OLED Sealing Buffer Layer Mitigates Thermal Expansion Stress
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Solution Overview
Problem
Sealing portions in OLEDs with stacked structures formed by atomic layer deposition (ALD) and chemical vapor deposition (CVD) can experience cracking due to linear expansion coefficient differences between the covering layers and intermediate layers.
Innovation Solution
A light emitting device with a sealing portion comprising a first covering layer of insulating inorganic material, an intermediate layer with a different linear expansion coefficient, and a buffer layer with a ductility greater than both, positioned between the intermediate and covering layers to mitigate stress and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sealing portion with stacked covering layers is formed by ALD and CVD to protect the organic layer, then the sealing effectiveness is improved, but cracking occurs due to linear expansion coefficient difference between layers
Solution Approach 1:
An intermediate layer is introduced between the first covering layer and the second covering layer to act as a stress buffer. This intermediate layer has a linear expansion coefficient that is different from both adjacent covering layers, allowing it to absorb thermal expansion stresses and prevent cracking that would otherwise propagate through the sealing structure.
Solution Approach 2:
The sealing portion employs a composite multi-layer structure where each layer is made of different materials with specific linear expansion coefficients. The first covering layer, intermediate layer, and second covering layer are composed of distinct materials that collectively provide both sealing effectiveness and cracking resistance through their coordinated thermal expansion properties.
2Reliability
If covering layers with different linear expansion coefficients are stacked to provide sealing, then sealing effectiveness is improved, but stress accumulation occurs leading to cracking
Solution Approach 1:
The intermediate layer serves as a mediator that absorbs and distributes thermal stresses between the first and second covering layers. By having a linear expansion coefficient that differs from both adjacent layers, it prevents stress concentration and cracking while maintaining the integrity of the sealing structure.
Solution Approach 2:
The linear expansion coefficient is deliberately varied across different layers of the sealing structure. The intermediate layer is specifically designed with a linear expansion coefficient that creates a gradient, allowing progressive stress distribution and preventing sudden stress accumulation that would cause cracking.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The buffer layer effectively relieves stress and prevents cracking of the covering layer, ensuring high reliability and durability of the OLED by reducing the linear expansion coefficient difference and enhancing the sealing effectiveness.
Implementation Method 1
cracking of the covering layer due to a linear expansion coefficient difference between the covering layers and the intermediate layer
Implementation Method 2
a first covering layer comprising an insulating inorganic material; wherein the sealing portion comprises: a first covering layer comprising an insulating inorganic material formed by atomic layer deposition
Data Source
AI summary
A covering layer (240) is formed by atomic layer deposition (ALD) and contains an insulating inorganic material. An intermediate layer (220) contains a material having a linear expansion coefficient different from that of a material of the covering layer (240). A buffer layer (230) has a surface in contact with the intermediate layer (220), that is, a first surface. The buffer layer (230) has a surface in contact with the covering layer (240), that is, a second surface. A linear expansion coefficient difference between a material of the buffer layer (230) and the inorganic material of the covering layer (240) is less than a linear expansion coefficient difference between the material of the intermediate layer (220) and the inorganic material of the covering layer (240).