Design and characterization of in-plane silicon stress sensors with isotropic sensitivity

Abstract

This paper reports on the development and characterization of novel in-plane CMOS-based stress sensors featuring equal sensitivities towards the two mechanical shear stress components sigmaxy = (sigmax'x' - sigmay'y') / 2 and sigmax'y'. The sensor structures are based on symmetric n-well resistors with eight contacts. A geometric parameter variation is performed using FEM simulations to adjust the stress sensitivities of different sensor layouts. For characterization, in addition to a four-point bending bridge used to exert normal stresses (sigmax'x' - sigmay'y'), a novel torsional bridge setup was developed to apply well-defined shear stress sigmax'y' to the surface of silicon beams diced parallel to the crystal direction of silicon and containing the stress sensor elements. The measured sensitivities are consistent with simulated values.