LCD Array Substrate 4-Mask Process and Transparent Electrodes
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Solution Overview
Problem
The existing manufacturing processes for liquid crystal display (LCD) array substrates require multiple mask steps, leading to increased costs, time, and yield loss due to exposure of intrinsic amorphous silicon layers, causing photo-leakage currents and wavy noise in displayed images, and reducing the aperture ratio.
Innovation Solution
The array substrate is manufactured through 4 mask processes with an active layer formed over and within the gate electrode, and source and drain electrodes made of transparent conductive material, eliminating the exposure of semiconductor layers under the data line and reducing contact resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If multiple mask steps are used in the manufacturing process, then the array substrate can be manufactured with conventional processes, but the manufacturing cost increases, manufacturing time increases, and yield decreases due to photo-leakage currents
Solution Approach 1:
The patent combines the formation of the data line and the protective layer over the semiconductor layer into a single mask step. The data line and protective layer are patterned simultaneously using one photolithography process, eliminating the need for separate mask steps and reducing manufacturing complexity while maintaining conventional process compatibility
Solution Approach 2:
The patent applies for-formations (such as ITO layers) and protective layers over the intrinsic amorphous silicon layer before subsequent processing steps. This preliminary action protects the semiconductor layer from photo-leakage currents during manufacturing and eliminates the need for additional mask steps to protect these layers later
2Ease of manufacture
If multiple mask steps are used, then conventional manufacturing processes can be utilized, but manufacturing time and costs increase
Solution Approach 1:
Multiple functional layers (data line, protective layer, and ITO layer) are formed in a single mask step using concurrent patterning techniques. This merging of steps reduces the total number of photolithography cycles from multiple separate operations to one unified process, significantly reducing manufacturing cycle time while maintaining compatibility with conventional manufacturing equipment and processes
3Device complexity
If intrinsic amorphous silicon layers are exposed, then the manufacturing process is simplified, but photo-leakage currents occur causing wavy noise in displayed images
Solution Approach 1:
The patent extracts the harmful effect of light exposure by introducing a protective layer (such as ITO) that specifically covers the intrinsic amorphous silicon layer. This protective layer is selectively formed only where needed to prevent photo-leakage currents, while leaving other areas of the device structure simple and uncovered, thus maintaining overall structural simplicity while eliminating the reliability issue
Solution Approach 2:
The patent introduces an intermediary protective layer (ITO or similar transparent conductive material) between the light source and the intrinsic amorphous silicon layer. This intermediary layer blocks photo-leakage currents while being transparent to display light, thus preventing wavy noise in displayed images without compromising the optical performance or requiring complex structural changes
4Reliability
If opaque conductive material is used for data lines, then conductivity is improved, but aperture ratio decreases due to light blocking
Solution Approach 1:
The patent uses composite material structures for the data line, combining opaque conductive materials (such as aluminum or copper) with transparent conductive materials (such as ITO). The opaque layer provides high electrical conductivity, while the transparent layer allows light transmission. This composite structure achieves both high conductivity and high aperture ratio by leveraging the complementary properties of different materials
Solution Approach 2:
The patent applies different material properties to different parts of the data line structure. The lower layer uses opaque conductive material for maximum conductivity, while the upper layer uses transparent conductive material for light transmission. This local differentiation of material quality allows the data line to simultaneously achieve high electrical performance and high optical performance in different spatial regions
5Reliability
If conventional transparent conductive material is used for source and drain electrodes, then contact resistance is reduced, but the electrodes block light transmission
Solution Approach 1:
The patent employs composite material structures for source and drain electrodes, combining thin layers of opaque conductive material with transparent conductive material. The opaque layer provides low contact resistance at the electrode-semiconductor interface, while the transparent layer ensures light transmission through the electrode region. This composite approach achieves both low contact resistance and high light transmission by optimizing the thickness and material composition of each layer
Data Source
AI summary
An array substrate for a liquid crystal display device includes a substrate, a gate line on the substrate, a data line crossing the gate line to define a pixel region, a thin film transistor connected to the gate line and the data line and including a gate electrode, an active layer, an ohmic contact layer, a buffer metallic layer, a source electrode and a drain electrode, and a pixel electrode in the pixel region and connected to the thin film transistor, wherein the data line includes a transparent conductive layer and an opaque conductive layer, and each of the source and drain electrodes and the pixel electrode includes a transparent conductive layer.