Planarizing Film for TFT Substrates Suppressing Linear Defects
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Solution Overview
Problem
Flexible electronic display devices using plastic film substrates are prone to linear defects and malfunctions due to the surface characteristics of the plastic film, leading to fatal flaws in thin-film transistors (TFTs) formed directly on these substrates.
Innovation Solution
A method for producing a planarizing film with a binder resin and inorganic filler on a transparent resin base, applied using gravure coating with specific solids concentration and rotation ratios to minimize foreign matter and achieve a flat surface, reducing the number of defects in TFTs formed on the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a TFT is directly formed on a plastic film substrate, then device integration is achieved, but linear defects and malfunctions occur due to surface characteristics of the plastic film
Solution Approach 1:
The patent introduces a planarizing film as an intermediary layer between the plastic film substrate and the TFT. This planarizing film has a flat surface that eliminates the surface irregularities of the plastic substrate, preventing line defects while allowing direct TFT formation. The planarizing film mediates between the incompatible surface characteristics of the plastic substrate and the TFT requirements.
Solution Approach 2:
The patent segments the substrate system into multiple functional layers: the plastic film substrate provides flexibility, the planarizing film provides a flat surface for TFT formation, and the TFT layer provides device functionality. This segmentation allows each layer to optimize its specific function without compromising the others.
2Shape
If a planarizing layer is formed on a transparent resin base, then surface flatness is improved, but foreign matter increases leading to defects
Solution Approach 1:
The patent optimizes multiple parameters of the coating liquid including solids concentration (20-40 mass%), viscosity (50-200 cP), and composition ratios to achieve the right balance. By carefully controlling these parameters, the coating forms a flat surface while minimizing foreign matter incorporation during the coating process.
Solution Approach 2:
The patent replaces mechanical coating methods that might introduce foreign matter with a controlled coating process using specifically formulated liquids. The coating liquid is designed to flow and level automatically, reducing mechanical interference and foreign matter introduction while achieving the desired surface flatness.
3Productivity
If coating liquid with high solids concentration is used, then coating efficiency is improved, but surface quality deteriorates due to foreign matter and irregularities
Solution Approach 1:
The patent identifies an optimal solids concentration range of 20-40 mass% that balances coating efficiency and surface quality. Within this range, the coating liquid maintains adequate viscosity for efficient application while containing enough solvent to allow proper leveling and minimize foreign matter inclusion. This optimized parameter range achieves both productivity and precision.
Solution Approach 2:
The coating liquid is formulated as a composite system containing binder resin, inorganic filler, and solvent in specific proportions. This composite structure allows the liquid to maintain stability at optimized solids concentrations while preventing premature gelation and reducing foreign matter formation, thus achieving both efficient coating and high surface quality.
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
The method effectively suppresses linear defects and malfunctions in TFTs, providing a stable and high-quality planarizing film suitable for TFT substrates, enhancing the reliability of flexible electronic displays.
Implementation Method 1
dried/cured to form a planarizing layer
Data Source
Figure 1~2
AI summary
An object of the invention is to provide a planarizing film with fewer flaws, particularly to provide a planarizing film which, when the planarizing film is used for a thin-film transistor substrate, is capable of suppressing linear defects even he case where a thin-film transistor is formed directly on the film. The invention is a planarizing film including a planarizing layer containing a binder resin and an inorganic filler as constituents on at least one side of a transparent resin base. The planarizing layer is such that the number of foreign matters with an average diameter of 20 µm or more and 100 µm or less on a surface thereof is not more than 5/m2.