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
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 Show Abstract
1 Micromachined Products Div., Analog Devices, Inc., Cambridge, Massachusetts, United States
Minimizing 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 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Chemical 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 Show Abstract
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
Ultrananocrystalline 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 Show Abstract
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
10:45 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 Show Abstract
1 , IMEC, Leuven Belgium, 2 ESAT, K.U.Leuven, Leuven Belgium
Motivation 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 Show Abstract
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
This 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 Show Abstract
1 ElectroOptics Research Institute and Nanotechnology Center, University of Louisville, Louisville, Kentucky, United States
Recently 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 Show Abstract
1 , U Minnesota, Minneapolis , Minnesota, United States
12:15 PM - GG1.9
Dicing of Fragile MEMS Structures.
Peter Lange 1 , Norman Marenco 1 , Sven Gruenzig 1 , Stephan Warnat 1 , Thilo Semperowitsch 2 Show Abstract
1 Microsystem Technology, Fraunhofer ISIT, Itzehoe Germany, 2 , Accretech GmbH, Munich Germany
Conventional 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
Monday PM, December 01, 2008
Room 306 (Hynes)
2:30 PM - **GG2.1
BioMEMS Technologies for Regenerative Medicine.
Jeffrey Borenstein 1 Show Abstract
1 Biomedical Engineering, Draper Laboratory, Cambridge, Massachusetts, United States
The 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 Show Abstract
1 Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Water 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 Show Abstract
1 Chemical Engineering, MIT, Cambridge, Massachusetts, United States, 2 Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Continuous 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 Show Abstract
1 Nano Advanced Technology, GE Global Research Center, Niskayuna, New York, United States
Many 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 Show Abstract
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
Small 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 Show Abstract
1 , Northwestern University, Evanston, Illinois, United States, 2 , Argonne National Laboratory, Argonne, Illinois, United States
As 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 Show Abstract
1 , National Institute of Standards & Technology, Gaithersburg, Maryland, United States
5:30 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 Show Abstract
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
GG3: Poster Session
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 Show Abstract
1 , U.S. Army Research Laboratory, Adelphi, Maryland, United States
Microdevices 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 Show Abstract
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
9:00 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 Show Abstract
1 Material and Chemical Research Laboratories, Idustrial Technology Research Institute, Hsinchu Taiwan
AlN 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 Show Abstract
1 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Previous 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 Show Abstract
1 Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Understanding 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 Show Abstract
1 Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania, United States, 2 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
An 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 Show Abstract
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
9:00 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 Show Abstract
1 , University of Colorado, Boulder, Colorado, United States
Recent 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 Show Abstract
1 Dept. Materials Science & Engineering, Kumamoto University, Kumamoto Japan
Fatigue 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 Show Abstract
1 Dept. Materials Science & Engineering, Kumamoto University, Kumamoto Japan, 2 P&I laboratory, Tokyo Institute of Technology, Yokohama Japan
To 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 Show Abstract
2 , Yale University, New Haven, Connecticut, United States, 1 Functional Properties Group, Ceramics Division, NIST, Gaithersburg, Maryland, United States
Analysis 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 Show Abstract
1 Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology, Tokyo Japan
In 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 Show Abstract
1 , North Carolina State University, Raleigh, North Carolina, United States
Wrinkling 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 Show Abstract
1 Mechanical Engineering, University of South Florida, Tampa, Florida, United States
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 Show Abstract
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
Nano-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 Show Abstract
1 Department of Mechanical Engineering, Columbia University, New York, New York, United States
The 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 Show Abstract
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
Films 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 . 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 ), which is compared against toughness measurements obtained via tensile characterization using polymer substrates (channel cracking of brittle films ). 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 Show Abstract
1 Department of Biomedical Engineering, The Ohio State University, Columbus, Ohio, United States
One-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 Show Abstract
1 , Korea Institute of Machinery & Materials, Daejeon Korea (the Republic of), 2 , Lehigh University, Bethlehem, Pennsylvania, United States
Metal 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 Show Abstract
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
We 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 . The theoretical results also reconfirm the experimental observation that the performance of piezoelectric nanogererators sensitively depends on the free electron concentration in ZnO nanowires.
 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 Show Abstract
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)
Direct 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 Show Abstract
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)
9:00 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 Show Abstract
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
A 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 Show Abstract
1 Department of Materials Physics, Univeristy of Leoben, Leoben Austria
A 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 Show Abstract
1 AMRI, AIST, Tsukuba, Ibaraki, Japan
9:00 PM - GG3.33
Metal Wafer Bonding for MEMS Applications.
Viorel Dragoi 1 , Gerald Mittendorfer 1 , Franz Murauer 1 , Erkan Cakmak 2 , Eric Pabo 2 Show Abstract
1 Technology Development, EV Group, St. Florian/Inn Austria, 2 Technology Development, EV Group Inc., Tempe, Arizona, United States
Wafer 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 Show Abstract
1 Institute of Materials Science and Nanotechnology, Bilkent University, Ankara Turkey, 2 Department of Physics, Bilkent University, Ankara Turkey
Calorimetry 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 Show Abstract
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
9:00 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 Show Abstract
1 LAAS, CNRS, Toulouse France, 2 Physics, University of Athens, Athens Greece
The 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 Show Abstract
1 Material Engineering, Auburn Univerity, Auburn University, Alabama, United States, 2 Mechnical engineering, Auburn University, Auburn, Alabama, United States
A 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 Show Abstract
1 , Florida International University, Miami, Florida, United States
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 Show Abstract
1 , McGill University, Montreal, Quebec, Canada
The 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 Show Abstract
1 Institute of Materials Science and Nanotechnology, Bilkent University, Ankara Turkey, 2 Department of Physics, Bilkent University, Ankara Turkey
We 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 Show Abstract
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
We 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 Show Abstract
2 , SUNY Stony Brook, Stony Brook, New York, United States, 1 Mechanical and Industrial Engineering, Northeastern University, Boston, Massachusetts, United States
Accurate 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 Show Abstract
1 , Air Force Research Laboratory, Hanscom AFB, Massachusetts, United States
A 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 Show Abstract
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
Nanofluidic 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