An Integrated Gas Sensor Fabricated on a Silicon Substrate

Abstract

We have developed an integrated thin-film gas sensor using semiconducting thin-films on an SiO₂ diaphragm, which is formed on an Si substrate. A micro heater is fabricated on the same diaphragm. The fabrication procedure is based on thin-film and micromachining technologies and IC fabrication process. The two sensing films are composed of multi-layered metal oxides; an SnO₂-based film on an Fe₂0₃-based film and a WO₃-based film on an Fe₂0₃-based film.
Both of the films are sensitive to reducing gases such as hydrogen (H₂), isobutane (i-C₄H₁₀), and carbon monoxide(CO) as well as NO_x gases when they are heated to 400°C by feeding an electric power of 540mW to the heater.
The advantageous features of the sensor are as follows. It is a small and light-weighted device. It does not consume much materials and energy in the fabrication process. It does not contain any hazardous or poisonous materials that contaminate the environment. It can be mass-produced. It would be promising as a smart sensor in conjunction with electronic circuits on the same substrate.