LCD Light-Shielding Metal Layer Reduces Parasitic Capacitance
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Solution Overview
Problem
LCD devices face issues with reduced aperture ratio and increased parasitic capacitance due to the use of inorganic insulating materials for the passivation layer, leading to light leakage, flicker, image sticking, and non-uniform luminance, especially in small-sized devices where overlapping of pixel electrodes with data lines is not possible.
Innovation Solution
The introduction of a light-shielding metal layer that projects from the gate line and overlaps with the data line and pixel electrode, formed from materials like copper, aluminum, or molybdenum, to prevent parasitic capacitance and reduce the bonding margin of the black matrix layer, thereby enhancing the aperture ratio and picture quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an inorganic insulating material is used for the passivation layer, then the device structure is simplified and manufacturing is easier, but parasitic capacitance increases causing vertical crosstalk, flicker, and image sticking
Solution Approach 1:
A light-shielding metal layer is introduced as an intermediary component between the data line and pixel electrode. This metal layer acts as a shield that reduces parasitic capacitance while allowing the passivation layer to be formed of inorganic insulating material for manufacturing simplicity. The light-shielding layer serves as a mediator that eliminates the harmful capacitive coupling without complicating the overall fabrication process.
2Object-affected harmful factors
If the pixel electrode is prevented from overlapping with the data line, then light leakage is reduced, but the aperture ratio decreases
Solution Approach 1:
The light-shielding metal layer serves as a mediator that allows the pixel electrode to overlap with the data line while preventing light leakage. By positioning this shielding layer between the data line and pixel electrode, the design enables aperture maximization through overlapping geometry while the shielding layer blocks light paths that would otherwise cause leakage, thus resolving the contradiction between aperture ratio and light leakage prevention.
3Area of stationary object
If the bonding margin of the black matrix layer is reduced, then the aperture ratio increases, but light leakage control becomes more difficult
Solution Approach 1:
The light-shielding metal layer acts as an intermediary that compensates for the reduced bonding margin of the black matrix layer. By introducing this additional shielding component, the design allows the black matrix bonding margin to be minimized for aperture maximization while the light-shielding layer provides the necessary light leakage prevention, effectively decoupling these two requirements.
4Reliability
If a light-shielding metal layer is added to reduce parasitic capacitance, then picture quality improves, but device complexity increases
Solution Approach 1:
The light-shielding metal layer is designed to perform multiple functions simultaneously: it reduces parasitic capacitance between the data line and pixel electrode, prevents light leakage, and can serve as part of the common electrode structure. By making this layer multi-functional, the design improves picture quality without adding excessive complexity, as the same structural element addresses multiple problems rather than requiring separate components for each function.
Data Source
AI summary
An LCD device with improved an aperture ratio and decreased parasitic capacitance has a passivation layer of an inorganic material and which includes a gate line on a first substrate; a gate insulating layer on an entire surface of the first substrate including the gate line; a data line on the gate insulating layer in perpendicular to the gate line, to define a pixel region; a thin film transistor at a crossing portion of the gate and data lines; a passivation layer on the entire surface of the first substrate including the thin film transistor; a pixel electrode on the passivation layer, for being connected with a drain electrode of the thin film transistor; and a light-shielding metal for receiving a voltage, formed between the data line and the pixel electrode, to prevent a parasitic capacitance between the data line and the pixel electrode.