Increasing-Depth Grating Fabrication in a Single Etch Process
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Solution Overview
Problem
Conventional fabrication processes for stepped gratings in wearable head-mounted displays (HMDs) are time-consuming due to the need for multiple fabrication steps, increasing complexity and cost.
Innovation Solution
A single fabrication process is used to create a substantially linearly increasing depth grating within a substrate, eliminating the need for multiple steps and reducing production time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple fabrication steps are used to create stepped gratings, then manufacturing precision can be achieved, but production time and process complexity increase significantly
Solution Approach 1:
The patent combines multiple fabrication steps into a single lithography and etching process. The graded depth grating is formed in one operation by using a resist layer with spatially varying thickness or refractive index, eliminating the need for multiple separate lithography steps that would traditionally be required to create stepped gratings with different depth levels.
Solution Approach 2:
The patent changes the parameter of resist layer thickness or refractive index across the grating structure to create the graded depth profile. By varying these parameters spatially within a single lithography process, the grating depths are differentiated without requiring multiple fabrication cycles, thus reducing production time while maintaining precision.
2Manufacturing precision
If multiple fabrication steps are used to create stepped gratings, then manufacturing precision can be achieved, but device complexity and cost increase
Solution Approach 1:
The patent merges multiple fabrication operations into a single integrated process. Instead of performing separate lithography and etching steps for each grating depth level, the invention uses a single lithography process with a specially designed resist layer that encodes the depth information, followed by a single etching process that creates the complete graded depth grating structure.
Solution Approach 2:
The patent replaces the mechanical multi-step fabrication process with an optical field-based approach. By using a resist layer with spatially varying optical properties (thickness or refractive index) that is exposed to light in a single lithography step, the invention substitutes repeated mechanical processing steps with a single optical patterning operation, thereby reducing process complexity.
3Reliability
If conventional grating structures are used, then light coupling efficiency can be maintained, but the ability to control light direction and reduce glare is limited
Solution Approach 1:
The patent applies local quality by creating grating features with varying depths at different locations across the grating structure. Each region of the grating has a specific depth tailored to control light coupling and directionality for that particular area, enabling differentiated optical performance across the entire grating surface while maintaining overall coupling efficiency.
Solution Approach 2:
The graded depth grating creates a dynamic optical response by varying the local refractive index and scattering properties across the grating structure. This gradual depth variation allows the grating to adaptively control light direction and reduce glare in different regions, providing enhanced versatility compared to uniform grating structures.
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 simplifies the manufacturing process, reducing complexity and cost while maintaining or improving the efficiency of light coupling and guiding in HMDs.
Implementation Method 1
light from an image source is coupled into a light guide substrate, generally referred to as a waveguide, by an input optical coupling such as an in-coupling grating
Implementation Method 2
the light beams are 'guided' through the substrate, typically by multiple instances of total internal reflection (TIR)
Data Source
AI summary
A method includes disposing a hardmask coating atop a substrate and forming first openings through the hardmask coating. The method further includes forming a ramped resist coating atop the hardmask coating, the ramped resist coating sloping from a first end of the substrate to a second end of the substrate. The method even further includes etching a plurality of varying depth notches having varying depths within the substrate at locations corresponding to the first openings, the plurality of varying depth notches forming a substantially linearly increasing depth grating within the substrate.