Display Device Protective Insulation at Wiring Intersections
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Solution Overview
Problem
In high-resolution display devices using oxide semiconductor thin film transistors, the flattening film made of organic resin material can adversely affect the TFT characteristics due to hydrogen content, leading to deterioration, especially at wiring line intersections.
Innovation Solution
A display device design with a protective insulating film having thinner portions at wiring line intersections, using inorganic insulating films and an organic resin material for the flattening film, reduces hydrogen exposure and surface unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wiring line is thickened to suppress increase in wiring line resistance, then the wiring line resistance is reduced, but the surface unevenness becomes large at the intersection of wiring lines
Solution Approach 1:
The protective insulating film is designed with different thicknesses at different locations: it is thicker in regions where wiring lines are not present and thinner at the intersections of wiring lines. This local variation in film thickness allows the flattening film to better conform to the underlying surface topology, reducing surface unevenness at critical intersection points while maintaining adequate insulation elsewhere.
2Shape
If the flattening film is thickened to eliminate surface unevenness, then the surface flatness is improved, but the hydrogen content in the flattening film increases and adversely affects the TFT
Solution Approach 1:
The protective insulating film thickness is locally optimized to reduce the overall thickness of the flattening film required. By making the protective film thinner at wiring line intersections where surface unevenness is most problematic, the total flattening film thickness can be reduced, thereby decreasing hydrogen content while still achieving adequate surface flatness for high-resolution display performance.
Solution Approach 2:
The protective insulating film is formed with a pre-determined non-uniform thickness profile before the flattening film is deposited. This preliminary structuring of the protective film creates a surface that requires less additional flattening, thereby reducing the total amount of organic material that would otherwise be needed and the associated hydrogen content.
3Illumination intensity
If the aperture ratio is increased to improve display quality, then the display quality is enhanced, but the wiring line resistance increases due to reduced wiring line width
Solution Approach 1:
The protective insulating film is designed with localized thickness variations that correspond to the wiring line layout. At wiring line intersections, the film is thinner to reduce surface unevenness, while in other areas it provides adequate protection. This allows wiring lines to be made thinner for higher aperture ratios while maintaining acceptable surface flatness and electrical performance at critical locations.
Data Source
AI summary
In a thin film transistor layer, a first semiconductor film made of an oxide semiconductor, a first gate insulating film made of an inorganic insulating film, a first metal film, a first interlayer insulating film made of an inorganic insulating film, a second metal film, a protective insulating film made of an inorganic insulating film, and a flattening film made of an organic resin material are sequentially layered. The protective insulating film includes a thin film portion provided at a portion where a plurality of first wiring lines formed of the first metal film and a plurality of second wiring lines formed of the second metal film intersect with each other so as to be thinner than a portion of the protective insulating film around the intersecting portion.