Flexible OLED Spacer Structure for Fold-Induced Peeling Control

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Solution Overview

Problem

Flexible organic light emitting display devices face peeling defects due to tensile and compressive stress from folding, particularly affecting the organic light emitting layer with weak adhesion and difficulty in stress relief.

Innovation Solution

A flexible display device structure featuring an inverse taper shape in the spacer to distribute stress and improve adhesion, including a substrate with a thin film transistor, intermediate layer, first and second electrodes, and a bank with a first structure tapered toward the substrate to prevent peeling and lateral current leakage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a flexible organic light emitting display device is folded, then the device achieves flexibility and portability, but tensile and compressive stress cause peeling defects in the organic light emitting layer

Engineering Contradiction:

ImproveflexibilityVSAvoidpeeling defect

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The device is divided into multiple layers (substrate, buffer layer, hole transport layer, light emitting layer, electron transport layer, cathode) with each layer having specific stress management functions. The inverse taper structure is segmented into specific regions (first region on anode, second region on cathode) to distribute stress locally at critical interfaces

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The inverse taper structure extends in the vertical dimension (thickness direction) with different cross-sectional areas at different heights. The structure has a larger cross-sectional area at the top surface and a smaller cross-sectional area at the bottom surface, creating a gradient stress distribution through the thickness of the device that prevents peeling at layer interfaces

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Length of moving object

If the organic light emitting layer is made thinner to reduce device thickness, then the package becomes more compact, but adhesion strength decreases making the layer more vulnerable to stress

Engineering Contradiction:

Improvedevice thicknessVSAvoidadhesion strength

Core Design Contradiction:

Length of moving objectVSStrength

Solution Approach 1:

The inverse taper structure is positioned beforehand at critical stress points (interfaces between organic layers and electrodes) to provide stress relief before folding occurs. The structure acts as a pre-positioned cushion that distributes stress away from the thin organic light emitting layer during device operation and folding

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The device employs a composite structure combining the thin organic light emitting layer with the inverse taper structure made of stress-resistant materials. This composite approach allows the organic layer to remain thin for device flexibility while the inverse taper structure provides mechanical reinforcement and stress distribution

Inventive Principle:

Principle #40Composite materials

3Reliability

If a spacer with conventional taper shape is used, then the structure provides stress relief, but the device thickness increases

Engineering Contradiction:

Improvestress reliefVSAvoiddevice thickness

Core Design Contradiction:

ReliabilityVSLength of moving object

Solution Approach 1:

Instead of using a conventional taper shape with larger cross-sectional area at the bottom and smaller area at the top, the invention inverts the taper shape so that the structure has a larger cross-sectional area at the top surface and a smaller cross-sectional area at the bottom surface. This inversion allows the stress relief function to be achieved with reduced overall thickness while maintaining structural integrity

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS11785808B2Flexible display device and method of manufacturing the same

Publication Date: 2023.10.10 LG DISPLAY CO LTD

AI summary

The present disclosure relates to a flexible display device including: a substrate over which a thin film transistor is disposed, an intermediate layer disposed to cover the thin film transistor, a first electrode located on the intermediate layer and connected to the thin film transistor, a bank located on the intermediate layer and the first electrode and defining a first region exposing a part of the intermediate layer, a second region exposing a part of the first electrode, and a third region excluding the first and second regions, a first structure located in the first region defined by the bank and tapered toward the substrate, an organic light emitting layer located on the first electrode exposed in the second region, and a second electrode disposed on the organic light emitting layer. Both lateral surfaces of an inverse-tapered structure are disposed to contact the bank, and as a result, corresponding adhesion can be improved, and peeling defects can be reduced or corrected.