Boosting Quality Factor in 15 GHz Film Bulk Acoustic Resonators (FBAR)

Attaining a high quality factor in bulk acoustic wave (BAW) resonators becomes increasingly difficult as the resonant frequency rises, particularly beyond 10 GHz. This research examines the shape effect on 15 GHz Sc<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.2</inf>Al<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.8</inf>N-based BAW resonators, revealing that the quality factor (Q factor) is significantly influenced by the device shape, with the area reduced to a few hundreds of μm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to ensure impedance matching at 15 GHz. Among all the investigated device shapes, round-shaped BAW resonators possess the largest Q factor, and can achieve a Q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> of up to around 500. On the other hand, the effective coupling coefficient is not influenced by shape in the same way as the Q factor.