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Microfabricated silicon cantilevers with integrated heating elements are powerful tools for manipulation and interrogation at the nanoscale. They can be used for highly localized heating of surfaces and also serve as electrothermal probes such as topography and position sensors. A thorough understanding of the dynamics of these heating elements is essential for an effective design and operation of such devices. In this paper, we present a tractable feedback model that captures the dynamics of these microheaters. The operator model separates the thermal and the electrical response of the microheater into two operators, with a linear dynamic operator mapping the applied electrical power to the heater temperature and a second nonlinear but memoryless operator mapping the heater temperature to the electrical resistance. We present experimental results that show the identification of a write heater used in probe-based thermomechanical data storage and the accurate synthesis of arbitrary temperature profiles. In the application of microheaters as electrothermal probes, the signals being measured are believed to perturb the thermal system. Therefore, an extension of our model is presented to analyze the response to this perturbation. The extended model is used to identify and forecast the performance of electrothermal sensors, such as the read heater in probe-based data storage. Also presented are results on thermal position sensors, in which microheaters are employed as nanoscale position sensors for a MEMS-based microscanner. Index Terms--Microcantilevers, microheaters, nanoscale position sensors, thermal analysis, thermal sensing, thermal transport, topography sensing.

Hot-swicthed low-force gold electrical contact testing was performed using a nanomechanical test apparatus to ascertain the sensitivity of simulated microelectromechanical systems (MEMS) contact to silicone oil contamination. The observed cyclic contact resistance degradation was dependent on both closure rate and noncontact applied voltage. The decomposition of silicone oil from electrical arcing was hypothesized as the degradation mechanism. Index Terms--Contact resistance, microelectromechanical systems (MEMS), silicones, surface contamination.

An entire set of silicon-based microtechnologies is developed for a high-performance [H.sub.2]/air self-breathing microproton-exchange-membrane fuel-cell ([micro]PEMFC) pack. For improving the performance of the silicon-based [micro]PEMFC, microflow-fields together with the electrodes at the cathode and the anode are optimally designed. For simplifying the microfabrication, a bulk-micromachining process is developed for fabricating both the cathode and the anode. Besides that the optimally designed flow-fields and electrodes are accurate fabricated, both the cathodes and the anodes can be fabricated in a same wafer with identical process. Optimized packaging conditions, such as the compression ratio and the current-collecting layer for the membrane electrode assembly (MEA), are experimentally obtained for both high fuel-cell performance and reliable silicon micropackaging. Attributed to the optimized design and the precise microfabrication, the peak power-density of the self-breathing [micro]PEMFC is measured as high as 141.0-147.2 mW/[cm.sup.-2]. For adapting the output voltage to handheld electronic systems, a thin-pad planar configuration is designed for the [micro]PEMFC pack that consists of six single cells connected in series. The planar-configured self-breathing [micro]PEMFC pack is micropackaged on a silicon-micromachined base-chip, with the specific power as high as 271 mW/[cm.sup.3] measured. Experimental results demonstrate that the fuel ceils can reliably work under normal environmental temperature and humidity. 1200-h continuing power supply of the [micro]PEMFC pack is performed, resulting in stable output of about 3 V. [1643] Index Terms--Fuel-cell stack, optimized design, proton exchange membrane (PEM), silicon-based micromachining.

This paper reports the design, fabrication, and experimental characterization of a planar array of micro-fabricated electrospray emitters intended for space propulsion applications in micro-satellites. The engine uses the ionic liquid EMI-B[F.sub.4] as propellant. Electrospray engines take advantage of the electrohydro-dynamic effect known as Taylor cone to produce thrust. The array is designed with an open architecture and it is composed of a set of spikes, i.e., emitters, coming out from a propellant pool. There are two configurations for the emitters: fully sharpened slender emitters, i.e., pencils, and truncated pyramidal emitters, i.e., volcanoes. The arrays have between 4 and 1024 emitters in an active area of 0.64 [cm.sup.2]. The surface of the engine (tank and emitters) is covered with 'black silicon' that acts as wicking material. The micro-fabrication of the engine is described. The paper reports experimental characterization of the hydraulics system including wettability tests, current/emitter-voltage characteristics, and imprints of the exit stream on a collector. Preliminary results demonstrating the feasibility of obtaining substantially larger emission currents at the same extraction voltage by controlling the temperature are also reported. The paper compares the experimental current/emitter-voltage characteristics with relevant theories of field emission of electrons. [1433] Index Terms--Black silicon, electrospray emitter array, ionic liquid propellant, propulsion.

Electrical isolation of bulk-micromachined single crystal silicon (SCS) microelectromechanical systems (MEMS) devices is demonstrated using through-wafer junction isolation. Through-wafer junctions of alternating n-type and p-type silicon (npn junctions) are fabricated using 'temperature gradient zone melting' (TGZM) or thermomigration of aluminum in n-type silicon. The npn regions electrically isolate various regions of the SCS from one another by acting as series connected backbiased diodes. Thermomigration is a potentially high throughput process that is consistent with batch fabrication principles. Practical demonstration of this technique is shown by fabricating and testing a full wafer thickness (~300 [micro]m) electrostatic actuator fabricated from a single silicon wafer, and driven at 360 Vpp at resonance of 1933 Hz. Breakdown voltages of single thermomigrated npn junctions in excess of 189 V with leakage currents less than 70 nA were measured. For multiple junctions in series, overall breakdown voltages greater than 1500 V were demonstrated. Compatibility of thermomigration with standard p-channel metal-oxide-semiconductor (PMOS) transistors is also demonstrated. [1345] Index Terms--Bulk micromachining, deep reactive ion etching (DRIE), diodic isolation, electrical isolation, inductively coupled plasma (ICP), junction isolation, temperature gradient zone melting (TGZM), thermomigration.

A hermetic package based on localized aluminum/silicon-to-glass bonding has been successfully demonstrated. Less than 0.2 MPa contact pressure with 46 mA current input for two parallel 3.5-[micro]m-wide polysilicon on-chip microheaters can raise the temperature of the bonding region to 700 [degrees] C bonding temperature and achieve a strong and reliable bond in 7.5 min. The formation of aluminum oxide with silicon precipitate composite layer is believed to be the source of the strong bond. Accelerated testing in an autoclave shows some packages survive more than 450 h under 3 atm, 100% RH and 128 [degrees] C. Premature failure has been attributed to some unbonded regions on the failed samples. The bonding yield and reliability have been improved by increasing bonding time and applied pressure. [594] Index Terms--Activiation energy, aluminum/(silicon)-glass bonding, Hermetic MEMS package, localized heating, reliability.