Paper Review

Highly Coupled ZnO/Quartz Structure Surface Acoustic Wave Device with Good Temperature Characteristics

Original Paper | “Improvements in Temperature Characteristics and Bandwidth for ZnO/Quartz Structure with Large Coupling Factor,” Japanese Journal of Applied Physics, 49 (2010)07HD25
“The Improvement of Temperature Characteristics for Highly Coupled ZnO/Quartz Structure,” the 30th Symposium on Ultrasonic Electronics, pp.601-602, 2009

Takaki Murata, Michio Kadota, Kenji Matsuda, Tetsuya Kimura, Ken-ya Hashimoto* [*Graduate School of Engineering, Chiba University]
[The lead author received the 2009 USEYoung Scientist Award.]

Surface acoustic wave (SAW) filters have always had a wide bandwidth which was desired, whereby a good temperature coefficient of frequency (TCF) was not much paid attention to. Recently, however, relatively narrow bandwidth SAW filters are required for applications such as multimedia broadcasting MediaFLOTM for mobile terminals, and thus demand for a good TCF is strongly increasing. In order to meet this demand, our research team studied relatively narrow bandwidth SAW filters exhibiting a good TCF. The research team testeda piece of substrate which is a combination of a quartz wafer positive TCF and a negative ZnO thin film TCF..By optimizing the electrode design, we confirmed that a good TCF and a desirable electro-mechanical coupling coefficient can be obtained based on both theoretical calculation and actual measurements. This structure achieved TCF≒0 and relatively narrow bandwidth filters by adopting a multi-mode resonator filter design which had not previously been accomplished.