Reza Ghodssi

Virus-Enabled Silicon Anode for Lithium- Ion Batteries

A novel three-dimensional Tobacco mosaic virus assembled silicon anode is reported. This electrode combines genetically modified virus templates for the production of high aspect ratio nanofeatured surfaces with electroless deposition to produce an integrated nickel current collector followed by physical vapor deposition of a silicon layer to form a high capacity silicon anode. This composite silicon anode produced high capacities (3300 mAh/g), excellent charge-discharge cycling stability (0.20% loss per cycle at 1C), and consistent rate capabilities (46.4% at 4C) between 0 and 1.5 V. The biological templated nanocomposite electrode architecture displays a nearly 10-fold increase in capacity over currently available graphite anodes with remarkable cycling stability.

Chitosan: an integrative biomaterial for lab-on-a-chip devices

Chitosan is a naturally derived polymer with applications in a variety of industrial and biomedical fields. Recently, it has emerged as a promising material for biological functionalization of microelectromechanical systems (bioMEMS). Due to its unique chemical properties and film forming ability, chitosan serves as a matrix for the assembly of biomolecules, cells, nanoparticles, and other substances. The addition of these components to bioMEMS devices enables them to perform functions such as specific biorecognition, enzymatic catalysis, and controlled drug release. The chitosan film can be integrated in the device by several methods compatible with standard microfabrication technology, including solution casting, spin casting, electrodeposition, and nanoimprinting. This article surveys the usage of chitosan in bioMEMS to date. We discuss the common methods for fabrication, modification, and characterization of chitosan films, and we review a number of demonstrated chitosan-based microdevices. We also highlight the advantages of chitosan over some other functionalization materials for micro-scale devices.

Investigation of gray-scale technology for large area 3D silicon MEMS structures

Micromachining arbitrary 3D silicon structures for micro-electromechanical systems can be accomplished using gray-scale lithography along with dry anisotropic etching. In this study we have investigated two important design limitations for gray-scale lithography: the minimum usable pixel size and maximum usable pitch size. Together with the resolution of the projection lithography system and the spot size used to write the optical mask, the maximum range of usable gray levels can be determined for developing 3D large area silicon structures. An approximation of the minimum pixel size is shown and experimentally confirmed. Below this minimum, gray levels will be developed away due to an excessive amount of intensity passing through the optical mask. Additionally, oscillations in the intensity are investigated by the use of large pitch sizes on the optical mask. It was found that these oscillations cause holes in the photoresist spaced corresponding to the pitch used on the gray-scale mask and penetrate the thickness of the photoresist for thin gray levels. From the holes in the photoresist, significant surface roughness results when used as a nested mask in reactive ion etching, and the very thin gray levels are lost.

High-speed microfabricated silicon turbomachinery and fluid film bearings

A single-crystal silicon micromachined air turbine supported on gas-lubricated bearings has been operated in a controlled and sustained manner at rotational speeds greater than 1 million revolutions per minute, with mechanical power levels approaching 5 W. The device is formed from a fusion bonded stack of five silicon wafers individually patterned on both sides using deep reactive ion etching (DRIE). It consists of a single stage radial inflow turbine on a 4.2-mm diameter rotor that is supported on externally pressurized hydrostatic journal and thrust bearings. This work presents the design, fabrication, and testing of the first microfabricated rotors to operate at circumferential tip speeds up to 300 m/s, on the order of conventional high performance turbomachinery. Successful operation of this device motivates the use of silicon micromachined high-speed rotating machinery for power microelectromechanical systems (MEMS) applications such as portable energy conversion, micropropulsion, and microfluidic pumping and cooling.

Development of a deep silicon phase Fresnel lens using Gray-scale lithography and deep reactive ion etching

We report the first fabrication and development of a deep phase Fresnel lens (PFL) in silicon through the use of gray-scale lithography and deep-reactive ion etching (DRIE). A Gaussian tail approximation is introduced as a method of predicting the height of photoresist gray levels given the relative amount of transmitted light through a gray-scale optical mask. Device mask design is accomplished through command-line scripting in a CAD tool to precisely define the millions of pixels required to generate the appropriate profile in photoresist. Etch selectivity during DRIE pattern transfer is accurately controlled to produce the desired scaling factor between the photoresist and silicon profiles. As a demonstration of this technology, a 1.6-mm diameter PFL is etched 43 /spl mu/m into silicon with each grating profile designed to focus 8.4 keV photons a distance of 118 m.

MEMS materials and processes handbook

Introduction - Reza Ghodssi and Pinyen Lin.- The MEMS Design Process - Tina Lamers and Beth Pruitt.- Additive Processes for Semiconductors and Dielectric Materials - Chris Zorman, Robert C. Roberts and Li Chen.- Additive Processes for Metals - David Arnold, Monika Saumer and Yong Kyu-Yoon.- Additive Processes for Polymeric Materials - Ellis Meng, Xin Zhang, and William Benard.- Additive Processes for Piezoelectric Materials - Ronald Polcawich, Jeff Pulskamp, Takashi Mineta, and Yoichi Haga.- Materials and Processes in Shape-Memory Alloy - Takashi Mineta and Yoichi Haga.- Dry Etching for Micromachining Applications - Srinivas Tadigadapa and Franz Laermer.- MEMS Wet-Etch Processes and Procedures - David Burns.- MEMS Lithography and Micromachining Techniques - Daniel Hines, Nathan Siwak, Lance Mosher and Reza Ghodssi.- Doping - Alan D. Raisanen.- Wafer Bonding - Shawn Cunningham and Mario Kupnik .- MEMS Packaging Materials - Ann Garrison Darrin and Robert Osiander.- Surface Treatment and Planarization - Pinyen Lin, Roya Maboudian, Carlo Carraro, Fan-Gang Tseng, Pen-Cheng Wang, and Yongqing Lan.- MEMS Process Integration - Michael Huff, Stephen Bart, and Pinyen Lin.

Fabrication of micronozzles using low-temperature wafer-level bonding with SU-8

This paper describes a method for fabricating micronozzles using low-temperature wafer-level adhesive bonding with SU-8. The influence of different parameters on the bonding of structured wafers has been investigated. The surface energies of bonded wafers are measured to be in the range of 0.42–0.56 J m−2, which are comparable to those of some directly bonded wafers. Converging–diverging nozzle structures with throat widths as small as 3.6 µm are formed in an SU-8 film bonded with another SU-8 intermediate layer to produce sealed micronozzles. A novel interconnection technique is developed to interface and test the micronozzles with a macroscopic fluid delivery system to demonstrate the feasibility of the fabrication process. Leakage test results show that this low-temperature wafer bonding process is a viable MEMS fabrication technique for microfluidic applications.

Hierarchical Three-Dimensional Microbattery Electrodes Combining Bottom-Up Self-Assembly and Top-Down Micromachining

The realization of next-generation portable electronics and integrated microsystems is directly linked with the development of robust batteries with high energy and power density. Three-dimensional micro- and nanostructured electrodes enhance energy and power through higher surface area and thinner active materials, respectively. Here, we present a novel approach for the fabrication of hierarchical electrodes that combine benefits of both length scales. The electrodes consist of self-assembled, virus-templated nanostructures conformally coating three-dimensional micropillars. Active battery material (V(2)O(5)) is deposited using atomic layer deposition on the hierarchical micro/nanonetwork. Electrochemical characterization of these electrodes indicates a 3-fold increase in energy density compared to nanostructures alone, in agreement with the surface area increase, while maintaining the high power characteristics of nanomaterials. Investigation of capacity scaling for varying active material thickness reveals underlying limitations in nanostructured electrodes and highlights the importance of our method in controlling both energy and power density with structural hierarchy.

An electrostatic induction micromotor supported on gas-lubricated bearings

This paper reports the first successful fabrication and demonstration of an electrostatic induction micromotor supported on gas-lubricated bearings for electrical-to-mechanical energy conversion. The device consists of a stack of five (5) deep reactive ion etched (DRIE) fusion bonded silicon wafers, with an enclosed 4.2 mm diameter rotor driven by a high-voltage, high-frequency thin-film stator. Testing has demonstrated a torque of 0.3 /spl mu/Nm at a rotation rate of 15,000 revolutions per minute, corresponding to a shaft power of 0.5 mW. This development effort serves to support the creation of a wide array of power MEMS devices such as micro-scale pumps, compressors, generators, and coolers.

Mechanical property measurement of InP-based MEMS for optical communications

We investigate mechanical properties of indium phosphide (InP) for optical micro-electro-mechanical systems (MEMS) applications. A material system and fabrication process for InP-based beam-type electrostatic actuators is presented. Strain gradient, intrinsic stress, Young’s modulus, and hardness are evaluated by beam profile measurements, nanoindentation, beam bending, and electrostatic testing methods. We measured an average strain gradient of δe0/δt = 4.37 × 10 −5 m −1 , with an average intrinsic stress of σ0 =− 5. 4M Pa for [0 1 1] beams. The intrinsic stress results from arsenic contamination during molecular beam epitaxy and (MBE) can be minimized by careful MBE growth and through the use of stress compensating layers. Nanoindentation of (1 0 0) InP resulted in E = 106. 5G Pa and H = 6.2 GPa, while beam bending of [0 1 1] doubly clamped beams resulted in E = 80.4 GPa and σ0 =− 5.6 MPa. We discuss the discrepancy in Young’s modulus between the two measurements. In addition, we present a method for simultaneously measuring Young’s modulus and residual stress using beam bending. Electrostatic actuation in excess of 20 V is demonstrated without breakdown.