Observation of GHz Modes in Quartz Circular Surface Acoustic Wave Resonator

A novel form of Surface Acoustic Wave (SAW) resonators functions by exciting SAW modes in a circular acoustic cavity formed on a ST-cut quartz substrate. The resonant and harmonic frequencies of these devices is dependent on the diameter of the cavity. Based on the acoustic properties of ST quartz, devices with dimension in the range of 100's of μm are expected to have resonant frequencies in the range of 10's to 100's of MHz. These modes are indeed observed, however additional modes with frequencies in the GHz range (between 1-8 GHz) have also been observed. These modes do not appear to be part of the harmonic series associated with the MHz range modes. Moreover, specific aspects of these modes are inconsistent with the known acoustic properties of ST-cut quartz. Progress on understanding these modes will be presented.