AVS2009 Session MN-ThP: MEMS and NEMS Poster Session

Thursday, November 12, 2009 6:00 PM in Hall 3

Thursday Evening

Time Period ThP Sessions | Topic MN Sessions | Time Periods | Topics | AVS2009 Schedule

MN-ThP-1 Imprinting of Guide Structures to Weave Nylon Fibers
Harutaka Mekaru, Masaharu Takahashi (AIST, Japan)
We are developing a large-area display and a wearable health checker by weaving fibers with an electrical circuit on their surface. In this technique, a guide structure that determines the position to fix fibers was processed on the fiber by a thermal nanoimprint technology. We used two kinds of molds with guide structures with different cross-sectional shapes (rectangle and arc). Micropoles to connect the fiber were arranged in the bottom side of the guide structures. In the case of guide structure with a rectangular pattern, the multilayer structure was formed on a Si substrate using MEMS technology; and Ni mold was made by electroforming. Fifteen convex rectangles with their length, width, and height as 14.4 mm, 100 μm and 50 μm were arranged in a 1-mm pitch formation. And, 10-μm deep column holes with the diameters of 5, 10, and 20 μm, were fabricated on the upper side of the guide structure. The other kind of guide structure with an arc pattern was processed by precision machining. A 150-μm-thick Ni-P layer was electroless-plated on an Inconel-600 alloy substrate and the layer was then coarse-processed by dicing. The finish processing employed a 20-μm-diameter diamond endmill and a Robonano α-0iB (FANUC Ltd.). Thirteen arc guide structures with 20-μm-diameter holes were processed for 4 hrs. The length, bottom-width, and height of the individual guide structure were 15 mm, 160 μm, and 100 μm. Hemispherical holes with 20 μm diameter and a maximum depth of 10 μm were processed on the upper side of the guide structure. The size of each type of mold was the same 20 mm square. The guide structures from the two kinds of molds were imprinted on a 90-μm-diameter nylon fiber (Amilan, Toray Industries, Inc). In the imprinting experiments, a desktop thermal nanoimprint system NI-273 (Nano Craft Technologies Co.) was used. Molding conditions were: heating temperatures = 100 °C, cooling temperature = 70 °C, loading force = 100 N, and holding time = 1 s. The guide structure and micropoles were successfully transcribed from the mold onto the nylon fiber. The side-view of the guide structure was examined with an optical microscope and the pressed depth was measured as 21 μm, regardless of the kind of mold used. After the imprinting, the weaving of the fiber was carried out with tweezers under an optical microscope. Each guide was confirmed to be connected to each fiber. It was easy to weave the arc guide structure processed with machining because the guide sidewall was curved. In future, weaving of fiber with variety of electric circuit patterns will be presented.
MN-ThP-2 Test Instrument for the Tensile Strength of Micro-Nano Materials
Akira Kasahara, Hiroshi Suzuki, Masahiro Goto, Hirosi Araki, Pihoshu Yuriy, Masahiro Tosa (NIMS, Japan)
There is considerable research at present on the performance and properties of nanosheets, nanofibers and other functional nanomaterials such as fullerenes and nanotubes. This is particularly true of carbon nanotube, made from carbon atoms, where many research projects throughout the world are looking at measurement techniques for evaluating electrical and electronic characteristics with a view to developing electronic device applications such as high-intensity field-emitted electron sources and ultra-fast transistors. However, we have not yet to see a genuine, flexible methodology for evaluating the key characteristic of mechanical strength essential to micro-nano structural materials development — the nanoscale equivalent of tensile strength testers for ordinary materials. This is due to the inherent difficulties associated with the manipulation and transportation of materials at the micro-nano scale level. Here, we will discuss our recent results on mechanical strength measurement of micro-nano wires in diameter several nm through several thousand nm and in length several mm by means of prepared micro-nano tensile strength tester device.
MN-ThP-3 Morphology and Mechanical Properties of Block Copolymer Films for Bone Regeneration Applications
Bharat Bhushan, Manuel Palacio, Scott Schricker (The Ohio State University)
Biocompatible polymers act as scaffolds for the regeneration and growth of bones. In dentistry, these can be used to treat diseases with accompanying bone loss, such as aggressive periodontitis. Surface morphology, specifically the presence of nanostructures, is expected to affect the adhesion of the cells adsorbed on the surface, which should be optimized for successful cell growth. Block copolymers are of interest as scaffold materials because a number of them are biocompatible, and their nanostructure is easily tunable with synthetic techniques. In this investigation, atomic force microscopy (AFM) studies were conducted for two block copolymers, namely, poly(methyl methacrylate-b-acrylic acid) and poly(methyl methacrylate-b-hydroxyethyl methacrylate). The topography, stiffness, phase angle, and friction maps were obtained in dry and aqueous environments in order to study the morphology, elasticity, viscoelasticity, and friction properties, respectively. Results of AFM imaging identified the presence of polymer domains corresponding to the copolymer components. Images taken in an aqueous medium reveal greater contrast as a consequence of the differential water absorption between the copolymer components.
MN-ThP-4 Mechanically Durable Superhydrophobic, Self-Cleaning, and Low-Drag Surfaces with Hierarchical Structure
Yong Jung, Bharat Bhushan (The Ohio State University)

Superhydrophobic surfaces exhibit extreme water-repellent properties. These surfaces with high contact angle and low contact angle hysteresis also exhibit a self-cleaning effect and low drag for fluid flow1-4. For t he development of superhydrophobic surfaces, which is important for various applications such as glass windows and solar panels, a lternative materials and fabrication methods need to be explored to improve durability5. It is necessary to perform durability studies on these surfaces in order to identify fabrication techniques and materials that can best withstand real world applications. Micro-, nano-, and hierarchical structures which would lead to superhydrophobicity and self-cleaning are prepared using different fabrication methods. In order to compare the durability of the various fabricated surfaces, f riction and wear studies are performed at the microscale using a pin-on-disk test, where a stationary pin applies a constant normal load while sliding on the sample surface. Waterfall and waterjet tests are also conducted to determine the loss of superhydrophobicity by changing the flow volume and pressure conditions, respectively. The changes in the surface morphology and structure and the wettability are examined by SEM and AFM imaging and contact angle measurements, respectively .

1Bhushan, B., Nanotribology and Nanomechanics – An Introduction, 2nd ed., Springer-Verlag, Heidelberg, Germany, 2008.

2Bhushan, B., “Biomimetics: Lessons from Nature - An Overview”, Phil. Trans. R. Soc. A 367, 1445-1486.

3Nosonovsky, M. and Bhushan, B., Multiscale Dissipative Mechanisms and Hierarchical Surfaces: Friction, Superhydrophobicity, and Biomimetics, Springer, Heidelberg, Germany, 2008.

4Bhushan, B. and Jung, Y. C., “Wetting, Adhesion, and Friction of Superhydrophobic and Hydrophilic Leaves and Fabricated Micro/Nanopatterned Surfaces”, J .Phys: Condens. Matter. 20, 225010 (2008).5Bhushan, B. Jung, Y. C. and Koch, K., “Micro-, Nano-, and Hierarchical Structures for Superhydrophobicity, Self-Cleaning and Low Adhesion”, Phil. Trans. R. Soc. A 367, 1631-1672 (2009).

MN-ThP-5 Tripod Honeycomb Shape Scaffold for Retina Cell Culture by Dynamic Mode Multidrectional UV Lithography
Jungkwun Kim, J. Yang, M.M. Slaughter, Gloria Kim, Yong-Kyu Yoon (University at Buffalo, the State University of New York)

Since the cytoskeletal properties of the cells cultured in two-dimensional (2D) culturing environment are different from those of the real biological cells constituting three-dimensional (3D) organs, the in-vitro cytokinetics from a 2D scaffold cannot be applied to in-vivo 3D cell culturing study. In this research, a 3D tripod honeycomb shape scaffold array fabricated using automated dynamic mode multidirectional ultra violet (UV) lithography [1] has been demonstrated for efficient 3D cell culture. A unit element of the scaffold consists of honeycomb shape confinement on the top, three posts at the bottom, and tapered openings in the side walls. This architecture provides advantageous properties for 3D cell culture: (1) sufficient nutrient supply paths through the openings in the side walls, (2) mechanically stable tripod structure, (3) moldable 3D geometry useful for mass production with various material selection, and (4) structural flexibility amenable to further 3D macro shaping. SU-8 (negative tone photoresist) mold masters made by multidirectional lithography, replicas with biodegradable polymer (poly lactic-co-glycolic acid: PLGA) after micromolding, and macroscopically deformed scaffolds are successfully demonstrated. As a test vehicle, retinal cells [2] are successfully cultured on the fabricated PLGA scaffold.

Polydimethylsiloxane (PDMS) has been used to make a negative form of the mold master. A broad range of materials can be used for the final polymeric structure. In this research, PLGA has been cast to form a final scaffold.

The structural compliance associated with the tapered sidewall provides macroscopic flexibility, one of the unique merits of this architecture. A rounded scaffold for the potential usage of artificial blood vessels or other implant devices is demonstrated. A unit scaffold layer has a height of 300mm and multilayer scaffolds can be implemented for much thicker 3D cell culturing by stacking multiple layers.

[1] J.K. Kim et al, “Automated dynamic mode multidirectional UV lithography for complex 3-D microstructures,” Proceedings of IEEE Micro Electro Mechanical Systems, Jan. 13-17, 2008, Tucson, AZ, pp. 399 – 402.

[2] X Luo et al, “Susceptibilities to and Mechanisms of Excitotoxic Cell Death of Adult Mouse Inner Retinal Neurons in Dissociated Culture,” Invest Ophthalmol Vis Sci., 45 (2004), pp. 4576–4582.

MN-ThP-6 Micro Accelerometer with Mechanically Nonlinear Self-Limited Bistable Suspension
Emil Amir, Slava Krylov (Tel Aviv University, Israel)
We report on operational principle, modeling and design of an electrostatically actuated accelerometric device with mechanically nonlinear suspension element. The device incorporates a proof mass actuated by a parallel-plate electrode and attached to a substrate by initially curved beams in such a way that both electrostatic and inertial forces are directed along the beam. In accordance with the exact extensible elastica and approximate reduced order models of the beam used for the analysis, the deformation of an initially curved slender beam subjected to an end force can be subdivided into two stages - the "bending" stage associated mainly with the straightening of the beam and the "tension" stage corresponding to elongation of the almost straight beam. Since the stiffness of the beam at the first stage is significantly lower than at the second stage, the force–displacement dependence of this kind of suspension is of self-limiting type and the beam can be viewed, in a sense, as one directional constraint. Application of nonlinear electrostatic force results in electrostatic (pull-in) instability followed by the steep increase in the straightened beam stiffness preventing contact with the electrode and resulting in appearance of an additional stable configuration and bistability of the beam.
 In this research we present two operational principles for measuring the acceleration - the pull-in voltage monitoring and the resonance frequency shift monitoring. The pull-in voltage approach is based on the (found to be close to linear) dependence between the pull-in voltage and the acceleration, while the self-limiting characteristic of the suspension prevents undesirable from the reliability point of view contact between the proof mass and the actuation electrode. The resonance frequency approach is based on the monitoring of the resonant frequency shift appearing due to acceleration and significantly enhanced in the vicinity of the pull-in instability points. Model results show that using suggested approach significant improvement, comparing to conventional designs with linear flexures, in the device performance could be achieved and µg resolution combined with extended dynamic range are feasible for relatively simple architecture and well established silicon on insulator (SOI) based fabrication process.
MN-ThP-7 Creation of Co-planar Oxide Pillars for Fabricating Overhanging Metal Structures
Steven Hickman, Eric VanWerven, Jeremy Ong, John Marohn (Cornell University)

Magnetic resonance force microscopy (MRFM) combines the nanoscale resolution of scanned probe microscopy with the three-dimensional, isotopically specific imaging capabilities of magnetic resonance imaging. The ultimate goal of MRFM is to achieve single-proton imaging resolution and create an atomic-resolution three-dimensional image of a individual molecule. At this level, the technique could achieve such feats as the structural determination of a single copy of a protein or macromolecular complex, making it a fantastic tool for biological study.

The key technology for MRFM is extremely sensitive, magnet-tipped cantilevers. While extensive effort has gone into fabricating such cantilevers, thermally-limited cantilever sensitivity is seldom achieved in practice because of surface-induced dissipation. The design of our cantilever minimizes this noise by extending the magnet past the cantilever tip. In our current cantilever fabrication scheme, we deposit the magnet on the device layer of a silicon-on-insulator wafer, and then create an overhanging magnet by using an isotropic sulfur hexafluoride etch to partially remove the silicon under the magnet. While successful, this process raises concerns over possible damage to the magnet from the etch species, and there is some degree of variability in the length of the overhang because of the very high silicon etch rate. To mitigate these issues, we have developed an alternative process in which the magnet is deposited over a pillar of silicon oxide extending through the device silicon layer and conformal with the top of this layer. This innovation removes the plasma etching step of our previous approach, and the length of overhang can be controlled by changing the lithographic placement of the magnet relative to the edge of this pillar. The pillar is created by localized oxidation of the device silicon, followed by chemical mechanical planarization. In this poster we will present our progress on this work, as well as present ideas for uses of our innovation well beyond cantilevers for MRFM.

MN-ThP-9 Fabrication of a Vibratory Gyroscope Based on Piezoelectric Actuators and Sensors using MEMS Technology
Veronica Rincon, Harshan Nampoori, Alton Highsmith, Sushma Kotru (University of Alabama)

Piezoelectric materials are commonly used in micro electro mechanical systems (MEMS) due to the self-generating sensing, large actuation amplitude with low voltage, and compatibility to integrated circuit process. In this work we have used Nb-doped Pb(Zr20,Ti80)O3 (PZT) films for fabricating actuators and sensors for a micromachined vibratory gyroscope. PZT films exhibit higher values of effective transverse piezoelectric coefficient (e31,f) and effective longitudinal piezoelectric coefficient (d33,f) compared to any other available piezoelectric materials.

The complete gyroscope device consists of one active wafer, two handler wafers and a Si post bonded together. The active and handle wafers were fabricated using MEMS technology. Entire processing was done in a clean room environment using the state of art micro fabrication facility (MFF) at the University of Alabama . First, PNZT was deposited on both side of the active wafer resulting in PNZT/Pt/TiO2/SiO2/Si/SiO2/TiO2 /Pt/PNZT stack. This step was followed by SiO2/Ti/Au deposition using an e-beam evaporator. Processing the active wafer involves five masks and twenty four photolithography steps. Sine the device is on both sides of the wafers, one side was always protected with photoresist while the other side of the wafer was being processed. The final structures were released by etching away various film layers using a combination of dry and wet etching techniques. This includes three different etching techniques viz., ion mill, oxide etcher, and wet etch.

For the handle wafers Cr films were deposited on Si wafers using an e-beam evaporator. A photo-defineable polyimide was then spun on these wafers and patterned. These patterns were transferred using two masks and two photolithography steps. The active and handle wafers were then bonded together and the Si post attached to it to form the complete device. Details of the fabrication process of the device and its evaluation will be presented.

Time Period ThP Sessions | Topic MN Sessions | Time Periods | Topics | AVS2009 Schedule