Fabrication and characterization of polysilicon-on-insulator (PolySOI) and a-SOI based micro piezoresistive pressure sensor for harsh environment applications

Micro sensors and actuators are widely used in this era. Micro pressure sensors are required in many applications and are the first sensors fabricated using MEMS technology. The work presents the fabrication of two micro pressure sensors viz., polysilicon on insulator (PolySOI) and amorphous silicon on insulator (a-SOI). Both sensors work on the principle of piezoresistive pressure sensing. The PolySOI sensor has a configuration Si-SiO₂-polysilicon and the a-SOI sensor has Si-SiO₂-a-silicon. The fabricated sensors consist of polysilicon and a-silicon piezoresistors. Nano-piezoresistors are patterned on the diaphragm to enhance the sensitivity and are connected in the form of a Wheatstone bridge. Both sensors are characterized for potential and sensitivity over a pressure range of 0–1 MPa. Two sensors exhibit high sensitivity, PolySOI sensor provides the sensitivity of 14.7 mV/bar (147 mV/MPa). Polycrystalline silicon is used as it has excellent mechanical properties and is compatible with high temperature processing and interfaces very well with thermally deposited SiO₂. a-SOI sensor has a sensitivity of 10.5 mV/bar (105 mV/MPa). Both sensors are fabricated using conventional MEMS technology and with a silicon wafer. The sensors fabricated are alternate to the use of SOI wafer which is expensive and hard to customize.