Reflective Array Substrate Flatness and Contrast
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Solution Overview
Problem
Reflective type liquid crystal displays face issues with murky grey display ground color, low contrast, and poor display quality due to the need for polarizers in TN and STN LCDs, and variations in reflectivity caused by differences in flatness of resin layers, leading to increased power consumption and reduced light transmittance.
Innovation Solution
An array substrate with a thin-film transistor and a reflective metal layer formed on a substrate, where the gate and source/drain layers are made of a single molybdenum layer, reducing altitude differences and improving flatness, and the reflective metal layer is electrically connected to the drain, using materials like Al, Ag, or AlNd for enhanced reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional transparent electrode is used, then the display has good light transmission, but the electrode is easily damaged during the ITO slurry coating process
Solution Approach 1:
The patent divides the transparent electrode into two separate functional layers: a reflective electrode layer (bottom electrode) and a transparent conductive layer (top electrode). This segmentation allows each layer to be optimized independently - the reflective layer provides mechanical strength and reflectivity, while the transparent conductive layer provides conductivity and light transmission, resolving the contradiction between durability and manufacturing ease.
Solution Approach 2:
The patent uses a composite structure combining a reflective electrode material (such as Alq3 complex or silver) with a transparent conductive material (such as ITO, IZO, or IFO). This composite approach allows the bottom layer to provide mechanical strength and reflectivity while the top layer provides transparency and conductivity, eliminating the fragility issue of conventional single-layer ITO electrodes.
2Reliability
If a totally reflective liquid crystal display is implemented, then the display achieves high reflectivity and wide viewing angle, but the liquid crystal layer requires precise alignment
Solution Approach 1:
The patent applies different surface treatments to different regions of the substrate: the first substrate receives a first alignment treatment (such as rubbing or photo-alignment) while the second substrate receives a second alignment treatment. This local quality approach allows precise control of liquid crystal orientation at each interface, ensuring proper alignment for totally reflective mode operation and achieving both high reflectivity and wide viewing angle.
Solution Approach 2:
Instead of relying on a single alignment layer, the patent inverts the traditional approach by providing alignment treatments on both substrates. The liquid crystal molecules are aligned by the combination of two alignment surfaces rather than one, which enhances alignment precision and stability, thereby improving display performance while managing the complexity of manufacturing.
3Strength
If the reflective electrode is placed at the bottom, then the electrode provides mechanical strength, but the manufacturing process becomes more complex
Solution Approach 1:
The bottom reflective electrode layer serves multiple functions simultaneously: it provides mechanical strength to the overall structure, acts as a reflective surface for the totally reflective display mode, and serves as an electrode for applying electric fields. This multi-functionality reduces the need for additional components, thereby managing device complexity while achieving the desired mechanical strength.
Solution Approach 2:
The patent changes the optical parameter of the bottom electrode from transparent to reflective, allowing it to serve dual purposes as both a structural support element and an optical component. This parameter change enables the bottom electrode to provide mechanical strength while also functioning as the reflective surface, simplifying the overall device structure despite the added manufacturing steps.
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 increases reflectivity, leading to improved light use efficiency, brightness, and contrast ratio by ensuring a more uniform and flat reflective metal layer, approximating specular reflection and reducing the impact of altitude differences between transistor and pixel electrode regions.
Implementation Method 1
a liquid crystal layer between the first substrate and the second substrate
Implementation Method 2
When a voltage is applied to the pixel electrode and the common electrode, the liquid crystal molecules are oriented in a direction influenced by an electrostatic force
Implementation Method 3
a reflective electrode on the rear surface of the second substrate
Data Source
Figure 1~2
AI summary
The present disclosure discloses an array substrate, comprising a substrate, a plurality of pixel regions on the substrate, and a thin-film transistor formed in each of the pixel regions, each of the pixel regions comprising a pixel electrode region, wherein, the thin-film transistor comprises a gate layer and a source/drain layer formed laminatedly on the substrate; the array substrate further comprises a flat layer and a reflective metal layer formed in sequence on the substrate and covering at least the pixel electrode region and the thin-film transistor; the reflective metal layer is electrically connected to a drain of the thin-film transistor; and at least one of the gate layer and the source/drain layer is formed of a single metal layer. The present disclosure further provides a method for manufacturing the array substrate and a totally reflective type liquid crystal display comprising the array substrate.