Dielectric And Flexoelectric Properties Of Potassium And Magnesium Ion Doped Barium Strontium Titanate Films

Barium strontium titanate(Ba_1-xSr_xTiO₃,BST for short)is a common dielectric material with excellent dielectric,flexoelectric,piezoelectric,and ferroelectric properties.It has extensive research and application in microwave,sensors,storage devices,etc.In recent years,with the continuous development of mobile terminals such as smartphones,tablets,and notebook computers,the requirements for integration,miniaturization,and lightweight of electronic devices have become higher and higher.Therefore,the research on BST thin film materials has been paid more and more attention,It has become a hotspot of current research.In this paper,the Ba_0.6Sr_0.4TiO₃ film has been prepared by the sol-gel method,and the process of the sol-gel method has been improved.The differential thermal analysis of the sample has been used to determine a reasonable heat treatment system.The BST film has been doped with K⁺and Mg²⁺.It can solve the problems of low dielectric constant,large dielectric loss,and weak flexoelectric signal.By studying the effects of different doping methods and different doping concentrations on the dielectric and flexoelectric properties of BST films,the similarities and differences of different doping methods are compared to obtain the best doping scheme.In this paper,the BST sol with stable and uniform properties has been first prepared by a sol-gel method.Then a spin coating method has been used to form a film.The BST thin film has been prepared on Pt/Ti/SiO₂/Si substrates through multiple spin coating,wet film drying,heat treatment and other processes.The microscopic properties of the film have been improved by adding PVP.When the annealing temperature of the film is 800°C and the holding time is 30 min,the dielectric constant of the prepared BST film is 262,the dielectric loss is 0.044,the flexoelectric coefficient?₁₂ is 1.81?C/m,and the equivalent piezoelectric constantd₃₃^eff is 3.077×10⁵?C/N.Then K-BST thin films have been prepared by different concentrations of K⁺doping.When the doping concentration is 7mol%,the microstructure of K-BST thin films is denser and the surface cracks are less.The dielectric constant is 446,the dielectric loss is 0.031,the flexoelectric coefficient?₁₂ is 2.67?C/m,and the equivalent piezoelectric constantd₃₃^eff is 4.539×10⁵?C/N.By doping Mg²⁺ions with different concentrations,M-BST thin films with dense structure and good surface microstructure has been prepared.When the doping concentration is 5mol%,the dielectric constant of the M-BST thin film is 401,the dielectric loss is 0.025,the flexoelectric coefficient?₁₂ is 2.45?C/m,and the equivalent piezoelectric constantd₃₃^eff is 4.165×10⁵?C/N.The K⁺ions and Mg²⁺ions have been alternately doped with BST films.The K⁺and Mg²⁺doped film structures have been designed,and the K/M-BST films are prepared.The microstructure of the K/M-BST film has been significantly improved,and the dielectric and flexoelectric properties have been significantly improved.When the doping concentration is 7mol%K⁺and 5mol%Mg²⁺,the dielectric properties are the best,the dielectric constant is 479,and the dielectric loss is 0.016;the flexoelectric properties are also the best,and the flexoelectric coefficient?₁₂ is 3.61?C/m,the equivalent piezoelectric constantd₃₃^eff is 6.137×10⁵?C/N.The paper also has studied the co-doping of BST films with K⁺ions and Mg²⁺ions.KM-BST films with high microstructure density and smooth surface are obtained.When the doping concentration is 7mol%K⁺and 5mol%Mg²⁺,KM-BST film has the best properties,the dielectric constant is 486,the dielectric loss is 0.019,and the flexoelectric coefficient?₁₂ is 3.62?C/m,and an equivalent piezoelectric constantd₃₃^effff is 6.154×10⁵?C/N.By comparison,it is found that the dielectric loss of alternating doping is lower,and the dielectric constant of co-doping is slightly higher.There is no significant difference in flexoelectric properties between the two.