| The role of the ferro/piezoelectric in the design of microelectronic devices is very important.Since the Second World War,this material system has always been at the forefront of high-tech advanced materials research.However,the use of a large amount of lead-based ferro/piezoelectric materials has caused severe environmental problems,and also the toxic lead has caused great harm to human health.Therefore,the development of high-performance lead-free ferro/piezoelectric materials has become very urgent.Among them,the potassium sodium niobate(KNN)-based material is favored by researchers due to its excellent piezoelectricity and high Curie temperature,and it has long been considered as a promising alternative to the lead-based one.So far,the preparation of high-quality KNN-based films is difficult,despite the rapid development of modern film preparation method.During the deposition of KNN-based films,the volatile nature of alkali metal ions will cause the loss of A-site elements,forming many defects in the film,and cause the appearance of second phase,which will seriously affect the ferroelectricity and other properties of these films.These shortcomings greatly impact the application of KNN-based films.Moreover,with the miniaturization of new high-tech electronic devices,the exploration of high-performance KNN-based ferro/piezoelectric film will usher in new opportunities and possibilities.The thesis is divided into 7 chapters as follow:Chapter 1 As an introduction to this article,we will first review the background of KNN-based materials,including the research history of KNN-based ceramics and films,and methods for performance optimization.Secondly,a vertical heteroepitaxial(VHN)structure and its application in thick film for performance regulation are briefly described.Chapter 2 This chapter is the experimental part,which mainly introduces the methods of sample preparation and characterization.Chapter 3 Using La0.67Sr0.33MnO3 as the bottom electrode,we achieve strong ferroelectricity and ultra-high Curie temperature(Tc)in KNN-based ferroelectric thin films.By co-doping of MnO2 and CaZrO3,a VHN structure is formed in the(K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3 films,which makes the performance of the KNN-based film can be tuned by the stress in the vertical direction.Robust ferroelectricity and high Tc are obtained in these films.Among them,CaZrO3 is the inducement of VHN structure formation,and the incorporation of MnO2 promotes the formation of VHN structure.The realization of the strong ferroelectricity of KNN-based thin films has taken a big step forward to replace lead-based ferroelectric materials.Chapter 4 We use epitaxial strain to tune the electrical properties and phase transition of KNN-based ferroelectric thin films.We selected La0.07Sr0.93SnO3(LSSO)and SrRuO3(SRO)as the bottom electrodes for growing KNN-based film heterostrucrures.LSSO and SRO can provide in-plane tensile and compressive stress to the upper KNN-based film,respectively.As a result,we found that the epitaxial strain can well regulate the electrical properties and phase transition behavior of the experimental KNN-based films.Chapter 5 In this part,we study the effect of neutron irradiation on the electrical properties of KNN-based lead-free ferroelectric thin films.The applications of KNN-based ferroelectric thin films not only meet the basic conditions of use in conventional environments,but also be able to meet applications in special environments.Therefore,in this part,we choose metal and oxide electrodes as the top electrodes of KNN-based thin film heterostrucrures to study their ability to resist neutron radiation.It was found that the KNN-based film is more resistant to neutron radiation using an oxide electrode.Chapter 6 In this part,we explore and study the optical characteristics and electrical properties of KNN-based films from an optical perspective,and provide experimental support for their application in transparent devices.Chapter 7 We summarize all the works of this thesis. |
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