Symposium MD10 : Micro-Assembly Technologies

Assembly of single and large number of parts has been possible with different precision and stochastic methods. In the sense of precision methods, mobile microrobotic and elastomeric transfer printing based assembly methods have become promising in recent years for 2D or 3D assembly tasks. In this talk, the two methods proposed in the presenter’s group are presented and their pros and cons are discussed. First, gecko foot-hairs inspired angled and vertical microfibers based dry adhesives with rigid or inflatable soft elastic membrane backings are proposed as transfer printing stamps for manipulation of planar and non-planar complex and fragile parts. Moreover, muscle-inspired DMA coatings based hydrogel stamps are proposed to transfer print thin metallic layers underwater conditions. As the next approach, untethered magnetic mobile microrobots are proposed as new microassembly tools in enclosed spaces such as closed microfluidic channels or inside the human body. Such microrobots are shown to manipulate parts in 2D using mechanical contact or microfluidic non-contact forces. Next, complex microrobot designs with an integrated gripper are shown to pick-and-place microparts inside enclosed fluidic spaces. As an application demonstration, microgels with embedded cells are assembled in 3D towards tissue engineering applications.

This paper presents an overview of recent activities of FEMTO-ST institute in the field of micro-nanomanipulation. Current proof of concept of robotic manipulations are currently limited by the number of degree of freedom addressed and also are very limited by their throughput. Two ways can be considered to improve both the velocity and the degrees of freedom : non-contact manipulation and dexterous micromanipulation. Indeed in both ways movement including rotation and translation are done locally and are only limited by the micro-nano-objects inertia which is very low. It consequently enable to generate 6DOF and to induce high dynamics. The paper presents recent works which have shown that controlled trajectories in non contact manipulation enable to manipulate micro-objects in high speed. Dexterous manipulation on a 4 fingers microtweezers have been also experimented and show that in-hand micromanipulations are possible in micro-nanoscale based on original finger trajectory planning. The paper opens to future perspectives regarding markets and future scientific challenges of robotic micro-nanohandling.

Due to the dominant surface force over body force in micro-scale objects, manufacturing processes in micro scale heavily rely on two-dimensional (2D) photolithographic process that is repetitive sequences of deposition and etching of desired materials. While such manufacturing process has successfully miniaturized integrated circuit (IC) and microelectromechanical systems (MEMS), its 2D nature limits realization of devices with three-dimensional (3D) form factor. Lego-like microassembly, based on transfer printing, is an alternative route to integrate heterogeneous material micro-scale objects (termed ‘ink’) onto target are in conjunction with proper bonding technique borrowed from wafer-scale for mechanically sturdy joined interface. Lego-like microassembly enables assembly of micro scale objects in the absence of adhesive intermediate layer that allows the joining of heterogeneous materials while keeping their intrinsic material properties. The inks are first prepared by photolithography in compact form, which are suspended by photoresists for minimal adhesion to the fabricated donor substrate. The inks were previously limited to silicon (Si) and gold (Au), which are expanded to both silicon dioxide (SiO₂) as well as SU8. These ink materials are joined by fusion, eutectic or adhesive bonding mechanism to provide sturdy joined interface for more reliable and robust device operation. With expansion of ink materials, Lego-like microassembly now accommodates four major material classes; semiconductor (Si), metal (Au), dielectric (SiO₂) and polymer (SU8), which are broadly used materials in IC and MEMS fields. This presentation covers description of ink fabrication schemes of all four different materials, transfer printing and bonding protocols as well as some demonstrative 3D microstructures and devices fabricated solely relying on Lego-like microassembly process.

Micro-Transfer-Printing is a demonstrated versatile micro-assembly technology developed for over ten years since originally conceived at the University of Illinois [1]. Micro-Transfer-Printing involves the release, transfer and printing of an array of devices from their growth substrate to a different substrate in a massively parallel manner (i.e. thousands of devices per transfer) with a high degree of positioning accuracy (±1.5 µm), using an elastomeric stamp as the transfer element. X-Celeprint has demonstrated this technology in a wide range of diverse applications spanning from OLED and micro-LED displays to concentrated photovoltaics, storage and photonics [2, 3]. This technology provides an excellent solution to challenges involving the integration of III-V devices with silicon and other application specific substrates such as engineered substrates, flexible substrates and glass substrates.

This paper presents recent advances in the fabrication of micro-assembled devices using micro-transfer printing. Processes to print micro-scale devices grown on different native substrates such as Silicon, Gallium Arsenide, Gallium Nitride and Indium Phosphide will be described. Recent advances in print yield, device pitch, print accuracy, array size, and number of devices transferred per print will be reported. The devices printed are micro-scale, less than 10um in thickness and less than 100um in lateral dimensions. We continue to make rapid progress in our ability to print smaller and smaller micro-components and this paper will discuss the current state of the art. Finally, we will identify new applications that leverage the integration of III-V devices with non-native substrates.

[1] E. Menard, K. J. Lee, D. Y. Khang, R. G. Nuzzo, J. A. Rogers, Appl. Phys. Lett. 84, 5398 (2004)
[2] C.A. Bower, M.A. Meitl, S. Bonafede, D. Gomez, A. Fecioru and D. Kneeburg, “Heterogeneous integration of microscale compound semiconductor devices by micro-transfer printing, IEEE Electronic Components and Technology Conference, p 963 (2015)
[3] C.A. Bower, E. Menard, S. Bonafede, J.W. Hamer, R.S. Cok, “Transfer-printed microscale integrated circuits for high performance display backplanes,” IEEE Transactions on Components, Packaging and Manufacturing 1 (12), 1916-1922 (2011)

Abstract not available 12/16/15

Fan-out wafer level packaging (FOWLP) is an increasingly important topic in device packaging. In the most mature FOWLP processes, singulated die are assembled face-down onto an intermediate substrate, embedded in molding compound and then released from the intermediate substrate creating the “reconfigured wafer”. The fan-out redistribution metal (RDL) and bumps are fabricated on the reconfigured molding compound wafer. Due to the serial nature of the traditional assembly process, fan-out packaging encounters cost challenges as die and packages shrink in size. This work demonstrates how a massively parallel assembly process can be used to expand fan-out packaging into currently unexplored size regimes.

This paper describes and demonstrates a high-throughput strategy for making fan-out packages for very small, sub-millimeter, devices. First, micro-transfer printing [1] was used to deterministically assemble large arrays of devices, face-up, onto 200mm wafers. In micro-transfer printing, a viscoelastic polymer print-head is used to pick-up and transfer the device arrays. The device used in this study was an 80um x 40um chip with a redistribution metal and six contact pads designed to be used as an electrical test vehicle. The printed devices are approximately one micron in thickness and are attached to the package substrate using a thin layer of organic dielectric (e.g. polyimide). Following assembly of the chips, the 200mm wafers undergo metal redistribution (RDL) and bumping processes typical of a standard wafer-level package (WLP). Here, the final package pitch on the 200mm wafer is 1.4mm x 1.0mm with six bumps. After dicing the six-bump fan-out packages are approximately 1.3mm x 0.9mm. The packages were next assembled, using a standard pick and place tool, and reflowed onto FR4 test boards specifically designed for this study. The process and interconnect yield will be reported, as well as thermal cycling results. In summary, we have demonstrated a new strategy for cost effective fan-out packaging of very small chips. This strategy depends on a massively parallel deterministic assembly process capable of delivering very thin devices to the destination package wafer. A key advantage of this approach is that no molding compound is required in the package, which mitigates the thermal and planarity challenges that are typical in mold compound fan-out packaging processes.

[1] C.A. Bower, M.A. Meitl, S. Bonafede, D. Gomez, A. Fecioru and D. Kneeburg, “Heterogeneous integration of microscale compound semiconductor devices by micro-transfer printing, IEEE Electronic Components and Technology Conference, p 963 (2015)

Stretchable circuits are a new class of electronics, often designed as hybrid systems where solid-state devices are interconnected with elastic wiring on an elastomeric substrate. Recently gallium based liquid metals have emerged as an interesting approach to achieve soft electrical connections, since they can maintain metallic electrical conduction under very large applied strains (>800 %). However, none of current patterning methods of liquid metals combine scalability to large area, high throughput and fine resolution.
We report on a high precision and high throughput method to pattern highly conductive thin film of liquid metal (The soft interconnects are prepared by physical vapor deposition (PVD) of pure gallium (Ga) on elastomeric substrates pre-coated with a thin layer (60 nm) of gold (Au). The resulting thin film consists of a biphasic film with the solid phase (GaAu₂ alloy) interpenetrated by liquid Ga. The process is compatible with lift-off patterning with critical dimension of 10 µm and arbitrary shapes on extended surface area (50X50 mm²).
The electrical and electromechanical properties of the soft biphasic film are similar to those of liquid metals yet have an average thickness of 1µm or less. We quantified the electromechanical performance of the soft biphasic thin film under extended uniaxial strain (>80%). The film displayed a low gauge factor (≈1) and no dependence on previously applied strain. Next, we tested the robustness of the film by performing 1 million stretch-relaxation cycles (0% to 50% at a frequency of 1.4 Hz) and no increase in resistance was measured. Furthemore, this metallization process is compatible with a wide variety of elastomer and plastic substrates including polyimide, polyurethane, polyethylene and silicone elastomer. We also demonstrated the integration of standard electronic components (0402 packaged surface mounted LEDs) in soft, multilayer interconnected microcircuits. We produced a 4 by 4 Led matrix (15 mm pitch) embedded in a thin (0.3mm) silicone elastomeric membrane. The circuits remained functional under complex bi-axial strains resulting from the inflation of the membrane.

On-demand printing of electrical interconnects have wide-spread potential use in efficient realisation of the next generation of flexible sensing, haptics and soft robotics applications. The benefit of printing based manufacture is that it can be used as the final step in the design of these flexible devices without interfering with existing process chain. To this end, realisation of low cost metallic interconnects is a crucial milestone. Prior literature has primarily focused on silver and gold based printed interconnects which, although functional, are expensive. Copper will be an excellent, low cost alternative. Here we demonstrate copper interconnects with controllable features sizes from 2 to 50 microns on flexible polyimide substrates using pneumatic ejection of copper nanoparticle suspension through in house created glass nozzles with 2-10 microns in diameter. The copper nanoparticle ink was synthesized through simple, one-pot green synthesis carried with water as a suspending medium and using ascorbic acid as reducing and capping agent. The effect of additional dispersants such as polyethylene glycol and polyvinylpyrrolidone was also analysed. The viscosity and particle loading of the as synthesised inks was tuned using vacuum evaporation of the water in the ink. Open air thermal evaporation on the other hand led to quick oxidation of the copper nanoparticles and thus resulted in non-conducting printed features. The vacuum annealing with a prior purging using an inert gas on the other hand helped in gradual reduction in the water content while avoiding particle oxidation. The rheological properties of the resulting copper inks such as shear and elongational viscosities and surface tension were measured to help correlate the feature size of printed interconnects with the ink properties. The adhesion of printed structures on polyimide was adjusted by substrate corona treatment. The printed interconnects were sintered to impart electrical conductivity. The resulting printed copper interconnects and inductors on polyimide were subjected to mechanical flexibility tests and demonstrated to conform to 5 mm bending radius and cyclic deformability tests. Next, we demonstrated printing on flexible fabrics as a first step towards new designs of high resolution sock electrodes for next generation of electrocardiographic imaging applications through flexible design of electrodes. Such flexible designs could also have use as piezoresistive sensors for tactile sensing applications. Lastly, the presentation will also show preliminary results towards 3D interconnects for implantable devices applications and address the issue of tuning viscoelastic properties of the copper inks to achieve them.

Micro-transfer-printing [1] is an emerging high speed massively-parallel assembly technology well-suited for deterministic integration of large arrays of microscale devices onto non-native receiving substrates. Originally conceived in the middle of the last decade [2], micro-transfer-printing utilizes an injection molded compliant viscoelastic [3] polymer stamp to pick-up and transfer arrays of semiconductor microdevices from their native source wafer onto a desired application substrate such as glass, plastic or other semiconductors. Most typically, the microdevices on their native wafer are prepared for transfer by undercutting the devices using combinations of sacrificial layers and chemically selective etchants [1]. Earlier reports have described transfer-printing of microscale Si CMOS integrated circuits], light emitting diodes, lasers and solar cells [1]. In these previous efforts, the electrical interconnection to the printed microdevices was formed after the printing step and most typically resembled a thin-film metallization (RDL) process where the metal interconnections were formed by physical vapor deposition and metal patterning using either lift-off, subtractive etching or semi-additive electroplating.

For the first time, we report on a novel interconnection technology designed to form the electrical interconnections of micro-assembled devices during the elastomer stamp printing process. The paper will describe how combination of deformable materials and stress-concentrating features are used to form interconnects during the room-temperature printing process. The paper will present the interconnect yield and resistance measured using daisy-chain test vehicles. Additionally, the paper will report on the reliability of the interconnections based on results from thermal cycling, thermal shock and pressure-humidity (pressure cooker) tests. Finally, the paper will include a discussion of the interconnection mechanism, thermomechanical modeling results and a comparison with experimental data and cross-section micrographs of the interconnection. Such an interconnection technology is low temperature, fine pitch and solder free, requires minimal processing after printing and provides an avenue for device repair. It is anticipated that this important new technique will find utility in many applications, ranging from displays to RFID tags.

[1] C.A. Bower, M.A. Meitl, S. Bonafede, D. Gomez, A. Fecioru and D. Kneeburg, “Heterogeneous integration of microscale compound semiconductor devices by micro-transfer printing, IEEE Electronic Components and Technology Conference, p 963 (2015)
[2] E. Menard, K. J. Lee, D. Y. Khang, R. G. Nuzzo, J. A. Rogers, Appl. Phys. Lett. 84, 5398 (2004)
[3] M.A. Meitl, Z. Zhu, V. Kumar, K.J. Lee, X. Feng, Y. Huang, I. Adesida, R.G. Nuzzo, J.A. Rogers, Nature Materials 5(1), 33 (2006).

Soft active polymeric composites are of great interest in many fields, including soft robotics, flexible electronics and wearable technologies. We have developed such an elastomeric active composite that can be used as a stamp for microtransfer printing processes. This multi-layered composite has an architecture consisting of an elastomeric contact post made of polydimethylsiloxane, an active layer with embedded PZT, an interconnect metallization layer and patterned SU-8 layers for compliance tuning and handling. This 3D heterogeneous integration of different materials to form a functional membrane is achieved through a novel fabrication process that includes both photolithography and microtransfer printing. By using this locally active composite stamp, we can have better control and selectivity in the pick and place processes in the transfer print cycle. However, such a flexible, active composite membrane’s uses can also be extended to other avenues like flexible sensor technologies. To this end, this architecture has also been extended towards the realization of a conformal dense array tactile sensor. The dense array consists of many of the active stamp modules, each acting as a tactile element. This is made possible by the scalable fabrication approach of microtransfer printing with good integration of mechanical and electrical components. This tactile sensor can be used for various functions like health monitoring, pressure sensing and as electronic skin.

Ultrathin forms of single-crystalline silicon derived from wafer-based source materials represent an excellent materials building block for high performance, low cost solar cells due to a number of unique advantages such as superior materials properties, reduced materials consumption, relaxed requirements of materials purity, and ability to form large area modules on unlimited choices of module substrates. Programmable materials assemblies via micro-transfer printing can create novel engineering designs, device functionalities, and cost structures with these materials, each with significant practical values in the next generation photovoltaics. This talk will provide an overview of recent advances in materials design and fabrication pathways for ultrathin single-crystalline microscale silicon solar cells, with a special emphasis on various heterogeneously integrated unconventional module designs and nanoscale photon management for maximizing the performance of optically thin microcells and their flexible modules on plastics.

Conventional MEMS devices generally use silicon springs as the deformable components in their free standing structures. Due to the rigidity and brittleness of silicon, such springs can only sustain limited deformation before failure such as fracture occurs. Elastomers, on the other hand, have low Young’s modulus and can undergo large deformation, making them a suitable material for the deformable mechanical components of MEMS. As silicon/elastomer hybrid devices use silicon and elastomer as the rigid and flexible components, respectively, they have the potential to utilize the distinct properties of both hard and soft materials to achieve enhanced performances. However, due to the incompatibility between elastomer processing and standard silicon micromachining, silicon/elastomer hybrid MEMS are rarely reported. To overcome the challenge encounter by monolithic micromachining process, a transfer printing-based microassembly approach is used to fabricate elastomer involved MEMS devices. To start with, the conductive elastomer structure is defined via molding process and will act as a receiver substrate in the assembling process. The silicon components, on the other hand, are generated on a silicon-on-insulator wafer referred to as the donor substrate. After the donor and receiver substrates are separately prepared, a deterministic transfer printing technique is employed to pick up the silicon components from the donor substrate and place them on the receiver substrate. The assembly process is completed by bonding the silicon and elastomer through surface hydroxyl condensation reactions. As a demonstration of the manufacturing capability, we construct a tip-tilt-piston mirror with a silicon reflector sitting on a conductive elastomeric universal joint. The single crystal silicon reflector provides high quality mirror surface, whereas the highly flexible elastomeric universal joint can undergo large deformation, which leads to the large deflection of the mirror. The device assembly is characterized and it shows comparable performance to the existing MEMS micromirrors, thus validates the device level capabilities of our microassembly.

With low-cost 3D printing systems proliferating among researchers, developing new filament materials to expand the design capabilities of 3D printed objects has become a significant focus worldwide. One material property that has been difficult to achieve though is high conductivity, which would enable the integration of embedded circuitry into functional 3D printed electronics. Here, we present possibility of low-melting alloy designs, which provide a unique opportunity for integrating new functionalities into additive manufacturing (AM). We demonstrate that low-melting metal alloy system shows high electrical conductivity, can be combined with standard thermoplastic extrusion materials, and are compatible with existing filament extrusion systems. This work focused on the tin-bismuth system, in the tin-rich non-eutectic region, which demonstrated good extrusion characteristics due to its viscous nature between its solidus and liquidus. In addition to the base alloy, the contribution of a number of different dopants was demonstrated, and their possible effects summarized. The addition of minor composition of silver changes the microstructure of the resulting filament, forming needle structures, which is believed can be used to improve the extrusion and 3D stacking characteristics of the material by introducing non-Newtonian rheology: thixotropy, and also slightly reduces the resistivity of the material. Cross sections of the printed material show the excellent fusion of the newly deposited material to the previous layer. Finally, co-deposition of the alloy into 3D printed plastic structures are demonstrated for the compatibility of the material with current 3D printing thermoplastic materials.

Electrophotography, or Xerography, is a widely used process to “manufacture” paper documents that has been used since the 1940s. Used in document printing, this process places puddles of color spheres onto digitally designated locations to form characters and graphics at high speed >10⁸ particles/s. If we can improve the precision and accuracy of the typical electrographic process to assemble individual components into well-defined locations and well-defined orientations, we will have a massivly parallel digital manufacturing tool that allows us to make complex heterogeneous systems at unprecedented speed. In a recent demonstration, PARC has shown the fundamental steps of this envisioned process. In this talk, we will report the status and progress of developing this approach, the exploration of this concept, as well as review previously related work in the field. Application areas, including both assembling nano constructs at the single micron length scale as well as assembling chiplets at the hundreds of micron scale will also be discussed.

Micro-Transfer-Printing is a demonstrated versatile micro-assembly technology developed for over ten years since originally conceived at the University of Illinois [1]. Micro-Transfer-Printing involves the release, transfer and printing of an array of devices from their growth substrate to a different substrate in a massively parallel manner (i.e. thousands of devices per transfer) with a high degree of positioning accuracy (±1.5 µm).

This work presents the process capability and the useful lifetime of the viscoelastic elastomer stamps used in transfer printing. A cost effective test chip was designed to enable statistical process control studies, process capability studies and also stamp lifetime studies. The test chips were fabricated on 150mm wafers and were comprised of silicon nitride with an embedded metal fiducial mark to facilitate print yield and print accuracy measurements. The silicon nitride chips were fabricated on crystalline silicon wafers and the chips were released from the wafer using an anisotropic hot aqueous base to remove the silicon underneath the chips. The dimensions of the test chip were 40um x 40um x 1.2um. To implement statistical process controls and to evaluate process capability, an elastomer stamp with a 20x28 post array was designed and fabricated. The target substrate was a 150mm silicon wafer with metal fiducial marks designed to allow automated optical placement accuracy measurements. Here, we will present how the process yield and placement accuracy varies over the course of many weekly process control checks. We will also report Cpk values for the print accuracy over many thousands of transfer cycles.

Last year [2], we reported on the lifetime of a single elastomer stamp that was used for more than 25,000 prints. In that work, we designed and fabricated stamps with a single post that transferred 2 adjacent chips at a time. By transferring only two chips per print cycle, the stamp allowed the assessment of stamp performance over many thousands of print cycles without changing the source substrate. In this work, we will report on an expanded study designed to assess the manufacturing lifetime of elastomer transfer stamps. Here, we will report on the lifetimes of multiple stamps, including 2x2 post array and 20x28 post array stamps. Finally, we will examine and discuss the failure modes observed in both the process capability and the stamp lifetime studies.

[1] E. Menard, K. J. Lee, D. Y. Khang, R. G. Nuzzo, J. A. Rogers, Appl. Phys. Lett. 84, 5398 (2004)
[2] C.A. Bower, M.A. Meitl, S. Bonafede, D. Gomez, A. Fecioru and D. Kneeburg, “Heterogeneous integration of microscale compound semiconductor devices by micro-transfer printing, IEEE Electronic Components and Technology Conference, p 963 (2015)

Nano-inkjet printing using the Electrohydrodynamic's (EHD) nano-drip has the potential to bring affordable additive manufacturing to the nanoscale. Ink technology is a major limitation of current EHD nano-drip techniques. Specifically, most EHD printing processes print either nanoparticles or polymers. The materials are structurally weak and often have poor electrical or mechanical properties. For example, printing nanoparticles effectively creates a cluster of nanoparticles that must be sintered to create a continuous material. To address these issues, we have been adapting reactive inks to work with EHD's nano-drip regime. Specifically, we demonstrate that silver and glass nano- and micron-scale structures can be printed using EHD's nano-drip regime. These inks produce solid structures without sintering steps and with good mechanical, electrical, and optical properties.

In this paper, we discuss the impact of impact of solvent properties (viscosity, vapor pressure, etc.), substrate temperature, capillary diameter and electric field strength on feature resolution, electrical resistance, and mechanical properties. Structures are characterized using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and 2-point probe resistance measurements. This work shows that reactive ink chemistries can be combined with EHD printing to produce fine resolution features consisting of solid metal/glass without an annealing step

The integration of bottom-up synthesized nanowires into a functional device architecture is a persisting key challenge. The transfer of nanowires from the growth to a target substrate is mostly required for device fabrication and is often realized out of a liquid without control over single-nanowire positioning on the target substrate. Based on its simplicity and effectiveness, mechanical nanowire transfer, such as nanoscale combing or contact printing, appears promising. Here, nanowires are transferred in high density and with parallel alignment by a shearing motion of the growth and target substrate. Patterned resists allow furthermore to confine nanowire deposition to certain areas. In order to expand the scope of mechanical nanowire transfer, we present a completely resist-free strategy based on dry friction with the motivation to position single-nanowires on a large-scale as required for instance in the field of sensor fabrication. Our approach avoids the constraining requirement of oil-based lubricants as well as the necessity of patterned resists to confine nanowire deposition. We show that localized surface features, such as material composition, surface morphology, or even nanoparticle decoration affect directly the local frictional force between an individual silicon nanowire and the target substrate enabling control over the deposited local nanowire density. By combining the materials Si₃N₄, SiO₂ and Au, silicon nanowire deposition was confined down to a single-nanowire. Due to the fact that the position of the localized surface features on the target substrate is well defined, the established individual nanowire integration within random assemblies becomes fully obsolete for device fabrication. The capability of our approach is demonstrated by a mask-assisted assembly of nanowire resistors in 36 target areas on a silicon-based substrate with an area of over 2 cm² yielding typically up to 80 % operative single-nanowire devices. In principle, our method is scalable and can be readily expanded to other material combinations or substrates.

Layer by Layer (LbL) is a deposition technique that can produce materials with unique physical properties. Traditional LbL however is very tedious and expensive. LbL. Fabrication method using LbL and self-assembly is a simple method allowing the design of multilayer ultrathin films. Self-assembly is a phenomenon through which an interaction drives the polymer and nanoparticle to form a larger nanostructured film spontaneously. This spontaneous organization can happen because of the direct or indirect specific interaction between the polymer and nanoparticle. Self-assembled gas barrier films have variety of applications inpackaging industry.There are several techniques that can be employed to make self-assembled gas barrier films including: spraying, inkjet printing and some other common commercial coating techniques. This research is focusing on using inkjet printing technique while explains the theory behind other approaching techniques and their advantages or drawbacks. Employing inkjet printing approach for producing LbL films are more efficient than other techniques since there is no need for any rinsing step thus saving cost, time, and material. Functional and physical properties of different materials were investigated in this research.The preparation of thin films on substrates via inkjet printing is an interesting subject sincethe size of the deposited film is tens or hundreds of a micron. In this approach, different concentrations of polymers and nanoclay solutions were analyzed for their effectiveness as a gas barrier film. Selection of materials allows functional thin films to be engineered for different applications.These thin films are consisting of polymers and nanoclays on a Mylar substrate, Poly Ethylene Terephthalate (PET). The films are characterized by using X-Ray Diffraction (XRD) and the barrier properties for oxygen diffusion aremeasured as well. The results clearly show a good oxygen barrier behavior of a combination of Polyvinylpyrrolidone (PVP) and Montmorillonite nanoclay (MMT).

Owing to the inherent two-dimensional nature of graphene, its principal applications are anticipated to be as a macroscopic film or sheet structures. Graphene’s outstanding material properties, including high electrical/thermal conductivity and superstrong mechanical properties along the two-dimensional graphene plane, can be exploited for diverse applications. Presently, transparent graphene film preparation relies principally on CVD growth from metal catalysts. CVD growth offers high-quality large-area graphene. Nevertheless, vacuum processing at high temperature is expensive and requires long batch times. Solution processing of pristine graphene based films has great potential for the cost-effective production. However, the low solution compatibility of pristine graphene, particularly in volatile solvents, makes it hard to employ conventional processing methods such as drop-casting, spin-coating, and rod-coating. As an alternative approach, chemically modified graphene with improved solution dispersibility, for instance graphene oxide with aqueous dispersibility up to more than 5 wt %, is frequently used as a precursor for solution processing. But, intrinsic degradation of the structures and properties of graphene is hard to avoid. In this work, we demonstrate unusually fast interfacial assembly of pristine graphene platelets as a cost-effective and high-yield route to large-area based films. We find that pristine graphene platelets temporarily suspended in aqueous media assemble into an arbitrarily large area uniform graphene based film in a few minutes by adding ethyl acetate to the suspension.

Polymer cold-drawing is a process in which applied stress along the fiber axis causes the polymeric chains to orient themselves, reducing the diameter of a drawn fiber (or thickness of a drawn film). Cold-drawing has long been employed in the industrial production of high-strength fibers, such as polyester and nylon threads. Here we show that in a multimaterial fiber composed of a brittle core embedded in a cladding that undergoes cold-drawing, surprising new phenomenon arises: as the neck propagates along the fiber the brittle core fractures predictably, producing uniformly sized rods along meters of fiber. Furthermore, by using a stack-and-draw method to produce fibers with a high density of cores, the fragmentation process can be parallelized to produce large numbers of embedded micro- or nano-rods.
Embedded structured cores having arbitrary multimaterial transverse geometry – from sub-millimeter to sub-micron scales – are thus fragmented into a periodic train of rods held stationary in the polymer. Two options exist at this stage in the process: the rods may either be easily extraction via selective dissolution or, alternatively, self-healing of the brittle thread is possible via thermal restoration. This process is not limited to cylindrical threads embedded in a ductile, polymeric cladding. The cross section of the resulting rods is determined by the shape of the rod used as the core of the preform that produces the drawn fiber. We demonstrate this flexibility by producing multimaterial rectangular rods, multimaterial hollow cylindrical rods, and hollow triangular rods with a rectangular hole. The method is also applicable to composites with flat rather than cylindrical geometry, whereupon cold-drawing leads to the breakup of an embedded or coated brittle film into narrow parallel strips aligned normally to the drawing axis.
The fragmentation effect is applicable to a wide range of materials in the core, as long as the core material is brittle enough that it does not stretch or itself cold-draw. We demonstrate this by using various materials in the core ranging from silicon, germanium, gold, and glasses, to silk, polystyrene, biodegradable polymers, and even ice. We observe, and verify through nonlinear finite-element simulations, a linear relationship between the smallest transverse scale and the longitudinal breakup period. This work may lead to dynamical camouflaging via a nanoscale Venetian-blind effect, scalable fabrication of micro- and nanoparticles with arbitrary cross sections, and large-area meta-surfaces for highly sensitive detection of pathogens.

Low-cost high-efficiency alternatives to conventional Silicon-based solar cells are needed for a decentralized energy supply and might be provided by organic or dye-sensitized solar cells (DSSCs). Hence, much research has been devoted to improving the power conversion efficiencies of organic solar cells (OSCs), especially by developing new photostable and processable chromophores with tuneable electronic features. For each new material system a mostly empirical optimization of manifold device fabrication parameters is necessary to achieve a reliable material evaluation and higher power conversion efficiencies. Since the fact, that the morphology changes towards the thermodynamic minimum during optimization process like tempering and but maybe away from the performance maximum, self-assembling of chromophores is a promising way to reduce the optimization efforts. Long term stability could be achieved through determinated supra-molecular structures.
Here we present our approach to utilize amphiphilicity of dyes to control supra-molecular geometries and to stabilize interfaces^[1,2]. Furthermore, it is shown that amphiphilic dyes can be deposited as smooth monolayers for the fabrication of model devices with well-defined interfaces and tunable molecular order. As donor chromophores we use 4-hydroxy-1,3-thiazoles, which are a long-known class of chromophores which experienced a renaissance in recent years^[3]. Thiazoles are photochemically stable, possess high molar extinction coefficients as well as fluorescence quantum yields up to 95% and in addition, exhibit solvatochromism and were successfully tested in DSSCs[^4,5,6]. We present the synthesis and characterization of amphiphilic dyes for development of improved organic solar cells and OLED's.
References:
¹: M. Kaufmann, T. Sachse, S. Fischer, S. H. Habenicht, D. Weiss, T. Martínez, B. Dietzek, R. Beckert, M. Presselt 2015, to be submitted.
²: S. H. Habenicht, S. Schramm, S. Fischer, T. Sachse, F. Herrmann, B. Dietzek, M. Presselt, D. Weiss, R. Beckert, H. Görls 2015, to be submitted.
³:U. W. Grummt, D. Weiss, E. Birckner, R. Beckert, J. Phys. Chem. A,111 (2007) 1104-1110
⁴: R. Menzel, D. Ogermann, S. Kupfer, D. Weiss, H. Görls, K. Kleinermanns, L. González, R. Beckert, Dyes and Pigments, 2012, 94(3), pp 512–524
⁵: E. Täuscher, D. Weiss, R. Beckert, H., Synthesis, 10 (2010) 1603-160
⁶: Lorena K. Calderón-Ortiz, Eric Täuscher, Erick Leite Bastos, Helmar Görls, Dieter Weiss, and Rainer Beckert; Eur. J. Org. Chem. 2012, 2535-2541
Acknowledgement:
We acknowledge the Bundesministerium für Bildung und Forschung (FKZ 03EK3507) for financial support.

Micropatterning 2D materials grown on a large area substrates of different materials has become a challenging task and absolutely necessary preliminary step in developing electronic and optical devices from 2D materials. Substrates like for ex. sapphire has charging problems upon interaction with an electron beam, which makes e-beam lithography difficult and time consuming process for micro/nanopattering. In this work, we present results comparing two methods to pattern a monolayer of 2D material (molybdenum disulphide) (MoS₂) grown on a sapphire substrate using chemical vapor deposition method. The first method being a multistep e-beam lithography and the second method using a flexible poly (dimethylsiloxane) (PDMS) stamp.

The non-lithographic and simple patterning scheme using an inexpensive PDMS stamp or mold is a two-step process. In the first step, we were able to transfer the pattern from PDMS mold by bringing the PDMS mold into hard contact with sample coated with the photoresist at a temperature of 90° C. In the final step, were able to etch the 2D material using inductively coupled plasma reactive ion etching with boron trichloride gas transfering the pattern further onto MoS₂, followed by a liftoff to get rid of the photoresist. We used a combination of microscopy and raman spectroscopy techniques to systematically characterize and analyze samples before and after transfer printing. The flexible PDMS stamp could be reused after following simple cleaning methods. We were also able to use a PDMS stamp to transfer few layers of MoS₂ exfoliated from bulk crystal, from one substrate to another substrate, very useful for device applications involving heterojunctions.

We have successfully transfer printed patterns with features sizes varying form 1-10 microns on the same sample using different PDMS stamps having different features sizes, thereby a larger area of few hundred microns can be micro/nanopatterned quickly avoiding the expensive and time consuming e-beam lithography or photolithography. This flexible PDMS stamp transfer printing method gives us flexibility, not limited by the material, scalable to accommodate larger areas and is inexpensive.

Graphene is a two-dimensional carbon material, which exhibits extraordinary thermal and electrical conductivity. To realize graphene materials in practical applications such as flexible or wearable devices, development of graphene assembly techniques is essential. Researchers have developed spinning (wet, dry, or electro-) methods for preparing graphene fibers. Conventional strategies require specialized spinnerets and related equipment such as pump, spin bath, and etc. Herein, we proposed an efficient method to prepare a graphene fiber using a branched cationic polymer, poly(ethylenimine) (PEI), as a backbone (i.e. main chain). Simple, interfacial contact of two droplets for which one contains chemically modified graphene (CMG) and the other does PEI instantaneously generates graphene/PEI micro-fibers by lifting the interface between the two solutions using a conventional pipette tip. We were able to continuously extract an assembled macroscopic graphene fibers up to ~ 60 cm. In addition, we controlled the thickness of fibers ranging from approximately 500 μm to 1300 µm by adjusting the ratio of two different substances. The diameter of fibers was further controlled from approximately 150 µm to 500 µm by changing the wettability of the substrate. This technique is easy to perform and cost-effective, facilitating the next generation electro-textiles.

We present a novel printing mechanism via dry transfer of chemically reduced graphene oxide (r-GO) thin film. We discover that shear stress induced on the elastomeric stamp surface facilitates delamination of the deposited r-GO thin film from the stamp. Shear stress is introduced in a roll-to-roll printing system by rotating the stamp roller faster than the substrate roller. Energy-balance theory for thin film transfer is suggested to analyze the film delamination behavior with induced shear stress. We found that the use of other adhesives can be avoided by employing shear load to increase strain energy release rate. Successful dry transfer of r-GO thin film onto flexible substrates is demonstrated in a roll-to-roll printing system at a printing rate of 5mm/min. The transferred r-GO thin film is demonstrated as flexible transparent electrode by fabricating a flexible transparent touch sensor. It is expected that technologies introduced here will improve manufacturing systems for printed electronics especially where dry film transfer is required. There should be many other thin films that can employ shear-induced transfer mechanism.

Reference
[1] H. Jang and W.S. Kim*, “Shear-induced Dry Transfer of Reduced Graphene Oxide Thin Film via Roll-to-roll Printing” to be published (2015).
[2] R. Kazemzadeh, K. Andersen , L. Motha and W.S. Kim*, “Highly Sensitive Pressure Sensor with Reduced Graphene Oxide” IEEE Electron Device Letters 36, pp.180-182 (2015).

3D heterogeneous system integration and packaging in which different-sized chips and various materials/devices can be highly integrated is increasingly becoming essential for the advent of new societies called IoT (Internet of Things), M2M (Machine-to-Machine), and Trillion sensors. Such 3D heterogeneous systems with through-Si vias (TSVs) require 3D chip stacking technologies with high production throughput and yield. To realize the 3D systems, Tohoku Univ. has developed various advanced technologies. It is notable that we have first proposed and developed advanced multichip-to-wafer 3D integration technologies with self-assembly using liquid capillary as a driving force. The self-assembly can dramatically improve both assembly throughput and alignment accuracy that have been a trade-off in conventional pick-and-place methods. Unlike conventional chip bonders, the self-assembly does not require sophisticated machines such as high-resolution image recognizing apparatus, high-precision multiaxis petitioners, and ultrafast operation robots.

From the practical point of view, it is necessary to provide tolerability for misalignment to the self-assembly process. However, chip alignment accuracies of the self-assembly are affected by extrinsic parameters. In our self-assembly studies, we evaluated the several parameters: chip sizes, liquid volumes, substrate tilting, positioning misalignment before releasing the chips, wettability contrast between hydrophilic assembly sites and the surrounding hydrophobic areas, and the edge heights of chips and the assembly site on the substrate. At the beginning, we discuss a series of studies on these parameters that successfully and reproductively provide the self-assembly to realize high-alignment accuracy and high-yield 3D systems.

And then, we describe several demonstration results applicable to the 3D hetero systems using the self-assembly. First, we present the self-assembly for optical interconnection enabling high-speed and high-bandwidth data transmission in or between the 3D systems. The self-assemblies of small optical devices are very useful because of their demand for precise alignments. Here, the successful self-assembly using long rectangular vertical-cavity surface-emitting laser is demonstrated. In addition, we talk about 3D chip stacking method via microbump bonding having the high reliability and productivity. Non-conductive film (NCF) is a promising material for high-throughput 3D chip stacking with fully wafer-level underfilling. Precise self-assembly and excellent electrical connections of the resulting microbump chain have been successfully demonstrated using NCF-laminated chips.

“Alignment”, “Bonding”, and “Interconnect” are of crucial importance in the self-assembly technologies for advanced 3D heterogeneous system integration and packaging. In this presentation, we introduce our recent capillary self-assembly technologies toward upcoming next-generation IT societies.

Integrated nanoelectronic and nanoelectromechanical systems based on nanomaterials have potential applications in sensors, actuators and energy conversion. To fabricate function systems, nanomaterials must be assembled in large scale with controlled orientation and distance. Here we report a polymer-based bubble method to assemble both one- and two-dimensional nanomaterials over large area, and then fabricate graphene-hybridized structures consisting of aligned nanomaterials for advanced electronic nanodevices.
Polymer is the key for blowing large-size bubbles, as well as aligning the embedded nanomaterials. Here we select polymethylmethacrylate (PMMA), a conventional polymer used as photoresist for device fabrication. By this way, we obtain many assembled configurations, such as aligned Te nanowire or nanospring arrays, crossed multi-walled carbonnanotube (MWCNT) networks, and uniformly distributed graphene oxide (GO) sheets.^[1-3] Particularly, the initially straight nanowires can be converted in situ into buckled nanosprings during bubble blowing, which offers a promising way to assemble nanostructures with controlled shape during assembly process. These assembled arrays and GO sheets have been directly fabricated into photo-detectors, gas sensors (NO₂) or silicon solar cells with high performance.
Furthermore, PMMA can act as solid carbon source for graphene growth, so various composite structures containing assembled nanomaterials have also been fabricated. Combined blown bubble method with thermal annealing, we utilized the PMMA bubble film to grow graphene in situ among the assembled MWCNT networks or wrapped on the surface of the melted Cu nanowires, resulting in MWCNT-graphene hybrid films^[2] and aligned graphene nanotubes partially filled by Cu NWs, respectively. The hybrid structures integrate the advantages of both materials, and that the hybrid films enable electrical conductivity and structural integrity of the initial MWCNT network. Also the graphene nanotubes wrapped on the Cu nanowires enhance the chemical stability of the aligned Cu arrays.
In conclusion, our blown bubble method achieves efficient assembly of both one- and two-dimensional nanomaterials over large area, and offers a strategy to produce a variety of graphene-related hybrid structures. It is possible to co-assemble one- and two- dimensional nanomaterials simultaneously and enable broad applications with future.
References
1.Shiting Wu, Kai Huang, Enzheng Shi, Wenjing Xu, Ying Fang, Yanbing Yang, Anyuan Cao. ACS Nano 2014, 8, 3522- 3530.
2. Shiting Wu, Enzheng Shi, Yanbing Yang, Wenjing Xu, Xinyang Li, Anyuan Cao. Nano Research 2015, 8, 1746-1754.
3. Shiting Wu, Yanbing Yang, Yitan Li, Chunhui Wang, Wenjing Xu, Enzheng Shi, Mingchu Zou, Liusi Yang, Xiangdong Yang, Yan Li, Anyuan cao. ACS Appl. Mater. Interfaces, accepted, DOI: 10.1021/acsami.5b08646.

The ability to controllably and rapidly engineer nano to micro- sized self-assemblies from C₆₀ fullerene molecules is demonstrated in this work. Of particular interest is the fact that fullerene self-assemblies can be shape-shifted in the form of rods, tubes, cubes as well as more complex shapes such as flowers using a straightforward wet chemistry procedure that involves coating fullerene solutions on different substrates and suitably modifying self-assembly conditions based on temperature, substrate surface roughness, solvent-substrate wetting, solvent boiling point and solubility of the fullerene molecules. A salient feature of this substrate-mediated approach is that the self-assembly occurs very rapidly (less than a minute) and the size and shape of the self-assemblies can be readily reconfigured by altering the kinetics of self-assembly. This ability to reconfigure the shape-shifting fullerene self-assemblies opens up new avenues for multifunctional agile materials-systems. In this context, we discuss and demonstrate the role of the fullerene self-assemblies as supercapacitor electrode constituents as well as for phononic applications.

Alignment of microchips with receptors is an important step in microassembly for building highly integrated micro- and nanosystems. Assembly towards microchips requires high alignment accuracy. Surface-tension driven microassembly technique has been reported to be able to achieve sub-micrometer alignment accuracy, where it was essential for microchips to have sufficient overlap with receptor sites. In this work, we demonstrate that microscopic rain and hydrophilic/superhydrophobic patterned surfaces can be used for self-transport and self-alignment of microchips and tolerate extremely large placement errors well beyond the current state-of-art. The patterned surface consists of hydrophilic silicon receptor sites surrounded by superhydrophobic black silicon, having a water contact angle of 50° and 170°, respectively. Rain-induced microscopic droplets are used as a medium for surface-tension driven self-transport and self-alignment. The boundary conditions for self-transport and self-alignment have been explored by modeling and confirmed experimentally. The maximum permitted gap between a microchip and a receptor site is determined by the volume of the liquid and the wetting contrast between receptor site and substrate. Microscopic rain applied on hydrophilic-superhydrophobic patterned surfaces greatly improves the capability, reliability and error-tolerance of the process, avoiding the need for accurate initial placement of microchips, and thereby greatly simplifying the alignment process.

With the increasing prevalence of micro assembly technologies a number of complex and difficult challenges have arisen. Recent advances in ElectroHydroDynamic (EHD) printing have shown that 3D nanostructures can be readily fabricated and used to form nano-sized interconnects and optical devices. This “nano-drip” regime is accessed by bringing the EHD nozzle to within 3 – 5 µm of the substrate so that the droplets leaving the nozzle “auto-focuses” towards the target structures. Precisely locating 1 µm diameter nozzles in 3 dimensional space fast enough so that the nozzle doesn’t dry out can be a significant challenge.

This paper details a non-contact method of locating small nozzles and pipettes in three dimensions in a manner that is rapid, accurate, and inexpensive. Targeting 1 µm placement accuracy, we discus physics and correction algorithms behind the process along with our data validating the accuracy. Alignment to pre-existing electronic structures are demonstrated with 100 nm electrical interconnects using self-reducing silver reactive inks along with optical structures from printed SiO₂.

In this work, we report a simple approach for controlling surface morphology of polymer substrate through a solvent/non-solvent coating technique based on improved phase separation. The technique involves a process of coating a volatile mixture of solvent and non-solvent onto the surface, which yields an outermost layer which is a polymer solution, and subsequently allows phase separation through solvent evaporation under ambient air, which spontaneously creates a micro-porous surface. It was found that a mixture of chloroform and methanol, used as a solvent/non-solvent pair, shows a high efficiency for controlling the surface morphology of poly(lactic acid), poly(methyl methacrylate) and poly(styrene). Both size and density of pores formed were controlled by varying solvent compositions as well as modulating experimental conditions. Moreover, the underlying mechanism of the formation of the porous structures has been theoretically proposed and experimentally verified. The resulting porous surface has potential in the creation of a super-hydrophobic surface, interestingly revealing high adhesion force with liquid droplets.

About the active component, as for the production, commoditizing was accelerated for the high-performance production, because of the integration and the miniaturization of the semiconductor process. Therefore, the mixed mounting method using the passive components is highly interested in the market so that the semiconductor technology is developed in computerizing of the wearable technology, the automotive components, and the medical equipment.
On the other hand, the passive component, electronic components manufactures are proposing ultra-miniature sizes such as 03015 (0.30 mm x 0.15 mm) and 0201 (0.25 mm x 0.125 mm or 0.20 mm x 0.10 mm) size part downsized more from 0402 (0.40 mm x 0.20 mm) which is the smallest size part at the present mass production level, for the miniaturization and high-function of electronics production. Furthermore, electronic components manufactures start to develop 01005 (0.10 mm x 0.005 mm) size part aiming at further downsizing, focus on the highly-miniaturized production.
Consequently, the market is interested in the mounting system which can mount the ultra-miniature size part with sufficient accuracy and speed, and checks possibility to produce highly-miniaturized product which is improving thinner and weight-saving than a current product. We introduce one end of our development technology in this time.

A major challenge in planar and 3D printing is the ability to pattern materials over a wide range of physical properties. Commercial printing techniques are limited to narrow range of ink viscosities (e.g., inkjet printing) or materials set (e.g., thermoplastics for fused deposition modeling) as dictated by the specific printing mechanism. Decoupling the physical properties of the ink from the printing process would allow unprecedented freedom in the type of materials that can patterned, ranging from electronic to biological inks. Here, we introduce, model, and experimentally verify acoustophoretic printing, in which nonlinear acoustic forces are harnessed to print droplets of disparate classes of materials on demand. Specifically, we show that ink viscosities spanning more than four orders of magnitude (0.5 mPa to 5000 mPa) can be printed by this nascent method. Moreover, the ejected droplet size can be varied continuously by more than two orders of magnitude by controlling the acoustic forces, from the subnanoliter to microliter range. To highlight its flexibility, we have printed a broad palette of materials, including concentrated polymer solutions, colloid suspensions, liquid metals and, even, more complex droplets, such as double emulsions. In summary, acoustophoretic printing represents a new paradigm for patterning functional, structural and biological materials in both planar and 3D form factors.

Three dimenional(3D) assembly of nanoparticles still remains challenging. We present a novel method to fabricate the multifurcated 3D nanoparticle assemblies via aerosol technology. Via electrotatic focusing lens effect that we reported before (nature nanotechnology(2006), nano letters(2011)), we successfully position charged aerosol nanoparticles with nanoscale resolution at ambient pressure and put each nanoparticle building block to manufacture versatile 3D nanostructures. When the 3D metal nanoparticle assembled structures are grown from neighboring three openings of photoresist under a given electric field, electric potential fields are evolved so that charged nanoparticles are assembled in the region of minimum potential fields that occur between two neighboring 3D nanostructures. If we assemble nanoparticles from three neighboring openings, the assembly process for the nanoparticle structure grown from the central hole could be bifurcated into two split directions so that the 3D nanoparticle structures face each other 3D nanoparticle structures grown from other openings. Depending on the arrangement of prepatterned holes, the electric potential fields can be manipulated and multi-furcation assembly of nanoparticles could be realized. We demonstrate that bifurcation, tri-furcation, tetra-furcation, penta and hexa-furcation assembly of charged nanoparticles are possible with nanoscale resolution at ambient condition. Based on the effects of the alignment angles and distances between patterns, we designed diverse types of hole arrangement for guiding charged nanoparticles to the three dimensional and multidirectional assembly. Electrostatic calculations show the electrical potential trap could limit the movement of charged aerosol particles around the hole enabling the multi-furcation assembly. In accordance with the growth time, interconnections between neighboring structures were precisely controlled and electrical characteristics were measured to check the growth state and the formation of the electric network. As an application, multifurcated bridge structures connecting the separated electrodes were prepared by copper nanoparticle assembly and applied to the metal oxide semiconductor gas sensor showing much enhanced sensitivity by 300 % compared to conventional particle film type gas sensor. This presentation is the first demonstration of multi-furcated 3D self assembly process in gas phase.

Efficient and controlled nanoscale propulsion in harsh environments requires careful design and manufacturing of nanomachines, which can harvest and translate the propelling forces with high spatial and time resolution. Here we report a new class of artificial nanomachine, named magneto–acoustic hybrid nanomotor, which displays efficient propulsion in the presence of either magnetic or acoustic fields without adding any chemical fuel. These fuel-free hybrid nanomotors, which comprise a magnetic helical structure and a concave nanorod end, are synthesized using a template-assisted electrochemical deposition process followed by segment-selective chemical etching. Dynamic switching of the propulsion mode with reversal of the movement direction and digital speed regulation are demonstrated on a single nanovehicle. These hybrid nanomotors exhibit a diverse biomimetic collective behavior, including stable aggregation, swarm motion, and swarm vortex, triggered in response to different field inputs. Such adaptive hybrid operation and controlled collective behavior hold considerable promise for designing smart nanovehicles that autonomously reconfigure their operation mode according to their mission or in response to changes in their surrounding environment or in their own performance, thus holding considerable promise for diverse practical biomedical applications of fuel-free nanomachines.

Electrophoretic deposition (EPD) has been used industrially for nearly century for deposition of paint and barrier coatings. Traditionally, it has been used to create unpatterned thin films of various materials such as metals, ceramics, and polymers. Recently, we have demonstrated the ability to use a photoconductive electrode system to create millimeter scale patterns and structures in electrophoretically deposited films[1,2], the first steps to turning EPD into an additive manufacturing technique. Here, we present improvements to the technique that increase overall resolution and material set as well decrease feature size to 10s of microns by using a novel projection system. We will also present results on modeling the deposition process.

[1] Pascall, et al. Adv. Mat. 26(14) (2014): doi:10.1002/adma.201304953.
[2] Pascall, et al. Key Eng. Mat. 654 (2015): doi:10.4028/www.scientific.net/KEM.654.261.

Prepared by LLNL under Contract DE-AC52-07NA27344.

This contribution presents the use of MicroElectroMechanical Systems (MEMS) functionality for the high precision alignment of photonic chips. The MEMS functions are integrated with one of the photonic chips, to fine align mechanically flexible waveguides in multiple directions.
A key challenge in the manufacturing of advanced photonic packages is the assembly and alignment of the components. This needs to be done with high precision to prevent unacceptable loss of coupled power, while meeting demands relevant for volume production scenarios. A new generation of photonic packages is based on Photonic Integrated Circuits (PICs), i.e. micro-fabricated photonic chips, which can nowadays be fabricated against acceptable cost levels. The packaging into devices is technologically and cost-wise a key bottleneck for their market entrance.
Moderns PICs are multi-port components, and interface to other multi-channel PICs or a fibre array, which requires alignment in multiple directions. The required precision is high, e.g. ±0.1μm waveguide-to-waveguide precision for a spot size of 3μm. The classic approach to photonic alignment uses precision manipulators and precision fabricated components, which are joined using e.g. adhesives or solder. While the conventional approach can meet precision demands, other approaches are needed to lower the cost.
Our proposal is to replace the assembly machine with on-chip micro-fabricated assembly functions integrated with one of the photonic chips. This is part of a larger photonic packaging concept which combines two elements. First, advanced industrial state-of-the-art die bonding equipment is used to place and bond the two PICs on a common substrate. The precision is determined by the machine performance and the bonding process and is in the order of 3-5μm. Secondly, the waveguide structures on one of the chips are released during their fabrication, leading to mechanically flexible waveguide structures. MEMS functionality, i.e. micro-fabricated actuators, is integrated with the PIC to move the waveguide structure and to compensate the placement error originating from the component assembly. The optimal position is found by measuring the coupled power.
The MEMS functions are realised in a 16μm thick SiO₂/Si₃N₄ waveguiding layer. The SiO₂ is under compressive stress after fabrication, and a process had to be developed for the release of the structures without fracturing. Thermal bimorph actuators are realised by depositing a poly-Si layer and heaters. The resulting material stack has significant bending, and a dedicated bimorph actuator design is proposed to keep the out-of-plane deflection of the waveguides within acceptable limits. Current tests show that waveguide arrays can be moved in multiple directions over ranges varying from 3 to >6 μm, which is sufficient to compensate the initial chip positon error.

This research is supported by Dutch STW grant 11355 “Flex-O-Guides” and EU FP7 grant 619267 “PHASTFlex”.

The three-dimensional (3D) clustering of Janus cylinders are controlled by simply tuning the cylinder geometry and hydrophobic interactions. Janus cylinders were prepared by combining two approaches: micromolding and initiated chemical vapor deposition (iCVD). Hydrophilic cylinders with a flat- or convex-top curvature were prepared by micromolding based on surface tension-induced flow. The iCVD process then provides a hydrophobic domain through the simple and precise deposition of a polymer film on the top surface, forming monodisperse Janus microcylinders. We use these Janus cylinders as building blocks to form 2D or 3D clusters via hydrophobic interactions in methanol. We investigate how cylinder geometry or degree of hydrophobic interaction affects the resulting cluster geometries. The convex-top Janus cylinders lead to 3D clustering through tip-to-tip interactions, and the flat-top Janus cylinders lead 2D clustering through face-to-face attraction. Number of Janus cylinders in 3D clusters is tuned by controlling the degree of hydrophobic (or hydrophilic) interactions. The effects of geometry and surface chemistry on the self-assembly of cylinders investigated in this work will further the development of new microparticle assembly designs.

Recently solution processed single walled carbon nanotubes(SWNTs) have attracted great attention for their excellent electrical and mechanical properties. However, most of devices and circuits, reported in the literatures, have been implemented with highly purified, solution-processed SWNTs which typically resulted in deterimental effects associataed with intrinsic field effect mobility degradation (μ_eff), reduction of average length (~a few μm) of SWNTS, and non-cost-effective processes.
Therefore, we proposed the wafer-scale aligment and its purification scheme, which are fully compatible and required for the preparation of the next gneration ultra-high purity of aligned single walled carbonnanotubes. In this study, we reported the novel electrode materials (i.e, graphene, random networks of SWNTs) and their combination scheme with several nanometer(~ nm) range and their unique usage for the alignment scheme for semiconducting enriched, unpurified solution-processed single walled carbonnanotube, thereby signicantly reduces the process steps. Furthermore, the ultra-thin electrodes with carbon materials composition, which are easily etched by O₂ plasma reactive ion etching (RIE), were fullly utilzed for the perfect aligment of single walled nanotubes and its purification (i.e, thermalcaplliarity enabled purifcation(TcEP)) for preparation of wafer-scaled SWNT substrates with ultra-high purity (>99.999%) for the next generaration semicoduncting devices and circuit application. The wafer-scale aligned SWNTs on silicon substrates with thermal oxide are fully confirmed by scanning electron microscopy(SEM) and atomic force microscopy(AFM). In addition, electrical performance and their purity were fully validated via large scale statistical analysis for implemented SWNT FETs.

While conventional rigid electronics currently accounts for the majority of devices used in our daily lives, the field of flexible electronics has rapidly grown as a viable alternative over the last decade. The increasing need for real-time healthcare monitoring, light-weight mobile electronics, and wearable displays has increased the industrial importance of portable and flexible devices. Conventional strain sensors comprising metallic foil patterns and semiconducting piezoresistors are currently used for various applications. Although their process is well developed and requires a low fabrication cost, the fragile and rigid nature of metals and semiconductors present limitations in stretchability and durability. In this case, electrically stretchable structures and materials are greatly in need. Material approaches are mainly performed by developing conductive stretchable materials, such as polymer composites with conductive nanofillers embedded and distributed spatially in polymer matrices, two-dimensional (2D) conductive nano-networks on surface areas, polymer-infiltrated three-dimensional (3D) conductive foams, and conductive films stacked or inkjet-printed onto elastic polymer substrates. Of these, three-dimensional graphene foam (GF) with a macroporous network structure has achieved intense attention due to its large surface area and its excellent electrical and mechanical properties. It has been used in diverse area including energy storage devices, in addition to chemical and biological sensors. Here, when GF was combined with an elastomer such as polydimethylsiloxane (PDMS), it exhibited stable electrical and mechanical properties under various types of deformation, including stretching.

In the present study, we report on a facile synthesis of graphene foam via a simply reduction and self-assembly process. The as-prepared three-dimensional graphene foam shows ultralow density (as low as 4.9 mg cm ^-3), high porosity (as much as 99.8%) and great mechanical stability which facilitate the incorporation of PDMS elastomer into the graphene framework and the graphene/PDMS composite could be obtained easily without vacuum-assisted infiltration. Because of the great electrical conductivity of the reduced graphene which was benefit from the highly-efficient reduction agent and the continuous three-dimensional network of the graphene foam, the graphene/PDMS composite has demonstrated a great conductivity. Besides, the composite also shows good electromechanical and high sensitivity which is quite important for the strain sensor. Furthermore, the composite demonstrates great stability during the tensile strain processes. With unique electrical feature and high sensitivity as well as robust mechanical strength, the as-fabricated graphene/PDMS composite poses the great potential as elastic strain sensor materials.