Study On The Effect Of Inner Electrodes On The Microstructures And Electrical Properties Of The Glass-ceramic Capacitors

The electrical performance of the stacked glass-ceramic capacitors depends largely on the inner electrode structure and the interface quality. In this research, the effect of series inner electrode in "sandwich" structure with different preparation processes on the properties of the Na2O-PbO-Nb2O5-SiO2 glass ceramic capacitors was analyzed. The interface quality, the electrode conductivity and the controlled mechanism of the inner electrode in different sintering conditions were also investigated. Particularly, the feasibility of the electrode structure designed in the practical application was discussed. Phase identification of the glass-ceramic dielectric was performed by X-ray diffraction (XRD) using Cu-Ka radiation. The interface microstructures of the multi-layer inner electrode were studied by scanning electronic microscopy (SEM) and the interface element composition analysis were characterized by X-ray analyzer (EDS) matched the SEM.In the previous study, metal films were deposited by DC magnetron sputtering serving as inner electrode layers between the dielectric layer and the silver paste electrode of glass-ceramic capacitors to update the electrical performances. Eexperimental results show that this novel electrode structure could significantly improve the breakdown strength of the capacitors. In this study, firstly the effect of metal film electrode on the breakdown strength, leakage current, capacitance, and other electrical performance parameters of the capacitors were further analyzed. Particularly, special attention would be paid to the mechanism of the multi-layer inner electrode structure. The results reveal that the metal films as inner electrodes could improve the interface microstructure, inhibit the silver diffusion and enhance the overall performance. Based on the above research and in view of the process of capacitors, in the subsequent study, the firing process as the starting point for the improvement of the "sandwich" structured inner electrode through changing the electrode composition and preparation process. The main conclusions are listed as follows:(1) Compared with the "pre-deposited Au film" designed electrode structure sintered at medium temperature(～600℃), the "pre-deposited Ni film" designed electrode structure sintered at low temperature (<300℃) had advantages of the low cost and low firing temperature. However, the oxidation resistances of Ni films significantly lower than the precious metals, which result in the "pre-deposited Ni film" designed inner electrode structure is only suitable for low temperature and less exposure to atmospheric environment. (2) Compared with the low-temperature sintering, the capacitors produced at medium temperature had advantages of the electrode electrical conductivity and interface binding force. Noticing that the cost and the electrical properties of inner electrode are the two significant parameters to be considered in electrode preparation process, the effect of Au films pre-deposited with different time on the electrical properties of capacitors was studied. The results revealed that Au films pre-deposited for 6min were enough to effectively improve the electrical performance of the capacitors, forming the compact interface contact and inhibit the silver diffusion.(3) For the samples produced by the high temperature sintering process (≥800℃), it is found that this novel inner electrode structure not only has improvement on the interface quantity and electrical properties, but is worse than the capacitors produced at medium temperature. So this kind of novel electrode design is not suitable for the high temperature sintering process.In order to study the phenomenon of Ag+ diffusing into the Na2O-PbO-Nb2O5-SiO2 glass ceramic in air, the glass-ceramic/Ag laminated samples were sintered at 600℃and characterized. The elemental mapping results indicated that Ag diffused into the glass and the Pb2Nb2O7 in the sintering process. Then the glass-ceramic/Ag laminated samples were sintered at 800℃and characterized. The SEM observations indicate that the abnormal grain growth phenomenon near the glass-ceramic/Ag interface, which further confirmed that Ag diffused into the Pb2Nb2O7 by the EDS analysis. Ag diffused into the glass-ceramic led to the carrier densities increased, making the decline in insulation resistance and the increase of leakage current. This is very unfavorable for the reliability of the high energy capacitors.