Fabrication and modeling of inversion layer ultrasonic transducers using LiNbO3 single crystal

In this paper, the fabrication and modeling of inversion layer transducers using LiNbO₃ single crystal is reported. The transducer developed for this study use a 36° rotated Y-cut LiNbO₃ thin plate with an active element thickness of 115 μm. A 150 nm-thick Ti thin film was sputtered onto the positive surface of the plate, and an inversion layer was formed after the sample was annealed at a high temperature. The designed center frequency of these devices was 30 MHz. Silver powder/epoxy composite and parylene were used as matching layers. E-solder 3022 epoxy was used as the backing material. The thicknesses of the matching layers and the single crystal were measured using a scanning electron microscope (SEM). Using the analytical method, the electrical impedance for different inversion layer ratios was determined. The measured resonant frequency was consistent with the modeled data. The results show that broadband and even-order higher frequency ultrasonic transducers can be obtained by controlling inversion layer thickness.