Exploring the resistance change trends associated with integrated piezoresistive sensing elements

Compliant piezoresistive MEMS sensors exhibit great promise for improved on-chip sensing. As compliant sensors may experience complex loads, their design and implementation require a greater understanding of the piezoresistive effect of polysilicon in bending and combined loads. This paper presents experimental results showing the piezoresistive effect for these complex loads. Several n-type polysilicon test structures were tested. Results show that, while tensile stresses cause a linear decrease in resistance, bending stresses induce a nonlinear rise in resistance contrary to the effect predicted by available models. The experimental data illustrate the inability of published piezoresistance models to predict the piezoresistive trends of polysilicon in bending and combined loads, indicating the need for more complete models appropriate for these loading conditions and more complete understanding of the piezoresistive effect.