Kenji Nishiyama

Small surface acoustic wave duplexer for wide-band code-division multiple access full-band system having good temperature characteristics

A small surface acoustic wave (SAW) duplexer for a wide-band code-division multiple access (W-CDMA) system with a good temperature coefficient of frequency (TCF) has been required. However, the conventional SAW duplexer for W-CDMA using Al electrode/50–70° YX-LiNbO3 is large (3.8×3.8 mm2) and its TCF is not good (-80 ppm/°C). When a SiO2 film is deposited on this substrate to improve its TCF, good frequency characteristics cannot be realized. Thus, by using a new structure such as a flattened SiO2 film/Cu electrode/substrate structure to improve the TCF, YX-LiNbO3 substrate to obtain a large coupling factor, and flip-chip bonding to miniaturize the duplexer, a small (3×2.5 mm2) SAW duplexer having a low insertion loss and a good TCF has been realized for the first time.

Smaller surface acoustic wave duplexer for US personal communication service having good temperature characteristics

Using a flattened SiO2/Cu electrode/36–48° LiTaO3 structure, a small (5×5 mm2) surface acoustic wave (SAW) duplexer with a good temperature coefficient of frequency (TCF) for US personal communication services (PCS) was realized by the authors. However, a smaller duplexer is strongly required. Using the flip-chip bonding process of SAW chips and a Rayleigh SAW propagating on a flattened SiO2/Cu electrode/126–128° YX-LiNbO3 structure, which has a larger coupling factor than the above-mentioned substrate, a smaller (3×2.5 mm2) SAW duplexer with a good TCF was realized.

Surface acoustic wave duplexer for US personal communication services with good temperature characteristics

The transmission (Tx) and receiving (Rx) passbands of the Personal Communication Services (PCS) mobile phone system in the US are 1850–1910 MHz and 1930–1990 MHz, respectively. The transition bandwidth between Tx and Rx is very narrow, 20 MHz. A duplexer for the US-PCS employing surface acoustic waves (SAWs) requires a substrate which has good temperature stability, an optimum electromechanical coupling factor, a large reflection coefficient, and a good resonant mechanical Q value. Previously, there did not exist any substrate suitable for the US-PCS SAW duplexer. In this paper, we describe a new substrate that is suitable for the US-PCS SAW duplexer and a US-PCS SAW duplexer constructed with this new substrate.

SAW substrate, with coupling factor and excellent temperature stability suitable for duplexer of PCS in US

The pass-bands of a transmission (Tx) and a receiving (Rx) of the Personal Communication Services (PCS) Handy-phone in US are 1850-1910 MHz and 1930-1990 MHz, respectively. The transition bandwidth between the Tx and the Rx is very narrow as 20 MHz compared with other systems. A duplexer for the PCS using surface acoustic wave (SAW) requires a SAW substrate, which has a the good temperature stability, an optimum electromechanical coupling factor, and a large reflection coefficient. Some Rayleigh waves and leaky SAW (LSAW) on various substrate or structures have a good temperature characteristic, but almost all of them have not an optimum coupling factor and a large reflection coefficient for the US-PCS duplexer. In 2003, the authors reported a US-PCS SAW duplexer having good temperature stability, a steep frequency characteristic in transition band, a low loss, and a large out-of-band suppression. This paper describes the detail of the new substrate having the good temperature stability, the optimum electromechanical coupling factor, and sufficient reflection coefficient.

SAW substrate for Duplexer with Excellent Temperature Characteristics and Large Reflection Coefficient realized by using Flattened SiO2 Film and Thick Heavy Metal Film

Authors previously proposed a SAW PCS-duplexer with an excellent temperature coefficient of frequency (TCF) and a good frequency characteristic composed of a thick-SiO2/thin-Au-electrodes/LiTaO3 structure. However, a sheet resistance of thin Au electrode is large, compared with thick Al-electrode, so thin Au-electrode is not suitable for filters requiring low loss. Authors tried to use thick Cu electrodes with small resistance. By flattening large convex portions on the SiO2 surface, a SAW substrate suitable for US-PCS duplexer with low insertion loss and an excellent TCF was realized

Surface Acoustic Wave Duplexer Composed of SiO2/Cu Electrode/LiNbO3 Structure Having Convex and Concave Portions

The transition bandwidth of 20 MHz between the transmission (Tx: 1850–1910 MHz) and the receiving (Rx: 1930–1990 MHz) bands of personal communication service (PCS) handy phones in the United States (US) is very narrow compared with those of other systems. We have already realized surface acoustic wave (SAW) duplexers with sizes of 5.0×5.0×1.7 and 3.0×2.5×1.2 mm3 for PCS handy phones in the US with an excellent temperature coefficient of frequency (TCF) by using a shear horizontal (SH) wave on a flattened SiO2/Cu electrode/36–48° YX-LiTaO3 structure and a Rayleigh wave on a SiO2/Cu electrode/120–128° YX-LiNbO3 structure. Although the surface of the above-mentioned structures is flattened SiO2, we have also studied the shape of the SiO2 surface. As a result, in addition to increasing the stop-band width, which corresponds to the reflection coefficient, the TCF and power durability have been improved by forming convex portions on the surface of the SiO2 over the interdigital transducer (IDT) gaps.

Surface acoustic wave duplexer composed of SiO 2 film with convex and concave on Cu-electrodes/LiNbO 3 structure

Authors have already realized 3.0times2.5times1.2 or 2.5times2.0times0.48 mm3 size SAW duplexers for personal communication services in US with an excellent temperature coefficient of frequency (TCF) by using the Rayleigh wave on the SiO2/Cu-electrode/ 120deg-128degYX-LiNbO3 and 36deg-48degYX-LiTaO3 structures. This time, authors intentionally attempted to make the convex portions on the SiO2 film over the gap of interdigital transducers (IDTs). As the results, the calculated and measured results showed the increase of the reflection coefficient and the improvement of the TCF. In addition to them, the measured results showed that a power durability have been drastically improved without any deterioration in the frequency characteristics by making the convex portions on the SiO2 film over the gap of the IDTs.

Miniature surface acoustic wave devices with excellent temperature stability using high density metal electrodes and SiO 2 film

Currently, miniature surface acoustic wave (SAW) devices (filters and duplexers) with a good temperature stability are strongly required. In order to realize its requirement, various SAW substrates combining a high density metal electrode, a SiO 2 film, and LiTaO 3 or LiNbO 3 substrate were researched. Their combinations offer excellent properties such as large electrode reflection coefficient, large mechanical coupling factor, low velocity, and good temperature stability. This paper reviews realization of miniature SAW devices with low insertion loss and good temperature stability, such as SAW duplexers for personal communication service system in the United States (US-PCS) and wide band code division multiple access system (W-CDMA) using thier combinatios.

P2H-5 Small 3x2.5mm² Sized Surface Acoustic Wave Duplexer for US-PCS with Excellent Temperature and Frequency Characteristics

Using flattened-SiO₂/Cu-electrode/36~48deg LiTaO₃ structure, small size (5 x5mm²) surface acoustic wave (SAW) duplexer with a good temperature coefficient of frequency (TCF) for US-PCS was realized by authors. However, a smaller duplexer has been strongly required. Using flip-chip bonding process of SAW chips and Rayleigh SAW propagating on the flattened-SiO₂/Cu- electrode/126~128degYX-LiNbO₃, which has larger cou pling factor than above-mentioned substrate, a smaller sized (3x2.5mm²) SAW duplexer with a good TCF has been realized.