Organic Light-Emitting Display Bank Structure for Folding Crack Resistance
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Solution Overview
Problem
Organic light emitting display devices face issues with encapsulation layer cracking and separation of the organic light emitting diode during folding, leading to reduced impact resistance and affected display luminance due to lateral currents.
Innovation Solution
The device incorporates a substrate with a bank layer having a reverse tapered shape and spacers with tapered designs to reduce stress during folding, preventing separation and crack formation, and minimizing lateral current effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional encapsulation layer structure is used, then the device can be manufactured with standard processes, but the encapsulation layer cracks and the organic light emitting diode separates during folding
Solution Approach 1:
The encapsulation layer is divided into multiple segments: a first encapsulation layer, a second encapsulation layer, and a third encapsulation layer with different material compositions and thicknesses. This segmentation allows each layer to handle different stress conditions during folding, preventing crack propagation while maintaining structural integrity.
Solution Approach 2:
The encapsulation structure uses composite materials with different properties at different locations. The first encapsulation layer uses a materials with high flexibility, the second layer uses materials with high barrier properties, and the third layer uses materials optimized for stress distribution. This composite approach provides both crack resistance and prevents delamination during folding.
2Strength
If the encapsulation layer is made thicker to prevent cracks, then crack resistance improves, but the device thickness increases and flexibility decreases
Solution Approach 1:
Different regions of the encapsulation structure have different thicknesses and material properties optimized for their specific functions. The first encapsulation layer has greater thickness for crack resistance, while the second and third layers have reduced thickness to maintain flexibility. This local quality approach provides adequate protection without uniformly increasing overall device thickness.
Solution Approach 2:
The encapsulation structure is designed to dynamically respond to folding stresses by allowing controlled deformation in specific layers. The first encapsulation layer provides rigid support against cracks, while the second and third layers provide flexibility and adaptability during folding motion, enabling the structure to maintain both strength and flexibility.
3Ease of manufacture
If the bank layer has a vertical sidewall, then the opening unit is easier to form with standard lithography, but stress concentration occurs during folding causing separation
Solution Approach 1:
The bank layer sidewalls are designed with curved profiles instead of vertical sidewalls. This curvature distributes stress more evenly during folding, preventing stress concentration at sharp corners that would cause separation. The curved sidewalls maintain ease of manufacture through modified lithography processes while significantly improving reliability during folding operations.
4Device complexity
If spacers are not used at the opening unit edge, then the manufacturing process is simpler, but the organic light emitting layer separates from the panel during folding
Solution Approach 1:
A spacer is introduced as an intermediary element between the bank layer and the organic light emitting layer at the opening unit edge. This spacer acts as a mechanical bridge that prevents separation during folding while maintaining electrical isolation. The spacer is strategically positioned to provide support exactly where stress concentration occurs, adding minimal complexity while maximizing separation resistance.
Data Source
AI summary
An organic light emitting display device includes a substrate having a display area including a plurality of sub pixels and a non-display area which encloses the display area, a thin film transistor on the substrate, a planarization layer on the thin film transistor, an anode which is disposed on the planarization layer and is disposed for each sub pixel, a bank layer which is disposed on the planarization layer and includes a first opening unit exposing at least a part of the anode and a second opening unit spaced apart from the first opening unit, a first spacer on the bank layer, and a second spacer which is continuously disposed on the anode and the bank layer so as to overlap with a part of an edge of the first opening unit, and the bank layer has a reverse tapered shape and the second spacer has a tapered shape.