High Overtone Bulk Acoustic Resonators built using Aluminum Nitride thin films deposited onto AT-cut quartz plates

Compact high stability frequency sources devoted to on-board applications may be stabilized by acousto-electric devices such as SAW and BAW resonators. Many architectures have been proposed to improve the quality factor of such devices which directly influences the phase noise figures of the oscillator. However, the quality factor-frequency products of such acousto-electric devices mainly built on quartz hardly overcome 10¹³, which remains rather small compared to the intrinsic mechanical quality factor of the material. In the 80´s, Lakin et al. have emphasized the capability of high overtone bulk acoustic resonator (HBAR) to present high quality factors at frequencies in the GHz range. In this paper, we characterize the resonance properties of HBAR built on thick AT-cut quartz plates excited by a C-oriented aluminum nitride thin films deposited atop quartz, examining its behaviour versus temperature and its capability to stabilize a Colpitts oscillator