Doping Engineering for Optimizing Piezoelectric and Elastic Performance of AlN

The piezoelectric and elastic properties are critical for the performance of AlN-based 5G RF filters. The improvement of the piezoelectric response in AlN is often accompanied by lattice softening, which compromises the elastic modulus and sound velocities. Optimizing both the piezoelectric and elastic properties simultaneously is both challenging and practically desirable. In this work, 117 X_0.125Y_0.125Al_0.75N compounds were studied with the high-throughput first-principles calculation. B_0.125Er_0.125Al_0.75N, Mg_0.125Ti_0.125Al_0.75N, and Be_0.125Ce_0.125Al_0.75N were found to have both high C₃₃ (>249.592 GPa) and high e₃₃ (>1.869 C/m²). The COMSOL Multiphysics simulation showed that most of the quality factor (Q) values and the effective coupling coefficient (K²) of the resonators made with these three materials were higher than those with Sc_0.25AlN with the exception of the K² of Be_0.125Ce_0.125AlN, which was lower due to the higher permittivity. This result demonstrates that double-element doping of AlN is an effective strategy to enhance the piezoelectric strain constant without softening the lattice. A large e₃₃ can be achieved with doping elements having d-/f- electrons and large internal atomic coordinate changes of du/dε. The doping elements-nitrogen bond with a smaller electronegativity difference (ΔEd) leads to a larger elastic constant C₃₃.