Study On Copper Calcium Titanate As Insulator Layer Of Thin Film Electroluminescent Devices

Along with the progress of information technology,display devices act as an important interface of human beings and machines,and the effects of flat panel displays are more significant.As a popular kind of flat panel displays,electroluminescent devices attract worldwide attention due to its many merits of wide visual angel,light weight,low cost,high response speed,high brightness,spontaneous light emitting,high efficiency,whole colors,and so on.Inorganic thin film electroluminescent devices composed of electrode layers,luminescent layers and insulation layers are extensively studied.Insulation layers have a significant effect on luminous performance,such as operating voltage and aging performance.An insulating material with high permittivity,low dielectric loss and high isolation voltage is an important objective of researches.Copper calcium titanate(CaCu3Ti4O12,CCTO)is used as insulating material of inorganic thin film electroluminescent device in this paper.The permittivity of CCTO is more than 104 under the alternating current electric field of 1 kHz and remains fairly constant in a wide range of temperature,reported by literatures.The internal barrier layer capacitors model is a widely accepted explanation for why CCTO features high permittivity.In this model,internal barrier layer capacitors formed by insulated grain boundaries and semi-conductive grains exist in CCTO and result in high permittivity.CCTO powder was synthesized by the sol-gel method.The thermo-decomposition process of the xerogel precursors and the effects of pH,heat treatment temperature and time on the purity of CCTO powders were characterized by IR,TG/DSC and XRD.The thermo-decomposition took place at a critical temperature of 257 ? with strong oxidation-reduction processes.Appropriate pH was important for sol-gel reaction.Higher temperature and longer time of heat treatment were conducive to improve the purity of CCTO powders,but the time effect was not obvious.CCTO ceramic was prepared using CCTO powders as raw material through pelleting,tabletting,and sintering progresses.Then multilayer films were prepared on Si/SiO2/Ti/Pt substrate by pulsed laser deposition using CCTO ceramic target.The dielectric performances of both ceramics and films were characterized.Under the alternating current electric field of 100 kHz,the permittivity and the dielectric loss of CCTO ceramics were 1590 and 0.28,much worse than reported.The density of CCTO ceramic was 80%,indicating that the number of internal barrier layer capacitors declined.Moreover,the raw material was too pure to have good sintering performance.The permittivity of Pt/CCTO/ITO was 42,close to quantum mechanical calculations,and the dielectric loss was 0.60.Through SEM,no obvious grain can be seen on the smooth CCTO film surface.According to this,the low permittivity can be attributed to the loss of internal barrier layer capacitors.The electrodes also had an impact.The I-V curve of Pt/CCTO/ITO indicated that the breakdown voltage was higher than 100 V,and the quality factor was higher than 11.5 ?C/cm2.The nonlinear coefficient of I-V relationship was 2.2352.SEM graphs of Pt/CCTO/ZnS:Mn/ITO multilayer films showed that the thickness of CCTO film decreased by 20%,and the interface was not clear.XRD analysis indicated that the preferred orientations of CCTO and a-ZnS were(400)and(002),different from reported.CCTO may act as a guide to ZnS.The I-V curve showed that the current was 1000 times higher than Pt/CCTO/ITO,and the breakdown voltage was 68.5 V.The insulated grain boundaries of CCTO may be partially destroyed by ZnS through oxygen loss.