Optimizing AQP SAW resonators for reduced vibration sensitivity

All Quartz Package (AQP) SAW oscillators with low vibration sensitivity are achievable by minimizing the external stresses that might otherwise be transferred to the AQP SAW device. If these external stresses are at their lowest possible level, then frit geometry becomes a factor in limiting just how low the vibration sensitivity may be. Optimizing the frit geometry often involves trade-offs with the overall AQP SAW device's size requirements. Through the use of finite element modeling, it was determined that the AQP's cover and substrate thicknesses could also be used to improve vibration sensitivity. The model predicted a decrease in vibration sensitivity, with increasing cover thickness, for the vibration sensitivity component, /spl gamma//sub 1/, in a direction normal to the SAW substrate. The model also predicted a degradation in vibration sensitivity with increasing substrate thickness. These results were confirmed experimentally. The other benefit of increased cover thickness was a sizable decrease in the variation of performance among the devices tested. The increased cover thickness decreases the sensitivity of the AQP SAW to variations in the mounting material. The influence of AQP cover thickness on an insufficiently stiffened oscillator was also examined. The results were similar, except that the variation in cover thickness had a more dramatic affect than in the sufficiently stiffened case.