Shape change of Ag electrode with shrinkage difference between electrode and dielectric in PDP
Introduction
Silver has high electric conductivity, and has been used as an electrode material [1], [2], [3], [4]. The Ag electrode has many applications, such as plasma display panels (PDP), low temperature co-fired ceramics, and solar cells [5], [6], [7], [8]. In flat panel display, the Ag electrode is used to complement the low electric conductivity of the ITO transparent electrode on the front panel [9]. However, the Ag electrode has many problems. They include the yellowing phenomenon, bubbles around the electrode and edge-curl, which are generally encountered as a result of an interaction between the transparent dielectric and the Ag electrode [10], [11].
The bus electrode is formed by printing, drying, exposure, developing and firing [9]. In the electrode process, the bus electrode has an under-cut after developing. This under-cut causes the edge-curl phenomenon while sintering the bus electrode. Fig. 1 shows a schematic diagram of problems encountered in a bus electrode. Under-cut is the incohesive width between the electrode and the substrate, and edge-curl is difference in height between the edges and middle of the electrode. These phenomena increase the resistivity and decrease the electrical efficiency of the PDP. Overall, these problems can result in a low efficiency, which is one of the disadvantages of PDP.
The shape of the electrode can be changed while firing the transparent dielectric. It is believed that the shape of the electrode can be changed into one of the following three types, as shown in Fig. 2: height shrinkage, height and width shrinkage, and width shrinkage and height expansion. These shape changes of the electrode can affect the occurrence and deepening of the edge-curl. The aim of this study was to understand effect of the dielectric toward shape change of the electrode. This paper present the primary results of a study aimed at solving the problem of edge-curl. Shape change of the electrode was observed as a function of the sintering temperature, and thermal properties of both glass frit and silver powder on the electrode were measured (Fig. 3).
Section snippets
Experimental procedure
A commercial green sheet was used for the transparent dielectric and a glass substrate with the bus electrode was used to obtain reliable results. The transparent dielectric was formed using the green sheet method and the bus electrode was formed using the photosensitive paste method. The transparent dielectric consists of PbO-SiO2-ZnO-Al2O3-B2O3. The bus electrode has a black layer (Ag powders and frits with added Co3O4) and a white layer (Ag powders and frits). Thickness of the green sheet
Results and discussion
Fig. 4a shows the under-cut phenomenon in the Ag electrode. The bus electrode, which was patterned using a photosensitive paste method, has an under-cut after exposure and developing. This under-cut affects the occurrence of edge-curl after sintering the bus electrode (Fig. 4b). The shape change of the electrode after sintering appears to be due to the thermal behavior of the frits and Ag powder within the bus electrode. Table 1 shows the thermal properties of the dielectric and the electrode.
Conclusion
The shape of the bus electrode differed according to the sintering condition. In the case of the electrode coated with the dielectric, the difference in shrinkage between the dielectric and electrode affects the shape change of the electrode while firing the dielectric. This is why the shrinkage of the dielectric is larger than that of the electrode. Voids were placed in the edge of the electrode after coating the dielectric, and reaction of the dielectric around the electrode was faster than
Acknowledgements
This work was financially supported by the Ministry of Education and Human Resources Development (MOE), the Ministry of Commerce, Industry and Energy (MOCIE) and the Ministry of Labor (MOLAB) through the fostering project of the Lab of Excellency.
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