Observation of ferroelectric polarization in KNbO3 thin films and surface acoustic wave properties

In this paper, the properties of KNbO3 films, which are deposited on SrTiO3 (STO) substrate using the metal organic chemical vapor deposition (MOCVD) method, are investigated for surface acoustic wave (SAW) applications. As-grown KNbO3 films on STO substrates are sufficiently piezoelectric. The-experimental results show an electromechanical coupling coefficient (k(2)) Of 0.021 at the center frequency of 960 MHz and lambda/h = 0.24 (lambda: SAW wavelength, h: KNbO3 film thickness). These values show fairly good agreement with theoretical ones calculated by using the piezoelectric constants of single crystals. The ferroelectric polarization distribution of KNbO3 films is also measured using a scanning nonlinear dielectric microscope. The result shows that the polarizations of the as-grown film are in the same positive direction along the surface normal.