Preparation And Characterization Of Intergrowth CaBi₂Nb₂O₉-Bi₄Ti₃O₁₂Ferroelectric Thin Films By Magnetron Sputtering

Bismuth layer-structured ferroelectrics have broad application prospect in non-volatile ferroelectric random access memory and high temperature piezoelectric field,because of its good fatigue resistance characteristics and high Curie temperature.In addition,its electrical properties has obvious anisotropy,as the spontaneous polarization of this kind of material is confined to two-dimensional a-b plane.Intergrowth bismuth layer-structured ferroelectrics have more complicated structure than bismuth layer-structured ferroelectrics.Study found that due to the interaction between the structural unit,the polarization can be greater than its composition after the intergrowth,which has attracted more and more attention from researchers.Compared with the ferroelectric block materials,the performance of ferroelectric thin film materials are obviously different,mainly due to the substrate poses two-dimensional constraint to the ferroelectric thin film materials,and thus it is more complicated by stress.The stress mainly comes from the lattice mismatch and different thermal expansion coefficient,etc between the film and the substrate,thus the thickness of the film,the orientation of the substrate,etc all can affect the performance of the film.This article selects two kinds of more studied bismuth layer-structured ferroelectric materials at present,CaBi₂Nb₂O₉ and Bi4Ti3O12,prepared CBNO-BIT thin films with different thickness,on substrates with different orientations,on different substrates,and CBNO-BIT thin films grown under different temperature using magnetron sputtering technology,and characterized the structure,composition and electrical properties of these thin films.The main research contents and main results of this paper are as follows:?1?Intergrowth of highly oriented CBNO-BIT ferroelectric thin films.After studies of structure of highly oriented thin films grown on MgO?100?substrates,it has been proved that the expected 1-1 intergrowth ferroelectric thin films have been prepared successfully.The thin films have no obvious structure defect,the valence state of each element are normal and the stoichiometric ratio is in line with expectations.?2?The influence of thickness on CBNO-BIT thin films.Thickness can affect crystalline and preferred orientation of the thin films,and in turn,affect the electrical properties of the thin films,which make the thin films' properties have certain thickness dependence.The results of thin films grown on MgO?100?substrates showed that the ferroelectric properties of thin films had been improved,the residual polarization had been increased and the leakage current had been reduced with the increase of the thickness.?3?The influence of substrate orientation on CBNO-BIT thin films.Due to the matching degree between the films and the substrates are differ from one substrate orientation to another,which result in different stress states and crystalline orientation of the thin films,and in turn affect the electrical properties of the thin films.As for CBNO-BIT thin films grown on MgO substrates with different orientations,the dielectric and ferroelectric properties of the thin films grown on MgO?100?substrates are the best.As for CBNO-BIT thin films grown on STO substrates with different orientations,the preferred orientations and surface morphologies differ from one substrate orientation to another.Electrical properties of thin films vary with different STO substrates orientations,thin films grown on STO?110?substrates have the best dielectric,ferroelectric and piezoelectric properties,while thin films grown on STO?100?substrates have relatively the lowest.?4?Intergrowth of CBNO-BIT thin films using YSZ to enhance its orientation degree.By contrast,thin films grown on YSZ?100?substrates have better dielectric properties than those on Si?100?substrates.The thin films as well have bigger polarization under the same voltages.?5?Middle-to-low temperature preparation of CBNO-BIT thin films.Temperature affect the crystalline and surface morphologie of the thin films,thus affect the electrical properties of the thin films.Proper temperature is good for diffusion of atom on surface of the substrate,and get thin films with good crystalline and uniformity,but too high temperature may lead to the grain grew up abnormally,causing more bigger surface roughness,which is not good for getting uniform thin films.As for thin films prepared under the temperature of 450?,500? and 550?,the crystallinity of thin films improved with the increase of temperature,but when the temperature reaches to 550?,the roughness of thin films increased obviously compared to those under 500?.Thin films prepared under 550? have the best dielectric properties,thin films prepared under 500? have the best ferroelectric properties.