Oxide Semiconductor TFT Shading for Display Aperture Ratio
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Solution Overview
Problem
The aperture ratio of display devices using oxide semiconductor TFTs is limited due to light-induced deterioration of TFT characteristics, particularly negative threshold voltage shifts, which are exacerbated by the black matrix overlapping with the TFTs, hindering further improvement in pixel aperture ratio.
Innovation Solution
The display device incorporates a color filter layer with specific transmittance characteristics and a light blocking layer that minimizes shading of the TFTs, allowing for reduced or optimized TFT shading portions based on the oxide semiconductor layer dimensions, ensuring improved aperture ratio without compromising TFT reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a black matrix is provided on the counter substrate to block light, then light leakage is prevented, but the aperture ratio is reduced due to TFT shading portions
Solution Approach 1:
The light blocking layer is designed with spatially varying properties: in regions overlapping with TFTs, the TFT shading portion width is constrained to be less than or equal to the oxide semiconductor layer width, while in other regions the light blocking function is maintained. This local differentiation allows simultaneous achievement of light leakage prevention and aperture ratio improvement.
2Area of stationary object
If oxide semiconductor TFTs are used to improve mobility and reduce pixel area, then aperture ratio is improved, but TFT characteristics deteriorate when irradiated with light
Solution Approach 1:
The invention converts the harmful effect of light irradiation on oxide semiconductor TFTs into a beneficial design constraint. By carefully designing the TFT shading portion dimensions (width ≤ oxide semiconductor layer width) and using color filters with specific transmittance characteristics (0.2% or less for blue light), the light that would normally deteriorate TFT characteristics is controlled to provide necessary shading while minimizing negative impact, thus improving aperture ratio without sacrificing reliability.
3Area of stationary object
If the TFT shading portion width is reduced to improve aperture ratio, then more TFT area is exposed to light, causing greater threshold voltage shift
Solution Approach 1:
The invention changes the optical parameters of the system by specifying that color filters overlapping with TFTs must have an average transmittance of 0.2% or less for visible light with wavelength 450 nm or less. This parameter change in the color filter layer compensates for the reduced shading from narrower TFT shading portions, maintaining sufficient light blocking to prevent excessive threshold voltage shift while allowing aperture ratio improvement.
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 configuration enhances the aperture ratio by up to 9% compared to conventional designs, while maintaining TFT reliability by controlling the transmittance of visible light and the width of TFT shading portions, thus improving display efficiency and power consumption.
Implementation Method 1
the color filter layer includes a first color filter, a second color filter and a third color filter that allow light of different colors to pass therethrough
Implementation Method 2
at least one of the first color filter, the second color filter and the third color filter has an average transmittance of 0.2% or less for visible light having a wavelength of 450 nm or less
Data Source
AI summary
A first substrate of a display device includes a TFT provided for each pixel and including an oxide semiconductor layer. A second substrate includes a color filter layer and a light blocking layer. At least one of a first, second and third color filter included in the color filter layer has an average transmittance of 0.2% or less for visible light having a wavelength of 450 nm or less. In pixels provided with color filters having an average transmittance of 0.2% or less for visible light having a wavelength of 450 nm or less, the light blocking layer (a) includes a TFT shading portion extending along a channel length direction and having a width that is less than or equal to a length of the oxide semiconductor layer along a channel width direction; (b) includes a TFT shading portion extending along the channel width direction and having a width that is less than or equal to the length of the oxide semiconductor layer along the channel length direction; or (c) includes no TFT shading portion.