Experimental Studies in Micromachined AT-Cut Quartz-Based Differential Vacuum Gauges

In this paper, a micromachined differential pressure sensor based on force frequency effect in AT-cut quartz bulk acoustic wave resonators for vacuum measurements is presented. The frequency shift arising from the stresses generated in the quartz due to force application is known as the force frequency effect. Pressure is sensed by monitoring the shifts in the thickness shear mode resonance frequency of AT-cut quartz resonator due to the application of differential pressure across the micromachined quartz diaphragm. The sensors exhibit a large dynamic range of 1 mTorr-100 Torr with a resolution of 1 mTorr (in the medium vacuum regime). A parametric study has also been carried out to study the effect of resonator thickness and diameter on sensitivity. It was found that the sensor's response to pressure is extremely sensitive to mechanical boundary conditions, which results in performance characteristics such as dependence on the direction of the applied pressure and unexpected scaling with the diaphragm radius.