Lithium niobate film bulk acoustic wave resonator for sub-6 GHz filters

Abstract

In this work, Film Bulk Acoustic Resonators (FBAR) based on 250 nm-thick Y+163°-cut LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> 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 (kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) reaches 17.6 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</sup> , and the quality factor at antiresonance (Qa) is around 200, leading to a Q×f product close to 900, which is slightly higher than previous realizations at 2.5 GHz [1]. This result demonstrates a first step towards introducing LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as an alternative to AlN for sub-6 GHz BAW filters.