Yasuhito Kanno

Synthesis and Surface Acoustic Wave Properties of AlN Thin Films Fabricated on (001) and (110) Sapphire Substrates Using Chemical Vapor Deposition of AlCl3–NH3 System

Thin films of AlN were prepared on sapphire C- and A-plane by chemical vapor deposition. Crystal orientations, oxygen impurity contents and surface acoustic wave properties (SAW) of the films were investigated. Under optimized conditions, epitaxial AlN films were deposited and the crystal orientation relationships were (001)[110]AlN//(001)[110]Al2O3 and (001)[110]AlN//(110)[110]Al2O3. The crystal orientation of the AlN films decreased as the thickness of the films increased slightly, and the oxygen impurity content was less than 1 atm% for both systems. The dependences of SAW velocity (V s) and the temperature coefficient of the center frequency (τ f) on the film thickness were measured, and τ f was found to increase as the film thickness increased for all measurment directions; however, zero-temperature coefficient was not achieved.

Synthesis of AlN Thin Films on Sapphire Substrates by Chemical Vapor Deposition of AlCl3–NH3 System and Surface Acoustic Wave Properties

Thin films of AlN were prepared on (012) sapphire substrates by chemical vapor deposition using AlCl3, NH3, H2 and N2 gases. Crystal orientations, surface microstructures, oxygen impurity contents of the films and surface acoustic wave (SAW) properties determined using an interdigital transducer were investigated. Under optimized conditions, epitaxial AlN films were deposited and crystal orientation of AlN films increased as the thickness of the films increased. Oxygen impurity contents were less than 1 atm%. The dependence of SAW velocity along the [001] AlN axis on the film thickness was in good agreement with the theoretical prediction and the temperature coefficients of the center frequency increased as the film thickness increased. These tendencies are considered to be explained by the high crystal orientation and low oxygen impurity content of AlN epitaxial films.

Surface Acoustic Wave Properties of Lithium Tantalate Films Grown by Pulsed Laser Deposition

Single-crystal films of lithium tantalate ( LiTaO3) have been grown on sapphire substrates (001), (110) and (012) by pulsed laser deposition. Surface acoustic wave (SAW) and optical properties of these films have been investigated. The refractive indices of a (012) LiTaO3 film are n e=2.1712 and n0=2.1651 at 632.8 nm. The SAW velocities of propagation (V s), the temperature coefficients of the center frequency (TCF) and the electro-mechanical coupling coefficients (k2) of the films have been measured, and theoretical calculations of V s and k2 have been done. Experimental V s and k2 coincide with calculated ones. Theoretical calculations show that LiTaO3 films deposited by pulsed laser deposition are superior materials for high frequency SAW devices.

Formation and surface acoustic wave properties of LiNbO3/AlN/sapphire

Thin films of LiNbO3 have been formed on AlN films (AlN/sapphire) by pulsed laser deposition. The epitaxial growth of LiNbO3 films is confirmed by X-ray pole figure analysis. Theoretical calculation of surface acoustic wave (SAW) properties has been performed for LiNbO3/AlN/sapphire. Preliminary results of experimental SAW properties have been shown.

Experimental Surface Acoustic Wave Properties of AlN Thin Films on Sapphire Substrates

Equivalent circuit model parameters of Rayleigh propagation along the [001] axis of AlN (110) thin films synthesized using chemical vapor deposition on a sapphire R-plane were measured. The electro-mechanical coupling constant was 0.63% at kh2, and the static capacitance was 46.3 pF/m in the case that the line/space ratio was unity. The acoustic impedance and the normalized susceptance were obtained as a function of wavelength of surface acoustic wave for various line/space ratios.

Development of High-Efficiency Strip-Coupled Surface Acoustic Wave Convolver Using GaSb/InSb/AlGaAsSb/LiNbO3 Structures

We have fabricated a strip-coupled surface acoustic wave [SAW] convolver using GaSb/InSb/AlGaAsSb heterostructures grown on a LiNbO3 substrate. An InSb thin film with an AlGaAsSb buffer layer was grown on a 128° Y-X LiNbO3 substrate by molecular beam epitaxy; a very high electron mobility of 7000 cm2/(Vs) in 200-nm-thick InSb films was achieved. We have fabricated a strip-coupled SAW convolver as a new device and have achieved a very high output efficiency (F value) of -14 dBm for modified semiconductor and electrode structures.