Organic Layer Thickness Control for TFT Contact Pads
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Solution Overview
Problem
In thin film transistor array panels, the excessive thickness of the organic layer at contact pad portions leads to increased contact resistance and signal transfer deterioration, while insufficient organic layer thickness in data line areas results in corrosion and wire disconnection due to misalignment issues during the manufacturing process.
Innovation Solution
A negative photosensitive organic layer (Nega-PR) is used with a photomask having a slit pattern parallel to the data wires, allowing varying light transmission to control the organic layer thickness, ensuring thicker layers over data wires for protection and thinner layers between them to facilitate easy contact, thereby minimizing contact resistance and corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the organic layer is thickly coated on the signal lines to reduce crosstalk and protect data lines, then the insulation and protection are improved, but the contact resistance increases and signal transfer deteriorates at contact pad portions
Solution Approach 1:
The patent applies local quality by creating different organic layer thicknesses in different regions: a first thickness in the display area for protection and insulation, and a second (smaller) thickness in the peripheral area for low-resistance contact. This is achieved through a two-stage coating process where the organic layer is first coated to a first thickness, then selectively coated again to a second thickness in the peripheral region, ensuring both protection and low contact resistance where needed.
2Object-affected harmful factors
If the organic layer is made uniformly thin to reduce contact resistance, then contact performance is improved, but the data line becomes vulnerable to corrosion and breakage
Solution Approach 1:
The patent implements local quality by spatially differentiating the organic layer thickness: the display area maintains a thicker layer for corrosion protection, while the peripheral contact area has a thinner layer for low contact resistance. This resolves the contradiction by ensuring each region has the appropriate thickness for its specific function.
Solution Approach 2:
The patent segments the organic layer into functionally distinct regions with different thicknesses. The display area region receives a first thickness for protection, while the peripheral region receives a second thickness for contact performance. This segmentation allows simultaneous optimization of both protection and contact characteristics in different parts of the device.
3Reliability
If the organic layer is thickly coated to protect data lines from corrosive attack, then the protection is improved, but misalignment during manufacturing may leave insufficient thickness in critical areas
Solution Approach 1:
The patent applies preliminary action by performing a first coating of the organic layer to a sufficient thickness across the entire device before any alignment-critical operations. This preliminary thick coating ensures that even if subsequent alignment is imperfect, there is adequate material remaining to provide protection in the display area while allowing selective thinning in peripheral areas.
Solution Approach 2:
The patent provides beforehand cushioning by initially coating the organic layer to a first thickness that serves as a protective cushion throughout the device. This preliminary layer acts as a buffer against potential misalignment issues, ensuring minimum protection is maintained even if subsequent processing steps have alignment variations.
4Object-affected harmful factors
If the organic layer is made thin in peripheral areas for good contact, then contact resistance is reduced, but the area for external circuit connection becomes smaller
Solution Approach 1:
The patent applies local quality by differentiating organic layer thickness between the display area and peripheral contact area. In the peripheral region, the organic layer is coated to a second (smaller) thickness that allows conductive balls to easily contact the pad metal, reducing contact resistance while maintaining sufficient connection area for external circuits.
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 reduces contact resistance and enhances the integrity of data lines by maintaining adequate organic layer thickness over data wires while minimizing it between wires, improving connection with external circuits and protecting against corrosive attacks.
Implementation Method 1
A negative photosensitive organic layer (Nega-PR) is used with a photomask having a slit pattern parallel to the data wires, allowing varying light transmission to control the organic layer thickness
Data Source
AI summary
A thin film transistor array panel includes a first insulation substrate, a plurality of data wires formed on the first insulation substrate and extending in a first direction, a data pad region formed on the first insulation substrate and having plural ones of the data wires extending therefrom, and an organic layer formed on the data wires, where the organic layer has a greater thickness where it is disposed over the data wires than the thickness it has between the data wires. The surface of the organic layer of the data pad region includes minute slit patterns that extend parallel to the first direction of the data wires, and the data wires have line boundaries of a zigzag shape.