Flexible OLED Display with Chiplets and Neutral Stress Plane
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Solution Overview
Problem
Flexible light-emitting display devices face challenges with brittle transparent conductive oxides cracking under stress, leading to reduced conductivity and degradation of light-emitting materials, and existing thin-film transistors on glass substrates exhibit non-uniformity and stress-related performance degradation when bent.
Innovation Solution
A flexible emissive display device with chiplets of 2-200 microns thickness, adhered to an adhesion layer with a neutral stress plane, reducing stress and cracking, and employing encapsulation layers to minimize moisture transmission and enhance durability, allowing for a bending radius of less than 2 cm without mechanical failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If transparent conductive oxides are used in flexible display devices, then light emission is enabled, but the electrodes crack under stress reducing conductivity
Solution Approach 1:
The patent replaces brittle transparent conductive oxides with thin-film metal electrodes deposited on flexible substrate. The metal films are sufficiently thin to accommodate bending stresses while maintaining electrical conductivity, thus enabling light emission without cracking under stress.
2Ease of operation
If thin-film transistors are deposited on glass substrate, then active-matrix control is achieved, but non-uniformity and stress degradation occur when bent
Solution Approach 1:
The patent transitions from glass substrate to flexible polymer substrate for thin-film transistor fabrication. This allows the entire active-matrix control layer to be sufficiently thin and compliant to bend without inducing stress-related non-uniformity or performance degradation.
3Ease of operation
If pixel-control devices are transferred from crystalline silicon substrates, then control functionality is achieved, but the thickness is too large for flexible applications with small bending radius
Solution Approach 1:
The patent fabricates pixel-control devices directly on flexible substrate using thin-film deposition techniques, achieving device thicknesses of less than 200 microns. This eliminates the need for thick crystalline silicon substrates and enables flexible applications with small bending radii.
4Adaptability or versatility
If the device is made flexible with small bending radius, then flexibility is improved, but stress and cracking increase
Solution Approach 1:
The patent employs thin-film structures deposited on flexible polymer substrate with appropriate thickness and material selection to achieve a neutral stress plane configuration. This allows the device to bend to small radii while keeping stress and cracking below critical thresholds, maintaining mechanical integrity.
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 solution provides a mechanically robust and flexible light-emitting display with improved uniformity and performance under stress, reducing the risk of cracking, slipping, and delamination, while maintaining efficient light emission and extending device lifetime.
Implementation Method 1
adhered to an adhesion layer with a neutral stress plane, reducing stress and cracking
Implementation Method 2
employing encapsulation layers to minimize moisture transmission and enhance durability
Implementation Method 3
the chiplets provides current through the connection pads to the LED bottom electrodes to drive the at least one layer of light-emitting material to emit light
Data Source
Figure 1
Figure 2~3
AI summary
A flexible emissive display device having an adhesion layer thinner than the device substrate; a plurality of duplets adhered to the adhesion layer wherein at least a portion of the adhesion layer extends above a portion of the chiplets; an OLED formed over the adhesion layer and wherein the OLED is thinner than the adhesion layer; a cover thicker than the adhesion layer located over the OLED and adhered to the device substrate; and wherein the ehiplets and OLED are at or near the neutral stress plane of the device and the bending radius of the device is less than 2 cm.