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

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 sigma_xy = (sigma_x´x´ - sigma_y´y´) / 2 and sigma_x´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 (sigma_x´x´ - sigma_y´y´), a novel torsional bridge setup was developed to apply well-defined shear stress sigma_x´y´ to the surface of silicon beams diced parallel to the <110> crystal direction of silicon and containing the stress sensor elements. The measured sensitivities are consistent with simulated values.