Reflective Layer Reduces Screen Door Effect in Head-Mounted Displays
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Solution Overview
Problem
Display devices, particularly head-mounted displays, suffer from the screen door effect due to non-emission areas between sub-pixels becoming visible, leading to increased fixed pattern noise and reduced fill factor.
Innovation Solution
A reflective layer is introduced on an overcoat layer of the display device, covering recessed areas to reflect light from sub-pixels and cover non-active areas between active areas, thereby increasing the fill factor and reducing the screen door effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If non-emission areas are used to separate sub-pixels, then sub-pixel definition is improved, but fill factor decreases and screen door effect increases
Solution Approach 1:
The patent converts the harmful effect of non-emission areas (which cause screen door effect) into a beneficial reflective surface. By placing a reflective layer in the non-emission areas between sub-pixels, the previously wasted space now reflects light from adjacent sub-pixels to fill in the dark gaps, transforming the harmful separation effect into a useful light-redistributing mechanism that reduces screen door effect while maintaining sub-pixel definition.
Solution Approach 2:
The patent applies different optical properties to different regions of the display. The sub-pixel active areas maintain their light-emitting properties, while the non-emission areas between sub-pixels are equipped with reflective layers having specific reflectivity characteristics. This local differentiation allows each region to perform its specialized function while the reflective layers in non-emission areas compensate for the fill factor reduction by redirecting light locally to adjacent emitting regions.
2Measurement precision
If non-emission areas separate sub-pixels, then sub-pixel boundaries are defined, but fixed pattern noise increases
Solution Approach 1:
The reflective layers in non-emission areas convert the previously harmful screen door pattern into a beneficial light-diffusing element. By reflecting light from adjacent sub-pixels into the non-emission areas, the reflective layers soften the harsh boundaries between sub-pixels and reduce the fixed pattern noise that arises from regular geometric arrangements, while still maintaining adequate sub-pixel definition.
3Ease of manufacture
If light is trapped within the display device, then manufacturing is simplified, but light efficiency decreases
Solution Approach 1:
The reflective layer serves multiple functions simultaneously: it maintains the simplified display structure by being integrated into the existing non-emission areas, improves light efficiency by redirecting trapped light toward the viewer, and reduces screen door effect by filling in the dark gaps between sub-pixels. This multi-functionality allows the patent to address multiple problems with a single structural modification.
Solution Approach 2:
The reflective layers utilize the light that would otherwise be trapped and wasted within the display device and redirect it back toward the viewer. This self-service mechanism converts the previously harmful trapped light into a useful resource, improving overall light efficiency without requiring additional light sources or complex optical systems.
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 reflective layer enhances the fill factor by approximately 20% and improves light efficiency by reflecting trapped light towards the viewer, reducing the visibility of non-active areas and minimizing the screen door effect.
Implementation Method 1
The reflective layer reflects light from sub-pixels of the display device to cover a portion of a non-active area between active areas of sub-pixels
Implementation Method 2
light that may be trapped within the display device could be reflected by the reflective layer towards a viewing user
Data Source
AI summary
A display device includes a thin film transistor (TFT) substrate, an overcoat layer on an upper substrate, and a reflective layer on the overcoat layer. The TFT substrate covers a light guide plate and includes TFTs configured to drive pixels of the display device. The reflective layer on the overcoat layer reflects light output from the light guide plate towards a viewing surface of the display device. The reflected light overlaps a portion of a non-active area between the active areas of pixels of the display device in at least one dimension.