Gas microsensing system with a FGMOS on a MEM structure

In this work a thin film gas microsensor based on both a double polysilicon micro-hotplate (MHP) and a polysilicon floating gate MIS transistor (FG-MIS) is described. Sensing section is a squared polysilicon plate which contains a doped Zinc Oxide (ZnO) thin film. The sensing section is heated by an U-shaped polysilicon stripe which is electrically isolated from the top and the bottom using oxide films. The micro-hotplate is both mechanically supported and thermally isolated using a deep cavity micromachined in the silicon substrate. The sensing film is electrically connected to the floating-gate transistor where the conductivity channel is modulated by the charged generated at the sensing film. The sensor structure was characterized for detecting carbon monoxide (CO) at 300 °C. The hot area is thermally isolated using an arrangement of cavities micromachined in the silicon substrate. Finally a complete layout of the sensor system is presented in this paper.