Evaluation of bulk and surface acoustic waves propagation properties of (K,Na)NbO₃films deposited by hydrothermal synthesis or RF magnetron sputtering methods

In this study, the bulk and surface acoustic waves (BAW and SAW) propagation properties of (K,Na)NbO3 (KNN) films deposited by hydrothermal synthesis or RF magnetron sputtering methods were evaluated to investigate the applicability of such films to high-frequency devices. For the {100} c -oriented KNN epitaxial films deposited by the hydrothermal synthesis method, a BAW phase velocity of 6900 m s-1 and an electromechanical coupling coefficient k t2 of 8.4% were obtained. From the measured Rayleigh-type SAW properties, a large electromechanical coupling coefficient K 2 of 4.0% in the 1st mode was obtained in the {110} c -oriented KNN epitaxial films. On the other hand, for the preferentially {100} c -oriented KNN film deposited on Pt(111) by RF magnetron sputtering, a BAW phase velocity of 7850 m s-1 and k t2 of 7.4% were obtained. For the 0th mode of the Rayleigh-type SAW, a propagation loss of 0.13 dB/λ (λ: wavelength) at 440 MHz and a temperature coefficient of frequency of -42 ppm °C-1 were obtained for the {100} c -oriented KNN epitaxial film deposited on STO(100) by the RF magnetron sputtering method.