A Wireless Thin Contact Stress Sensor Based on Surface Acoustic Wave Resonator in ZnO/Si Structure

A sensor based on surface acoustic wave resonator (SAWR) in ZnO/Si structure for wirelessly monitoring contact stress in thin gap is analyzed. Firstly, the scheme of SAWR stress sensor and surface effective permittivity for analyzing SAW in ZnO/Si structure are introduced. Then, the phase velocity and electromechanical coupling coefficient for Rayleigh mode as well as Sezawa mode are obtained in ZnO/Si structure. Next, the stress sensitivity of the sensor is estimated by combing changed elastic constants with surface effective permittivity for the Sezawa mode. The results show that the sensor exhibits good linear relation between applied stress and relative frequency shift with the adjustable stress sensitivity for different thickness of diaphragm. Finally, the temperature sensitivity of the stress sensor is estimated to -31 ppm/ °C for temperatures ranging from 20 to 60 °C. To reduce temperature disturbance, a differential measurement configuration is presented.