Development and characterisation of a surface micromachined FET pressure sensor on a CMOS process

This paper presents the development methodology and performance results of a surface micromachined FET pressure sensor integrated into a CMOS process. The working pressure range examined is 15 to 95 psi of absolute pressure. The sensor consists of a polysilicon pillbox structure which forms an evacuated cavity. The polysilicon is the gate electrode of an MOS device created using the cavity as the gate dielectric, deflection of the polysilicon with applied pressure can be sensed as a change in drain current of this MOS device. The finite-element program ANSYS is used to establish suitable values for the area and thickness of the diaphragm and the cavity height. A device simulator is used to predict the performance of the MOS structure for various deflections. The fabrication of the sensor element takes place after the source/drain anneal and before interlayer deposition of an otherwise standard CMOS process, The output current of a fabricated MOS sensor with diaphragm plate length of 75 mu m over the range of 15 to 95 psi increased from 70 to 170 mu A at a bias of V-ds = 11 V, V-gs = 13 V. (C) 1999 Elsevier Science S.A. All rights reserved.