A Thin-Film Gas Sensor Fabricated on a Diaphragm on a Silicon Substrate

Abstract

A thin-film gas sensor was fabricated on an SiO₂ diaphragm on an Si substrate. This sensor was composed of 2 parts; one was a gas-sensing part which had a semiconducting thin-film of an Fe₂O₃ based material, and the other was a heating part which had a metal thin-film with 3 layers of Cr/Pt+W/Cr. Both parts were fabricated on the same type of a diaphragm with thin-film and micromachining technologies, and were set face to face at a distance of 50μm.
The heater was operated at 600°C by feeding 70mA of DC current. The voltage was 6.6V and the consumed power was 462mW. The gas sensing part was heated up to about 400°C. The conductance of the gas sensing part was about 0.05μS in a fresh air, whereas it was increased when H₂ gas or i-C₄H₁₀ gas was introduced.
The fabrication technologies of the sensor are compatible with those of ICs, and the sensor is apparently a small, light-weighted, and low power-consuming device. Moreover, it would be a promising device as an intelligent or smart sensor.