Keiko Hosaka

Longitudinal-Type Leaky Surface Acoustic Wave on LiNbO3 with High-Velocity Thin Film

The loss reduction of a longitudinal-type leaky surface acoustic wave (LLSAW) by loading with a dielectric thin film with a higher velocity than the substrate is proposed. An aluminum nitride (AlN) thin film was adopted as a high-velocity thin film, and the propagation properties of an LLSAW on an X36°Y-LiNbO3 (LN) substrate were investigated. First, the elastic constants c11 and c44 of an amorphous AlN (a-AlN) thin film deposited by RF magnetron sputtering were determined from the measured phase velocities of two SAW modes with mutually perpendicular particle motion, and they were 78 and 96% of those of a single-crystal AlN thin film. Next, from the theoretical calculation for the LLSAW on X36°Y-LN using the determined constants, it was found that the LLSAW attenuation can be reduced to zero by loading with an a-AlN thin film. Then, the propagation properties of the LLSAW on X36°Y-LN were measured by using an interdigital transducer pair. It was found that the losses due to bulk wave radiation can be reduced by loading with an a-AlN thin film.

Control of Second Order Temperature Coefficient of SAW Propagating in Thin Film Layers

This study proposes the control method of the 1st- and 2nd-order temperature coefficients of two-layer substrate composed of ZnO and Ta2O5 thin films which have the 2nd-order temperature coefficients of delay time with the signs opposite to each other. As a result, a stable SAW substrate of [Ta2O5/ZnO/Fused quartz] showing the 3rd-order characteristics was developed.

Love-type surface acoustic wave on Y–X LiTaO3 with amorphous Ta2O5 thin film

In this study, to obtain a substrate structure with a lower phase velocity, the propagation properties of a Love-type surface acoustic wave (Love SAW) on Y–X LiTaO3 (LT) with an amorphous tantalum pentoxide (a-Ta2O5) thin film were investigated using a simple delay line and a resonator with a wavelength λ of 8 µm. The insertion loss of a simple delay line was decreased markedly by loading with an a-Ta2O5 film owing to a transformation from a leaky SAW (LSAW) to a non-leaky Love SAW. A phase velocity of 3,340 m/s, a coupling factor of 5.8%, and a propagation loss of 0.03 dB/λ were obtained for a normalized thickness h/λ of 0.120. Moreover, the resonance properties of the Love SAW were almost equal or superior to those for an LSAW on Al/36° Y–X LT, except for the fractional bandwidth.

Loss reduction of leaky surface acoustic wave by loading with high-velocity thin film

The propagation properties of a leaky surface acoustic wave (LSAW) on rotated Y-cut X-propagating lithium niobate (YX-LN) substrates loaded with an aluminum nitride (AlN) thin film with a higher phase velocity than that of the substrate were investigated theoretically and experimentally. From the theoretical calculation, it was found that the minimum attenuation can be obtained at a certain thickness of the AlN thin film for a cut angle ranging from 0 to 60° because the cut angle giving the minimum attenuation shifts toward a smaller cut angle as the film thickness is increased. The propagation properties of an LSAW on several rotated YX-LN substrates were measured by using an interdigital transducer (IDT) pair with a wavelength λ of 8 µm, and the predicted shifts of the minimum attenuation toward a smaller cut angle were demonstrated experimentally. For 0° and 10°YX-LN samples, the measured insertion loss and propagation loss were markedly reduced by loading with the AlN thin film. A larger electromechanical coupling factor (16.9%) than that at the cut angle giving zero attenuation without a film and a propagation loss less of 0.02 dB/λ were obtained simultaneously at a film thickness of 0.125 λ for the 10°YX-LN sample.

Longitudinal-type leky surface acoustic wave on LiNbO 3 with high-velocity thin film

The loss reduction of a longitudinal-type leaky surface acoustic wave (LLSAW) by loading with a dielectric thin film with a higher velocity than the substrate is proposed. An aluminum nitride (AlN) thin film was adopted as a high-velocity thin film, and the propagation properties of an LLSAW on an X36°Y-LiNbO3 (LN) substrate were investigated theoretically and experimentally. First, the elastic constants c11 and c44 of an AlN thin film deposited by RF magnetron sputtering were determined from the measured phase velocity of a Rayleigh-type SAW, and they were 61 and 68% of those of a single-crystal AlN thin film. Next, from the theoretical calculation for the LLSAW on the X36°Y-LN substrate, it was found that the LLSAW attenuation can be reduced to zero by loading with an AlN thin film. Then, the propagation properties of the LLSAW on the X36°Y-LN substrate were measured by using an interdigital transducer pair with a wavelength (λ) of 8 εm. When the film thickness was 0.25 λ, the measured propagation loss decreased from 0.28 dB/λ for the sample without a film to 0.03 dB/λ.