Variable Etch Height Gratings for Waveguide Displays
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Solution Overview
Problem
Conventional lithographic techniques are unable to modulate the etch depth of optical grating elements, limiting the manufacturing of optical gratings with variable depths and duty cycles, which is essential for near-eye displays requiring high out-coupling efficiency and compact design.
Innovation Solution
A manufacturing system comprising a patterning, deposition, and etching system that uses a gray-scale photomask to create optical gratings with variable etch heights and duty cycles by depositing an etch-compatible film, patterning a photoresist, and selectively etching to achieve desired heights and duty cycles, overcoming the limitations of conventional lithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional lithography methods are used to produce optical grating elements, then the duty cycle can be varied, but the height of the optical grating cannot be modulated
Solution Approach 1:
The patent segments the grating fabrication process into multiple sequential deposition and patterning steps, where each step creates a specific depth level. This allows independent control of etch heights at different spatial locations by selectively depositing material in stages, thereby achieving variable grating depths that conventional single-step lithography cannot provide.
Solution Approach 2:
The patent transitions from two-dimensional planar patterning to three-dimensional depth modulation by introducing vertical dimension control through multiple deposition cycles. Each cycle adds material at controlled thicknesses, creating gratings with varying heights across the substrate, thus adding the depth dimension to the traditional flat grating structure.
2Ease of manufacture
If a single etch height is used for all grating elements, then the manufacturing process is simpler, but the out-coupling efficiency is reduced due to size and shape mismatch
Solution Approach 1:
The patent applies local quality by assigning different etch heights to different spatial locations of the grating elements based on their specific optical requirements. Each region of the substrate can have gratings optimized for local out-coupling conditions, with taller or shorter gratings placed where needed to maximize light extraction efficiency, rather than using a uniform height across the entire substrate.
3Reliability
If variable etch heights and duty cycles are required for high out-coupling efficiency, then conventional lithography is insufficient, but a multi-step manufacturing system increases process complexity
Solution Approach 1:
The patent employs a multi-functional manufacturing system where the same deposition and patterning equipment is used repeatedly for multiple cycles to achieve both variable duty cycle and variable etch height. This universal approach allows a single manufacturing platform to perform multiple functions (patterning, thickness control, depth modulation) that would otherwise require different specialized processes, thereby managing complexity while achieving high out-coupling efficiency.
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
Enables the production of optical gratings with adjustable etch depths and duty cycles, enhancing the brightness, uniformity, and field-of-view of image light projected to the user's eye, addressing the inefficiencies of conventional methods.
Implementation Method 1
The manufacturing system performs a deposition of an etch-compatible film over a substrate
Implementation Method 2
The manufacturing system performs a lithographic patterning of a photoresist deposited over the created profile in the etch-compatible film
Implementation Method 3
The manufacturing system performs an etching of the photoresist to obtain at least one of the plurality of etch heights and one or more duty cycles
Data Source
AI summary
A manufacturing system performs a deposition of an etch-compatible film over a substrate. The etch-compatible film includes a first surface and a second surface opposite to the first surface. The manufacturing system performs a partial removal of the etch-compatible film to create a surface profile on the first surface with a plurality of etch heights relative to the substrate. The manufacturing system performs a lithographic patterning of a photoresist deposited over the created profile in the etch-compatible film to obtain the plurality of etch heights and one or more duty cycles corresponding to the etch-compatible film deposited over the substrate.