Laterally coupled narrow-band high overtone bulk wave filters using thinned single crystal lithium niobate layers

This work is devoted to the development of laterally coupled filters built on compound single crystal substrates. High overtone bulk acoustic resonators are built on LiNbO₃ thinned films bonded on thick LiNbO₃ or Quartz substrates. Two resonators are coupled via a narrow gap between their electrodes, yielding the possibility for their modes to interact and to produce coupled mode resonance conditions. The coupling efficiency is shown to be dependent on the frequency (wavelength), yielding well defined coupled-mode filters at intermediate frequencies (300-800 MHz) and single mode transfer functions above 1 GHz. The implementation of an oscillator stabilized by such a filter at 1.7 GHz is demonstrated.