Properties Of Barium Zirconate Titanate Ferroelectric Thin Films Prepared By Sol-gel Method

For the past 50 years,lead zirconate titanate（PZT）ceramics have demonstrated excellent ferroelectric and piezoelectric properties and have been widely used.However,their use is now facing global restrictions due to the toxicity of lead.Therefore,the development of lead-free ferroelectric ceramics that can compete with the PZT family is an urgent need worldwide.Ba Ti O₃-based ceramics have excellent dielectric and ferroelectric properties and are important lead-free ferroelectric ceramics.Examples include barium calcium titanate（BCT）,barium zirconium titanate(Ba(Zr_xTi_1-x)O₃,BZT),and barium strontium titanate（BST）.Among these,barium zirconium titanate（BZT）has high dielectric constant,low dielectric loss,and large tunability,and has broad application prospects in the fields of microelectronics,micro-mechanics,and nonlinear optical devices.This article specifically addresses the effects of adding water and heating on the quality of the sol-gel,and further optimizes the preparation process based on previous research.BZT films with different zirconium doping levels and barium calcium zirconium titanate（BZCT）films with different calcium contents were prepared,and the effects of zirconium and calcium doping on the microstructure and optoelectronic properties of BZT films were investigated.The study also explores the effects of interface phenomena on BZT films.Specifically,the research content is as follows:（1）The reaction temperature and the influence of water content for BZT sol,the spin rate,pyrolysis temperature,annealing temperature and other important process parameters on the influence of BZT thin films.The results show that the reaction temperature of precursor liquid and the amount of water added are very important for the preparation of sol.In 75℃water bath heating environment or adding appropriate amount of deionized water configuration of BZT sol,has better uniformity and stability.BZT films with pyrolysis temperature of 350℃,annealing temperature of 800℃and spin coating rate of 3000 r/min have better crystallinity and denser surface.（2）The effect of zirconium content on crystal structure and electrical and optical properties of BZT films was studied.The results show that different zirconium content will affect the crystallization of BZT,and the grain size of BZT decreases with the increase of zirconium content.When zirconium content x=0.2,BZT has the largest grain size and the largest dielectric constant.The phase transition temperature（T_c）is about 100℃.With the increase of zirconium content,the dielectric constant of BZT decreases slightly,and the Tc of BZT film decreases gradually at 10 k Hz.The ferroelectric and optical properties of BZT films with different zirconium content are also different.When zirconium content x=0.6,the maximum residual polarization intensity of BZT is 1.904μC/cm².When zirconium content x=0.4,BZT has a maximum polarization intensity of 17.055μC/cm².These results indicate that the doping amount of zirconium can improve the ferroelectric properties of BZT to a certain extent,but the ferroelectric properties of BZT will be decreased when the doping amount is excessive.When zirconium content is 0.2,the energy storage efficiency of BZT film can reach92.3%.The optical band gap of BZT decreases with increasing zirconium content.（3）To study the regulatory effect of calcium content on the properties of BZCT films.It is proved that the amount of calcium doping can regulate the phase structure of BZCT.When y=0.2,BZCT has the largest permittivity,and the permittivity decreases first and then increases with the increase of calcium doping.BZCT films with 0.4 calcium content have the best ferroelectric properties,and their maximum and residual polarization strengths are about 25.710μC/cm² and 5.822μC/cm²,respectively.In addition,the optical band gap of BZCT decreases with the increase of calcium content.（4）The effects of interface effects such as different bottom electrode,film thickness and insertion layer on the crystal structure and electro-optical properties of BZT films were studied.The results show that BZT grown on LNO is more likely to form large grains,and has better dielectric constant and ferroelectric properties.The BZT coated with 5 layers and thickness of 350 nm has the best crystallographic and dielectric properties.In addition,the insertion layer forms a BZT/Zn O/LNO heterostructure with good crystallinity,high（011）orientation,better dielectric properties,and better voltage resistance up to 100V.