The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use.Typesetting: Camera-ready copy by the author Cover design: MEDIO, BerlinPrinted on acid-free paper SPIN 10756695 62/3144/tr 5 4 3 2 1 o PrefaceAlthough the existence of the surface acoustic wave (SAW) was first discussed 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 performance.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.On the other hand, Japanese researchers also paid much attention to SAW devices from the 1960s, but were mainly concerned with consumer and communication applications. Starting with intermediate-frequency (IF) filters for TVs [7], various filters and resonators were developed and mass-produced from the mid-1970s. After that, though, many companies left the competition because of price reductions and fixed market shares. The same reasons forced even successful companies to shrink their research sections. So Japanese research activities were diminished until the mid-1980s.Rapid growth of the mobile communication market in the late 1980s changed the situation again. Many new-comers joined the surviving companies and very tight competition was restarted [8]. In Japan, more than 20 companies produce SAW devices now. The expanded market also stimulated research activities, and much innovative work has emerged in the last 10 years.

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This paper describes application of Sc-doped AlN (ScAlN) to wideband SAW devices in the 1 to 3 GHz range. First, it is shown theoretically that large SAW velocity and electromechanical coupling factor are simultaneously achievable when the ScAlN film is combined with a base substrate with extremely high acoustic wave velocities, such as diamond and SiC. Next, SAW delay lines are fabricated on the ScAlN/6H-SiC structure, and reasonable agreement between the theory and experiment is obtained. Finally, one-port SAW resonators are fabricated on the structure, and it is shown that high-performance is achievable in the 1 to 3 GHz range by use of the structure.

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In this paper, we describe the development of a miniature surface acoustic wave (SAW) duplexer for Band I in the standard of the Third-Generation Partnership Project (3GPP) at a 2 GHz band. We employed a shear-horizontal SAW on a SiO 2 overlay/ thick Al electrode/5 YX-LiNbO 3 structure, which offers a high electromechanical coupling coefficient (K 2 ) as well as a small temperature coefficient of frequency (TCF). This feature is crucial for the realization of a wide duplex gap between the transmitting and receiving bands in the Band I specification. We investigated experimentally that the spurious response caused by the Rayleigh-mode could effectively be suppressed by controlling the cross-sectional shape of a SiO 2 overlay on interdigital transducer (IDT) electrodes. In addition, the result also showed how this spurious response depends on IDT design parameters, i.e., electrode pitch and metallization ratio. The developed SAW duplexer was installed in a 2:5 Â 2:0 mm 2 package, and exhibited a low insertion loss, a high out-of-band rejection and a small TCF.