High quality and low loss surface acoustic wave SAW resonator based on chromium-doped AlN on sapphire

This paper aims to investigate the performances of surface acoustic wave (SAW) resonators based on chromium-doped aluminum nitride (AlCrN) piezoelectric thin film on c-cut sapphire substrate. The electromechanical properties of AlCrN (mass density, elastic, dielectric and piezoelectric constants) are obtained from density functional theory calculations for different Cr-doping concentrations. Piezoelectricity is enhanced for Al1 - xCrxN with different x concentrations. Using finite element analysis, the electroacoustic parameters such as phase velocity, electromechanical coupling factor K2 of surface acoustic modes are determined for different AlCrN thickness-to-wavelength ratios and different Cr-doping concentrations. Higher order SAW modes arise at Cr concentration x = 25%. The electrical admittance and scattering parameter S21 for the fundamental SAW modes are determined. High K2, low loss and high-quality factor are found after incorporating Cr dopant. The comparison of the obtained results with the available numerical and experimental data on AlN doped with Scandium Sc has shown a considerable improvement of SAW devices characteristics, confirming that AlCrN can be adopted as a new piezoelectric material for high performances SAW devices.