Preparation And Electrical Properties Of Bi(Mg_0.5Ti_0.5)O₃-PbTiO₃High Temperature Ferroelectric Thin Films

Bi（Mg1/2Ti1/2）O₃-PbTiO₃（BMT-PT） ceramics possess many advantages suchas high Curie temperature, excellent electrical properties, low lead content and lowcost near the morphotropic phase boundary （MPB）, showing potential applicationsin high-temperature ferroelectric devices. This dissertation mainly focuses on thestudy of BMT-PT. The preparation process and electrical properties of sol-gelderived BMT-PT thin films were investigated. The influences of Mn doping on thestructure and electrical properties of BMT-PT thin films were studied. In addition,the effects of the annealing method of the PT seed layer on the orientation behavior,microstructure and electrical properties were explored. The main contents of thisdissertation are as follows:The BMT-PT thin films were prepared on Pt（111）/Ti/SiO₂/Si substrates by anoptimized sol-gel thin film process. The effects of annealing temperature on themicrostructure and electrical properties of BMT-PT thin films were studied. Theresults indicated that the optimal annealing temperature of the BMT-PT thin filmsis675°C. The BMT-PT thin films annealed at675°C exhibit a pure perovskitestructure and a good crystallinity. The surface morphologies of BMT-PT thin filmsannealed at675°C were observed by an atomic force microscope, showingrelatively dense and uniform microstructures. In additional, the films possessexcellent dielectric and ferroelectric properties. At a test frequency of1kHz, thedielectric permittivity εrand remnant polarization Prwere1477and17.8μC/cm²,respectively.Mn doped BMT-PT thin films were fabricated on Pt（111）/Ti/SiO₂/Si substratesby a sol-gel method。The doping contents are0mol%,0.2mol%,0.3mol%,0.5mol%and1mol%, respectively. All the BMT-PT thin films exhibit a pureperovskite structure and dense surface morphologies. The addition of a smallamount of Mn effectively reduces the dielectric loss and leakage current of thefilms. As compared to the undoped BMT-PT film, the BMT-PT film doped with0.5mol%Mn exhibits lower leakage current density such that saturated hysteresisloops can be achieved. Mn doping reduced the dielectric permittivity and remanentpolarization of the BMT-PT thin films. In all the Mn doped BMT-PT thin films, the BMT-PT thin film doped with0.5mol%Mn shows the largest permittivity andremanent polarization.The BMT-PT thin films without seed layer and with PT seed layers annealedby different methods were prepared by sol-gel method on Pt（111）/Ti/SiO₂/Sisubstrates. The effects of the annealing method of seed layer on the orientationbehavior, microstructure and electrical properties were investigated. The X-raydiffraction results indicated that the BMT-PT thin films with PT seed layer allexhibit （100） orientation. However, as the PT seed layer was annealed by rapidthermal annealing method, the BMT-PT thin film shows a much higher （100）orientation degree. The thin films with PT seed layers show much denser and moresmooth surface and smaller grain size. The analysis of the electrical propertiesindicated that the dielectric permittivity increases while the remanent polarizationand coercive field decrease with increasing the （100） orientation degree of theBMT-PT thin films. Moreover, the loss tangent values of the BMT-PT thin filmswith PT seed layers were apparently reduced.