Preparation And Physical Properties Of Potassium Sodium Niobate-based Thin Films By Sol-gel Method

Ferroelectric materials have been widely researched and applied because of their excellent performance in dielectric,piezoelectric and optical fields.The typical representative and the most widely used are lead zirconate titanate(PZT)lead-based ferroelectric materials.Due to environmental and human health considerations,potassium sodium niobate(KNN)is considered to be one of the most likely to replace lead-based ferroelectric materials due to its excellent performance.However,the research on potassium and sodium niobate is mostly based on the research of bulk materials,and the research of KNN films is still insufficient,and there are many problems waiting to be solved.For example,production technology and cost constraints.Although the sputtering method and the pulse method and the like have low cost for preparing the KNN films,they have high requirements on instruments and equipment.The sol-gel method is the most widely used preparation technology and does not have high requirements on instruments and equipment.The KNN films prepared by the solgel method is generally prepared by the alkoxide method,but the niobium source used by the alkoxide method is ethanol niobium,which is expensive and not conducive to large-scale promotion.Secondly,the KNN films prepared on Si substrates are mostly polycrystalline,which is not conducive to the development of silicon-based devices.Finally,there is volatilization of potassium and sodium during the pyrolysis and annealing process of the sol-gel films,which will cause a large leakage current,which seriously limits the performance of the KNN films.Based on the above problems,this article uses low-cost niobium oxide as a raw material to prepare a KNN films,a highly preferentially oriented KNN films is prepared on a Si substrate through an improved process,and potassium is reduced by doping modification and changing the annealing atmosphere.Problems caused by sodium volatilization.The specific research is as follows:(1): The KNN films is prepared by the non-alkoxide method using niobium oxide as the raw material,and a suitable preparation process is obtained by studying the process conditions of the precursor solution and heat treatment,and by introducing the lanthanum nickelate(LNO)substrate Highly preferred KNN films.(2): A highly preferentially oriented KNN thin films was obtained on Si substrates through an improved non-alkoxide process,and the method steps and process parameters for obtaining a more suitable KNN thin films were studied.And found that compared with the unmodified non-alkoxide method,the improved preparation method pyrolysis temperature is reduced from 500 ° C to 150 ° C,from the process of reducing the evaporation of potassium and sodium.In addition,the effects of the number of coatings,annealing atmosphere and electrodes on the KNN films were studied.And on the platinum electrode,the annealing atmosphere prepared the KNN films with the number of coatings of 18 for the air,and its dielectric constant was as high as 868.(3): The KNN films is prepared by the alkoxide method,and the electrical properties of the films are improved by means of doping Li,Mn,and changing the annealing atmosphere.And study the effect of the content of doped Mn and Li on the performance of KNN thin films.It was found that annealing in oxygen improved the electrical properties of pure KNN films and Li-KNN films,while manganese-doped KNN films showed poor hysteresis loops.The KNN films doped with 5% molar ratio of Mn obtained by annealing in air has good dielectric properties and hysteresis loop.