LiNbO₃ Film Bulk Acoustic Resonator for n79 band

Abstract

We have designed and fabricated Y+36°-cut 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 (FBAR) compatible with the n79 band. Leveraging longitudinal waves and an energy trapping condition, a single-mode resonance is obtained at 4.7 GHz, with an effective electromechanical coupling coefficient (kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of 25 % and quality factor at antiresonance (Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</inf> ) of 574. This leads to Qxf and Q× kt <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> products of 2.7×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Hz and 139, respectively. A Temperature Coefficient of Frequency (TCF) of −75 and −70 ppm/°C respectively at resonance and antiresonance are obtained. These figure-of-merits are the highest reported up to date for LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> FBARs, highlighting the potentialities of LiNbO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> single crystal film as an alternative to AIN-based BAW devices for next generation of RF filters. To demonstrate this, a tentative filter design based on the measured resonator characteristics is proposed.