Active Matrix Substrate Pixel Electrode Extension for Parasitic Capacitance Control
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Solution Overview
Problem
Conventional liquid crystal display devices experience degradation in display quality due to variations in parasitic capacitance between the gate and drain of the TFT in the pixel circuit, leading to fluctuations in feed-through voltage, which can result in incorrect luminance, flicker, block-shaped, or band-like display unevenness.
Innovation Solution
The active matrix substrate design includes gate lines, data lines, and pixel circuits with a thin film transistor where the drain electrode is directly connected to the pixel electrode and has an overlapping portion with the gate electrode, and the pixel electrode extends to cover this overlap, ensuring a constant overlap area regardless of position shifts, and the common electrode has slits to generate a lateral electric field for improved view angle without affecting the alignment of liquid crystals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the pixel electrode extension part is formed only on one side of the gate line, then the structure is simpler, but the parasitic capacitance varies causing display quality degradation
Solution Approach 1:
The pixel electrode is segmented into a main body part and extension parts, with the extension parts positioned on both sides of the gate line. This segmentation allows the extension parts to function specifically for maintaining consistent parasitic capacitance, while the main body part serves the primary display function, thus resolving the contradiction between structural simplicity and display quality stability.
Solution Approach 2:
Different parts of the pixel electrode are given different functions: the main body part is positioned to cover the drain electrode for primary capacitance function, while the extension parts are specifically positioned on both sides of the gate line to maintain consistent parasitic capacitance. This local differentiation resolves the contradiction by optimizing each part's function without requiring complete structural redesign.
2Area of stationary object
If the drain electrode is formed on both sides of the gate line, then the aperture ratio increases, but backlight influence and display defects occur
Solution Approach 1:
The drain electrode is extracted from the second side of the gate line, leaving only the first side. This extraction eliminates the harmful effects of having the drain electrode on both sides (backlight influence and display defects) while maintaining the aperture ratio benefits through the extension part configuration. The extension part compensates for the reduced drain electrode area.
Solution Approach 2:
The configuration converts the potential harm of reduced drain electrode area into a benefit by using the extension part to maintain consistent parasitic capacitance. This resolves the contradiction by transforming what could be a disadvantage (smaller drain electrode) into an advantage (consistent capacitance without backlight influence).
3Ease of manufacture
If the parasitic capacitance varies among pixel circuits, then manufacturing is easier, but feed-through voltage fluctuates causing display unevenness
Solution Approach 1:
The extension parts are configured to create equipotential conditions for parasitic capacitance across all pixel circuits. By positioning the extension parts symmetrically on both sides of the gate line and extending them to consistent positions, the design ensures that all pixel circuits have approximately equal parasitic capacitance values, resolving the contradiction between manufacturing ease and capacitance consistency.
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
This configuration maintains consistent parasitic capacitance and feed-through voltage across pixel circuits, preventing display quality degradation, reducing defects from rubbing processes, aperture ratio fluctuations, and backlight influence, while enhancing the view angle and aperture ratio of the liquid crystal panel.
Implementation Method 1
In a liquid crystal panel of the lateral electric field system, the common electrode is formed on the active matrix substrate together with the pixel electrode, and an almost lateral electric field is applied to the liquid crystal layer by using the pixel electrode and the common electrode
Implementation Method 2
As a system for applying an electric field to the liquid crystal layer of the liquid crystal panel, a vertical electric field system and a lateral electric field system are known
Data Source
AI summary
A drain electrode 25 of a TFT 21 overlaps with a gate electrode formed integrally with a gate line 23. A pixel electrode 22 has a main body part formed on a first side of the gate line 23, and an extension part extending in an extending direction of a data line 24 and covering an overlapping portion of the gate electrode and the drain electrode 25. The drain electrode 25 is not formed on a second side of the gate line 23, whereas the extension part of the pixel electrode 22 is formed also on the second side of the gate line 23. Even when a position of the pixel electrode 22 is shifted in the extending direction of the data line 24, a parasitic capacitance between a drain and a source of the TFT 21 is kept constant, because an area of a portion where the extension part of the pixel electrode 22 overlaps with the gate line 23 does not change. With this, degradation of display quality due to a variation in the parasitic capacitance between the gate and drain of the TFT 21 can be prevented.