This paper gives a historical account of the development of Rayleigh-wave, or surface acoustic wave (SAW), devices for applications in electronics. The subject was spurred on initially by the requirements of pulse compression radar, and became a practical reality with the planar interdigital transducer, dating from 1965. The accessibility of the propagation path gave rise to substantial versatility, and a huge variety of devices were developed. Passive SAW devices are now ubiquitous, with applications ranging from professional radar and communications systems to consumer areas such as TV, pagers and mobile phones. The paper describes the extensive work, particularly in the 1970s, to investigate SAW propagation in crystalline media, including piezoelectric coupling diffraction and temperature effects. This led to identification of many suitable materials. Concurrently, many devices began development, including pulse compression filters, bandpass filters, resonators, oscillators, convolvers and matched filters for spread spectrum. In the 1970s, many of these became established in professional systems, and the SAW bandpass filter became a standard component for domestic TV. In the 1980s and 9Os, SAW responded to the new call for low-loss filters, particularly for mobile phones. With losses as low as 2 dB required (and subsequently achieved) at RF frequencies around 900 MHz, a raft of new technologies was developed. Additionally, for IF filters special techniques were evolved to reduce the physical size needed for narrow bandwidths. Such devices are now manufactured in very large quantities. In order to satisfy these needs, new types of surface wave, particularly transverse leaky waves, were investigated, and materials using such waves now have their place alongside more traditional materials.

History of SAW devices

The propagation characteristics of the layered structure consistingof anSiO2 film on 128"rotated Y-cut X-propagating LiNb03 structure are investigated for surface acoustic waves (SAWS). The SiOz fiis are fabricated by radio-frequency (RF) magnetron sputtering techniques. Rayleigh-type waves are excited and detected by conven- tional inter digital transducers (IDT's) fabricated on the LiNbO3 crystal plates. Excellent results have been obtained not only for the tempera- ture characteristics with a temperature coefficient of delay (TCD, of about 0 ppm/"C but also for the frequency characteristics with a very small spurious response. Also, the attenuation constant is found to be very small and the layered structure exhibits a high value of electro- mechanical coupling coefficient (K') of about 0.08. The spurious re- sponse characteristics of the layered structure have been investigated theoretically by analyzing the generation of acoustic waves using IDT's and the spurious response is found to be small.

SAW Properties of SiO 2 /128&#176; Y-X LiNb0 3 Structure Fabricated by Magnetron Sputtering Technique

http://ieeexplore.ieee.org/iel5/10287/32720/01535886.pdf

Improved Accuracy for Determining SAW Transducer Capacitance and K 2

Experimental Verification of SSBW and Leaky SAW Propagating on Rotated Y-Cuts of LiNbO 3 and LiTaO 3

This paper reviews the basic properties of shear-horizontal (SH)-type surface acoustic waves (SAWs) and bulk acoustic waves (BAWs). As one of the simplest cases, the structure supporting Bleustein-Gulyaev-Shimizu waves is considered, and their excitation and propagation are discussed from various view points. First, the formalism based on the complex integral theory is presented, where the surface is assumed to be covered with an infinitesimally thin metallic film, and it is shown how the excitation and propagation of SH-type waves are affected by the surface perturbation. Then, the analysis is extended to a periodic grating structure, and the behavior of SH-type SAWs under the grating structure is discussed. Finally, the origin of the leaky nature is explained.

Excitation and propagation of shear-horizontal-type surface and bulk acoustic waves

An analytical solution to the electric and acoustic fields generated by a surface charge source is obtained. As a result it is shown that four types of acoustic waves can propagate along the surface of a general anisotropic medium. Numerical examples are given for ST-cut quartz and rotated Y-cut X-propagating lithium niobate.

N. Goto

Papers

Analysis of generation of acoustic waves on the surface of a semi-infinite piezoelectric solid