Design of a polysilicon-on-insulator pressure sensor with original polysilicon layout for harsh environment

Abstract For conventional architectures of polysilicon-on-insulator (PSOI) piezoresistive pressure sensors, metal-on-polysilicon contacts located on the membrane are submitted to repetitive strains and a possible deterioration may occur after a long use period. The metallisation may also be damaged at high temperature or when a corrosive atmosphere is in contact with the membrane. The basic idea developed in this paper consists in reporting the metal-on-polysilicon contacts outside the membrane. A new sensor design based on this idea is presented. The resistance of the polysilicon patterns have been modelled and optimised by finite element analysis. After thermal oxidation, a 0.46 μm thick polysilicon film has been obtained by LPCVD (620 °C, 450 mtorr) then boron implanted (30 keV, 2 15 cm −3 ). A crystallisation RTA has been performed at 1100 °C during 20 s. The silicon etching of a 20 μm thick membrane has been achieved by means of an aqueous KOH solution. A 8.3 m Ω cm resistivity value has been measured on polysilicon Hall patterns. The measured resistances have been found in a very good agreement with the simulations. The low pressure sensor has been tested in a full Wheatstone-bridge configuration showing a good linearity in the [0–200] mbar range with a 50 mV bar −1 mA −1 sensitivity. These results demonstrate the feasibility of a pressure sensor without metal/polysilicon contact running over the membrane.