Miniature Surface Acoustic Wave Duplexer Using SiO₂/Al/LiNbO₃ Structure for Wide-Band Code-Division Multiple-Access System

Abstract

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.

Recent development of temperature compensated SAW Devices

“…Use of apodized IDTs is the traditional countermeasure [12,37]. Since the apodization may cause Q reduction and relatively large device size [37], various techniques were proposed as another means [17,18,38].…”

“…First one is based on deposition of an amorphous SiO 2 layer on interdigital transducers (IDTs) and reflectors fabricated on a traditional LN/LT substrate [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. This is based on a unique feature of SiO 2 , i.e., it becomes mechanically stiff with T, giving positive temperature coefficient of elasticity (TCE) and TCV.…”

Focus adjustment system for a fast-scanning and phase-sensitive laser probe for radio frequency surface and bulk acoustic wave devices

“…6 shows another example. A SAW device fabricated on a 5 o YX-LiNbO 3 substrate [12] is used as a DUT. An Al IDT with the line width of 0.5 µm is covered by a SiO 2 layer.…”

Frequency response study of surface acoustic wave devices with SiO x N y film using LiTaO3 substrate

“…There are also previous research studies that investigated the effect of the deposited shape of the SiO 2 film on SAW device characteristics. [14][15][16][17][18][19] The reason why research studies on the SiO 2 film have been actively conducted is that the SiO 2 film has TCF whereby positive and negative are different from those of the substrate materials. Therefore, when it is necessary to improve the TCF of the SAW devices, the SiO 2 film for passivation is better than the Si 3 N 4 film, which has the same sign of TCF as the substrate materials.…”