MEMS-based hydrogen gas sensors

The widespread use of hydrogen as both an industrial process gas and an energy storage medium requires fast, selective detection of hydrogen gas. This paper reports the development of a new type of solid-state hydrogen gas sensor that couples novel metal hydride thin films with a micro-electro-mechanical system (MEMS) structure known as a micro-hotplate. Micro-hotplate structures are fabricated via surface silicon micro-machining, resulting in a suspended platform with an embedded heater and thermally isolated from the substrate. A rare earth metal thin film, overcoated with a palladium capping layer, is deposited on this structure and serves as the active hydrogen-sensing layer. The change in electrical resistance of this bilayer when exposed to hydrogen gas is the sensor output. Sub-second response times to 0.25% hydrogen in air and sensitivity to hydrogen concentrations below 200 ppm are measured. Rise and decay times of the response depend on the effective temperature of the micro-hotplate and decrease with increasing heater power. These results suggest that this device has the potential to meet the sensing requirements of advanced hydrogen applications.