The Structural Design And Performance Research On Potassium Sodium Niobate Homo-Multilayer Films

Potassium sodium niobate((K,Na)NbO₃,KNN)has been extensively studied due to its high Curie temperature and excellent electrical properties,especially the thin film material of KNN based on the application of multi-functional micro-nano electronic components.Among the preparation technologies of KNN thin films,the Sol-gel method with low cost and easy process control is more suitable for the preparation of complex oxides such as KNN.The sol-gel preparation of KNN films usually uses niobium ethoxide(C₁₀H₂₅NbO₅,alkoxide method)or niobium oxide(Nb₂O₅,non-alkoxide method)as a niobium source to synthesize precursor sol,however,they are either extremely expensive or of poor quality for films.Based on the above two synthesis paths,this paper innovatively proposes a sol-gel synthesis process:alternate spin coating of two kind of niobium sources to obtain low-cost and high-quality KNN films.Specifically,the different niobium sources(alkoxide method and non-alkoxide method)are used to synthesize KNN sol with the same composition,and then alternately spin-coated on the substrate to form the KNN homo-multilayer films.The influence of the process parameters of the non-alkoxide method and the alkoxide method on the structure of each sublayer of the KNN film and the interaction between the sublayers are studied.At the same time,the effect of the introduction of the homo-interface on the microstructure and electrical and optical properties of the heterostructure of the KNN homo-multilayer film is discussed.The specific research content is as follows:(1)The influence of process parameters such as excess of alkali metal,pyrolysis temperature and annealing temperature on the crystalline phase of KNN_n films(non-alkoxide method)and KNN_m films(alkoxide method).The results show that the Si based KNN films with better crystallinity and higher degree of(h00)orientation was synthesized by using the process parameters such as the alkali salt(excess 10 mol%),pyrolysis temperature of 250 ^oC and annealing temperature of 700 ^oC.When comparing the crystal structure of the[KNN_m/KNN_n]_Q homo-multilayer films synthesized by the two Sol-gel routes and the single niobium source KNN film,it is found that the degree of(h00)orientation is higher,up to 96.4%.Moreover,the surface of[KNN_m/KNN_n]_Q films are denser.(2)The effect of period number,annealing temperature and excess of alkali metal on the microstructure,electrical and optical properties of([KNN_m/KNN_n]_Q/LNO)heterostructure films were studied.The results show that the the degree of(h00)orientation of KNN homo-multilayer film with 4 period number is as high as 96.6%,and the film has the better properties of ferroelectric and the smaller leakage current density(10^-5A/cm²@2V).In addition,the[KNN_m/KNN_n]₄homo-multilayer film annealed at 700 ^oC has good crystallinity and its ferroelectric properties are also excellent.While studying the effect of excess alkali metal on the[KNN_m/KNN_n]₄homo-multilayer film,it was found that the quality of film(excess of 10 mol%)was the best.In addition,the KNN homo-multilayer film with high period number and high annealing temperature have the highest transmittance and the largest optical band gap.(3)The[KNN_m/KNN_n]₄ homo-multilayer film was synthesized by the modified KNN_n sol(PVP,2-Methoxyethanol,acetic acid as solvent),and its crystal structure and properties were studied.The results show that the change of the solvent in the modified KNN_n sol did not increase the degree of(h00)orientation of the KNN homo-multilayer film on Si electrode and on the LNO electrode.However,the surface of the[KNN_m/KNN_n]₄ film synthesized with the modified KNN_n sol is denser and the dielectric loss of films is smaller.Among them,the dielectric loss of the KNN homo-multilayer film with the solvent of PVP,2-Methoxyethanol and acetic acid was 0.1,0.09 and0.07(@100k Hz),respectively.In addition,the[KNN_m/KNN_n]₄ film by using the PVP has the highest transmittance and the largest optical band gap.