LCD Array Substrate Four Mask Process Aperture Ratio
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Solution Overview
Problem
Conventional LCD array substrate fabrication processes, such as the five and six mask processes, face issues with production yield, cost, and competitiveness due to complexity, leading to photo leakage currents and wavy noise caused by exposed amorphous silicon layers, which degrade TFT properties and reduce aperture ratio.
Innovation Solution
A four mask process is adopted for fabricating the array substrate, where an opaque metal pattern is formed on the pixel electrode's end portions, and the semiconductor layer is not formed under the data line, preventing light leakage and improving aperture ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a five mask process or six mask process is used to fabricate the array substrate, then the manufacturing completeness is improved, but the device complexity and production cost increase, and the productivity decreases
Solution Approach 1:
The patent combines multiple fabrication steps into fewer mask processes. Specifically, the active layer formation and data line formation are merged into a single mask process, reducing the total number of mask processes from five or six to four, thereby simplifying the overall fabrication process while maintaining completeness
Solution Approach 2:
The patent makes the semiconductor layer serve multiple functions: it acts as both the active layer for the TFT and as the data line conductor. This multi-functionality eliminates the need for separate data line formation steps, reducing process complexity and improving productivity
2Manufacturing precision
If the semiconductor layer is formed extending beyond the data line, then the manufacturing completeness is improved, but photo leakage currents occur and wavy noise is generated, degrading TFT properties
Solution Approach 1:
The patent extracts or removes the harmful protruding portion of the semiconductor layer that extends beyond the data line. By preventing this extension through controlled etching and mask design, the source of photo leakage currents and wavy noise is eliminated, thereby improving TFT properties without compromising the necessary layer formation
Solution Approach 2:
The patent applies different quality requirements to different regions of the semiconductor layer: under the data line, the semiconductor layer is formed with sufficient thickness for electrical conductivity, while at the edges beyond the data line, the semiconductor layer is prevented from protruding to avoid photo leakage. This localized quality control resolves the contradiction between completeness and harmful effects
3Illumination intensity
If the aperture ratio is increased to improve display quality, then the transmittance is improved, but the black matrix width must be reduced, which may compromise light blocking performance
Solution Approach 1:
The patent converts the potentially harmful protruding semiconductor layer into a beneficial opaque pattern that serves dual purposes: it maintains light blocking performance where needed while allowing increased aperture ratio in the pixel region. The opaque pattern formed from the semiconductor layer acts as an additional light-blocking element that replaces part of the black matrix function, enabling larger aperture ratios without sacrificing light blocking performance
Data Source
AI summary
An array substrate for a liquid crystal display device comprises a substrate having a pixel region, a gate line on the substrate, and a data line crossing the gate line to define the pixel region. A thin film transistor (TFT) includes a gate electrode connected to the gate line, an insulating layer on the gate electrode, an active layer on the insulating layer, an ohmic contact layer on the active layer, a source electrode connected to the data line and a drain electrode spaced apart from the source electrode. A pixel electrode connects to the drain electrode and is disposed in the pixel region. An opaque metal pattern is provided on end portions of the pixel electrode.