Design and performance of a microcantilever-based hydrogen sensor

This paper describes the design of, and the effects of basic environmental parameters on, a microelectromechanical (MEMS) hydrogen sensor. The sensor contains an array of 10 micromachined cantilever beams. Each cantilever is 500 mum wide x 267 mum long x 2 mum thick and has a capacitance readout capable of measuring cantilever deflection to within 1 nm. A 20-nm-thick coating of 90% palladium-10% nickel bends some of the cantilevers in the presence of hydrogen. The palladium-nickel coatings are deposited in ultra-high-vacuum (UHV) to ensure freedom from a "relaxation" artifact apparently caused by oxidation of the coatings. The sensor consumes 84 mW of power in continuous operation, and can detect hydrogen concentrations between 0.1 and 100% with a roughly linear response between 10 and 90% hydrogen. The response magnitude decreases with increasing temperature, humidity, and oxygen concentration, and the response time decreases with increasing temperature and hydrogen concentration. The 0-90% response time of an unheated cantilever to 1% hydrogen in air is about 90 s at 25 degreesC and 0% humidity. (C) 2002 Elsevier Science B.V. All rights reserved.