Lithium niobate film bulk acoustic wave resonator for sub-6 GHz filters
Marie Bousquet, P. Perreau, C. Maeder-Pachurka, Alice Joulie, F. Delaguillaumie, Julien Delprato, Grégory Enyedi, G. Castellan, Clément Eleouet, Thierry Farjot, Christophe Billard, Alexandre Reinhardt
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.