Research On Synthesis Of Hydrothermal PZT Thick Films For High Frequency Ultrasound Transducer Application

The most important part of ultrasound transducer is piezoelectric material, thethickness of which determines the operating frequency of the device. With the advantageof the thickness and characteristics of the piezoelectric ceramic and thin film, piezoelectricthick film is the optimal choice for high frequency ultrasound transducer fabrication. Leadzirconate titanate (PZT) thick films at morphotropic phase boundary (MPB) which behavepiezoelectric, ferroelectric and dielectric properties have been regarded as the firstcandidate. Among all the ways used to prepare PZT thick films, hydrothermal method is afacile and economic route with many advantages. Hence, the research on synthesis of PZTthick films using hydrothermal method is of great importance for both fundamental studyand technical applications.The purpose of this thesis is to fabricate hydrothermally deposited PZT thick filmswith high uniformity, high purity and with composition at MPB, using Pb(NO3)2, TiCl4,ZrOCl2.8H2O as the raw materials and KOH as the mineralizer.This paper first briefly introduced the knowledge of PZT, hydrothermal technologyand the review of current research on hydrothermal PZT thick films. Then, we investigatedthe factors which affect the synthesis of hydrothermal PZT thick films such as theconcentration of the precursors, the stoichiometric ratio of the raw materials, theconcentration of mineralizer, the titanium source and the pretreatment of titaniumsubstrate. When the oven was chosen as the heating resource, the obtained films werezirconium-rich type and deviated from MPB. To overcome this issue, a new method---heating oil bath with stirring was proposed. The XRD, EDS and XPS results demonstratethat the ratio of Zr and Ti in the sample is52/48, indicating that the obtained PZT thickfilm is near MPB. The residual stress in the film was measured to be compressive one andincreased with the increase of the thickness.