A MEMS capacitive pressure sensor compatible with CMOS process

Abstract

This paper reports a capacitive pressure sensor. Like a common capacitor, it consists of three parts: the top electrode, the dielectric layer and the bottom electrode. The dielectric layer consists of the silicon oxide and an air gap. The fabrication process of this structure combines the CMOS process with the post-CMOS MEMS process. The bottom electrode made of polysilicon is formed during the CMOS process. the gap is formed by sacrificial layer release and the Al vapor process is used to seal the gap and form the top electrode, which is deformable and used to sense the pressure change. The sensor is tested under the pressure ranges from 100hPa to 1100hPa. The results show that the capacitance value increases with the pressure applied. For the structures with the membrane size of 100μm, 130μm and 150μm, their average sensitivity is about 0.085fF/hPa, 0.104fF/hPa and 0.099fF/hPa, respectively. For the latter two structures, the membrane contacts the substrate when the pressure is large enough.