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Effect of Buffer Electrodes in Crystallization of Zinc Oxide Thin Film for Thin Film Bulk Acoustic Wave Resonator

Published online by Cambridge University Press:  10 February 2011

Y. Yosho ,
N. Tsukai ,
K. Inoue ,
M. Takeuchi ,
T. Nomura ,
T. Makino ,
S. Arai  and
T. Hata
Y. Yosho
Affiliation:
Murata Mfg. Co., Ltd., R&D division, Shiga, Yasu, JAPAN, yoshino@murataco.jp,
N. Tsukai
Affiliation:
Murata Mfg. Co., Ltd., R&D division, Shiga, Yasu, JAPAN, yoshino@murataco.jp,
K. Inoue
Affiliation:
Murata Mfg. Co., Ltd., R&D division, Shiga, Yasu, JAPAN, yoshino@murataco.jp,
M. Takeuchi
Affiliation:
Murata Mfg. Co., Ltd., R&D division, Shiga, Yasu, JAPAN, yoshino@murataco.jp,
T. Nomura
Affiliation:
Murata Mfg. Co., Ltd., R&D division, Shiga, Yasu, JAPAN, yoshino@murataco.jp,
T. Makino
Affiliation:
Murata Mfg. Co., Ltd., R&D division, Shiga, Yasu, JAPAN, yoshino@murataco.jp,
S. Arai
Affiliation:
Murata Mfg. Co., Ltd., R&D division, Shiga, Yasu, JAPAN, yoshino@murataco.jp,
T. Hata
Affiliation:
Graduate School of Natural Science & Technology, Kanazawa University, Kanazawa, JAPAN
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Abstract

A thin film bulk acoustic wave resonator (TBAR) has been fabricated using a ZnO thin film on a SiO2 diaphragm by MEMs techniques. The ZnO/SiO2 structure TBAR can be designed to cancel a temperature coefficient of frequency (TCF) by the ZnO/SiO2 thickness ratio, because the TCF of ZnO is negative, and that of SiO2 is positive. The ZnO thin film on the SiO2 shows a c-axis orientation almost equivalent to that of the ZnO thin film on a glass substrate by RF sputtering. However, the crystallinity of the ZnO thin film is influenced by the surface conditions of substrates. ZnO thin films have been deposited on Au/Cr, Au/NiCr and Au/Ti. The Au/Ti/ZnO/Au/Ti/SiO2 structure TBAR shows the best resonant characteristics in this experiment. The resonant characteristics of the TBAR depend on the crystallinity of the ZnO thin film. The resonant resistance of the TBAR at 205MHz using a Au/Ti under electrode is about 10% less than that using an Au/Cr electrode. The x-ray diffraction result shows that the crystallinity of ZnO is greatly influenced by the crystallinity of the lower electrode. The buffer layer between an Au electrode and substrate has an influence on both the crystallinity of the ZnO thin film and the resonant characteristics of the TBAR through the Au electrode.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 605: Symposium MM – Materials Science of Microelectromechanical Systems Devices II , 1999 , 267
Copyright
Copyright © Materials Research Society 2000

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