Microfabricated Crevice Former with a Sensor Array
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Microfabricated Crevice Former with A Sensor Array Xiaoyan Wang, Robert G. Kelly1, and Michael L. Reed Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, VA 22904-4743, U.S.A. 1 Department of Materials Science and Engineering, University of Virginia, Charlottesville, VA 22904-4745, U.S.A. ABSTRACT 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, ionselective 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. INTRODUCTION Crevice corrosion is an accelerated corrosion process that occurs in a very small localized region. For crevice corrosion studies, a comprehensive, accurate, and reliable model has not been built because well-defined crevice corrosion samples, which should be comparable to the ideal crevice structures used in theory modeling, could not be made by conventional techniques. Microfabrication techniques and computational model, CREVICER, developed at the University of Virginia, have provided a solution to above hurdles [1-4]. In the previous work, the crevice corrosion samples have been fabricated using techniques developed for standard semiconductor processing and microelectromechanical systems (MEMS) [3]. The fabricated crevice consisted of a substrate and a crevice former, which mimicked a real crevice structure. The substrate included thick, uniform and well-defined metal electrodes in the form of a single strip, one or two-dimensional array segmented by dielectric SU-8 photopolymer. These thick electrodes were obtained by electroplating nickel onto a seed layer that had been evaporated on thermally grown silicon dioxide; each of the electrodes was connected to their respective wiring area by a buried contacting path. The basic crevice former had SU-8 posts or walls built on (100) silicon wafer, which determined a uniform crevice gap with a range from 5 µm to 100 µm. The crevice was constructed by aligning the crevice former to the crevice substrate [3]. The schematic of a basic crevice sample is shown in Figure 1. When the crevice is put in a barely c
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