Theoretical analysis of ultrahigh electromechanical coupling surface acoustic wave propagation in Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 crystals

The propagation characteristics of surface acoustic waves (SAWs) on the Y-cut X-propagating Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 (PIN–PMN–PT) substrate are theoretically analyzed. The results indicate the existence of a shear horizontal (SH)-type SAW with an ultrahigh electromechanical coupling factor K2. Different metal layers (Au, Al, and Cu) were examined as the electrode material. With gold, the maximum K2 for the SH SAW reaches 72.6%, while it is smaller (69.7%) for Al or Cu. There also exists a Rayleigh SAW causing the spurious response. It is shown that the response can be suppressed sufficiently by properly adjusting the thickness of the metal layer. This feature is very attractive for the realization of ultrawideband SAW filters. Variation of SAW properties with the substrate rotating angle θ was also investigated. The result indicates that θ = 0° is the best due to the relatively larger K2 for SH SAW and lower value for Rayleigh spurious response.