Single-mode high frequency LiNbO₃Film Bulk Acoustic Resonator

Abstract

In this paper, Y+163°-cut LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LNO) Film Bulk Acoustic Resonators (FBAR) with patterned bottom electrodes (AlSi or W) and a sacrificial layer cavity have been fabricated using a layer transfer process (4-inch). Unlike previous work based on films oriented towards the X axis [1], the Y+163° orientation provides a single resonance at 2.2 GHz, with an effective electromechanical coupling factor (k <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) of 26 %. Thanks to this single mode behavior and to the energy trapping induced by the heavy tungsten electrodes, the quality factor at antiresonance (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a</sub> ) is increased to 600. Moreover a Temperature Coefficient of Frequency (TCF) of -45 ppm/°C is obtained. This demonstrates a significant improvement 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 in Bulk Acoustic Wave (BAW) filters for the new generation of RF filters.