Enhanced performance of AIN SAW devices with wave propagation along the < 11-20 > direction on c-plane sapphire substrate

摘要

This paper investigates the effect of acoustic wave propagation direction along the a-direction (< 11 -20 >) and m-direction (< 1-100 >) on the frequency responses of c-plane AlN based surface acoustic wave (SAW) devices systematically. The experimental results indicate that the resonant frequency (f(r)), quality factor (Q), electromechanical coupling coefficient (K-t(2)), insertion loss and out-of-band rejection can be improved for the a-direction compared with the m-direction of an AlN based SAW resonator on sapphire. The Q is 1347 for a one-port SAW resonator along the a-direction, and the minimum insertion loss is 8.71 dB for a two-port SAW resonator along the a-direction. The insertion loss is 3.23 dB lower for the a-direction compared to the m-direction of the AIN film, which may be attributed to the larger acoustic power flow density. The K-t(2) is 45% higher for the a-direction compared to the m-direction of the AlN film, which may be attributed to the larger elastic constant. In addition, our finite element model simulation results reveal the C-11 and C-44 for the m-direction are 345 GPa and 102 GPa, while C-11 and C-44 for the a-direction is increased to 429 GPa and 128 GPa, respectively. Our work demonstrates that the a-direction is better than the m-direction of the AlN film for high performance SAW device applications.