Development of MEMS-based Piezoresistive Three Dimensional Stress/Strain Sensor with Temperature Compensation

Abstract: In this research, a developed n-type piezoresistive three dimensional (3D) stress sensor with full temperature compensation is presented. The proposed sensing rosette benefits from the stress insensitivity of the full-circular n-type piezoresistor, oriented over (111) silicon plane, to detect only temperature changes for compensation. Moreover, the unique behavior of shear piezoresistive coefficient (π44) of n-Si is utilized to construct a piezoresistive stress sensing rosette over (111) silicon plane that is capable of extracting 3D stress components. Prototype stress sensing chip was microfabricated to test the capability of the developed sensing rosette to accurately extract stress applied on structures at different thermal environments. The fabricated sensing chip was subjected to different mechanical loads using a loading rig with a four-point bending fixture. The testing was carried out over a temperature range of -20 to 60 °С. The results showed that the proposed sensing chip has the capability of capturing the stress applied at different temperatures. Also, the developed sensing rosette showed less sensitivity to the uncertainty in piezoresistive coefficients’ values compared to the other developed 3D piezoresistive stress sensors. Further improvements of the proposed sensor were achieved by developing a hybrid smart temperature compensation system to reduce the temperature effect on both resistivity and sensitivity of the sensing rosette. The developed compensation system integrates a temperature sensor, placed in close proximity to the stress sensing rosettes, with the artificial neural networks (ANNs). The results showed an improvement in stress measurement accuracy compared to the other developed compensation systems for such 3D stress sensors. The proposed compensation system has merit since the employed temperature sensor shares the same thermal environment with the stress sensing rosette. Moreover, the developed system has the capability to compensate for both resistance and sensitivity, for 3D stress sensor, with no need for additional circuitry on the sensing device itself.