OLED Pixel Defining Layer for Charge Migration Prevention
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Solution Overview
Problem
Conventional OLED display devices suffer from decreased gradation characteristics and color purity due to lateral charge migration across common functional layers in all pixel regions, leading to unwanted light emission from undesired pixels.
Innovation Solution
The OLED display device incorporates a reversed trapezoidal pixel defining layer that separates organic functional layers between adjacent pixels, with each layer being formed at different heights and orientations to prevent lateral charge migration, using materials like acryl series resin, benzocyclobutene, and polyimide, and a method of fabricating this structure through negative photoresist application and anisotropic wet etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If common functional layers are formed over all pixel regions, then device complexity is reduced and manufacturing is simplified, but lateral charge migration occurs causing decreased gradation characteristics and color purity
Solution Approach 1:
The pixel defining layer is divided into multiple segments (first pixel defining layer and second pixel defining layer) that are formed at different stages. The first pixel defining layer is formed before the functional layers to provide initial separation, while the second pixel defining layer is formed after to complete the isolation. This segmentation allows functional layers to be commonly formed over all pixel regions while still preventing lateral charge migration between adjacent pixels, thus maintaining both manufacturing simplicity and color purity.
Solution Approach 2:
The first pixel defining layer is formed preliminarily before the functional layers are deposited. This preliminary structure provides the necessary isolation framework that prevents charge migration during subsequent processing steps, ensuring that when functional layers are commonly formed over all pixels, the lateral charge migration problem is already mitigated by the pre-existing pixel defining structures.
2Manufacturing precision
If functional layers are separated between adjacent pixels to prevent charge migration, then gradation characteristics and color purity are improved, but device complexity and fabrication difficulty increase
Solution Approach 1:
The pixel defining function is merged with the insulating layer structure. The pixel defining layers are integrated into the existing insulating layer formation process, utilizing the same deposition and patterning equipment and procedures. This merging allows the pixel defining structures to provide charge migration prevention while being fabricated using standard manufacturing processes, thus improving color purity without proportionally increasing device complexity.
Solution Approach 2:
The pixel defining layers serve multiple functions: they provide electrical isolation between adjacent pixels to prevent charge migration, serve as insulating layers in the device structure, and define the pixel boundaries for proper light emission. This multi-functionality reduces the need for separate dedicated isolation structures, thereby improving color purity while minimizing the increase in device complexity.
3Ease of manufacture
If a conventional pixel defining layer structure is used, then fabrication process is simple, but charges migrate laterally across functional layers causing unwanted light emission from undesired pixels
Solution Approach 1:
The pixel defining structure is extended into the vertical dimension with multiple layers at different heights. The first pixel defining layer is formed at a lower level before functional layers, and the second pixel defining layer is formed at a higher level after functional layers. This three-dimensional arrangement creates multiple isolation barriers that effectively block lateral charge migration paths while maintaining compatibility with standard fabrication processes.
Solution Approach 2:
The pixel defining layers act as intermediary structures between adjacent pixels, providing physical and electrical isolation. These intermediary layers are positioned strategically to intercept and block charge migration paths that would otherwise allow charges to move laterally across functional layers to undesired pixels, thus improving charge isolation effectiveness while maintaining fabrication simplicity.
Data Source
AI summary
An OLED display device includes a substrate, a TFT on the substrate, the TFT including a semiconductor layer, a gate electrode, and source and drain electrodes, a first electrode electrically connected to one of the source and drain electrodes, a pixel defining layer on the substrate, the pixel defining layer exposing the first electrode and having a reversed trapezoidal shape, an emitting layer on the exposed first electrode, and a second electrode on the emitting layer.