Surface Acoustic Wave Phase Velocity Research Articles

Laser generation and detection of surface acoustic waves: Elastic properties of surface layers

A noncontact all-optical method for surface photoacoustics is described. The surface acoustic waves (SAWs) were excited employing a KrF laser and detected with a Michelson interferometer using a 633-nm HeNe laser. Due to an active stabilization scheme developed for the interferometer a surface displacement of 0.2 Å could be detected. The materials investigated included pure materials such as polycrystalline aluminum, and crystalline silicon; films of gold, silver, aluminum, iron, and nickel on fused silica; and a-Si:H on Si(100). In the case of pure materials the shape of the acoustic pulse and the phase velocity were determined. The dispersion of the SAW phase velocity observed for the film systems was used to extract information on the film thickness, density, and transverse and longitudinal sound velocity. Models for the theoretical treatment of film systems and the calculation of dispersion curves are presented.

Strain effect in single-crystal silicon-based multilayer surface acoustic wave structures

A method for calculating the characteristics of surface acoustic wave (SAW) propagation in a deformable piezoelectric multilayer medium is presented. The effect of longitudinal and lateral mechanical strain on the SAW phase velocity in a (ZnO or AIN)/SiO2/Si thin film structure for {001}, {111} and {110} silicon crystal planes within the temperature range 293–673 K is studied. The effects of thickness and internal mechanical stresses in the ZnO or A1N piezoelectric film and SiO2 dielectric film on the sensitivity of the SAW phase velocity to strains in the structure are investigated. The Si{110}-based SAW structure with the SAW wavevector oriented in the 〈110〉 direction is shown to possess maximum operating frequency sensitivity to both longitudinal and lateral strain. The parameters of SAW structure stable to mechanical loads are determined. ZnO and SiO2 layer deposition on silicon is shown to increase the SAW phase velocity sensitivity to longitudinal strain and to decrease its sensitivity to lateral strain in the structure.

Measurement and Mapping of Elastic Anisotropy of Solids Using a Leaky SAW Excited by an Interdigital Transducer

Abstmt-Methods of measuring the acoustic properties of solids using acoustic beams in a liquid generated by interdigital transducers (IDT) are described. An IDT can radiate acoustic waves into a liquid in oblique directions with respect to the substrate, and the wave fronts can be arbitrarily controlled by designing the IDT shape. When the acoustic beam is incident on the solid sample-water interface near the Rayleigh angle, the reflection field is equal to the superposed fields of the specular reflection and the reradiation from the leaky surface acoustic wave (SAW) excited on the sample. One normal IDT pair on a piezoelectric substrate is used to measure the acoustic properties of a solid sample. The velocity and the attenuation of the leaky SAW on the sample can be obtained by measuring the trailing field due to the reradiation. A new method for focusing the beam from an IDT and mapping a leaky SAW velocity on a solid sample surface is shown. An interdigital electrode is divided into several sections, each of which is positioned to form a one-dimensional Fresnelphase-plate interdigital transducer (FPP IDT) on a piezoelectric substrate. It has been found that the FPP IDT generates a converging beam onto a focal plane, and the present system is suitable for measuring the two-dimensional variation of the leaky SAW phase velocity on a sample surface. T

Uniaxially strained ZnO/SiO2/Si SAW resonators

Surface-acoustic-wave (SAW) resonators fabricated on a ZnO/SiO2/Si layered medium have been cantilever-mounted. By deflecting the free end of the substrate, uniaxial biasing strains are induced in the SAW resonator. The effect of these static strains on resonant frequency and SAW phase velocity is assessed.