Flexible Display Neutral Plane Adjustment via Light Transmissive Layer
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Solution Overview
Problem
Flexible display devices suffer from whitening and damage to the driving and display element layers when bent, due to changes in physical properties of the protective and polarizing film layers, leading to issues like disconnection of signal lines and damage to thin film transistors.
Innovation Solution
A flexible display device structure featuring a light transmissive layer with an inorganic film, such as silicon dioxide, is applied over the display element layer to adjust the neutral plane of the device, minimizing tensile and compressive forces during bending, and a back plate film with a cut-out center region allows the center to bend freely, while a hard-coating layer on the light transmissive layer prevents scratches.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the flexible display device is bent, then the device can be made flexible and portable, but the protective film layer and polarizing film layer undergo changes in physical properties causing whitening and damage to the driving element layer
Solution Approach 1:
The patent divides the protective structure into multiple functional layers: a light transmissive layer with neutral plane positioning, a hard coating layer for surface protection, and a protective film layer. This segmentation allows each layer to address specific issues - the neutral plane positioning handles bending stresses while the hard coating prevents scratches, resolving the contradiction between flexibility and reliability.
Solution Approach 2:
The patent changes the physical parameter of the light transmissive layer by positioning its neutral plane at the driving element layer, and modifies the hard coating layer's mechanical properties to provide scratch resistance. These parameter changes enable the structure to maintain integrity during bending, allowing flexibility without compromising reliability.
2Strength
If the protective film layer is made thicker to prevent damage, then protection against moisture and impact is improved, but the device becomes less flexible and more prone to whitening when bent
Solution Approach 1:
The patent uses a multi-layer thin film structure where the light transmissive layer with positioned neutral plane provides flexibility, while the hard coating layer provides protective strength. This allows the device to maintain both flexibility and protection without the trade-off implied by using a single thick protective layer.
Solution Approach 2:
The patent creates a composite structure combining the light transmissive layer with specific mechanical properties (neutral plane positioning) and the hard coating layer with scratch resistance. This composite approach allows simultaneous achievement of flexibility and strength that cannot be obtained with a single material layer.
3Strength
If the neutral plane is positioned at the protective film layer, then the protective film is better protected, but the driving element layer suffers from tensile and compressive forces causing damage
Solution Approach 1:
The light transmissive layer acts as an intermediary between the neutral plane positioning and the driving element layer. By positioning the neutral plane at the driving element layer through this intermediary structure, the patent minimizes tensile and compressive forces on the driving elements while still providing overall structural protection.
Solution Approach 2:
The patent changes the positional parameter of the neutral plane from the protective film layer to the driving element layer. This parameter change redistributes the bending stresses, protecting the driving element layer from excessive tensile and compressive forces while maintaining protective film integrity through the intermediary light transmissive layer.
Data Source
Figure 1A~1B
Figure 2
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AI summary
In various embodiments, a flexible display device is provided. The flexible display device includes a substrate and a driving element layer including a plurality of transistors on the substrate. The flexible display device further includes a display element layer including organic light-emitting diodes electrically connected to the transistors, and a back plate film attached to a back side of the substrate and having a cut out portion formed in a center region of the flexible display device.