A new polysilicon surface micromachining technique for fabricating and assembling three- dimensional structures has been developed. Single-layer polysilicon elements and laminated polysilicon panels incorporating trapped-glass reinforcement ribs have been successfully fabri- cated on a silicon substrate with robust and continuous hinges that facilitate out-of-plane rotation and assembly. To realize a stable three-dimensional structure, one of the device's elevatable panel components is terminated with an array of open windows, and the mating rotatable element has a matched set of protruding arrowheads/microrivets with flexible barbs that readily flex to facilitate their joining and assembly. Because the arrowhead/microrivet barb tip-to-barb tip sepa- ration is larger than the opening in the mating window, the barbs flex inward as they pass through the open window and then expand to their original shape upon exiting the window, re- sulting in a permanently latched joint and a three-dimensional structure. Three novel arrow- head/microrivet designs have been micromachined to facilitate the latching process, including a simple arrowhead, a high-aspect ratio arrowhead, and a rivet-like structure with a hemispherical shaped cap and a flexible split shank.

Microfabrication of crevice corrosion samples is of importance in developing an accurate, comprehensive, and reliable crevice corrosion model, and real-time acquisition of corrosion information is also essential. Solid-state microsensor arrays have been used for detecting potential, pH, and ion concentrations, and their integration into crevice corrosion testing samples will provide real-time spatial information of crevice corrosion. The crevice corrosion testing sample is constructed by coupling a crevice former to a crevice substrate and has a uniform crevice gap. In this paper we present a crevice former incorporating a potentiometric, ion- selective membrane microelectrode pH sensor array. The crevice former is built on a silicon wafer using microelectromechanical systems (MEMS) fabrication and thin film semiconductor processing techniques, and consists of an array of five independent sensing microelectrodes. The array configuration allows for in-situ spatial pH analysis of crevice corrosion based on information from each sensor. The fabrication details of the crevice former with microelectrode sensor will be elaborated.

A novel palladium-based micromembrane has been fabricated and tested which has the potential to be used for carbon monoxide shift reaction and hydrogen gas separation in a miniature fuel processor for micro fuel cells. The micromembrane structure is built in silicon substrate, using standard MEMS microfabrication processes. The four layers, viz., copper, aluminum, spin-on-glass (SOG) and palladium form the composite micromembrane. Copper, aluminum and SOG serve as a structural support for the palladium film. Copper also acts as a catalyst in the shift reaction that converts unwanted carbon monoxide gas into hydrogen, which in turn is separated by the palladium micro-membrane. For a particular combination of thicknesses for various layers, the composite micro-membrane withstands a pressure gradient up to 1 atm. The micromembrane separates hydrogen from a 20% hydrogen balance nitrogen gas mixture at room temperature.