T. C. Lim

Czochralski single crystal growth of Sr.61Ba.39Nb2O6 for surface acoustic wave applications

Abstract Ferroelectric Sr.61Ba.39Nb2O6 (SBN) single crystals approximately 2 cm. in diameter and 5–6 cm. long have successfully been grown by the Czochralski technique. All the crystals were grown in the [001] direction in argon or oxygen, and it was found that the degree of difficulty of growth increased as the diameter of the crystals increased. Temperature dependence measurements on the poled Z-cut SBN crystals showed that this composition has temperature compensated orientations which make this material useful for surface acoustic wave devices.

Nonlinear Materials for Acoustic‐Surface‐Wave Convolver

Acoustic‐surface‐wave convolution by nonlinear mixing has been observed in cubic, hexagonal, and trigonal crystals. The magnitudes of the phenomenological nonlinear surface‐wave coupling constants are tabulated and compared with the linear electromechanical coupling factor 2(ΔV/V). It has been found that the basal plane of PZT‐8 has a larger nonlinear coupling constant than that of the commonly used Y‐cut Z‐propagating LiNbO3.

ACOUSTIC SURFACE WAVES ON METALLIZED AND UNMETALLIZED Bi12GeO20

New values for the elastic and piezoelectric constants of Bi12GeO20 and for their temperature derivatives are reported. With these new constants, the predicted value of Δv/v for acoustic surface waves is significantly increased. This prediction has been verified by measurements of the acoustic surface‐wave velocity on the metallized and unmetallized (001) surface of Bi12GeO20 and by comparing the observed values with theory. On the (001) plane, the maximum Δv/v occurs in the 〈110〉 direction. The predicted Δv/v is 66×10−4 and the experimentally observed value is (77±15)×10−4.

An exploration of the limits of stability of the LiNb03 structure field with A and B site cation substitutions

Abstract A comparative study of crystal chemistry of LiM5+03, M = Nb5+ or Ta5+ was carried out. The limits of stability of the LiNb03 structure and the Tc appear to be controlled primarily by the sizes of the substitutional ions. The LiNb03 films were grown by the liquid phase epitaxy (LPE) technique, using the Li2 0-V2 05 flux. The Na-doped LiNb03 films showed a 30% reduction in the temperature coefficient of SAW velocity.

Structural and dielectric properties in the system LiTaO3CaZrO3

Abstract A study of solid state reactions and dielectric properties has been made for the binary system LiTaO3CaZrO3. Apart from the already known structures ilmenite and perovskite, one additional phase has been claimed for the compositions in the region Li.79Ca.21Ta.79Zr.21O3 to Li.30Ca.70Ta.30Zr.70O3. The dielectric measurements for the ilmenite solid solutions indicate that the ferroic transition temperature Tc decreases substantially with increasing amounts of CaZrO3 in LiTaO3. A phase-composition diagram for the LiTaO3CaZrO3 system has been constructed on the basis of electric and X-ray diffraction studies.

Temperature coefficient of SAW velocity on epitaxial Li1−xNaxNbO3 thin films

Liquid‐phase epitaxy of doped Li1−xNaxNbO3 films on LiNbO3 has been performed. Sodium‐doped films show a 30% reduction in the temperature coefficient of surface acoustic wave velocity.

DISPERSIVE PROPERTIES OF THE FUNDAMENTAL RAYLEIGH WAVE MODE (M11) IN A HETEROEPITAXIAL ZINC OXIDE FILM ON A SAPPHIRE SUBSTRATE

The dispersion characteristics of an anisotropic ZnO layer on an anisotropic sapphire substrate have been calculated for the fundamental Rayleigh mode. A typical example of the group delay as a function of frequency is illustrated. The time‐bandwidth products for the linear regions of the group delay‐frequency curves are tabulated. For the cases studied, it has been found that using the basal plane of ZnO on y‐cut sapphire with propagation direction at right angles to the trigonal axis of sapphire yields the largest time‐bandwidth product (902/in. for a layer thickness of 4μm).

Mutual doping effects between epitaxial ZnS films and GaAs substrates

The problem of strong self‐activated luminescence in undoped ZnS films grown on GaAs substrates by chemical vapor deposition is analyzed. Tests made by changing substrates in conjunction with photoluminescence and optical transmission measurements are described. It is concluded that mutual doping effects take place between the ZnS film and the GaAs substrate with Ga doping the ZnS films while Zn dopes the GaAs substrate.

Application of nonlinear interactions in ferroelectric ceramics to microwave signal processing

We have observed a strong quadratic nonlinear relation in certain ferroelectric ceramics between electric field and applied strain. The effect is strong enough for device application and we have successfully fabricated several nonlinear surface acoustic wave devices using ferroelectric ceramics. Such devices provide electronically variable time delay, signal convolution, and pulse compression as well as a number of other signal processing functions.

Temperature and wavelength dependence of the photoenhancement of nonlinear surface‐wave convolution

Temperature‐dependent structure in the photoenhancement of nonlinear surface‐acoustic‐wave convolution on ZnO is reported. Measurements of the temperature dependence of surface‐wave convolution without light, thermally stimulated conductivity, and photoconductivity suggest that the photoenhancement effect in ZnO is sensitive to trapping and surface preparation. A possible model for the dependence of photoenhancement on photon wavelength is proposed.