Electromechanical coupling coefficient for surface acoustic waves in proton-exchanged 128°-rotated Y-cut lithium niobate

The attenuation of surface acoustic waves propagating along crystallographic X axis in proton-exchanged 128° rotated Y-cut lithium niobate during the evaporation of copper film on the crystal surface has been measured as a function of sheet resistivity of the film. From the magnitude of attenuation maxima, the effective electromechanical coupling coefficients for samples with different thicknesses of HxLi1−xNbO3 layers have been evaluated, and from the position of maxima in the resistivity scale, the effective dielectric permittivities of the structure have been estimated. The electromechanical coupling coefficient is found to be reduced practically to zero with increasing thickness of protonated layer and acoustic frequency, and the dielectric permittivity is not significantly affected by the proton exchange.