Double-port AlN/Sapphire high overtone bulk acoustic resonators for the stabilization of radio-frequency oscillators

The interest of double-port AlN/Sapphire high overtone bulk acoustic resonators for the stabilization of radiofrequency oscillators is investigated. Resonators are built by depositing AlN onto Sapphire to provide high quality factors, as required for stable oscillators. The resonators are based on laterally-coupled single resonators exchanging energy via a gap of few tens of μm separating them and adjusted to optimize the quality factor. Combining AlN with high acoustic quality materials finally has provided a quality factor of 53,000 at 1.8 GHz (Q.f product of about 9.5 × 10¹³) at room temperature. An oscillator stabilized with this resonator has been characterized, yielding a phase noise floor of -155 dBc/Hz and an Allan deviation of 10^-9 for τ = 1 s.