| Summary: | 碩士 === 國立臺灣大學 === 應用力學研究所 === 104 === Based on the band gap of phononic crystals (PCs), this thesis presents the design and fabrication of a dual-mode surface acoustic wave (SAW) resonator system with 2-D air/ST-cut quartz PCs as reflective gratings and 2-D periodic wave guiding grating layer on ST-cut quartz substrate. There are two types of SAWs operated in the dual-mode SAW resonator system. One is the Rayleigh wave (in-sagittal-plane polarized) mode along the x-direction and the other is the surface transverse wave (shear-horizontal polarized) mode along the y-direction. By using finite element method (FEM), the dispersion relations of 1-D periodic IDT electrodes, 2-D periodic wave guiding grating layer and phononic crystals are calculated. Furthermore, we optimize the distance from wave guiding grating layer and from the PCs to the electrodes, to achieve the resonant effect. The SAW devices were fabricated by using the microelectromechanical system (MEMS) technology. We utilize electron-beam lithography to make the sub-micrometer IDT electrodes and PCs. The result of the experimental dual-mode SAW resonator performance shows that the minimum insertion loss is 21.45 dB in the surface transverse wave (STW) resonator with 2-D air/ST-cut quartz phononic reflective gratings in the y-direction, which is lower 14 dB than that without the PCs (35.8 dB). The insertion loss decreases and the Q-factor is also enhanced. The results of this study may be applied to develop SAW devices with the reflective PC gratings.
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