Experimental and theoretical studies of effective piezoelectric coefficients of 2-2 connectivity AlN/AlScN composite piezoelectric films

Abstract

Aluminum nitride (AlN) and Sc-doped AlN have become the most popular piezoelectric thin-film materials in the fields of RF and smart sensing. AlN/AlScN composite films based on 2-2 connectivity exhibit stronger interaction and better lattice matching between AlN and AlScN, resulting in improved nucleation, growth kinetics, crystal quality, piezoelectric response, and surface morphology. In this work, a method for predicting the effective coefficients of AlN/AlScN composite piezoelectric thin films is proposed and validated. This prediction method is based on first-principles calculations, the Reuss model theory, and the Mori-Tanaka (MT) method. It also conforms to the mean strain and stress theory of the micromechanical approach. The precise compliance, dielectric and piezoelectric properties (Sij, ε, dij) of AlN/Al0.8Sc0.2N composite film with different thickness ratios are calculated. Through the deflection measurement of piezoelectric cantilever with proof mass based on AlN/Al0.8Sc0.2N composite film, the experimental piezoelectric stress coefficient (d31) is calculated. The correctness of the prediction method is verified by comparing the theoretical calculation (d31* = −3.1pC/N) and experimental data (d31 = −3.4pC/N), showing excellent agreement within experimental error. Meanwhile, the voltage sensitivity of the accelerometer is significantly enhanced by the AlN/AlScN composite piezoelectric film. It is believed that this work will broaden the theoretical study and application of the AlN/AlScN composite piezoelectric film.