A Theoretical and Experimental Study of Layered SAW Devices

• Main Authors: Chen, Yung-Yu, 陳永裕
• Other Authors: Wu, T.-T.
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/30261996036206781964

博士 === 國立臺灣大學 === 應用力學研究所 === 90 === Propagation of surface waves in layered structures has been of interest in the development of dispersive SAW devices and SAW sensors. By including a high velocity layer between a piezoelectric layer and a substrate, the surface wave velocity can be increased significantly. This results in an increase of the SAW frequency without decreasing the electrode spacing into the sub-micron region. On the other hand, a careful design of the over layer thickness, layered SAW device can be utilized as a sensor for biomedical applications with very high sensitivity. The purpose of this dissertation is to set up a formalism to analyze the propagation of waves in layered piezoelectric media, and then, applied to the investigations of the layered SAW devices as well as a viscous liquid sensor. In addition, based on the forward simulation and measurement of dispersion in the layered medium, an inverse algorithm has also been developed to measure the thin film properties with thickness in the sub-micron range. In the first part of the dissertation, the formulation based on the matrix method for calculating the dispersion relations for a general piezoelectric layered medium is given. A general-purpose computer program was written for the subsequent analyses. In the second part, the frequency response of a ZnO/Diamond/Si layered SAW was calculated using the effective permittivity approach. The effective permittivity and phase velocity dispersion of a ZnO/Diamond/Si layered half space was calculated. The frequency response of a unapodised SAW transducer was then calculated based on the effective permittivity method and discussions were given on the shifting of the center frequency. The electromechanical coupling coefficients of the ZnO/Diamond/Si layered half space based on two different formulae are compared and discussed. Finally, based on the results of the study, we propose an exact analysis for modeling the layered SAW device. In the third part, a Love wave sensor for the measurement of viscosity of synovial fluid, which is important in the quantitative evaluation of arthritis diseases, has been developed and tested. The design and the manufacturing process using MEMS technique of a Love wave sensor were investigated and established. The home-made Love wave sensor was then utilized to measure the viscosity of various viscous fluids as well as the synovial fluids from arthritis patients. Clinical correlation between the measured viscosity and the degree of disease has shown the Love sensor has great potential in the clinical application. In the last part of this dissertation, a nondestructive method for the measurement of the properties of thin film in the sub-micron range has been developed based on the SAW sensors. The thin film induced dispersion on the surface waves was studied and used to design an optimized sensing configuration. An inverse algorithm was used to recover the thickness and the elastic properties of the thin film. Results show that the proposed method can be used to measured thin film with thickness in the sub-micron range.