| Film capacitors are widely used in bypass,filtering or energy storage unit.In recent years,with the development of the device to miniaturization and integration,the dielectric material of the thin-film capacitor has been proposed to the high energy storage density.The energy storage density of dielectric material is jointly determined by its dielectric performance and breakdown field strength.At present,there are some deficiencies in conventional energy storage materials.For example,ferroelectric ceramics have high dielectric constant and low breakdown field strength,while polymers have high breakdown field strength and low dielectric constant.In order to further improve the energy density.the new type of dielectric material with high dielectric constant and high breakdown field is urgently needed to develop.Glass ceramics become the hotspot research in the field of energy storage materials,because of its high dielectric constant ceramic phase and high impact field glass phase,and the structure is dense and nonporous,showing high energy storage density.The research group independently developed the niobate system glass ceramics which is applicable to the preparation of high-voltage ceramic capacitor.After recent years of research,in terms of material composition,Salt metaniobate elements in substitution,the proportion of glass and ceramic facies,structure of tungsten bronze and perovskite structure facies,proportion of rare earth elements and other factors were studied to change the dielectric properties of materials.In the preparation of energy storage device,the influence of electrode structure design,electrode process and epoxy encapsulation technology on the performance of glass ceramic for high voltage energy storage device was studied.However,the previous studies in the study group focused on the dielectric properties of block glass ceramics.In this paper,after further improving the dielectric properties of glass ceramics,the effects of the preparation process parameters of glass ceramic films on dielectric properties are studied,it lays the foundation for the application of glass ceramic film in high energy storage density film capacitor.Firstly,the paper carried out a research on the performance of glass ceramics with low dielectric constant,The BS30 was selected as the base material system,and the glass ceramics with low ceramic content were prepared by gradually reducing Nb2O5 content in the system.While reducing the content of Nb2O5 we gradually replaced Ba+Sr in the original composition with Pb(Ba or Sr)to explore the structure and performance characteristics of low-dielectric constant glass ceramics.The results show that with the decrease of Nb2O5 content,the ceramic phases such as NaNbO3 and PbSrNb2O6,are reduced and the crystallinity decreased,and the dielectric constant of the material gradually decreased.At the same time,the transition point and softening point of the material decrease,and the forming performance is improved.Through the study of this paper,several kinds of material systems with large processing temperature range are found,and which dielectric constant is greater than 200.Secondly,for the high dielectric constant system,the dielectric properties of ANb2O6-NaNbO3-SiO2(ANNS,A is Pb1-xSrx,Pb1-yBay,Ba1-zSr,)glass ceramics system were studied.The study shows that MPB effect can significantly improve the dielectric properties of the material.Therefore,for the P1-xSxNNS30,P1-yByNNS30,B1-zSzNNS30 system,the MPB interval is reduced from 0.4<x,y,z<0.8 to 0.575<x<0.597,0.718?y?0.741 and 0.494?z?0.516,The dielectric constant increased by 27.4%,14.90%and 22.3%respectively.On this basis,in order to further improve the dielectric constant,the pbl-xsrxnns24 system with higher dielectric constant was studied by adding the content of ceramic phase in the system.The MPB has been systematically studied.Studies have shown that the MPB region is between 0.4<x<0.6.The MPB interval was refined to 0.44?x?0.48 and the dielectric constant increased f-rom 690(x=0.6)to 727(x=0.46)by interval interpolation method.Subsequently,different concentrations of Bi2O3 or Fe2O3 were added to the Pb0.54Sr0.46NNS24 system.The initial crystallization temperature of the ceramic phase was reduced by the addition of trace elements,and the grain growth was promoted.The dielectric constant was increased from 727 to 837 and 920 respectively.A new system with high dielectric properties was obtained,and the preparation of niobate glass ceramic film was also studied.The effects of substrate materials,oxygen pressure,deposition temperature and subsequent heat treatment on microstructure and dielectric properties of the substrate were studied systematically.For Si/SiO2/Ti/Pt,heavy doped silicon and Si/SiO2 substrate,AFM analysis shows that the dielectric film deposited on the heavily doped silicon substrate has a low roughness,and the medium of dense and smooth is favorable Lower leakage current.In addition,the oxygen pressure that can compensate the oxygen without reducing the mean free range of the molecule is IPa.(PbSr)2Nb2O7 gradually precipitated from the sedimentary state of amorphous glass by increasing the heat treatment temperature of the film.As the heat treatment temperature increased to 900?,the main crystal phases in the films changed to NaNbO3 and PbSrNb2O6,at the same time,the grain of the film increases significantly with the increase of heat treatment temperature.TEM analysis shows that a layer of amorphous transition was formed between the dielectric layer and the substrate due to lattice mismatch and chemical bond breakage.The thickness of the transition layer increases with the increasing of heat treatment temperature,which greatly influences the dielectric property of the film.The glass ceramic film capacitor prepared by the optimal component system and process parameters is adopted.Due to its dense structure and glass matrix,the breakdown field of the thin film capacitor is greater than 210kV/mm,and the dielectric constant reaches 60-173.Through the analysis of polarization curve and the calculation of linear dielectric energy storage formula,it's shown that the energy storage density of the film capacitor is 15-37J/cmJ.The capacitance of the glass-ceramic thin film capacitors shows good frequency stability within the test range of 1-1000kHz.and the change rate of the capacitance of the film capacitors is<10%at the test temperature range of-20-70?. |
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