Capacitive micro pressure sensors with underneath readout circuit using a standard CMOS process

Abstract

A capacitive micropressure sensor with readout circuits on a single chip is fabricated using commercial 0.35μm complementary metal oxide semiconductor (CMOS) process and post‐processing. The main break through feature of the chip is the positioning of its readout circuits under the pressure sensor, allowing the chip to be smaller. Post‐processing included anisotropic dry etching and wet etching to remove the sacrificial layer, and the use of plasma enhanced chemical vapor deposition (PECVD) of nitride to seal the etching holes on the pressure sensor. The readout circuit is divided into analog and digital parts, with the digital part being an alternate coupled RS flip‐flop with four inverters that sharpened the output wave. The analog part employed switched capacitor methodology. The pressure sensor contained an 8×8 sensing cells array, and the total area of the pressure sensor chip is 2mm×2mm.