LCD Storage Capacitor Design for Aperture Ratio and After-Image
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Solution Overview
Problem
In liquid crystal display (LCD) devices, storage capacitors with a metal-insulator-semiconductor (MIS) structure lead to a disparity in accumulated electric charge between positive and negative polarities, causing kick-back voltage changes and after-image issues due to increased light absorption and reduced aperture ratios.
Innovation Solution
The design incorporates storage capacitors formed by overlapping extensions of pixel electrodes and power supplying lines without an MIS structure, using a planarization layer as a dielectric material to increase capacitance and reduce light absorption, thereby eliminating the MIS structure and its associated issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a storage capacitor with MIS structure is used, then the capacitance is increased, but the aperture ratio is reduced and after-image issues occur
Solution Approach 1:
The invention merges the storage capacitor electrode with the power supplying line by forming the storage capacitor electrode as an extension of the power supplying line. This integration eliminates the need for separate capacitor structures, thereby increasing the aperture ratio while maintaining sufficient capacitance through the overlapping area between the extended electrode and the liquid crystal layer.
2Quantity of substance
If a storage capacitor with MIS structure is used, then the capacitance is increased, but after-image formation occurs due to charge accumulation disparity
Solution Approach 1:
The invention changes the structural parameters of the storage capacitor by eliminating the MIS structure and using a simple parallel plate capacitor design where one electrode is formed as an extension of the power supplying line. This parameter change ensures symmetric charge accumulation for both positive and negative polarities, preventing after-image formation while maintaining adequate capacitance.
3Quantity of substance
If additional capacitor structures are added to increase capacitance, then the capacitance is improved, but the number of process steps increases
Solution Approach 1:
The power supplying line serves multiple functions: it provides power supply to the pixel circuit and simultaneously forms one electrode of the storage capacitor through its extension. This multi-functionality eliminates the need for separate capacitor electrode structures and reduces the number of patterning and deposition process steps while achieving the required capacitance.
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 approach enhances the aperture ratio, reduces the number of process steps, and prevents after-image formation by maintaining consistent electric charge distribution, resulting in improved image quality and reduced manufacturing costs.
Implementation Method 1
using a planarization layer as a dielectric material to increase capacitance
Data Source
AI summary
A liquid crystal display device includes; a plurality of data lines disposed on a substrate, a plurality of gate lines disposed substantially perpendicular to the data lines, wherein the data lines and the gate lines together surround a plurality of pixel regions, a plurality of power supplying lines disposed substantially parallel to the data lines, a plurality of pixel electrode pairs, wherein each of the pixel electrode pairs includes a first and a second pixel electrode respectively disposed in each pixel region, and a pixel driving circuit including at least one transistor and a plurality of storage capacitors in each pixel region, wherein the pixel electrode pairs have portions where the pixel electrode pairs and at least one of the plurality of data lines and the plurality of power supplying lines are vertically aligned with each other, and the storage capacitors are disposed at the vertically aligned portions.