| The mixing piezoelectric ceramics with polymers combine the advantages of both materials have higher piezoelectric constant, lower mechanic-electric, dielectric loss of ceramics, the lower density, and acoustic impedance of polymers. The 1-3 piezocomposites have a strong anisotropy for the piezo-ceramic rods or fibers are aligned in a direction parallel to the poling direction as compared with 0-3 piezocomposites. These types of composites have relatively good piezoelectric performance along the aligned direction. Therefore, 1-3 piezocomposites are widely used in the military, medicine, scientific research and et.al.In recent years, photoacoustic imaging(PAI) technology attracts much attention of researchers for endoscopy imaging application. Piezoelectric micromachined ultrasonic transducers(p MUTs) attract much attention of researchers for the critical component in PAI. A common p MUT is made of a sandwich structure of piezoelectric films, which has poor acoustic impedance matching with biological tissue. Coupling agent is used for ultrasonic imaging in vitro. Obviously, this method can not be used for an endoscope of internal organs. Therefor, it is a workable way to fabricate p MUTs with piezocomposites for photoacoustic endscopy application. Another requirement for photoacoustic endscopy application is to fabricate array p MUTs, especially integration with Si-based integrated circuits(IC). This dissertation focuses on the 1-3 piezocomposites p MUT and IC integration. The following aspects are carried out:1. Highly c-axis oriented Al N thin films were deposited by middle frequency reactive sputtering at room temperature. The sputtering power, sputtering pressure and N2 percentage were systematically studied. The texture, stress and piezoelectric properties of Al N films were characterized. The results showed that the c-axis texture was significantly improved by N-riched buffer layer by using a two-steps growth method. The FWHM value of Al N(002) peak and residual stresses reduced while the d33 coefficent increased. A maximum d33 value of 3.4 p C/N was obtained, which provided a foundation for studing and fabrication of Al N based p MUTs.2. The Al N micro-column array /polymer 1-3 piezocomposites were fabricated by lithography-filling method. The influences of Al N volume fraction and polymer species on the piezoelectric and dielectric properties of composites were investigated. The d33 value of Al N/PVDF 1-3 piezocomposite was 6 p C/N, which provided the reliable foundation for fabricating Al N p MUTs integrated with Si-based IC.3. In order to enhance the piezoelectric coefficient of the piezoelectric films and the output single of the p MUTs, the exploration of PMN-PT 1-3 piecocomposite used in p MUTs application are carried out. The hydrothermal method was used to synthesis the PMN-0.3PT nanorods, which is compatible with IC technology. The influences of hydrothermal parameters and surface active agent on the synthesis progress of the PMN-PT nanorods were investigated. PMN-0.3PT nanorods with MPB were obtained by the optimized process. The microstructures and electric properties of PMN-0.3PT nanorods were characterized. The results showed that the perovskite PMN-0.3PT nanorods grown along [100] direction, the d33 value was 409 ± 4 pm/V, the coercive field strength was 2.8 k V/mm, the remnant polarization strength was 17.2 μC/cm2, the spontaneous polarization was 31.3 μC/cm2 and the breakdown field strength was 2.8×106 V/m.4. Based on the synthesis of nanowire PMN-PT nanowires, the research on properties of PMN-PT/PVDF 1-3 piezocomposites was carried out. The PMN-PT/PVDF 1-3 nano piezocomposites were fabricated by tape-casting method. The influences of nanorods content on the mechanical and electrical properties of nanocomposites were investigated. The influences of PMN-PT morphology, polymer species and polarization condition on output characteristics of nanocomposites were also investigated. The results showed that the piezoelectric output characteristics of 1-3 nanocomposites were much larger than that of 0-3 nanocomposites. PVDF matrix could significantly improve the output characteristics of nanocompersites as compared with PDMS matrix. The output characteristics of piezocomposites could also be improved by increasing in polarization electric field, polarization temperature and polarization time.5. PMN-PT/PVDF nanogenerators were fabricated and the output performance of nanogenerators had been tested to demonstrate the potential of the ultrsonic transducer. The PVDF/PMN-PT nanogenerator had an optimum output voltage of 20 V, output current of 60 n A and current density of 20 n A/cm2. It showed a good performance as ultrsonic transducer material and a linear relationship between output voltage and strain had been observed. Finally, the fabrication of PMN-PT nanowire array was investigated to realize the integration with IC, A preliminary method to fabricate ordered PMN-PT arrays on Pt/Si substrate was carried out, which provided a material foundation for the following research on the integratable PMN-PT pMUTs. |
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