Overmoded high Q resonators for microwave oscillators

High-overtone bulk acoustic wave resonators operating in the 1-6 GHz range have been fabricated on sapphire, lithium niobate, dilithium tetraborate, and quartz substrates in an effort to obtain high-Q C-axis normal aluminum nitride films were used for transduction for all the substrates, yielding longitudinal modes. The resonators on Z-cut sapphire exhibited an unloaded fQ product in excess of 1 × 10¹⁴ at frequencies between 1.6 and 4.0 GHz. The resonators on Z-cut sapphire exhibited Qs as high as 68,000 at 1.6 GHz with highly inductive response. Lithium niobate exhibited a Q of 54,000 at 1.6 GHz. When used in combination with a mode-select filter these resonators would make good feedback elements for low phase noise oscillators where inherent high temperature stability is not necessary