Efficiency of Generation of Surface Acoustic Waves in Barium Strontium Titanate Thin Films

The excitation of surface acoustic waves (SAWs) on the surface of the ferroelectric film [barium strontium titanate (BST)] located on the dielectric substrate (silicon) was studied theoretically. We found that the most effective SAW excitation takes place when spontaneous polarization occurs in the film plane and the wave propagates along the direction adjacent to the direction of the spontaneous polarization vector. Based on a nonlinear model of phase transitions in solid BST solutions, the dependency of the material constants of piezo-effect equations on the misfit strain with a fixed concentration was obtained numerically. The effect of various misfit strains on SAW characteristics was studied for the film located on single-crystal silicon. It was shown that the effectiveness of SAW excitation increases as the misfit strain nears the boundary of phase transition.