Via-Hole Positioning in OLED Pixel Electrodes
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Solution Overview
Problem
In organic light-emitting display apparatuses, the pixel defining layer (PDL) surrounding the edge of a pixel electrode tends to fall down due to via-holes formed near the pixel electrode, leading to unclear outer limits of the light-emitting portion and reduced display quality.
Innovation Solution
The via-holes are positioned farthest from the outer limits of the light-emitting portions, with the pixel defining layer's thickness maintained to prevent sinking into the via-holes, ensuring clear definition of the light-emitting area and improved display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If via-holes are formed near the pixel electrode to electrically connect TFT and pixel electrode, then electrical connection is achieved, but the pixel defining layer surrounding the pixel electrode edge falls down into the via-holes
Solution Approach 1:
The via-hole formation process is segmented into multiple stages: first forming via-holes through the planarization layer, then forming the pixel defining layer to cover the via-holes, and finally forming pixel electrodes that extend into the via-holes. This segmentation allows each layer to be optimized independently, preventing the pixel defining layer from falling into via-holes while ensuring proper electrical connection.
Solution Approach 2:
The pixel defining layer is formed in advance before the pixel electrode material is deposited. This preliminary action ensures that the pixel defining layer is already in place to prevent material from falling into via-holes during subsequent pixel electrode formation processes, maintaining manufacturing precision.
2Manufacturing precision
If pixel defining layer thickness is reduced to improve resolution, then display resolution is improved, but the pixel defining layer becomes unstable and falls down
Solution Approach 1:
The pixel defining layer is designed with varying local properties: it has greater thickness and stronger adhesion at regions adjacent to via-holes where stability is critical, while maintaining thinner profiles in other areas to preserve resolution. This local quality differentiation allows the layer to prevent falling without sacrificing overall definition precision.
Solution Approach 2:
The pixel defining layer uses composite material structures with enhanced adhesion properties, combining materials that provide both thin-film characteristics for high resolution and strong bonding to prevent falling into via-holes, thus maintaining stability at reduced thickness.
Data Source
AI summary
An organic light-emitting display apparatus includes: a plurality of thin film transistors (TFTs); a planarization layer covering the plurality of TFTs; a plurality of pixel electrodes formed on the planarization layer, each of the pixel electrodes being connected to a corresponding one of the plurality of TFTs using a via-hole passing through the planarization layer and having a light-emitting portion and a non-emitting portion, and each of the via-holes being located at a point farthest from each of the light-emitting portions surrounding the via-hole; a pixel defining layer formed on the planarization layer to respectively cover each of the via-holes and the non-emitting portions; organic layers, each organic layer including an emission layer and being disposed in a corresponding one of the light-emitting portions; and a counter electrode disposed on each of the organic layers.