Piezoelectric Micromachined Ultrasonic Transducer Based On PZT Thick Film

Ultrasonic transducer takes charge of the transformation between sonic and electricity energy, and plays a significant role in the acoustic system. Piezoelectric Micromachined Ultrasonic Transducer(pMUT) represents a new approach to ultrasonic system and generation that overcome the shortcomings of conventional ultrasonic transducer. The use of MEMS(Micro electronic mechanic system) technologies allows for convenient fabrication of multi-dimensions of arrays of identical elements. Meanwhile, pMUT offers the advantages of compact designs and the possibility of integrating the transducer and the supporting receive and send electronics on the same chip, which contributes to the reduction of parasitic capacitance and noise levels significantly as well as a cost advantage due to the adoption of the matured IC fabrication techniques.This dissertation mainly focuses on the pMUT based on PZT thick film. Structure optimization and fabrication techniques are investigated in the dissertation.For the driving material of the pMUT, a new type of thick film with excellent properties (d31=-280pm/v), which is obtained by etching down the PZT bulk ceramic, is employed. The device with this material shows not only strong driving force and high resonance frequency, but also high Effective electromechanical coupling coefficient and large transmitting sound pressure.Structure optimization of the pMUT is performed by FEM(ansys10.0). The optimization result shows that transducer can obtain the resonance frequency of 170KHz, the effective coupling coefficient of 7.19%, and the central displacement of 1.2μm@100v, which indicates a excellent performance.According to the optimization result, pMUT based on PZT thick film is fabricated and characterized. The device has the largest effective coupling coefficient of 6.39% compared to other pMUTs. Meanwhile, the resonance frequency and center resonant amplitude were measured and are 120 KHz, 4.8μm@50v, respectively. This device can be used as a transmitter due to its large amplitude.In summary, the dissertation proposed a new type of pMUT based on PZT thick film, which contains following advantages: driving material with excellent properties, large effective coupling coefficient and vibration amplitude which indicates very good transmitting ability. This pMUT can be applied in various fields such as medical imaging, nondestructive examination.