Temperature derivative of stress coefficients of SAW resonator frequency from pressure sensor measurements

A study of the temperature dependence of the stress coefficients of a surface acoustic wave (SAW) resonator is described. A phenomenological model provides expressions for the temperature dependence of the pressure sensitivity in terms of the temperature derivative of the stress coefficients of frequency and the biasing stresses in the active area of the SAW resonator resulting from an externally applied hydrostatic pressure on the probe structure. It is shown that the pressure induced shift in the turnover temperature of the SAW resonator is linearly dependent on the temperature dependence of the pressure sensitivity. This analysis indicates a way of minimizing the pressure induced shift in the turnover temperature by a proper selection of the crystalline orientation in conjunction with the compressive biaxial stress ratio in the active area of the SAW resonator. On the basis of predictions of this model and experimental data, an improved design of a SAW pressure sensor is proposed where a more effective temperature compensation is achieved by a proper optimization of the crystalline orientation and the biaxial stress ratio in the active area of both the SAW devices