Grayscale Lithography Waveguide Thickness Modulation
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Solution Overview
Problem
Existing waveguide display systems using liquid crystal polymers (LCPs) face challenges in achieving color uniformity and high operational efficiency due to pupil replication and intrinsic absorption by liquid crystal media.
Innovation Solution
The use of grayscale lithography and plasma dry etching in the fabrication of LCP-based waveguides introduces freeform thickness variation and active edge profile control, improving optical properties and reducing haze, thereby enhancing pupil efficiency, color uniformity, contrast, and clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If liquid crystal polymers are used in waveguide displays, then the display can be manufactured with current technology, but color uniformity and operational efficiency deteriorate due to pupil replication and intrinsic absorption
Solution Approach 1:
The patent applies local quality by creating spatially varying thickness in the LCP waveguide layer. Specifically, the waveguide thickness is reduced in regions corresponding to the pupil area to compensate for the intrinsic absorption and pupil replication effects of the liquid crystal material. This local thickness modulation ensures uniform color and brightness across the display while maintaining manufacturability with existing LCP fabrication processes
2Ease of manufacture
If liquid crystal polymers are used in waveguide displays, then the display can be manufactured with current technology, but operational efficiency deteriorates due to intrinsic absorption by liquid crystal media
Solution Approach 1:
The patent addresses energy loss by implementing local thickness variation in the LCP layer. The thickness is optimized in different regions to compensate for intrinsic absorption, ensuring sufficient light transmission efficiency while maintaining compatibility with current manufacturing capabilities
3Device complexity
If traditional lithography is used for waveguide fabrication, then the manufacturing process is simpler, but manufacturing precision and edge profile control deteriorate
Solution Approach 1:
The patent employs grayscale lithography as a preliminary action that directly writes the desired freeform thickness profile and edge features into the LCP waveguide layer during the patterning step itself. This eliminates the need for subsequent complex etching processes to achieve precise edge profiles, as the final three-dimensional structure is created in a single lithography exposure step
Solution Approach 2:
The patent transitions from traditional two-dimensional planar patterning to three-dimensional freeform thickness modulation by using grayscale lithography. This allows direct control of the waveguide thickness in the vertical dimension, creating precise edge profiles and variable thickness regions without requiring additional etching steps
4Manufacturing precision
If grayscale lithography and plasma dry etching are used, then manufacturing precision and edge profile control improve, but device complexity increases
Solution Approach 1:
The patent merges the lithography and etching functions into a single integrated process step. The grayscale lithography pattern directly transfers the final three-dimensional thickness profile to the LCP layer, combining what would traditionally require separate lithography and etching steps into one operation, thereby maintaining precision while reducing overall process complexity
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 results in waveguides with improved brightness, color uniformity, and image contrast, simplifying the fabrication process and reducing unit marginal costs in mass production.
Implementation Method 1
directing exposing light though a grayscale photomask having transparent areas corresponding to a gray-tone pattern to produce masked light, directing the masked light onto the layer of photoresist, developing the photoresist to produce a three dimensional structure in the layer of photoresist
Implementation Method 2
plasma etching the layer of photoresist and the layer of reactive mesogen to form the three dimensional structure in the layer of reactive mesogen
Data Source
AI summary
An optical grating includes a layer of a liquid crystal polymer, the layer having an internal grating pattern defined by locally polymerized liquid crystal molecules, where a cross-sectional shape of the layer varies across the internal grating pattern.