LCD Fabrication 4-Mask Process Reducing Defects
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Solution Overview
Problem
The existing liquid crystal display (LCD) fabrication processes are complex and costly, leading to increased defect rates and decreased production yield, with the 4-mask process causing image quality degradation due to active layer width issues and height differences in electrode formation.
Innovation Solution
A simplified 4-mask process for LCD fabrication, where a gate line and data line intersect to define a unit pixel region, with a thin film transistor (TFT) and pixel electrode directly contacting the drain electrode, eliminating the need for a passivation layer and reducing the number of mask processes, and using an oxide layer for protection instead, to prevent contact defects and enhance image quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a 5-mask process is used to form the source electrode, drain electrode, and active layer, then the fabrication process is more complete, but the fabrication process becomes complicated and manufacturing cost increases
Solution Approach 1:
The patent combines the formation of source electrode, drain electrode, and active layer into a single mask process (4th mask process). The metal layer is formed to simultaneously create source electrode (6a), drain electrode (6b), and the electrodes extend under the data line to form data contact pads, eliminating the need for separate mask processes for each component.
Solution Approach 2:
The metal layer formed in the 4th mask process serves multiple functions: it creates the source electrode, drain electrode, and data contact pads simultaneously. This multi-functional approach reduces the number of fabrication steps while maintaining complete device formation.
2Ease of manufacture
If the active layer is formed wider than the data line width in the 4-mask process, then the source and drain electrodes can be formed properly, but the image quality degrades due to active tail defects
Solution Approach 1:
The patent applies different properties to different regions of the active layer. The active layer width is precisely controlled to match the data line width in the pixel region, while extending appropriately under the data line for contact formation. This localized precision prevents active tail defects while maintaining proper electrode formation.
Solution Approach 2:
The pixel electrode is formed before the source and drain electrodes in the revised 4-mask process. This preliminary action allows the pixel electrode to be precisely positioned and formed to the correct width before the active layer and electrodes are created, preventing image quality degradation from premature active layer formation.
3Reliability
If a passivation layer is formed and contact hole process is performed, then the device protection is improved, but the fabrication process complexity and defect rate increase
Solution Approach 1:
The patent removes the passivation layer formation and contact hole opening steps from the fabrication process. Instead of forming a separate passivation layer and then creating contact holes through it, the design directly forms electrodes that make contact with underlying structures, eliminating these complex fabrication steps while maintaining device functionality and protection.
Data Source
AI summary
A method of fabricating a liquid crystal display device includes performing a first mask process to form a gate line, a gate pad, and a gate electrode on a substrate. The method of fabricating a liquid crystal display device further includes performing a second mask process to form an active layer on the gate electrode, performing a third mask process to form a pixel electrode contacting the active layer, and performing a fourth mask process to form a source electrode and a drain electrode on the active layer.