Distributed Bridge Circuit for High-Temperature Silicon MEMS Pressure Sensors

Abstract

Abstract

This paper presents a distributed-parameter full-bridge measurement circuit for silicon integrated piezoresistive mechanical transducers operating in the range 0–300◦C (withpossible extension to −60◦C to +325◦C). Conventional approaches—heteroepitaxial siliconon-sapphire, dielectric-isolated mesa structures, shear-mode (X-ducer) elements, and classical resistor full-bridge circuits with isolating p–n junctions—are limited by upper temperature ceilings of approximately 180–200◦C, mechanical stresses caused by lattice mismatch, and poor reproducibility of the elastic-element dimensions. In the proposed method the silicon elastic element is doped to increase the majority-carrier concentration; the average resistivity ρee ≈ 0.5–10 Ω · cm and the channel depth are chosen so that the piezoresistive channels remain 2–10 times more conductive than the surrounding material, thereby eliminating the need for isolating p–n junctions. Current redistribution is modeled by a system of differential equations solved with the aid of modified Bessel functions, yielding closed-form expressions for the strain-sensitivity coefficient K(T, εy ) and the input resistance Rin(T ). Experimental verification on beam and membrane transducers confirms intrinsic errors ≤ 1 % and complementary temperature errors of sensitivity < 0.05 %/◦C