Organic EL Display Cathode Segmentation Parasite Capacitance
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Solution Overview
Problem
In organic EL displays, the overlap of the cathode electrode with signal lines leads to unnecessary parasite capacitance, causing signal delay and inaccurate image display, which is difficult to address without compromising the display's compactness.
Innovation Solution
The use of an insulating layer with recesses or projections between light emitting elements separates the second electrode layers, allowing the wiring in the drive circuit to be positioned in the overlap region, thereby avoiding or reducing parasite capacitance and ensuring accurate image display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the cathode electrode is formed to extend over the entire image display region, then the configuration is simple and manufacture is easy, but unnecessary parasite capacitance is formed between the cathode electrode and signal line, causing signal delay
Solution Approach 1:
The cathode electrode is segmented into multiple independent cathode electrodes corresponding to different sub-pixels, rather than forming a single continuous electrode. This segmentation prevents the formation of large-area overlap regions with signal lines, thereby reducing parasite capacitance while maintaining manufacturing simplicity through systematic patterning
Solution Approach 2:
The cathode electrode structure is optimized locally in different regions: in regions where signal lines are present, the cathode electrode is positioned or shaped to minimize overlap, while in other regions it maintains full coverage for proper device operation. This local optimization reduces parasite capacitance without compromising overall device performance
2Reliability
If the distance in the thickness direction between the signal line and cathode electrode is increased, then parasite capacitance is reduced, but the display device becomes less compact
Solution Approach 1:
Instead of increasing separation in the thickness direction (vertical dimension), the solution shifts to optimizing the planar arrangement and positioning of the cathode electrode in the horizontal plane. By controlling the lateral position and shape of the cathode electrode relative to the signal line, parasite capacitance is reduced without requiring increased vertical separation, thereby maintaining device compactness
Data Source
AI summary
A display device includes, on a substrate, light emitting elements each formed by sequentially stacking a first electrode layer, an organic layer including a light emission layer, and a second electrode layer and arranged in first and second directions which cross each other, a drive circuit including drive elements that drive light emitting elements, and a wiring extending in the first direction, and an insulating layer disposed in a gap region sandwiched by the light emitting elements neighboring in the second direction and having a recess or a projection. The wiring is disposed in an overlap region overlapping with the recess or the projection in the insulating layer in a thickness direction, in the gap region, and the second electrode layers in the light emitting elements neighboring in the second direction are separated from each other by the recess or the projection in the insulating layer.