Highly Enhanced Electro-acoustic Properties of YAlN/Sapphire Based Surface Acoustic Wave Devices for Next Generation of Microelectromechanical Systems

Abstract

The characteristics and performances of SAW devices based on YxAl1―xN/Sapphire are demonstrated. The electromechanical properties such as elastic, dielectric and piezoelectric constants of YxAl1―xN crystals with (0≤ x ≤ 0.375) are calculated by using first-principles calculations within the new Perdew-Burke-Ernzerhof-sol functional. Analysis of the elastic constants indicates that wurtzite YxAl1―xN are elastically stable for the full range of Y concentrations. The mechanical moduli (bulk modulus B, Young modulus Y, shear modulus G) are found to decrease by increasing Y contents. The 3D contours of surface anisotropy show that wurtzite YxAl1―xN is anisotropic material which slightly decreases with yttrium composition. We observed a decrease in Debye temperature ΘD and sound velocities as yttrium increases. Moreover, the piezoelectric coefficients are found to be d33= 17.5 pC/N, d15= ―11.07 pC/N and d31= ―8.65 pC/N for Y0.375Al 0.625N, which are respectively ∼ 300 %, ∼ 400 % and ∼ 370 % higher than that of pure AlN-crystal. The dielectric constants (ε11, ε33) increase from (3.7, 5.1) for AlN to (5.3, 5.7) for Y0.375Al 0.625N. To test the performance of the SAW device based on YxAl1―xN/sapphire substrates, the electromechanical coupling factor, phase velocity, insertion loss and quality factor are determined and analysed. It is observed that the phase velocity (Vphase) decreases by increasing normalized thickness and yttrium content. In contrast, the electromechanical coupling (K2) is improved by the incensement of the normalized thickness of YxAl1―xN layer and the Y dopants, the K2 can reach an improvement of ∼650 % than AlN. The insertion loss (IL) is found to be ―7.66 dB at fR=931.4 MHz for Y0.375Al 0.625N, less than ―27 dB at fR = 1.363 GHz for AlN devices. The quality factor enhances up to 1920 for Y0.375Al0.625N, by ∼6% higher than that for AlN SAW. The wurtzite YAlN is highly promising material for developing low-loss electroacoustic devices as surface acoustic wave (SAW) resonators and RF filters to be used for next generation of mobile communications.