Electro-Acoustic Properties of Scandium-Doped Aluminum Nitride (ScxAl1-xN) Material and its Application to Phononic Crystal-Coupled SAW Devices

Abstract

Within the framework of the Density Functional Theory, the elastic, dielectric, and piezoelectric coefficients of w-ScxAl1−xN material were investigated for scandium (Sc) concentrations x = 0 to 0.375. The electro-acoustic properties are used to investigate the frequency response of the SAW delay line, based on the tilt θ° of the normal c-axis of the w-ScxAl1−xN piezoelectric thin film. We found that the piezoelectric response is improved as the Sc concentration increases, which is consistent with existing works in the literature. A 2D-phononic crystal pillars was then grafted on top of the surface, and the dependence of the acoustic band gaps is investigated with the help of the finite element method as a function of the Sc concentration and the tilted angle of w-Sc0.375Al0.625N. It was found that the two first band gaps exhibit a shift toward low frequencies with increasing Sc concentration. Moreover, the second acoustic bandgap is more sensitive to the inclination angle than the first. Furthermore, the insertion loss (S21) of w-Sc0.375Al0.625N is improved by 22 dB at θ° = 60°. The c-axis tilted Sc0.375Al0.625N-SAW delay line coupled with 2D-phononic crystals is a promising structure for low-loss and high-frequency SAW devices.