Finite Element Analysis of SAW Propagation Characteristics in c-plane (0001) and a-plane (11-20) AlScN Thin Films

Al _1-x Sc _x N (AlScN) is known for its large elastic and piezoelectric constants and thus is a favorable material for applications in novel radio frequency (RF) components. We investigated a-plane AlScN on r-plane Al ₂ O ₃ (AlScN(11-20)/Al ₂ O ₃ (1-102)). The surface acoustic wave (SAW) propagation properties of AlScN(11-20)/Al ₂ O ₃ (1-102) and AlScN(11-20)/Al ₂ O ₃ (1-102) were analyzed using finite element method (FEM) simulations and the results were compared. Rayleigh-type and Sezawa-type wave modes were identified and the acoustic parameters such as phase velocity, electromechanical coupling coefficient, and reflectivity were evaluated. An increased effective coupling of 5.5 % was detected for Rayleigh-type waves on AlScN(11-20)/Al ₂ O ₃ (1-102). The Sezawa-type modes show an even higher coupling up to 6.2 %. Furthermore, we detected increased reflectivity of AlScN(11-20) films compared to c-plane AlScN(0001). Our results reveal the potential of using a-plane AlScN for increasing the electromechanical coupling, which is needed for the upcoming piezo-acoustic filter requirements.