Micromachined Catalytic Combustible Hydrogen Gas Sensor Based on Nano-structured SnO2

Abstract

A new type of micro catalytic combustible gas sensor system was designed and fabricated using micro-electro mechanical system (MEMS) technology. A chemical vapor deposition (CVD) method is used to coat porous nano-crystalline SnO2 catalyst layer. Tin chloride anhydrate vapor was used as the precursor, and it reacted with ammonium sulfide ((NH4)2S) to form tin disulfide (SnS2) nanoparticles. The tin disulfide was dried up, annealed in air, then it transformed into polycrystal- line SnO2 nanoparticles. The X-ray diffraction (XRD) measurement was used to investigate the structural properties of the SnO2 films. The morphology of the samples was investigated by field-emission scanning electron microscopy (FESEM). X-ray photoelectron spectroscopy (XPS) provided the information on chemical composition of the SnO2 films. The sensing elements and the reference elements were connected to a Wheatstone bridge circuit for the measurement of gas-sensing prop- erties. The catalytic combustion sensor exhibited relatively higher sensitivity (75.4 mV/1% H2) and good linearity (99.4%) to H2 from 0 to 4% V/V. The response and recovery times to 4% H2 were 0.65 s and 2.32 s, respectively. Finally, the sensor signal was very stable during a 200 d long term operation (accuracy>95%). It was noteworthy that the nano-structured SnO2 as catalyst film in a catalytic combustible gas sensor could considerably improve the performance of the gas sensor. It can be used in realizing portable sensing devices such as hydrogen analyzers and hydrogen leak monitors. Keywords nano tin oxide; catalytic combustible gas sensor; micro-electro mechanical system (MEMS); hydrogen detection