Torsional Piezoresistive Effect in Polysilicon

This paper presents a microelectromechanical test device and calibration method for finding torsional piezoresistive coefficients for micro sensing applications. The test device consists of a slider-crank connected to two torsional legs. The slider-crank creates torsional stress in the legs which causes a change in the electrical resistance through the legs. A model that predicts the effects of a scissor hinge on the slider-crank is presented. Torsional stresses in the legs are calculated and the legs are discretized into long parallel resistors and the stresses applied to each resistor. Assuming a second-order piezoresistance, an optimization is then done to find the piezoresistive coefficients by changing them until the model prediction fits the test data. These coefficients can be used to predict angular displacement from resistance measurements in fully integrated torsional sensors.