data will be discussed, especially the means by which initial contact between the nanoindenter tip and the graphene films was determined. The force-displacement behavior is interpreted within a framework of non-linear elastic stress-strain response, from which the second- and third-order elastic moduli are determined. In addition, we show that the breaking strength of the monolayer graphene represents the intrinsic strength of a defect free sheet.
9:00 PM - GG3.51
XeF2 Etching of Metallic Films.
Ozgur Celik 1 , Yi Xu 1 , Leszek Wielunski 1 , Eric Garfunkel 1 , X. Yan 2 , Ana Londergan 2 , Evgeni Gousev 2
1 Department of Chemistry, Rutgers University, Piscataway, New Jersey, United States, 2 , Qualcomm MEMS Technologies, San Jose, California, United States
Show Abstract9:00 PM - GG3.52
Growth of Epitaxial Potassium Niobate Film on (100)SrRuO3/(100)SrTiO3 by Hydrothermal Method and their Electromechanical Properties.
Mutsuo Ishikawa 1 , Takashi Fujisawa 1 , Shintaro Yasui 1 , Takafumi Kamo 1 , Masaki Hirano 1 , Tomoaki Yamada 1 , Minoru Kurosawa 3 , Takeshi Morita 2 , Hiroshi Funakubo 1
1 Innovative and Engineered Materials, Funakubo Lab., Tokyo Institute of Technology, Yokohama, Kanagawa, Japan, 3 Information processing, Tokyo Institure of Technology, Yokohama, kanagawa, Japan, 2 Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba, Japan
Show Abstract9:00 PM - GG3.53
Bio-compatible Micro-sensor for Blood Pressure Measurement using SiC Technology.
Gary Harris 1 , Nupur Basak 1 , Ken Wise 2 , James Griffin 1
1 HNF, Howard University , Washington, District of Columbia, United States, 2 WMIS, University of Michigan, Ann Abor, Michigan, United States
Show Abstract9:00 PM - GG3.54
Stability Improvement of Tactile Sensor of Normal and Shear Stresses Using Ni-Cr Thin Film Gauge.
Masayuki Sohgawa 1 , Hiroyuki Onishi 1 , Yu-Ming Huang 1 , Hiroto Tachibana 1 , Minoru Noda 2 , Takeshi Kanashima 1 , Kaoru Yamashita 2 , Masanori Okuyama 1 , Haruo Noma 3
1 Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan, 2 Graduate School of engineering of Science and Technology, Kyoto Institute of Technology, Kyoto, Kyoto, Japan, 3 Knowledge Science Laboratory, Advanced Telecommunications Research Institute International, Keihanna Science City Japan
Show AbstractTactile sensing is important to detect objects and their weight for various robots especially used for nursing-care and precise parts assembly. This tactile sensing of the robots must be similar to humans sensing. So in order o fulfill these requirements, we propose tactile sensor of micro-cantilevers which can detect both normal and shear stresses and have human-friendly surface. Micro-cantilevers were fabricated on SOI wafer ( ~2 μm thick Si layer, 1 - 2 μm thick BOX layer) by the surface micromachining and were adequately inclined using internal stresses produced by deflection control layer (200 nm thick chromium or 2 μm thick perfluoropolymer) . Micro-cantilevers are covered with elastomer (PDMS) to protect micro-cantilevers and to control stress detection range. When the stress is added to the surface of elastomer, the deformation of micro-cantilevers along with elastic polymer is detected as resistance change of strain gauge layer formed on the cantilevers. The normal and shear stresses can be distinguished by using two face-to-face cantilevers. When only shear stress is added to the tactile sensor, the summation of resistance change of two cantilevers becomes very small, but the differential of resistance change increases. In the case of normal stress, the summation increases but the differential becomes very small. Therefore, our tactile sensor can detect both normal and shear stresses independently.In earlier work, Si piezo-resistance gauge to sense the stress is used as sensing element, but Temperature Coefficient of Resistance (TCR) of the gauge is large and resistance drift may disturb the sensing precision. To decrease the resistance drift, we use NiCr thin film as strain gauge. TCR of NiCr changes with the deposition condition. Vacuum evaporation and sputtering are used for NiCr deposition, and sputtering temperature is changed between RT and 600°C. As a result, TCR is 0.054%/K (vacuum evaporation), 0.0082%/K (sputtering, RT) and 0.0065%/K (sputtering, 600°C). TCR of Si piezo-resistance is 0.25%/K but NiCr thin film decreases TCR well. By using NiCr thin film, temperature drift of this sensor is suppressed enough and the minimum sensitivity is obtained to be 0.5kPa (5g/cm2). This work was supported by NEDO.
9:00 PM - GG3.55
Engineering the Bi-based Materials for Piezoelectric Micro-Accelerometer.
Shanthy Sundaram 1 , Sushil Singh 2
1 Centre for Biotechnology, Allahabad University, Allahabad , U.P., India, 2 Si-MEMS Division, Solid State Physics Lab., Delhi, Delhi, India
Show Abstract9:00 PM - GG3.6
Fast and Controlled Integration of Carbon Nanotubes into Microstructures.
Wenjun Xu 1 , Richard Shafer 2 , Mark Allen 2
1 Polymer,Textile, and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Electrical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractSo far, many efforts have been made to incorporate carbon nanotubes into microelectronics such as chemical/biological sensors. To integrate this versatile material into microstructures or miniature devices, micromanipulation is required. Thickness control is also important to quantitatively study their properties in microsystems and optimize the device performance. However, the reported patterning methods usually involve high temperature catalyzing reactions or slow self-assembly process. In this paper, we report the results of fast and room temperature integration of CNTs into microstructures/device via electrophoretic deposition (EPD). Uniform 2-D and 3-D micropatterning of CNTs on large area has been successfully achieved within several minutes with the thickness controlled from 100nm to micro range. Several interesting characteristics of the EPD in confined microscale were also observed. Circular microwell arrays were fabricated via UV lithography of photoresist SU-8 on Ti/Si substrate and CNTs were then electrically directed into the microstructures. SEM images showed that CNTs assembled conformally around the microwell inner surface and generated a 20um wide circular belt around the well opening, creating a continuous 3-D coating in each isolated well. Similar assembly was revealed in rectangular microchannels, where the CNTs belt around the channel opening was in rectangular shape. Large scale orientation of CNTs inside the microchannels was observed, which may partly due to the directional movement of CNTs under the distorted electric field around the geometrically confined microstructures. The microstructures with different water wettability showed different patterning profile under EPD. Oxygen plasma turned the bare SU-8 from hydrophobic to hydrophilic by reducing the contact angle to 0° and increasing the surface roughness to 12.149 nm. The microwell arrays pattern exhibited higher hydrophobicity than the flat surface after plasma treatment. During EPD, CNTs were deposited across the whole surface of the hydrophilic SU-8 microstructures, instead of assembling locally in each isolated well as in hydrophobic ones. This wettability effect was verified in the case of gold interdigital fingers patterned on top of four isolation layers, parylene, SiC, SiNx and SiO2. The contact angles of the above four in the device system are 58°, 44°, 40° and 33° respectively. CNTs formed a continuous assembly on those hydrophilic non-conductive regions, which is unusual since EPD only happens on conductive surface. One possible explanation is that CNTs aqueous solution can form a good interface with the hydrophilic surface where the moving CNTs under dc field collide and aggregate with those in the interface layer. This effect can be reduced and 2-D pattern of CNTs on microelectrodes can be achieved. This approach can be further extended to fabricate 3-D patterns of multilayer materials on flexible substrate via the aid of micromolding technique.
9:00 PM - GG3.7
Through Silicon Vias in Micro-Electromechanical Systems.
Stephan Warnat 1 , Ramona Ecke 2 , Norman Marenco 1 , Wolfgang Reinert 1 , Sven Gruenzig 1 , Peter Lange 1
1 , Fraunhofer Institute for Silicon Technology, Itzehoe Germany, 2 Center for Microtechnologies, Chemnitz University of Technology, Chemnitz Germany
Show AbstractThe packaging of Micro-Electromechanical systems (MEMS) is an important process during their integration inside new sensor applications. Vacuum packages are required for inertial sensors for example, which is realized by a bonded cap to the MEMS on wafer level. The electrical contacts are located on the MEMS and therefore two different dicing steps are required in order to open the contact area and separate the devices. Mass flow sensors for gases or fluids are another example; corrosion of the pads and the wire bonds takes place if these areas are not protected from the media investigated. Organic protection layers (glob top) limit the device functionality and reliability under several measurement conditions. The realization of mass flow controllers for hot and/or toxic gases is not possible with this conventional packaging technology. Therefore, separation of the active MEMS and the interconnections area is preferable, which is possible with so called Through Silicon Vias (TSV). TSV connect the front side pad with the wafer rear side by a hole etched through the complete wafer thickness, followed by isolation and metallization deposition, structuring of the metal film and a final passivation layer. Solder balls or stud bumps are used to connect these MEMS with a substrate or directly to an ASIC. The requirements/challenges of TSV for MEMS applications are not comparable with TSV for integrated circuit devices. A wafer thinning down to a thickness from 10µm to 100µm, like it is frequently seen in other TSV approaches, changes the MEMS working behavior due the fact that MEMS devices are stress sensitive and wafer stress effects increase by wafer thinning. This paper shows a TSV integration approach inside MEMS-wafer with thicknesses of >300µm and a hole aspect ratio of 6 to 10. We will show a process flow which is so called "post-CMOS" compatible. That means that the maximum temperature of the technologies used is not above 400°C. This allows a high freedom for the MEMS designer in choosing the required materials like Al conduction lines in order to minimize the parasitics. The technological challenges of the given geometries will be discussed. Examples are the surface roughness of deep reactive ion etched holes or the step coverage of the deposited anorganic isolation layer and a TiN/Cu metallization. Electrical measurements of TSV test structures will be shown and the TSV reliability with respect to the MEMS will be discussed.
9:00 PM - GG3.8
Complex Pattern Formation by Adhesion-Controlled Anisotropic Wrinkling.
Pil Yoo 1
1 Chemical Engineering, Sungkyunkwan University, Suwon, Kyungki-Do, Korea (the Republic of)
Show Abstract The ability to fabricate and manipulate micro- or nano-structures is becoming essential in modern science and technology. While conventional photolithography and unconventional lithographic techniques can be used for fabricating these structures, manipulating the patterning to obtain various structures that are different from the original pattern of a photomask or mold is quite another matter. This manipulation, if it can be accomplished by self-organization, is attractive on account of its simplicity and the large area applicability that is made possible by the nature of self-organization. Wrinkle formation in layered systems is a ubiquitous phenomenon and is often encountered in many examples in nature. Wrinkles are believed to form spontaneously as a result of abrupt compressive stress that is generated when the stress exceeds the critical compressive stress of the system, and arises from a mismatch in expansion (or shrinkage) between the layers constituting the system. When a thin bilayer of metal and polymer is heated above the glass transition temperature (Tg) of the polymer, isotropic wrinkles form to relieve the mechanical stress generated. In confinement-induced wrinkling, the isotropic wrinkles transform to anisotropic structures through self-organization when a patterned elastomeric poly(dimethylsiloxane) (PDMS) mold is placed on the bilayer surface. Using the spatial length or the time duration of wrinkling as a manipulating variable, a unique structure of wrinkles that is difficult to produce with other methods can be generated over a large area. Here, we present that the work of adhesion at the interface between a PDMS mold and a bilayer surface can be used as a controlling parameter for pattern formation by wrinkling. In particular, manipulation of the mold surface energy and the accompanying change in the work of adhesion can be utilized to make the pattern concave or convex in shape. Normal positive convex wrinkles are formed when the work of adhesion is sufficiently larger than the total free energy of bilayer deformation. On the other hand, inverted negative, concave wrinkles form when the work of adhesion is comparable to the total free energy. Furthermore, we establish that the ratio of the mold pattern period to the intrinsic wrinkle wavelength can also be used to control the convexity. This robust and straightforward method could be useful for generating unique patterns for optics and microfluidics in a simple and cost effective manner.
9:00 PM - GG3.9
Effects of Aspect Ratio of Micro-sized Photoresist Patterns on Bond Strength between a Si Substrate with AFM Fracture Observation.
Chiemi Ishiyama 1 , Akinobu Shibata 1 , Masato Sone 1 , Yakichi Higo 1
1 P & I Laboratory, Tokyo Institute of Technology, Yokohama Japan
Show AbstractMicrofabrication techniques for micro-electro mechanical system (MEMS) devices are based on photolithography using two dimensional photoresist patterns in semiconductor industry, and moreover, three dimensional microfabrication techniques, “micromachining” are specifically utilized for microsized mechanical elements. MEMS devices consist of multi-layering fine patterns made by those two microfabrication techniques, thus, the devices include many interfaces between micro-sized patterns and/or a Si substrate. The delamination sometimes occurs at the interfaces in MEMS devices during the manufacturing and in use, because there are many sources of stress concentration, for example, natural defects, residual stress, contact angle and shape of photoresist patterns on a substrate, and so on. The fine patterns for MEMS devices are particularly thicker with higher aspect ratio than that of semiconductor ones. It should strongly affect the above factors which cause the delamination at the interfaces. Therefore, it is necessary to quantitatively evaluate the bond strength between three dimensional micro-sized pattern and Si substrate. In this study, bond strength between micro-sized pattern and Si substrate was evaluated, and especially focused on effects of aspect ratio of the fine pattern. Micro-sized cylindrical shape is employed as bond testing specimens on a substrate, because the simple shape makes easy to fabricate multiple specimens on a substrate under the same condition and to properly apply the bending load onto the end of the cylinder. Many micro-sized cylinders were fabricated on a silicon chip using a permanent epoxy photoresist, SU-8, because it is able to easily manufacture the thicker pattern with high aspect ratio using UV lithography. The diameter of the cylindrical specimens was 125 μm and the height is 88-110 μm, to convert into the aspect ratio, 0.6-0.9. Bond strength between SU-8 cylindrical specimens and Si substrate were measured using a mechanical testing machine for micro-sized materials, which has been developed in our previous investigation. The load was applied to the end of the cylinder at a constant displacement rate of 0.37 μm /s at 296 K in a clean room.All the load-displacement curves behaved in brittle manner and all the specimens were failed from the edge of SU-8 near by the bonding interface at the maximum load. The maximum bend moment is 9.2 x 10 -6 Nm in average and lineally increases with increasing aspect ratio. On the other hands, the maximum load is 104 mN in average and almost constant with increasing aspect ratio. In the other words, the shear stress at delamination is almost constant in this study. This phenomenon is discussed with fracture initiation site analysis by AFM.
Symposium Organizers
Srikar Vengallatore McGill University
S. Mark Spearing University of Southampton
Joerg Bagdahn Fraunhofer Institute for Mechanics of Materials
Norman Sheppard MicroCHIPS, Inc.
GG4: Micro/Nanomechanics
Session Chairs
Tuesday AM, December 02, 2008
Room 306 (Hynes)
9:30 AM - **GG4.1
CMOS-Integrated Stress Sensor Systems for Mechanical Sensing and Packaging Reliability Testing.
Oliver Paul 1
1 Dept. of Microsystems Eng., University of , Freiburg Germany
Show Abstract10:00 AM - GG4.2
Evaluation of the Mechanical Properties of Aluminum Thin Films as a Function of Strain Rate using the Wafer-Scale Microtensile Technique.
Joao Gaspar 1 , Marek Schmidt 1 , Jochen Held 1 , Oliver Paul 1
1 Department of Microsystems Engineering (IMTEK), University of Freiburg, Freiburg, BW, Germany
Show AbstractThe mechanical properties of ductile materials are known to be dependent on the rate of applied deformation. These dependences have been extensively studied on macroscopic bulk samples, the strength of which tends to increase at higher strain rates. Few data exist however for the microscale case. Ductile materials such as patterned metal films used in ICs and MEMS devices may be subjected to a wide range of elongations and elongation rates and, therefore, apart from obvious scientific interest, their mechanical characterization under such operation conditions is of utmost importance. This motivates the work presented here, which reports on the strain rate dependence of the mechanical properties of aluminum (Al) thin films using wafer-scale microtensile testing. Parameters extracted include the Young's modulus E, fracture strain εmax, ultimate tensile strength σmax, 0.2% offset yield strength σ0.2%, strength coefficient K and strain-hardening exponent n, obtained for strain rates dε/dt between 10−4 to 101 s−1.An array of test structures is processed and sequentially measured on the same silicon substrate, thus eliminating delicate handling of individual samples. An automated setup enables the fast acquisition of load-displacement data with statistical relevance. The method exploits a test structure where the evaporated 400-μm-long, 50-μm-wide, 2-μm-thick Al microtensile specimens are produced on a frame with coplanar fixed and movable components, connected by parallel springs, defined by deep reactive ion etching. Such design allows a linear in-plane motion of the inner frame when a force is applied to it and, consequently, leads to the uniaxial elongation of the bridging tensile specimen.Engineering stress-strain curves are obtained by normalizing the force-displacement data by the appropriate specimen dimensions, from which the mechanical parameters are then extracted. The Young’s modulus, E = 63±8 GPa, shows no dependence on dε/dt, within the span of strain rates tested. The fracture strain varies between 1.27±0.19 and 33.2±3.9%: a power law decrease is observed for rates from 10−4 to 10−1 s−1, εmax = 0.15(dε/dt)−0.76 %, followed by a saturation at εmax = 1.27% for dε/dt > 10−1 s−1. Opposite trends are obtained for the strength parameters σmax, σ0.2% and K: σmax increases logarithmically with dε/dt, σmax = 153{1+0.197 ln[(dε/dt)/10−4]} MPa, for 10−4 < dε/dt < 10−1 s−1, suggesting a deformation mechanism governed by Johnson-Cook thermally activated dislocations. Beyond 10−1 s−1, the material reaches its maximum strength at σmax = 380±6 MPa with no dependence on strain rate. A strain-rate independent strain-hardening exponent of n = 0.48±0.08 is extracted. Current work involves the method extension to temperature series for the identification of plastic deformation mechanisms in MEMS ductile materials and online monitoring of the local cross section reduction (necking) via resistance measurements for more accurate stress-strain relations.
10:15 AM - GG4.3
In-situ Nanomechanical Testing of Nanowires.
Dongfeng Zhang 1 2 , Jean-Marc Breguet 2 , Reymond Clavel 2 , Laetitia Philippe 1 , Johann Michler 1
1 Mechanics of Materials and Nanostructures Laboratory, EMPA-Materials Science and Technology, Thun Switzerland, 2 Laboratory of Robotic Systems LSRO2, Swiss Federal Institute of Technology Lausanne, Lausanne Switzerland
Show AbstractA new nanotensile stage based on a micro-electromechanical system (MEMS) with integrated actuator and force sensor was developed to probe mechanical properties of individual nanowires. Two types of testing stages were designed and fabricated. One consists of an electrostatic actuator and a fixed-fixed beam structure as force sensor. The other combines an electrostatic actuator with a differential capacitive force sensor. Cobalt nanowires were synthesized by electrodeposition and placed via electron microscopy based nanomanipulation techniques onto the MEMS devices. The system is mounted inside a scanning electron microscope (SEM) and allows assessing electrical properties under strain due to a four-point resistivity measurement. Prior to loading the nanowires were fixed via electron beam induced deposition. The tensile test results are compared with mechanical properties inferred from resonance tests. The paper discusses also the novel design concepts with respect to existing experimental setups.
10:30 AM - GG4.4
Micro-Tensile Tests on Metal on Polymer and Self-standing Specimens.
Cedric Seguineau 1 2 , Michel Ignat 2 , Christophe Malhaire 3 , Jean-Michel Desmarres 4 , Xavier Lafontan 1 , Sébastiano Brida 5 , Pierre-François Calmon 6 , Patrick Pons 6 , Paolo Martins 3 , Benjamin Destouches 4 , Jean-Baptiste Labbe 1
1 , NOVAMEMS, Toulouse France, 2 SIMAP UMR 5266, ENSEEG INPG, Saint-Martin d'Heres France, 3 , INL, CNRS UMR 5270, Villeurbanne France, 4 DCT/AQ/LE, Centre National d'Etudes Spatiales, Toulouse France, 5 , AUXITROL S.A, Bourges France, 6 , LAAS - CNRS, Toulouse France
Show AbstractThe knowledge of the mechanical properties and the response under monotonic or cyclic solicitations of submicron thin films is essential to address reliability issues in MEMS and microelectronic devices based on flexible technology (metals and /or dielectrics on polymers). Because thin films mechanical behavior depends on microstructure, and because the microstructure depends strongly on the process conditions, specific and accurate characterization methods have to be developed to avoid substrate effect and to obtain direct measurements. We present and discuss some results obtained through micro-tensile tests on self-standing metallic films (as thin as 500nm thick), as on copper on polymer substrates. These specimens were tested under monotonic and cyclic solicitations. Two different technologies have been chosen to fabricate the specimens: silicon standard micromachining process (KOH or dRIE etching) and metal on polymer process. We have first developed silicon frames sustaining Al, Cu or Au films. The polymer based specimens have been achieved on a 50µm thick A4 polymer sheet by laser cutting. Several kinds of samples have been achieved and studied: bare Polimide specimens, fully coated samples by a electrodeposited copper film (8.5µm), and beams with copper patterns. These metal patterns have been observed by microscopy during and after the tensile test to determine local strains and plastic deformations by Digital Image Correlation (DIC) and compared to FEM results. Several experimental results are shown: a linear behavior is observed in the initial portion of the stress-strain curves. Then, the overall response is typical of a very ductile material up to fracture. Cyclic solicitations have been applied in order to observe damage effects on the mechanical properties. These samples show tensile flow and rupture strengths of about: 160MPa and 350MPa, and a total elongation of about 2µm. Cycling experiments with piezoelectric actuators (100Hz) show a polymer stress relaxation phenomenon. Moreover, the amplitude of the resulting displacement also tends to zero. These two observations are linked with the viscoelastic behavior of the polymer. Local damages have been observed in-situ with an optical microscope on polymer beams with Cu patterns. Cracking is nucleating at the circular copper/polimide interfaces singularities. As for self-standing films, Al and Au specimens have been obtained and tested with a 5% repeatability. The elastic properties seem to be in good agreement with the literature. Yet, Yield stress seems to be linked with the thickness of the film. Moreover, the comparison of the experimental results obtained by several techniques (nanoindentation, bulge test, beam-bending experiments) are discussed.
10:45 AM - GG4.5
Stress Imaging of Deformation and Crack Defects in Silicon by Confocal Raman Spectroscopy.
Yvonne Gerbig 1 , Robert Cook 1 , Stephan Stranick 2 , Jeroen Schoenmaker 2 , Mark Vaudin 1
1 Ceramics Division, NIST, Gaithersburg, Maryland, United States, 2 Surface and Microanalysis Science Division, NIST, Gaithersburg, Maryland, United States
Show AbstractDue to the brittle nature of most materials used in microelectronic and microelectromechanical devices, stress-induced fracture is the main factor determining device yield and reliability. On the other hand, the microelectronics industry is increasingly taking advantage of strain-engineered semiconductors in order to improve carrier mobility. As a consequence, research on stress at suitable length scales has become crucial to the proper reliability evaluation of devices, as well as the better understanding of stress related issues regarding device design, processing and performance.In this paper we analyze the correlation between stress distribution, mechanical behavior and crystallographic orientation of silicon. For this purpose, spherical indentations were formed on Si(100) and Si(111) wafers, and the residual stress fields around the indentations mapped using a confocal Raman microscopy technique. Combined with appropriate peak fitting and super resolution methods, this technique allows stress measurement with a resolution of approximately 20 MPa at spatial resolution of approximately 100 nm. The effect of load and crystallographic orientation on the stress fields around plastic indentations is demonstrated. As long as the threshold for crack initiation is not reached, the “stress signature” does not change significantly with increasing load whereas the local stress value in the stress field does. The main difference between the two orientations lies in the symmetry of the stress field, threefold for Si(111) and fourfold for Si(100). On exceeding the threshold for crack initiation, the occurrence of cracks may alter the residual stress field significantly, dependent on the crack size. The interactions between the stress field around a crack tip and the superimposed stress field of the indentation are demonstrated for different stages of crack development.
11:30 AM - GG4.6
Measuring Strain at the 10-4 Level with Great Spatial Resolution.
Mark Vaudin 1 , Yvonne Gerbig 1 , Stephan Stranick 2 , Robert Cook 1
1 Ceramics Division, NIST, Gaithersburg, Maryland, United States, 2 Surface and Microanalysis Science Division, NIST, Gaithersburg, Maryland, United States
Show AbstractThe ability to measure strain at the nanoscale is a significant advantage in a number of advanced technologies, including microelectronics, photonics, and microelectromechanical devices. Strains in indented silicon as low as 10-4 have been measured using electron back scatter diffraction (EBSD), with spatial resolution better than 20 nm, and Raman confocal spectroscopy (RCS) with spatial resolution of about 100 nm. Analysis by a commercial software package of several hundred high-quality EBSD patterns recorded along a line crossing the mid point of a 20 µm by 2 µm wedge indentation in Si allowed the elastic deformation of the Si crystal to be characterized at each point. Thus, the full strain and stress profiles across the indentation were determined. Equivalent experiments have been performed using RCS to measure Raman line shifts at each point on a similar scan line across the indentation, and these shifts have been interpreted as biaxial stresses. Comparisons of the results show extremely good agreement except very close to the indentation, where the EBSD results, which come from closer to the sample surface than the RCS, indicate higher stresses. Decreasing the RCS excitation wavelength to probe smaller sample depths indicates that the two measurements converge as the wavelength and depth probed are decreased. The stress profiles can be well fitted by an inverse square power law as predicted from an Eshelby analysis. These results show that one of the holy grails of nanocharacterization is being realized.
11:45 AM - GG4.7
Application of Moire Interferometry to Whole Field Strain Measurement in Thin Film Specimens.
Arash Tajik 1 , Hamid Jahed 1
1 Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Ontario, Canada
Show Abstract12:00 PM - GG4.8
Characterization and Finite Element Analysis of a Viscoelastic Response for Micro Actuators Constructed with Thin Metal Films on Silicon.
Steven Meredith 1 , Richard Savage 1
1 Materials Engineering, California Polytechnic State University - San Luis Obispo, San Luis Obispo, California, United States
Show AbstractA fully recoverable non-linear viscoelastic response has been observed in electrostatically driven micro actuators employing torsional hinges of silicon covered with thin metal films. The viscoelastic response occurs over a time period of 60 minutes at an operating temperature of 35°C. This viscoelastic phenomenon is similar to that reported in articles addressing anelastic behavior associated with viscous grain boundary slippage. In order to investigate this viscoelastic response as a function of metal film composition and thickness, bi-layer torsional hinge actuators consisting of Si with a deposited metal layer were fabricated. The actuators were micromachined by deep etching 100mm diameter, 425µm thick, double side polished, single crystal (100) wafers to create a 6µm thick device layer. Subsequent etching of the device layer released the fixed-fixed torsional hinge test actuators. Physical vapor depositions of Au, Al and Al/Ti in three different thicknesses (50nm, 100nm, and 150nm) were deposited in order to investigate the impact of metal film thickness and composition on the viscoelastic response. Grain size and orientation of the deposited films were characterized using EBSD. Rotational actuation of the test actuators was achieved by using a modified Ambios XP-1 surface profiler that applies a constant force of 0.29mN while measuring the displacement of the actuator with respect to time. Additionally, a finite element model of the viscoelastic response based on the empirical data gathered from the electrostatically driven actuators was developed. This model was used to correlate the influence of grain orientation, size and the thickness of the deposited films with the non-linear viscoelastic response in an effort to minimize the phenomenon.
12:15 PM - GG4.9
Strength and Fatigue Life of Nanocrystalline Titanium/Platinum Multilayer Membranes for Implantable MEMS Reservoir Array Devices.
Karl Yoder 1 , John Maloney 2 , Jonathan Coppeta 1
1 , MicroCHIPS, Inc., Bedford, Massachusetts, United States, 2 Materials Science and Engineering , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Show AbstractThin-film metal membranes that can be electrically opened when desired are used in MEMS reservoir array devices designed for long-term medical implants in order to protect and isolate drugs or biosensors. Their unique role as reservoir covers directly impacts safety, efficacy, and the potential lifetime of the medical implant. Consequently, in addition to their electrical properties, criteria governing the selection of these sub-micron metal films include biocompatibility, yield stress, and fatigue life. Mechanical properties of sputtered titanium and platinum multilayer membranes of thickness 3800Å and 6800Å were investigated with bulge, rupture, and nanoindentation tests. Additionally, a novel fatigue apparatus was designed and used for high-cycle fatigue testing of hundreds of membranes, in parallel, in simulated in vivo conditions.
GG5: MEMS Reliability and Tribology
Session Chairs
Tuesday PM, December 02, 2008
Room 306 (Hynes)
2:30 PM - GG5.1
Effect of Sidewall Morphology on the Fracture and Fatigue Properties of Micron-Scale Polycrystalline Silicon.
Daan Hein Alsem 1 2 , Brad Boyce 3 , Eric Stach 4 , Robert Ritchie 1 5
1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Materials Science and Engineering Center, Sandia National Laboratories, Albuquerque, New Mexico, United States, 4 School of Materials Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States, 5 Department of Materials Science and Engineering, University of California, Berkeley, Berkeley, California, United States
Show AbstractSurface properties can markedly affect the reliability of structural thin films used in microelectromechanical systems (MEMS) applications. This study highlights the striking difference in the sidewall morphology of n+-type polysilicon films from two popular MEMS processes and its effect on fracture and fatigue properties. Atomic force and analytical transmission electron microscopy show that the oxide layers are not always thin native oxides, as often assumed; moreover, the roughness is influenced by the oxidation mechanism. Thick silicon oxides (20 ± 5 nm) found in PolyMUMPsTM films are caused by galvanic corrosion from the presence of gold on the chip, whereas in SUMMiT VTM films, with no gold on the chip, a much thinner (3.5 ± 1.0 nm) native oxide was observed. These thicker oxide layers, in combination with differences in sidewall roughness (14 ± 5 nm for PolyMUMPsTM and 10 ± 2 nm for SUMMiT VTM) have a significant effect on the fracture and fatigue properties of polysilicon structures; this is shown by measuring fracture strength (3.8 ± 0.3 GPa for PolyMUMPsTM and 4.8 ± 0.2 GPa for SUMMiT VTM) and stress-lifetime high-cyclic fatigue curves.
2:45 PM - GG5.2
New Test-Specimen Geometries for MEMS-Scale Measurement of Tensile and Bending Strength.
Michael Gaither 1 , Frank DelRio 1 , George Quinn 1 , Richard Gates 1 , Robert Cook 1
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States
Show Abstract3:00 PM - GG5.3
Tribological Metrology at the Micro-nanoscale: A Device for Calibrated Contact Force Measurements using Atomic force Microscopy.
Mark Reitsma 1 , Richard Gates 1 , Edwin Fuller 1 , Robert Cook 1
1 Materials Science and Engineering Laboratory, National Institute of Standards and Technology (NIST), Gaithersburg, Maryland, United States
Show Abstract3:15 PM - GG5.4
Investigation of Gold Sputter Coated Vertically Aligned Multi-walled Carbon Nanotubes for RF MEMS Contact Surfaces.
Esa Yunus 1 , Mark Spearing 2 , John McBride 3
1 Electromechanical Research Group, University of Southampton, Southampton, Hampshire, United Kingdom, 2 Head of School, SES, University of Southampton, Southampton, Hampshire, United Kingdom, 3 Head of Electromechanical Engineering Research Group, University of Southampton, Southampton, Hampshire, United Kingdom
Show AbstractA novel approach has been developed for the long-standing problem of durable contact surfaces for RF MEMS switches. In this work the performance of gold sputter-coated vertically aligned carbon nanotubes are investigated under the low force electrical contact conditions typical of MEMS switches. The carbon nanotubes provide an elastic support for the conducting gold surface layer, minimizing the plastic deformation and adhesion between the contact surfaces which is the principal source of wear and degradation in such contacts. Contact surfaces were prepared by the chemical vapour deposition of a “forest” of multiwalled carbon nanotubes on a silicon wafer surface. A thin gold layer is then sputter-deposited on top of the nanotube forest. The counter surface was formed using a gold sputter-coated stainless steel sphere. Quasi-static and cyclic loading was applied to these contact surfaces. Quasi-static loading using a modified nanoindentor was used to determine the mechanical properties of gold coated vertically aligned carbon-nanotubes (Au/MWCNT) surfaces. The study reveals that the Au/MWCNT deforms elastically during the penetration of the indentor. The surfaces are compared with a reference Au-Au contact and Au-Au/MWCNT contact pair under the same experimental conditions. Similar contact resistances were obtained for the Au-Au/MWCNT contact as were achieved for conventional Au-Au contacts. Cyclic loading was conducted using a piezo-driven micro-cantilever, with load measured using an ultra-high resolution load cell. Electrical contact resistance was monitored throughout. Tests were run out to 1 million cycles. At 1 mN load, the Au-Au contact exhibited a significant increase in contact resistance, and accompanying surface degradation at ~400 cycles. The Au-Au/MWCNT contact resistance consistently remained unchanged at this load level out to 1 million cycles and there was significantly less surface degradation. A combination of scanning electron microscopy, atomic force microscopy and con-focal white light scanning were used to characterize the surfaces before and after quasi-static and cyclic loading. Additional cyclic loading tests at other load levels and “hot switching” tests will have been conducted by the time of the conference. This initial study shows the very exciting potential for the application of metal-coated CNT surfaces as contact surfaces in RF MEMS electrical switching applications.
3:30 PM - GG5.5
An Improved Nanotribological System for Hard Disk Drives.
Xuan Li 1 , James Economy * 1
1 Materials Science and Engineering , University of Illinois at Urbana-Champaign, Urbana , Illinois, United States
Show AbstractA new family of aliphatic polyester lubricants has been developed for use in micro-electromechanical systems (MEMS) specifically for hard disk drives that operate at high spindle speeds (>15000rpm). Our program was initiated to address current problems with spin-off of the perfluoroether (PFPE) lubricants. The new polyester lubricant appears to alleviate spin-off problems and at the same time improves the chemical and thermal stability. This new system provides a low cost alternative to PFPE along with improved adhesion to the substrates. In addition, it displays a much lower viscosity which may be of importance to stiction related problems. The synthetic route is readily scaleable in case additional interest emerges in other areas including small motors.