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This paper proposes a new single-layer electrostatic microactuator design that generates three-axis motion resulting in vertical translation and out-of-plane tilting. The new actuator design combines a micrometer-scale three-dimensional (3-D) polydimethylsiloxane (PDMS) structure fabricated using soft lithography with comb drives processed using a single mask on a silicon-on-insulator (SOI) wafer. The multi-axis actuation capability of the proposed actuator is enabled by coupling the in-plane actuation motion of the comb drives with the elastic bending of PDMS flexural microjoints. To predict the static and dynamic performance of the actuator, this paper develops a four-bar-linkage model and applies Lagrangian dynamics theory. The developed analytical model is validated using finite element analysis (FEA) and allows us to perform parametric design of the actuator. The analysis indicates that the proposed PDMS-on-silicon hybrid actuator can yield the desired multi-axis actuation capability with a dynamic bandwidth as large as 5 kHz. [1378] Index Terms--Comb-drive actuator, finite element analysis (FEA), multi-axis microactuator, parametric design, PDMS-on-silicon microsystems.

This paper reports on fabrication and characterization of a new electrostatic microactuator that achieves out-of-plane multi-axis motion with a single silicon device layer. The multi-axis motion with the simple actuator design is possible by incorporating a three-dimensional (3-D) polydimethylsiloxane (PDMS) microstructure. This paper develops a new device processing method named 'Soft-Lithographic Lift-Off and Grafting (SLLOG)' to fabricate the previously designed PDMS-on-silicon hybrid actuator structure. SLLOG is a low-temperature (less than 150[degrees]C) process that allows replica molded PDMS microstructures to be integrated in silicon micromachined device patterns. The fabricated actuator is characterized using laser vibrometry. The experimental results demonstrate actuation motions achieved in three independent axes with fast dynamic response reaching a bandwidth of about 5 kHz. The fabricated PDMS-on-silicon actuator yields a vertical displacement up to 5 [micro]m and rotational motions with a 0.6-[degrees] tilting angle at a 40-V peak-to-peak ac actuation voltage. [1442] Index Terms--Comb-drive actuator, deep reactive ion etching (DRIE), laser vibrometry measurement, multi-axis microactuator, PDMS-on-silicon microsystems.

Powder blasting micro-erosion is a fast and flexible technique for the micropatterning of brittle materials. We have combined 10 [micro]m diameter [Al.sub.2][O.sub.3] eroding particles with a new masking technique to realize the smallest possible structures with the powder blasting process (30 [micro]m). Our masking technology is based on the sequential combination of two polymers: 1) the brittle epoxy resin SU8 for its photosensitivity and 2) the elastic and thermo-curable poly-(dimethyl siloxane) (PDMS) for its large erosion resistance. We have micropatterned glass microstructures with aspect ratio 1 and structural details down to 20 [micro]m. We compare the mask size-dependent etching rate using both 10 and 30 [micro]m diameter [Al.sub.2][O.sub.3] particles and find a decreasing etching rate for structures that are smaller than about 10 times the particle size. Combining SU8 with PDMS proves to be a very easy and accurate masking technology that allows exploring the fundamental dimensional limits of the powder blasting micro-erosion process. [1329] Index Terms--Glass, high-resolution, masking technology, poly(dimethyl siloxane) (PDMS), powder blasting.

One of the final steps in fabricating microelectromechanical devices often involves a liquid-etch release process. Capillary forces during the liquid evaporation stage after the wet-etch process can pull two surfaces together resulting in adhesion of suspended microstructures to the supporting substrate. This release-related adhesion can greatly reduce yields. In this paper, we present a wet-etch release method that uses polystyrene microspheres in the final rinse liquid. The polystyrene microspheres act as physical barriers between the substrate and suspended microstructures during the final liquid evaporation phase. A plasma-ashing process is utilized to completely remove the polystyrene microspheres from the microstructure surfaces. Using this process, release yields > 90% were achieved, as compared to yields of 20-50% when the polystyrene microspheres were not included. This release process is inexpensive, easy to implement, and is effective for both singlecrystal and polycrystalline silicon MEMS devices. [1295] Index Terms--Etching, wafer bonding.

An issue in microfabrication of the fluidic channels in glass/poly (dimethyl siloxane) (PDMS) is the absence of a well-defined study of the bonding strength between the surfaces making up these channels. Although most of the research papers mention the use of oxygen plasma for developing chemical (siloxane) bonds between the participating surfaces, yet they only define a certain set of parameters, tailored to a specific setup. An important requirement of all the microfluidics/biosensors industry is the development of a general regime, which defines a systematic method of gauging the bond strength between the participating surfaces in advance by correlation to a common parameter. This enhances the reliability of the devices and also gives a structured approach to its future large-scale manufacturing. In this paper, we explore the possibility of the existence of a common scale, which can be used to gauge bond strength between various surfaces. We find that the changes in wettability of surfaces owing to various levels of plasma exposure can be a useful parameter to gauge the bond strength. We obtained a good correlation between contact angle of deionized water (a direct measure of wettability) on the PDMS and glass surfaces based on various dosages of oxygen plasma treatment. The exposure was done first in an inductively coupled high-density (ICP) plasma system and then in plasma enhanced chemical vapor deposition (PECVD) system. This was followed by the measurement of bond strength by use of the standardized blister test. [1336] Index Terms--Advancing contact angle, bond strength, hydrophilicity, hydrophobicity, oxygen-plasma, poly (dimethyl) siloxane (PDMS), reactive ion etching (RIE).

The limitations of the photolithography-based micromachining technologies defines the upper-bound on the performance and robustness of micromachined gyroscopes. Conventional gyroscope designs based on matching (or near-matching) the drive and sense modes are extremely sensitive to variations in oscillatory system parameters that shift the natural frequencies and introduce quadrature errors. Nonconventional design concepts have been reported that increase bandwidth to improve robustness, but with the expense of response gain reduction. This paper presents a new approach that may yield robust vibratory MEMS gyroscopes with better gain characteristics while retaining the wide bandwidth. The approach is based on utilizing multiple drive-mode oscillators with incrementally spaced resonance frequencies to achieve wide-bandwidth response in the drive-mode, leading to improved robustness to structural and thermal parameter fluctuations. Enhanced mode-decoupling is achieved by distributing the linear drive-mode oscillators radially and symmetrically, to form a multidirectional linear drive-mode and a torsional sense-mode; minimizing quadrature error and zero-rate output. The approach has been implemented on bulk-micromachined prototypes fabricated in a silicon-on-insulator (SOI)-based process, and experimentally demonstrated. [1285] Index Terms--Inertial sensors, micromachined gyroscopes, MEMS, rate sensors.

The design, fabrication, and characterization of a multiple-stage Si microfabricated preconcentrator-focuser ([micro]PCF) for a micro gas chromatography ([micro]GC) system that can provide real-time quantification and identification of complex organic vapor mixtures are presented. The [micro]PCF consists of a Si microheater loaded with Carbopack B, Carbopack X, and Carboxen 1000 carbon adsorbent granules, and a Si micromachined cover plate. Deep reactive ion etching is utilized to produce mechanically robust fluidic interconnection adapters hermetically sealed to fused silica capillary tubing for connection to the other components in the [micro]GC. This three-stage device is designed to capture compounds spanning up to 4 orders of magnitude in volatility. The dead volume, thermal mass, heating efficiency, and pressure drop of the three-stage [micro]PCF are improved significantly over its single-stage [micro]PCF predecessor. We demonstrate the successful capture, desorption, and high-resolution chromatographic separation of a mixture of 30 common organic vapors using our three-stage [micro]PCF in a conventional GC system. The peak width at half height is Index Terms--Adsorbent, gas detection, micro gas chromatography ([micro]GC), microelectromechanical systems (MEMS), microheater, preconcentrator-focuser (PCF).

A low-voltage, low-power microvalve for compact battery-powered portable microfluidic platforms is designed, fabricated and experimentally characterized. The microvalve employs laser-machined piezoelectric unimorphs mechanically linked to surface micromachined nickel structures anchored on corrugated [Si.sub.x][N.sub.y]-Parylene composite membrane tethers. The Parylene layer also serves as a compliant sealing layer on the valve seat for reducing the leakage in the off state. A mechanical linking process to connect the bulk piezoelectric unimorphs to micromachined diaphragms in a self-aligned manner has been developed. The design enables large strokes (2.45 [micro]m) at low-actuation voltages (10 V) consuming a comparatively low switching energy (678 nJ). The dependence of the measured flow rates on the modulated clearance over the orifice was found to be in good agreement with the theory of laminar flow in the low (1-100) Reynolds number regime. The microvalve was experimentally characterized for both gas and liquid flows. For example, at 10 V unimorph actuation, a gas flow rate of 420 [micro]L/min at a differential pressure of 9.66 kPa was measured. The off-state leakage rate for 0 V actuation is estimated to be 10-20 [micro]L/min. Typical flow rates with pulse width modulated (PWM) actuation with 50% duty cycle at 20 [V.sub.pp] (1 kHz) were measured to be 770 [micro]L/min at 6.9 kPa for gases and 2.77 [micro]L/min at 4.71 kPa for liquids. [1259] Index Terms--Magnetic extrusion, microvalve, piezoelectric unimorph.