Low-temperature Sintering And Electrical Properties Of Ba_0.68Sr_0.32TiO₃ Thick Films

Barium strontium titanate（BST）,as a typical dielectric material,has been widely used in various electronic devices due to its excellent dielectric,ferroelectric,piezoelectric and flexoelectric properties.With the development of electronic components towards miniaturization and integration,membrane materials have been widely studied because of their smaller volume.Compared with thin film materials,thick film materials have the advantages of high pressure resistance and high power.Many researchers have conducted in-depth research on it.As a common method,screen printing has the advantages of low cost and simple operation,but it also has the disadvantage of low density,especially at low sintering temperature.This paper mainly focuses on solving this problem and realizing the dense sintering of screen printing thick film at low temperature.In this subject,Ba_0.68Sr_0.32Ti O₃ thick films were prepared on the fluorophlogopite substrate by screen printing.Firstly,the effect of B₂O₃-Li₂CO₃ doping on the thick films was studied.The results show that:with the increase of doping content,the glass phase content in the thick film increases,and the density increases obviously.When the doping content is 4.5%,the maximum dielectric constant is 326（10 k Hz,room temperature）.At this time,the dielectric loss is 0.035,the remanent polarization is 3.7μC/cm²,the coercive field is 46.3 k V/cm,and the transverse flexoelectric coefficient is0.54μC/m（1 Hz）.The electrical properties of thick films are not ideal.A new method of cold sintering（CSP）was used to further improve the electrical performance.The slurry was improved by using Ba_0.68Sr_0.32Ti O₃ precursor.The effects of different cold sintering pressure,time,temperature and annealing temperature on thick films were studied.The results show that the density of BST thick films prepared at 20 MPa,170℃for 30 min is significantly improved（The annealing temperature is950℃）,and the films have the best electrical properties.Under the same test conditions,the dielectric constant and dielectric loss are 773 and 0.025,respectively.The remanent polarization is 5.3μC/cm²,the coercive field is 38.1 k V/cm,and the transverse flexoelectric coefficient is 1.23μC/m.In the absence of doping,the BST thick film and silver electrode were co-fired at low temperature,and the phase structure of the thick film is pure BST phase.The sol-gel method was used to prepare Ba_0.68Sr_0.32Ti O₃ nano powder.Based on the former experiment,nanometer powder was used to replace the original micron powder.A large number of cracks were found in thick films prepared under the original process conditions.This problem was solved by layered pretreatment,and the influence of different treatment conditions on thick films were explored.After further improvement,when annealed at 950℃,the thick film sample has high density.When the magnification of scanning electron microscope is 30000 times,almost no pores can be observed.At this time,the dielectric constant of the thick film sample is increased to 1342（10 k Hz,room temperature）,which is greatly improved.The results show that the dielectric loss is 0.023,the remanent polarization is 5.9μC/cm²,the coercive field is 32.7k V/cm,and the transverse flexure coefficient is 1.73μC/m.It has good electrical properties.