Single-mode high frequency LiNbO3 Film Bulk Acoustic Resonator

In this paper, Y+163°-cut LiNbO
₃
(LNO) Film Bulk Acoustic Resonators (FBAR) with patterned bottom electrodes (AlSi or W) and a sacrificial layer cavity have been fabricated using a layer transfer process (4-inch). Unlike previous work based on films oriented towards the X axis [1], the Y+163° orientation provides a single resonance at 2.2 GHz, with an effective electromechanical coupling factor (k
_t
²
) of 26 %. Thanks to this single mode behavior and to the energy trapping induced by the heavy tungsten electrodes, the quality factor at antiresonance (Q
_a
) is increased to 600. Moreover a Temperature Coefficient of Frequency (TCF) of -45 ppm/°C is obtained. This demonstrates a significant improvement towards introducing LiNbO
₃
as an alternative to AlN in Bulk Acoustic Wave (BAW) filters for the new generation of RF filters.