An anode of an organic EL display panel is normally a transparent electrode formed from an ITO film. Compared with general metals used for an electrode, the electrical resistance of the ITO film is high. Also unlike a liquid crystal display panel driven by voltage, an organic EL display panel is driven by current. Thus, with high wire resistance, the signal voltage tends to drop, and signal waveforms tend to loose sharpness. The drop of signal voltage and loss of sharpness of signal waveforms should be prevented because they cause a brightness unevenness on the display screen and an irregularity of color balance in full color mode. These phenomena particularly occur in a simple matrix type where large current flows momentarily, and tend to occur more easily as the panel size becomes larger. Referring to FIG. 12, a conventional solution for this is to provide an auxiliary electrode 92 made of e.g. chrome on an anode 91 formed of an ITO film.
The organic EL display panel illustrated in FIG. 12 is a simple matrix type, where a plurality of anodes 91 and auxiliary electrodes 92, formed on a transparent substrate 90, extend in a direction and are lined up with spaces in another direction perpendicular to the first direction. On the anodes 91 and auxiliary electrodes 92, a plurality of organic EL strips 93, cathodes 94 and cathode separators 95 are layered extending in one direction perpendicular to the above electrodes, and are lined up with spaces in a longitudinal direction of the electrodes. The cathode separators 95 are for electrical insulation between adjacent cathodes 94. The light emitted from the organic EL strips 93 transmit through the anodes 91 and the substrate 90, and travel downward. Thus, each auxiliary electrode 92 on an anode 91 is formed not to cover the anode 91 entirely, but to be locally disposed along one of the longitudinal edges of the anode 91.
The combination of the anodes 91 and the auxiliary electrodes 92 serves to decrease their electrical resistance as a whole, whereby the problem mentioned above can be solved or alleviated.
However, in the conventional structure, the auxiliary electrodes 92 extend over almost the full length of the anodes 91 in the longitudinal direction, which causes the following problem.
As FIG. 13a shows, cathode separators 95 are formed by forming a resist film 95A on the anodes 91 and auxiliary electrodes 92, and then performing exposure of light and development processing on the resist film 95A using a photolithography method. The resist film 95A is a negative type. In the prior art, when light exposure is performed on the portions 95′, which correspond to the cathode separators 95, of the resist film 95A using the mask 99, the light which transmits through this portion 95′ is reflected and scattered upward by the auxiliary electrodes 92. The auxiliary electrodes 92, made of chrome, have high light reflectance. This causes the portion near the bottom surface of the resist film 95A to be sensitized by the reflected light. So when the development processing is performed after this, the cathode separators 95 present a cross-sectional profile broadening toward the bottom, as seen in FIG. 13b. 
If the cathode separators 95 have a profile broadening toward the bottom in this way, when the organic EL strips 93 and cathodes 94 are formed by deposition, as shown in FIG. 14, the film is formed not only on the top surfaces 95a of the cathode separators 95 but also on the side surfaces 95b and 95c thereof. This causes the adjacent cathodes 94, sandwiching the cathode separator 95, to be electrically conducted, which is not appropriate. It is possible to electrically insulate the adjacent cathodes 94 by partially removing the top area of the cathode separator 95 by etching. Even with such processing, the films of the organic EL strip 93 and cathode 94 remain on both side surfaces 95b and 95c of the cathode separators 95. This is not desirable in terms of insulation of the adjacent cathodes 94 sandwiching the cathode separators 95.
USPTO Backgrounds
USPTO Backgrounds