Enhanced Cross-Axis Rejection Capacitive Strain Gauge

A novel bending plate capacitive strain gauge is designed, fabricated, and tested to measure strain in the range of 1 to 1000 με. This silicon-based strain sensor uses a unique structural design to increase the on-axis gain through the use of a bending beam structure while attenuating signals due to cross-axis strain. A differential capacitive measurement is used to improve the output, reduce the parasitic capacitance, and eliminate the capacitance measurement error due to temperature. The device is fabricated using silicon-on-insulator (SOI) technology. Experimental results exhibit an on-axis sensitivity of 50 aF/με and attenuation of the cross-axis sensitivity to shear strain to less than 10 percent of the applied shear strain. A detailed mechanical analysis of the suspension and deflection-amplifying bent-beam capacitor will be presented. Furthermore, the capacitive plate analytical model is compared to finite element simulations and verified with experimental results. In addition, a noise assessment of the device shows the electronics noise dominates the Brownian noise.