SAW waveguiding in high aspect ratio transducers

Efficient acoustic waveguides with a confinement in 3-dimensional space were obtained using high aspect ratio interdigital transducers (HAR IDTs). Energy trapping at the substrate surface is ensured by mass loading effect, while lateral confinement is preserved while reducing the acoustic aperture of the HAR IDTs down to one acoustic wavelength. A detailed analysis of such HAR IDTs fabricated on X-cut lithium niobate, with Y-propagating waves is presented. Reflection scattering parameter measurements were performed and are here reported. They show the existence of several modes with a resonance frequency much lower than the one expected for a Rayleigh wave. The wave velocity is indeed reduced from 3639 m/s down to 781 m/s. Using heterodyne laser scanning interferometry, measurements of out-of-plane displacement induced by the generated surface waves were performed. The measurement results show that the elastic energy is strongly localized within the acoustic aperture of the transducer.