Staggered Shading Portions for LCD Aperture Ratio
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Solution Overview
Problem
The aperture ratio of liquid crystal display devices using oxide semiconductor TFTs is limited due to light irradiation-induced degradation of TFT characteristics and the visibility of the screen-door effect, particularly in applications like head-mounted displays where the distance to the observer is close.
Innovation Solution
A liquid crystal display device configuration with a staggered arrangement of second shading portions in the light-blocking layer, aligned with columnar spacers, to thin out shading portions and improve aperture ratio while suppressing the screen-door effect, including a stripe arrangement of red, green, and blue pixel columns with alternating first and second pixel boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a black matrix is provided on the counter substrate side to shield oxide semiconductor TFTs from light irradiation, then TFT characteristic degradation is prevented, but the aperture ratio is reduced due to TFT shading portions
Solution Approach 1:
The black matrix is segmented into first shading portions and second shading portions with different configurations. The first shading portions are provided on the active matrix substrate side with openings aligned to pixel boundaries, while the second shading portions are provided on the counter substrate side with staggered arrangement relative to the first shading portions. This segmentation allows selective shielding of TFTs while minimizing impact on aperture ratio.
Solution Approach 2:
The shading portions are strategically positioned to provide light shielding only where TFTs are located, rather than uniformly across the entire display area. The first shading portions are configured with openings at pixel boundaries where no TFTs exist, allowing light transmission in those regions while maintaining shielding over TFT regions.
2Area of stationary object
If the black matrix is thinned out to improve aperture ratio, then the aperture ratio increases, but the screen-door effect becomes visible particularly in close-proximity applications
Solution Approach 1:
The first and second shading portions are arranged asymmetrically in a staggered configuration rather than being perfectly aligned. The second shading portions are shifted relative to the first shading portions, creating an irregular pattern that disrupts the periodicity that causes the screen-door effect while maintaining effective light shielding.
Solution Approach 2:
The shading portion arrangement extends into the spatial dimension with staggered positioning in both row and column directions. By offsetting the second shading portions relative to the first shading portions, the pattern creates a more complex two-dimensional arrangement that reduces visibility of regular patterns at close viewing distances.
3Ease of manufacture
If oxide semiconductor TFTs are used to reduce manufacturing steps and cost, then manufacturing complexity is reduced, but TFT characteristics deteriorate when irradiated with light
Solution Approach 1:
The first shading portions are provided in advance on the active matrix substrate side before the oxide semiconductor TFTs are exposed to light during operation. This preliminary shielding structure is built into the device architecture from the outset, preventing light-induced degradation before it can occur during the device lifetime.
Solution Approach 2:
The first and second shading portions act as intermediary structures between the light source and the oxide semiconductor TFTs. These shading portions intercept and block harmful light rays before they reach the sensitive TFT regions, thereby protecting the TFT characteristics while allowing the benefits of oxide semiconductor technology to be realized.
Data Source
AI summary
A liquid crystal display device includes a first substrate, a second substrate, a liquid crystal layer, and a plurality of columnar spacers. The pixel arrangement is a stripe arrangement including red, green and blue pixel columns. The first substrate includes TFTs, one for each pixel, wherein each TFT includes an oxide semiconductor layer. The second substrate includes a color filter layer and a light-blocking layer. The light-blocking layer includes a plurality of first shading portions extending along the column direction, and a plurality of second shading portions extending along the row direction. Each of the columnar spacers is aligned with one of the second shading portions. At least one of the red, green and blue pixel columns has first pixel boundaries, where one of the second shading portions is present, and second pixel boundaries, where none of the second shading portions present, alternating with each other in the column direction, and the second shading portions are arranged in a staggered arrangement.