Lithium Niobate Film Bulk Acoustic Wave Resonator For Sub-6 Ghz Filters

In this work, Film Bulk Acoustic Resonators (FBAR) based on 250 nm-thick Y+163 degrees-cut LiNbO3 films have been fabricated using a layer transfer process (4-inch) including patterned bottom electrodes and a sacrificial layer cavity. As previously reported, this orientation provides a single resonance, whose frequency is here pushed up to 4.78 GHz due to the reduced piezoelectric film thickness. The effective electromechanical coupling factor (k(t)(2)) reaches 17.6%, and the quality factor at antiresonance (Q(a)) is around 200, leading to a Qxf product close to 900, which is slightly higher than previous realizations at 2.5 GHz [1]. This result demonstrates a first step towards introducing LiNbO3 as an alternative to AlN for sub-6 GHz BAW filters.