Enhancement of electromechanical coupling coefficient by proton exchange in Z-cut LiNbO3

The electromechanical coupling coefficient K for surface acoustic waves (SA Ws) in proton-exchanged Z-cut X-propagation lithium niobate has been experi mentally investigated by the method of evaporating a thin metal film and me asuring in situ the SAW attenuation. The enhancement in K-2 value by as muc h as two times caused by the proton exchange has been observed. It is attri buted to the redistribution of electric potential of the acoustic wave due to formation of a HxLi1-xNbO3 layer at the surface. The change of electrome chanical coupling coefficient in samples fabricated under different conditi ons depends on the acoustic wavelength-layer thickness product kd. The K-2 value attains a maximum of about 0.8x10(-2) at kd approximate to 0.4, where as it is equal to 0.46x10(-2) in nonexchanged lithium niobate. The increase in electromechanical coupling coefficient can be applied for enhancement o f the SAW interdigital transducer efficiency. (C) 2000 American Institute o f Physics. [S0003-6951(00)02604-8].