Fabrication and characterization of acoustic waveguides using Silicon/PPT/Silicon structures and analysis of diffraction effects for various modelings

In this paper, we present new results on the development of a new acoustic waveguide concept using an. acoustic wave excited by a Periodically Poled Transducer (PPT) and guided by guiding layers. Periodically poled transducers have been investigated recently as an alternative to classical inter-digital transducers for the excitation and detection of guided acoustic waves. The fabrication of PPTs operating in the range 50 - 500 MHz has been achieved on 3 and 4 inches 500 μm thick lithium niobate (LiNbO₃) and tantalate (LiTaO₃) Z-cut wafers. The compact structure proposed allows high frequency operation with a simplified package based on Si/LiNbO₃/Si material combination. Dispersion properties have been studied for this structure in order to find operating points corresponding to a specific thickness/period ratio. Two main devices have been fabricated, a Si/500 μm thick PPT/Si structure in order to validate the concept and a Si/20 μm thick PPT/Si structure to excite only one acoustic wave in the purpose of diffracting this wave. The experimental responses of the tested devices are compared to the predicted harmonic admittances, showing a good agreement between both results. The temperature sensitivity of the excited wave of both structures are also been measured and predicted. Finally, we expose different structures with impedance mismatches generating scattering effects.