Preperation And Physical Properties Related To Nanometer Size PZT/YBCO Heterostructure

This dissertation presents an extensive study on the growth, microstructures, and the physical properties of ferroelectriclhigh Tc superconductor heterostructures, Pb(Zr_53TO₃(PZT)／YBa₂Cu₃O_7-8(YBCO), grown by pulsed laser deposition(PLD), on (100) oriented SrTiO₃(STO) single crystal substrates. By optimizing the growth parameters, high quality PZT/YBCO heterostructures, suitable for device applications, have been successfully obtained. XRD, AFM, SEM, TEM and RBS were used to characterize the microstructure, the surface morphology and the interface of these thin films. The results show that with a fixed laser power, the substrate temperature and oxygen pressure are dominant parameters for the films quality. With the optimized parameters, deposited integrated films are in highly c axis oriented . The interface between PZT and YBCO layers is sharp, no obvious reaction interface was observed. PZT layer shows column growth mode. The surface is smooth and free of large particles. The excellent ferroelectricity and fatigue resistance shows that such heterostructure is suitble for the application of ferroelectric thin film devices. But the over high substrate temperature and the long annealing time resulted to the rougher surface morphology and inter-diffused layer in the interface was observed. Such unreasonable process also induced the growth of second phase in the PZT layer which was identified by RBS and TEM measurements and the degradation of the insulating strength of PZT/YBCO heterostructure. A multi-function system with temperature monitor was used to study the capaci- tance jump phenomenon of PZT/YBCO heterostructure at the superconducting critical transition temperature. A equivalent physical parameter model was proposed to explain this phenomenon. We found that the capacitance jump behavior is dominated by the equivalent insulate resistance of PZT/ YBCO, the change of the resistance of the YBCO and the frequency used to estimate the capacitance and the good fit to experiment data was obtained. A C-AFM was used to probe the leakage current distribution in PZT/YBCO heterostructure. It was found that for a poor sample, this inhomogeneous distribution of leakage current induced mainly by the inter-diffusion due to the long time annealing. The inter-diffusion layer was also identified by the RBS and TEM analyses. A new local analytic method was developed to probe the correlation of leakage current and ferroelectricity of the heterostructure on a nanometer scale. This is to realize the direct observation of correlation of leakage current and ferroelectricity in morphology of the surface of the heterrostructures by a modified AFM. For the first time, the relation of leakage and ferroelectricity, was imaged and quantitatively studied, on a nano-meter scale. It reveals that the leakage current can be well described by the space-charge-limited current model. A mini type heating stage was also developed which was directly combined with a AFM to construct a variable temperature AFM system (VT-AFM). The sample temperature was controlled during the AFM test. As an example of its application in ferroelectric materials research, the phase transition of ferroelectric single crystal TGS was observed in-situ.