Roughened Sub-Electrode Layer for Display Defect Masking
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Solution Overview
Problem
Existing display structures with metal electrodes as pixel electrodes suffer from specular reflection, leading to increased black levels and visibility of defects in light modulating layers, degrading display quality, especially in electrophoretic and liquid crystal displays.
Innovation Solution
A display structure with a roughened sub-layer surface beneath the electrode layer, having a roughness of 1<Ra<500 nm, preferably 1<Ra<50 nm, to reduce reflectivity and increase contact surface area, thereby masking defects and improving electrical contact and operational characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal electrode layer is used as pixel electrode material, then good electrical contact and conductivity are achieved, but specular reflection increases causing higher black levels and visibility of defects in light modulating layers
Solution Approach 1:
The sub-layer surface is roughened before depositing the electrode metal layer. This preliminary surface modification creates a diffuse reflection effect that masks the specular reflection of the metal electrode, preventing defects in the light modulating layer from being visible while maintaining good electrical contact.
Solution Approach 2:
The roughened sub-layer surface converts the harmful specular reflection of the metal electrode into a beneficial diffuse reflection. The roughness features (1<Ra<500 nm) scatter light in multiple directions, masking the electrode's reflective properties and hiding defects in the light modulating layer, while the electrode maintains its electrical functionality.
2Object-affected harmful factors
If a non-reflecting or light-absorbing electrode material is used, then specular reflection is reduced and defects are hidden, but electrical contact with the sub-layer may be compromised
Solution Approach 1:
The roughened sub-layer acts as an intermediary between the light modulating layer and the metal electrode. It provides the diffuse reflection effect to mask specular reflection and hide defects, while simultaneously ensuring good electrical contact between the electrode and the underlying structure through increased contact surface area.
Solution Approach 2:
The sub-layer is modified locally at its surface facing the electrode layer with specific roughness (1<Ra<500 nm). This localized surface modification provides the optical diffusion effect where needed, while the bulk properties of the sub-layer maintain electrical conductivity and contact quality.
3Object-affected harmful factors
If the sub-layer surface is roughened to reduce reflectivity, then defects are masked and black level is improved, but manufacturing complexity increases
Solution Approach 1:
The sub-layer surface is modified by changing its physical parameter - the roughness (1<Ra<500 nm). This parameter change creates the diffuse reflection effect to mask specular reflection and hide defects. The roughness can be achieved through various manufacturing methods including etching or replication, balancing the optical benefit with manufacturing feasibility.
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 effectively hides defects in light modulating layers, reduces reflectivity by a factor of 10, and enhances the operational characteristics of display pixels without increasing the display's thickness, improving overall display quality.
Implementation Method 1
a surface of the sub-layer facing the electrode layer is roughened having roughness 'Ra' preferably 1<Ra<500 nm, more preferably 1<Ra<50 nm
Implementation Method 2
An additional advantage of roughening the sub-layer is an increased contact surface area between the electrode metal layer and display effect layer
Data Source
AI summary
The invention relates to a display structure comprising an electrode layer (3) superposed on a sub-layer (5) wherein a surface of the sub-layer facing the electrode layer is roughened. In particular, the display structure may relate to a TFT stack comprising a layer of an electrode metal corresponding to a pixel electrode (3). The pixel pad together with the data line (1) is used for charging of the pixel pad. The gate electrode (4) used is separated from the source and drain electrode (1, 3) by a dielectric layer (6). The structural layers of the TFT may be deposited on a suitable flexible substrate (7). In order to prevent defects in the light modulating layer (9) from being visible, a surface of the sub-layer (5) underlying the electrode layer (3) is roughened. It is desirable to provide such improvement to, among others, electrophoretic-type displays and liquid crystal-type displays.