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Pad-Printed Curved-Surface EL DISPLAY
Keywords: EL display, pad printing, printed electronics
This paper presents the electro-luminescence (EL) display lamp which is patterned on a curved surface by the pad printing method. Due to the superior price competitiveness to the existent semi-conductor process including the photolithography, spin coating, sputter, and evaporation process, the printing technology has begun to get into the spotlight as a micro fabrication technology. The printing methods, including the gravure, screen, flexo, inkjet, and pad printing, have an advantage of one-step direct patterning. However, in general, the printing and semi-conductor process, except pad printing method, cannot be applied for patterning on a curved surface. Thus, in this paper, we used pad printing method for patterning an EL display lamp on a curved surface. The EL display lamp consists of 5 layers: Bottom electrode; Dielectric layer; Phosphor; Transparent electrode; Bus electrode. For proper pad printing, the ink of each layer should be formulated and the pad printing condition should be well controlled. As the bottom electrode, silver ink and carbon ink were used. Since the resistance of silver is low enough for electrodes, 1 time printing results in the sufficient conductivity, even though the printed thickness is as thin as 1.4um. However, in case of carbon, we printed 5 times for the sufficient conductivity. The pattern height of carbon was 5.77um. Since the dielectric layer should be thick in order to prevent a short circuit at a high voltage, we printed this layer 5 times. The phosphor and transparent layer was also printed 5 times for sufficient layer thickness. The bus electrode is same as the bottom electrode. However, since the bus electrode is printed on the transparent electrode, the adherence between the layers is critical. The adherence of the carbon ink is almost 5 times better than the adherence of the silver ink. We used the carbon ink for the bus electrode. Finally, we printed EL display lamp on a dish which has a radius of curvature 80mm. The EL display lamp was driven at AC 200V of 1kHz.
Taik-Min Lee, Senior Researcher
Korea Institute of Machinery and Materials
Daejeon 305-343,
South Korea

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