High overtone Bulk Acoustic Resonators: application to resonators, filters and sensors

Acoustelectric devices have been used now for several decade to stabilize oscillators, to filter radio-frequency signals or to allow for physical and even chemical detection and measures.Among all the structures that have been developed in that purpose, one has been revealing particularly interesting for the development of high quality factor resonator on an extended range of frequency. It is based on the generation of high overtones in bulk acoustic wave resonant structure and therefore are currently called HBARs. These devices may be fabricated along various approaches but they always consist of a thin (or thinned) piezoelectric layer deposited or bonded onto a high quality single crystal material. The spectral response of this kind of device exhibit a periodic comb of peaks modulated by the transducer response, yielding resonances on a very large spectrum with various characteristics and properties. We present here the basic principles of such devices, their remarquable properties, the etchnologies required to manufacture them and the various applications they can be applied for. A focus is partcularly dedicated to oscillator stabilization and to wirelss sensor development.