Temperature Stable Materials for SAW Devices

Kimura

2006

jjap

A surface acoustic wave (SAW) substrate for a duplexer, such as a Personal Communication Service handy phone system in the U.S.A, is required to have a good temperature stability, an optimum electromechanical coupling factor, and a large reflection coefficient. The conventional method of depositing a SiO 2 film on a thick Al electrode/LiTaO 3 substrate to improve its temperature coefficient of frequency (TCF) is not effective for SAW resonator-type devices, because good frequency characteristics are not obtained due to large convex portions on the surface of SiO 2 film. However, resonators having a large reflection coefficient, an excellent TCF, and good frequency characteristics were realized using the following two new structures: (I) SiO 2 film/grooved Al electrode/LiTaO 3 structure and (II) reflection of a shear horizontal (SH) wave at free edges on a SiO 2 film/thin Al electrode/LiTaO 3 structure substrate.

Section: Introductionmentioning

confidence: 99%

SiO₂/Grooved Al Electrode/LiTaO₃ and Edge-Reflection Surface Acoustic Wave Structures Having Large Reflection Coefficient, Large Coupling Factor, and Excellent Temperature Characteristic Even If Al Electrodes Are Used

Kimura

2006

jjap

“…On the other hand, the Rx filter is used in the SiO 2 /Cu electrode/36 -48 YX-LT structure, similarly to in previous reports. 1,2) Figure 10 shows the frequency responses of the Tx filter of the US-PCS SAW duplexer composed of structures (b) and (c) for h 1 ¼ 0:25, where h 2 for structures (b) and (c) is 0 and 0:02, respectively. The two characteristics are very similar at room temperature.…”

Section: Application To a Us-pcs Duplexermentioning

confidence: 99%

“…The TCF of Rayleigh, leaky SAW (LSAW), and boundary acoustic waves is improved by depositing a SiO 2 film with a positive TCF on a LiNbO 3 (LN) or LiTaO 3 (LT) with a negative TCF. [1][2][3][4] When the SiO 2 film is deposited on the interdigital transducer (IDT)/ substrate, the surface of the film always has periodic convex portions of the same thickness as the fingers of the IDT. These large convex portions cause deterioration in the frequency characteristics.…”

Section: Introductionmentioning

confidence: 99%

Surface Acoustic Wave Duplexer Composed of SiO₂/Cu Electrode/LiNbO₃Structure Having Convex and Concave Portions

Nakai

Nishiyama

2009

Jpn. J. Appl. Phys.

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.

“…By depositing a SiO 2 film with a positive TCF on Al-electrode/LiNbO 3 and LiTaO 3 substrates with a negative TCF, the TCF of the transversal SAW filters using Rayleigh waves and LSAWs were improved. [2][3][4] However, in the case of SAW resonator devices such as a double-mode SAW (DMS) resonator filter and a ladder filter, a large reflection coefficient is also required. The SAW resonator devices composed of SiO 2 / Al-electrode/LiTaO 3 or LiNbO 3 with convex and concave portions on the SiO 2 film do not have good frequency characteristics owing to their large convex and concave portions.…”

Section: Introductionmentioning

confidence: 99%

Improvement of Shape Factor and Loss of Surface Acoustic Wave Resonator Filter Composed of SiO₂/High-Density-Electrode/LiTaO₃

Murata

Matsuda

et al. 2009

Jpn. J. Appl. Phys.

Radio frequency (RF) filters in high frequencies using surface acoustic waves (SAWs), such as MediaFLOÔ, time division synchronous code division multiple access (TD-SCDMA) in China's handy phone system, and the global positioning system (GPS) in cars, require a narrow bandwidth. Thus, the SAW substrates for their RF filters also require an excellent temperature coefficient of frequency (TCF) and an optimum electromechanical coupling factor. The authors reported an RF SAW filter for MediaFLOÔ using a shear horizontal (SH) leaky SAW (LSAW) on a flattened SiO 2 film/high-density metal electrode/36 -48 YÁX-LiTaO 3 substrate. Although it had a good TCF and a large attenuation out of the pass band, it had a slightly large loss at the pass band only at room temperature compared with that of the conventional Al-electrode/42 YÁX-LiTaO 3 in the previous report. In this study, calculation using the coupling-of-modes (COM) theory showed the effect of a new phase inverse method of obtaining a steep slope at the right side of the filter frequency characteristic, although the previous paper showed only the measured frequency characteristics. In addition, an RF SAW filter with a lower loss at the pass band and a better TCF than that of the previous report has been realized.