Auxiliary Capacitor Insulation for LCD Aperture Ratio
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Solution Overview
Problem
In liquid crystal displays, achieving a large auxiliary capacity without reducing the aperture ratio is challenging, especially in high-definition or small-pixel areas, due to issues with short-circuiting between auxiliary capacity electrodes and the risk of display irregularities like crosstalk and flicker.
Innovation Solution
The solution involves forming a layer of aluminum or aluminum alloy coated with molybdenum for auxiliary capacity electrodes, with a first insulating film covering the pixel regions except for the auxiliary capacity electrode portions and a second insulating film of thinner thickness over the auxiliary capacity electrode portions, which reduces the occurrence of hillocks and voids, thereby minimizing short-circuits and maintaining adequate insulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the auxiliary capacity lines are made thicker to increase auxiliary capacity, then the auxiliary capacity is improved, but the aperture ratio of each pixel is reduced
Solution Approach 1:
The gate insulating film is made thinner only in the region where the auxiliary capacity electrode overlaps with the auxiliary capacity line, while maintaining normal thickness in other regions. This localized thinning allows increased auxiliary capacity without requiring thicker auxiliary capacity lines that would reduce aperture ratio.
Solution Approach 2:
Instead of increasing auxiliary capacity by making auxiliary capacity lines thicker (one-dimensional approach), the invention achieves increased capacity by reducing the thickness of the gate insulating film (transitioning to a different dimensional parameter), thereby maintaining aperture ratio while increasing capacity.
2Quantity of substance
If the gate insulating film is made thinner to increase auxiliary capacity, then the auxiliary capacity is improved, but short-circuits occur between auxiliary capacity electrodes
Solution Approach 1:
A composite structure is formed with a first insulating film (thicker, higher reliability) and a second insulating film (thinner, enabling higher capacity). The first insulating film prevents short-circuits while the second insulating film enables the thinner overall gate insulating film structure needed for increased auxiliary capacity.
Solution Approach 2:
The gate insulating film is segmented into two separate insulating film layers: a first insulating film that provides structural support and short-circuit prevention, and a second insulating film that enables the overall thinner structure for increased capacity. This segmentation allows both reliability and capacity improvement.
3Quantity of substance
If the auxiliary capacity area is enlarged to increase auxiliary capacity, then the auxiliary capacity is improved, but the aperture ratio is reduced
Solution Approach 1:
The invention changes the thickness parameter of the gate insulating film instead of changing the area parameter of auxiliary capacity structures. By reducing gate insulating film thickness in the overlap region, auxiliary capacity increases without requiring larger auxiliary capacity electrode areas, thereby maintaining aperture ratio.
Data Source
AI summary
A liquid crystal display 10 of the invention has a transparent substrate 11 on which are provided multiple signal lines 17, scan lines 16 and auxiliary capacity lines 18, plus TFTs and pixel electrodes 20 that are electrically coupled to the TFTs' drain electrodes D. The auxiliary capacity lines 18 are formed with an Al—Nd alloy layer coated with a layer of molybdenum. Each pixel region, except for the auxiliary capacity lower electrode 18a on the auxiliary capacity line 18, is coated over by a first insulating film 25 and by a second insulating film 26 that is thinner than the first insulating film 25. Further, the auxiliary capacity lower electrodes 18a are coated over by the second insulating film 26, and auxiliary capacity upper electrodes 18b are provided on the surface of the second insulating film 26 at the auxiliary capacity lower electrodes 18a. Thanks to such structure, a small-pixel-area or high-definition liquid crystal display, and manufacturing method therefor, can be provided whereby short circuits in the regions forming the auxiliary capacity are few, the auxiliary capacity is large, and display irregularities such as crosstalk or flicker are satisfactorily curbed.