Multidimensional CMOS in-plane stress sensor

This paper reports a novel multidimensional complementary metal-oxide semiconductor (CMOS) based stress sensor. The device uses an octagonal n-well in a p-substrate and eight peripheral contacts enabling the current to be switched in eight directions rotated by an angle of pi/4. By taking full advantage of the piezoresistive behavior of single-crystal silicon, the measurement of all in-plane stress tensor components, i.e., sigma(xx), sigma(yy) and sigma(xy), is demonstrated. This information is derived from the zeroth and second angular-order Fourier components of voltage signals parallel and perpendicular to the switched current. Nonlinearities of the system are reduced by proper bias conditions using a center contact. The device was calibrated by applying defined normal stresses using a bending bridge setup. The device behavior was modeled including piezoresistive effects and the junction field effect by a combination of the finite element method and a nonlinear simulation program with integrated circuits emphasis (SPICE) network simulation using junction field effect transistor (JFET) elements. Stress sensitivities of 200 mu V V-1 MPa-1 are demonstrated for the determination of the three stress components.