Design, fabrication and modeling of microbeam structures for gas sensor applications in CMOS technology

In this paper we discuss the design, fabrication, and modeling of an electrostatically actuated transducer that is operated in a resonant mode. The transducer is designed for gas sensor applications. The microstructure with high-aspect ratio laminated beam or bridge suspensions, has been fabricated using a 0.6 μm three metal, double poly CMOS process. The fabricated chip was post processed by a sequence of two maskless dry etching steps. A thin sorbent polymer layer is included in the design of the microbeam chemical sensor. The devices were designed to provide a relatively large surface area to coat with the sorbent polymer. Gas sorption in the polymer layer can be monitored as a function of the resonant frequency of the device. The device frequency is measured by piezoresistors mounted in a Wheatstone bridge configuration. The fabricated sensors are intended for use in monitoring hazardous gases and vapors. In order to optimize the device resonant frequencies, a variety of microbeam structures were designed with different dimensions. These structures were modeled with a finite element analysis program. A number of selected structures were fabricated in a single chip design.