MEMS Via Support Planarization for Micromirror Contrast
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Solution Overview
Problem
Micromirror-based display systems face challenges in achieving high contrast ratios due to light scattering from the via support indentation in micromirror structures, which affects the maximum brightness and minimum darkness achievable in displayed images.
Innovation Solution
The method involves fabricating MEMS devices with a via support structure where first and second member forming layers are deposited and patterned to form a plug that fills the via opening, followed by planarization and deposition of additional layers to eliminate the indentation, using BARC materials for improved planarity and reduced light scattering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conformal deposition of metal layers is used to form via support and mirror simultaneously, then manufacturing efficiency is improved, but surface planarity deteriorates due to central indentation
Solution Approach 1:
The patent applies preliminary action by depositing a planarization layer of dielectric material over the concave mirror surface before depositing the reflective metal layer. This preliminary planarization step ensures that the subsequent metal deposition occurs on a flat surface, eliminating the central indentation problem while maintaining the efficient conformal deposition process for forming both the via support and mirror structure.
2Device complexity
If via support indentation is present on mirror surface, then device complexity is reduced, but light scattering increases reducing contrast ratio
Solution Approach 1:
The patent performs preliminary planarization by depositing a dielectric planarization layer over the concave mirror surface before metal deposition. This preliminary action creates a flat surface that prevents light scattering when the mirror is in the ON position, thereby improving contrast ratio while maintaining the simple via support structure without requiring additional complex components.
3Object-generated harmful factors
If antireflective coating is applied to via support, then light scattering is reduced, but mirror reflectivity is compromised
Solution Approach 1:
The patent applies local quality by selectively positioning the planarization layer only in the concave region of the mirror surface where the via support indentation occurs. The reflective metal layer is then deposited over this planarized region, ensuring that antireflective properties are localized to the via support area while the main mirror surface maintains high reflectivity for optimal brightness.
4Ease of manufacture
If via support structure is simplified, then manufacturing ease is improved, but surface planarity deteriorates causing light scattering
Solution Approach 1:
The patent employs preliminary action by incorporating a planarization layer of dielectric material in the early stages of fabrication, before metal deposition. This allows the simple via support structure to be manufactured easily through conformal deposition, while the preliminary planarization step ensures that the resulting surface is sufficiently flat to prevent light scattering, thus resolving the contradiction between manufacturing ease and surface precision.
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 enhances the planarity of the mirror surface, reducing light scattering and improving the contrast ratio by minimizing light loss during the 'ON' and 'OFF' positions, thereby increasing the achievable brightness and darkness in the displayed images.
Implementation Method 1
first and second member forming layers are deposited and patterned to form a plug that fills the via opening
Implementation Method 2
using BARC materials for improved planarity and reduced light scattering
Implementation Method 3
In the 'ON' position, the micromirror is set to reflect incident light onto the display plane
Implementation Method 4
pixel elements in the form of mirrors supported on a via support or other underlying support structure above a substrate for movement between 'ON' and 'OFF' positions in response to electrostatic forces applied by associated CMOS integrated circuitry
Data Source
AI summary
A microelectromechanical (MEMS) device has a movable member supported above a substrate on a via support. The member and via support are fabricated integrally from first and second member forming layers. A first member forming layer forms a lower part of the member and supporting structure for the via support. First and second fill layers are deposited and patterned to form a plug that fills an inner cavity opening in the via structure. The plug is planarized to a planar part of the first member forming layer, and a second member forming layer is deposited over the first member forming layer and the planarized plug to form an upper part of the member. The via support may have a cavity filled by BARC layers.