A silicon micromachined conductometric gas sensor with a maskless Pt sensing film deposited by selected-area CVD

Abstract

Inexpensive, conductometric gas micro-sensor platforms have been micromachined using conventional silicon processing. The front end of these sensors is a conducting film that undergoes resistance changes when exposed to certain chemical species. A variety of sensing film materials needs to be explored to obtain a significant sensor response above noise level for selected gases and vapors over wide ranges of temperature and pressure. However, only a few sensing film materials are compatible with the etchants used for silicon micromachining. To open up a wider range of materials for the sensing element, a new selected area CVD process is used to deposit thin conducting films on sensor platforms that have fully functioning conductance probes and integrated microheaters. This paper describes this selected-area CVD process for maskless deposition of thin platinum films with in-situ monitoring of film resistance during growth. Film growth is terminated at a desired value of resistance suitable for sensing of gases and vapors. The structure of the deposited films is characterized by scanning force microscopy. The response of Pt CVD films to H 2, O 2, CO, and propylene gases is reported.