DocumentCode :
3452846
Title :
High-Frequency Resonators with Excellent Temperature Characteristics using Edge Reflection
Author :
Kadota, Michio ; Kimura, Tetsuya
Author_Institution :
Murata Manuf. Co. Ltd., Shiga
fYear :
2007
fDate :
May 29 2007-June 1 2007
Firstpage :
154
Lastpage :
159
Abstract :
Currently, some surface acoustic wave (SAW) devices, especially duplexers, are required to have a good temperature coefficient of frequency (TCF), because the bands between a transmission band (Tx) and a receiving band (Rx) of the duplexer such as personal communication services (PCS) mobile phone in US is very narrow (about 1%). However, a 36-48degYX-LiTaO3 substrate, which is used for most SAW radio frequency (RF) filters and most SAW duplexers in mobile phone systems, has an optimum electromechanical coupling factor for their applications but does not have a good TCF. It was reported that the TCF of a transversal SAW filter using thin Al electrodes on LiTaO3 and LiNbO3 substrates with negative TCF was improved by depositing thick SiO2 film with positive TCF on them. However, most R,F SAW filters and most duplexers are composed of resonator type SAW devices such as ladder-type or multi-mode resonator type filters using thick Al-electrodes on the substrate to obtain a large reflection coefficient. When the thick SiO2 films were deposited on the SAW resonator and the multi-mode SAW resonator filter consisting of thick Al-electrodes/36deg YX-LiTaO3 to improve their TCF, their frequency characteristics were markedly deteriorated. Because their coupling factor becomes smaller and their propagation loss larger due to large periodic convex portions as thick as the Al-electrodes produced on the SiO2 surface. To avoid influence due to these large periodic convex portions, a SiO2 with thin convex/thin Al-electrodes/LiTaO3 and a flattened SiO2 without convex/thick Al-electrodes/LiTaO3 structures were examined, but they didn´t show good characteristics because of the small reflection at the grating reflectors. On the other hand, it is considered that the reflection of a shear horizontal (SH) wave at a substrate edge of the SiO2/Al-electrodes/LiT- aO3 structure is large regardless of Al or SiO2 thickness, because the SH wave completely reflects at the free substrate edge. But, it has been considered that it is difficult to form a fine substrate edge for a high-frequency resonator using the edge reflections. This time, by developing of forming method for a fine substrate edge, high-frequency edge reflection type resonators with a good TCF and an excellent frequency characteristic, which were composed of a thick SiO2 with thin convex/thin Al-electrodes/36degYX-LiTaO3 and a flattened thick SiO2 without convex/thick Al-electrodes/36degYX-LiTaO3, have been realized for the first time.
Keywords :
acoustic wave reflection; multiplexing equipment; surface acoustic wave devices; surface acoustic wave resonators; SAW devices; SAW radio frequency filters; duplexers; edge reflection; electrodes; grating reflectors; high-frequency resonators; mobile phone; optimum electromechanical coupling factor; personal communication services; shear horizontal wave; substrates; surface acoustic wave devices; transversal SAW filter; Mobile handsets; Optical films; Personal communication networks; Radio frequency; Reflection; SAW filters; Substrates; Surface acoustic wave devices; Surface acoustic waves; Temperature;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Frequency Control Symposium, 2007 Joint with the 21st European Frequency and Time Forum. IEEE International
Conference_Location :
Geneva
ISSN :
1075-6787
Print_ISBN :
978-1-4244-0646-3
Electronic_ISBN :
1075-6787
Type :
conf
DOI :
10.1109/FREQ.2007.4319053
Filename :
4319053
Link To Document :
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