Surface Acoustic Wave Devices in Telecommunications

Although the existence of the surface acoustic wave (SAW) was first dis- cussed in 1885 by Lord Rayleigh [1], it did not receive engineering interest for a long time. In 1965, the situation changed dramatically. White suggested that SAWs can be excited and detected efficiently by using an interdigital transducer (IDT) placed on a piezoelectric substrate [2]. This is because very fine IDTs can be mass-produced by using photolithography, which has been well developed for semiconductor device fabrication, and proper design of the IDT enables the construction of transversal filters with outstanding perfor- mance. Then, in Europe and America, a vast amount of effort was invested in the research and development of SAW devices for military and communication uses, such as delay lines and pulse compression filters for radar and highly stable resonators for clock generation. Research activities are reflected in the various technical papers represented by special issues [3-5] and proceedings [6]. The establishment of design and fabrication technologies and the rapid growth of digital technologies, represented by the microcomputer, meant that the importance of SAW devices for the military decreased year by year and most researchers in national institutions and universities left this field after reductions or cuts in their financial support. Then the end of the Cold War forced many SAW researchers in companies to do so, too.