| Recently, integration and miniaturization are the inevitable trend of development of acousto-optic devices, and piezoelectric thin film bulk acoustic transducer working in fiber acousto-optic devices is becoming a hot research. Compared with the conventional ultrasonic transducers for acousto-optic devices, the piezoelectric thin film bulk acoustic transducer has high operating frequency, low insertion loss, wide bandwidth, high Q value, small size and easily integrate with acousto-optic crystals. Thus, it has widely application prospects, such as sensor dection, optical communications and ultrasonic medical machining. Zinc Oxide (ZnO) is a piezoelectric semiconductor material with hexagonal crystal wurtzite structure. Its outstanding piezoelectric properties makes it a suitable material to fabricate the thin film bulk acoustic wave transducers. It has been extremely applied in BAW resonators, surface acoustic wave (SAW) devices and piezoelectric sensors.ZnO thin film ultrasonic transducer is a key to success in fiber acousto-optic devices manufacture. Since technology complexity for ZnO thin film transducer and performance requirements for acousto-optic devices, in this thesis, we mainly focus on the comprehensive analysis theory and numerical simulation modeling for ZnO thin film transducer, and vibration modes optimization and suppression transverse mode. Following the analysis, we investigate and characterize the process parameters for ZnO piezoelectric thin film under various sputtering deposition conditions, and text the microcosmic properties of ZnO transducer, X-ray diffraction (XRD) and scanning electron microscopy (SEM) characterization results show that the highly c-axis oriented ZnO thin films have been deposited on the Si, and we test the diffraction efficiency of filber acousto-optic device, its results consistents with theoretical analysis. The main contents is as follows:On the basis of bulk acoustic wave theory, the sandwich panels mechanics model was introduced, adding the impact of shear stress from piezoelectric ZnO intermediate layer, avoiding the disadvantages of ignoring electrode thickness, electrode impedance and other physical parameters in the traditional model of Mason model, the thickness frequency dispersion equation (longitudinal wave) mode are obtained by using of electromagnetic waves and more reflections resonance theory, then a more universal model equations is obtained, its simplification is well agreement with the conclusions of MB VD modeWe analyzed the ZnO thin film transducer model by multi-physics coupling software (Comsol) on the basis of the universal model, obtained the influence of the transducer operating frequency and bandwidth from parameters, including of piezoelectric material, electrode materials, thickness and area of electrode and support layers. The results provide guidance for preparation of ZnO transducer to meet the performance requirements of the acousto-optic devices.In order to obtain high quality ZnO thin films, we study the effects of various deposition parameters of magnetron sputtering apparatus. With sputtering technologic parameters being optimized through XRD characterization results, the high quality (002) texture of ZnO thin films on Si substrate were prepared at a substrate temperature of 400?, Ar and O2 ratio of 40:20, and the atmosphere pressure:4.0 Pa, sputtering power: 200W prepared an high performance Si (002) ZnO thin film crystal orientation, AFM surface morphology of the grain diameter was 3.42nm.We studied the mechanism of circular and annular electrodes transverse mode overtone using Tiersten equation, explained the reasons that the ring electrode pattern transverse mode overtone is less than circular electric on base of electromagnetic field theory, and obtained the conclusion of agreement with the acoustic scattering resonances theory. The fundamental frequency of ring electrode ZnO thin film transducer is controlled by the ratio of inner and outer diameter ring electrode. Then, we analyzed the transverse mode overtone vibrational pattern from heterodyne laser interferometer and compared two transducer electrical impedance curves from network analyzers. The experimental results verify the theoretical results.From the coupled wave analysis for the acousto-optic interaction in medium, we analyzed the diffraction efficiency of the optical fiber acousto-optic devices using Matlab, obtained the simulation results which can provide a theoretical basis. Then, we studied the fiber acousto-optic devices using ZnO thin films ultrasonic transducer, the diffraction efficiency shows that changes by the wavelength of incident light or ultrasonic frequency. The results agree with theoretical simulation.In summary, these studies for ZnO film transducer from the theoretical model and performance experiment, it not only helps to understanding of the similar piezoelectric thin film devices and transverse modes optimization, but also has a guidiance for the performance development of acousto-optic devices using the film transducer. |
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