LiNbO3 Film Bulk Acoustic Resonator for n79 band

We have designed and fabricated Y+36°-cut LiNbO
3
Film Bulk Acoustic Resonators (FBAR) compatible with the n79 band. Leveraging longitudinal waves and an energy trapping condition, a single-mode resonance is obtained at 4.7 GHz, with an effective electromechanical coupling coefficient (kt
²
) of 25 % and quality factor at antiresonance (Q
a
) of 574. This leads to Qxf and Q× kt
²
products of 2.7×10
¹²
Hz and 139, respectively. A Temperature Coefficient of Frequency (TCF) of −75 and −70 ppm/°C respectively at resonance and antiresonance are obtained. These figure-of-merits are the highest reported up to date for LiNbO
3
FBARs, highlighting the potentialities of LiNbO
3
single crystal film as an alternative to AIN-based BAW devices for next generation of RF filters. To demonstrate this, a tentative filter design based on the measured resonator characteristics is proposed.