Electro-optic Display Pixel Drain Connection Reliability
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Solution Overview
Problem
Conventional electro-optic displays face issues with disconnection between pixel electrodes and underlying TFT drain electrodes due to cracking on organic interlayer insulating films at contact hole edges, particularly when using transparent materials like ITO or IZO, leading to point defects and reduced display quality.
Innovation Solution
An active-matrix substrate with an inorganic insulating film and an organic resin insulating film, where a contact conductor film made of ductile metal is placed at the bottom of the pixel-drain contact hole, allowing the pixel electrode to cover the organic resin insulating film and inner walls of the contact hole, ensuring electrical connection and preventing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the pixel electrode is made of transparent material such as ITO or IZO, then light transmission is improved, but the pixel electrode is prone to crack and disconnect on the organic interlayer insulating film at the peripheral edges of the contact hole
Solution Approach 1:
The patent employs a composite structure consisting of two pixel electrodes: a first pixel electrode made of ductile metal (such as aluminum or its alloy) and a second pixel electrode made of transparent conductive material (such as ITO or IZO). The first pixel electrode serves as a robust base layer that prevents cracking, while the second pixel electrode provides light transmission. This composite configuration resolves the contradiction by combining the mechanical strength of metal with the optical transparency of oxide materials.
Solution Approach 2:
The first pixel electrode is strategically positioned only in the contact hole region and its vicinity, rather than covering the entire pixel area. This localized placement provides mechanical support precisely where cracking is most likely to occur at the contact hole edges, while allowing the transparent second pixel electrode to cover the display area for optimal light transmission.
2Reliability
If the inorganic insulating film is over-etched to expose the drain electrode, then electrical connection is achieved, but the organic interlayer insulating film projects like eaves beyond the inorganic insulating film causing disconnection
Solution Approach 1:
The patent forms the first pixel electrode (ductile metal) in advance, before forming the second pixel electrode. This first electrode is deposited to cover the entire surface including the contact hole region, providing a preliminary protective and conductive layer. Subsequently, the contact hole is etched through the organic interlayer insulating film to expose this first electrode, ensuring that the ductile metal provides mechanical support even when the organic film projects beyond the inorganic film edges.
3Reliability
If the first pixel electrode is made of metal film, then cracking on organic interlayer insulating film is prevented, but the edges of the metal film are likely to be reversely tapered in cross section causing disconnection of the overlying second pixel electrode
Solution Approach 1:
The patent specifies that the first pixel electrode should have a gently tapered profile rather than a reverse taper. The film thickness gradually decreases from the center toward the edges, creating a convex curvature in cross-section. This gentle tapering prevents the formation of overhanging edges that would cause disconnection of the second pixel electrode, while still providing adequate mechanical support to prevent cracking of the organic interlayer insulating film.
Data Source
AI summary
A pixel electrode is disposed to cover the inner surfaces of a pixel-drain contact hole passing through a third insulating film and a second insulating film to reach a drain electrode. At the bottom of the pixel-drain contact hole, the pixel electrode is electrically connected with the drain electrode through a contact conductor film. The pixel-drain contact hole is formed of a connection of a contact hole passing through the second insulating film and a contact hole passing through the third insulating film. The dimensions of the opening end of the contact hole are larger than its dimensions at the bottom, and thus the inner surfaces of the contact hole are smoothly sloped and shaped like a crater in cross section.