4.2 GHz LiNbO₃ Film Bulk Acoustic Resonator

Abstract

We have designed and fabricated LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Film Bulk Acoustic Resonators operating around 4.2 GHz, suitable for C-band filters, with various bandwidths (60, 170, 300 and 500 MHz). They are based on common crystal cuts suitable for the excitation of longitudinal waves (Z, Y+64° and Y+36°cuts) and of shear waves (Y+163°-cut). Electromechanical coupling factors of 3.5, 9.2, 15.4 and 24% were respectively obtained. Electrodes and piezoelectric film thicknesses were optimized to ensure energy trapping in the resonators. In all cases, quality factors close to 300 are obtained, leading to a Q×f product higher than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Hz, which is the highest value reported so far for LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> film bulk acoustic wave resonators. Particularly, with an impedance ratio of 56 dB, an electromechanical coupling coefficient of 15.4% and a quality factor at antiresonance close to 390 at 4.1 GHz, Y+36°-cut LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> resonators offer promising performances towards filtering applications in the C-band.