Analyzing the frequency response of layered SAW filter by using coupling of modes model

• Main Authors: Zheng Tai Zhou, 周政泰
• Other Authors: Tsung Tsong Wu
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/21550097203167130103

碩士 === 國立臺灣大學 === 應用力學研究所 === 90 === Propagation of surface waves in layered structures has been a key subject in the development of dispersive SAW devices. By including a high velocity layer under a piezoelectric layer, the surface wave velocity can be increased significantly. The frequency of SAW device could be efficiently raised up under the same electrode spacing. As known, diamond has the highest acoustic wave velocity among all materials. So ZnO/IDT/Diamond structure had been used to achieve this goal in the past decade. In the first part of this thesis, we use coupling of modes model to analyze the frequency response of SAW filter with ZnO/IDT/Diamond layered structure. Because of the layered structure, the dispersion phenomenon will exist. So when we use COM model, we have to consider velocity dispersion effect. Some parameters of COM model such as reflection coefficient, transduction coefficient and velocity shift are dependent of frequency. So we must modify the parameters related to frequency when we use COM model to analyze this kind of structure. The simulated frequency response of a two-port 1.48 GHz ZnO/IDT/Diamond layered SAW filter, as we expected, is agreed with the existing experimental data in the reference [28]. In the second part of this thesis, we wish to decrease the insertion loss and raise up frequency. So we design the interdigitated interdigital transducer (IIDT) on ZnO/IDT/Diamond structure. The dispersion phenomenon also exists in this structure. As we mentioned in the first part, all parameters related to frequency must be modified when we use COM model to analyze the frequency response of SAW filter on layered structure. From the results we calculated, the insertion loss has been decreased and the frequency also has been raised successfully on this structure. And if the IIDT type of SAW filter were under the appropriate design of finger pairs, the side lobe will be reduced efficiently. So a kind of SAW filter with properties of high frequency, low insertion loss, and suppressant side lobe has been realized in this thesis.