Third Metal Layer Trenches for LCD Common Electrode Stability
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Solution Overview
Problem
Existing liquid crystal displays (LCDs) face challenges in stabilizing the common electrode voltage and preventing rubbing mura, which leads to color shifts and uneven luminance due to the addition of a third metal layer, impacting the performance and aperture ratio.
Innovation Solution
Incorporating a third metal layer with increased thickness on the common electrode, disposed over an organic insulation layer with trenches, to reduce resistance and prevent rubbing mura, thereby improving voltage stability and alignment of liquid crystal molecules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a third metal layer is added to the common electrode, then the resistance of the common electrode is reduced and voltage stability is improved, but rubbing mura is produced causing uneven luminance and color shifts
Solution Approach 1:
The common electrode is segmented into two distinct layers: a first metal layer (e.g., ITO) that covers the entire common electrode area, and a second metal layer (e.g., Al, Mo, W) that is deposited only in specific regions where the first metal layer has been removed. This segmentation allows the thicker second metal layer to reduce resistance without producing rubbing mura, while the first metal layer maintains uniformity across the entire electrode surface.
Solution Approach 2:
Different regions of the common electrode are assigned different metal layer configurations based on local requirements. The first metal layer provides uniform coverage and prevents rubbing mura in regions where it is present, while the second metal layer provides enhanced conductivity in specific areas. This local differentiation resolves the contradiction between voltage stability and rubbing mura prevention.
2Reliability
If the ITO film thickness is increased to reduce common electrode resistance, then voltage stability improves, but the aperture ratio is reduced
Solution Approach 1:
The common electrode uses a composite structure combining two different metal materials: a transparent conductive material (first metal layer, e.g., ITO) and a reflective metal (second metal layer, e.g., Al, Mo, W). This composite approach allows the electrode to achieve low resistance through the reflective metal while maintaining high aperture ratio through the transparent ITO layer, eliminating the need to increase ITO thickness.
3Reliability
If a metal layer is added to the ITO film to reduce resistance, then voltage stability improves, but rubbing mura is produced impacting LCD performance
Solution Approach 1:
The metal layer is segmented into two distinct configurations: the first metal layer (ITO) that spans the entire common electrode area and prevents rubbing mura, and the second metal layer (Al, Mo, W) that is selectively deposited only in regions where the ITO layer is removed. This segmentation allows the thicker metal layer to reduce resistance without producing rubbing mura, while the first metal layer maintains uniformity across the entire electrode surface.
Solution Approach 2:
The first metal layer (ITO) acts as an intermediary layer between the rubbing roller and the liquid crystal molecules. By removing the ITO layer in specific regions before depositing the second metal layer, the intermediary function is selectively applied only where needed for resistance reduction, while maintaining molecule alignment uniformity in regions where the ITO layer remains intact.
Data Source
AI summary
A liquid crystal display (LCD) includes an array of pixels over a thin film transistor (TFT) substrate. The TFT substrate includes a TFT that has a first metal layer to form a gate electrode and a second metal layer to form a source electrode and a drain electrode for each pixel. The LCD also includes an organic insulation layer disposed over the TFT substrate, where the organic insulator layer has trenches on a top surface. The LCD further includes a third metal layer disposed over the organic insulation layer in the trenches, the trenches having a trench depth at least equal to the thickness of the third metal layer. The LCD also includes a passivation layer over the third metal layer, and a pixel electrode for each pixel over the passivation layer. The LCD further includes a polymer layer over the pixel electrode, and liquid molecules on the polymer layer.