Preperation And Electric Properties Of (K_0.4Na_0.6)NbO₃/BiFeO₃/(K_0.4Na_0.6)NbO₃Multilayers Films

Lead based piezoelectric ceramics Pb（Zr1xTix）O₃（PZT） have dominated thecommercial market, and also PZTs are widely used for various applications, such asmedical transducers, actuators, sensors and high power piezoelectric transformersdue to their good piezoelectric, dielectric and mechanical properties. Due to itsenvironmentally unconformity, recently, it is necessarily to find a lead-freepiezoelectric material to replace it, however lead-free ceramics electric propertystill cannot match with it. Recently, Nano Nature reported a huge piezoelectricityfinds in epitaxial BiFeO₃, which can be explained by R-T phase transition. In thispaper, we prepare multi-layer sandwich structural KNN/BFO/KNN lead-freepiezoelectric thin films, by which to obtain the maximum piezoelectricity becauseof its huge stress intrigued by electric filed.Firstly, we prepare our multi-layer thin film at Pt/Ti/SiO₂/Si substrate varying inlayers. By view of facade and cross-sectional SEM photographs, we observe thesurface and cross-section of multilayer thin films. By XRD, we analyze the phasestructure, and discuss the relation between electric property and phase.The SEM indicates that pyrolysis and crystallization temperature can greatly affectsthe morphology of thin films, and suitable pyrolysis and crystallization temperatureis essential to get high quality thin-film. Due to the excessively huge residual stressin composite multilayer thin-films, the surface show light ribbons or particles,whose size can varied by the increase of layers, which similar to the reports of KNNbase composite thin films. The size of these light particle or ribbons areproportional to numbers of layers in thin films, which can be explained that lightparticles crystallized superior to other region of the thin films due to the big residualstress in thin films.Different crystallization temperature can influence the electric property of BFO thinfilms, and it shows lower dielectric constants and typical PE-Loop. Differentpyrolysis and crystallization temperature can greatly influence the electric propertyof multilayer thin-films. By comparing of electric property and morphology, we getthe optimized heat treatment processing. With the increase of layers of multilayerthin films, there are some differences in electric property. The whole multilayer thinfilms do not show the high dielectric constants which show in typical pure KNN.