Tiltable Mirror Array with Spring Elements for Stiction Mitigation
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Solution Overview
Problem
Spatial light modulators (SLMs) with digital mirror devices (DMDs) face challenges in achieving high optical efficiency and contrast due to small mirror pitch and stiction effects, which decrease switching speed and reliability.
Innovation Solution
A mirror system with tiltable mirrors equipped with spring elements on their underside, allowing for efficient switching between ON and OFF states by mitigating stiction, and featuring a mirror array with a pitch of less than 5 µm and a filling factor of over 90%, with discrete tilting positions and a Blazed grating configuration for improved light focusing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the mirror pitch is reduced to achieve fine pixel pitch, then the image resolution is improved, but the optical efficiency decreases and stiction effects occur
Solution Approach 1:
The support surface is segmented into discrete mirror elements with individual spring elements, allowing each mirror to be independently suspended and tilted without contacting the substrate, thereby maintaining optical efficiency while achieving fine pixel pitch
Solution Approach 2:
Spring elements are introduced as intermediary components between the mirrors and the support surface, providing mechanical support while preventing stiction effects through elastic deformation, thus maintaining reliability and optical efficiency at reduced mirror pitches
2Measurement precision
If the mirror pitch is reduced to achieve fine pixel pitch, then the image resolution is improved, but stiction effects increase
Solution Approach 1:
Spring elements are pre-installed on the underside of each mirror to provide cushioning against the substrate, preventing direct contact and stiction effects before they can occur during mirror tilting operations
Solution Approach 2:
Flexible spring elements are used instead of rigid supports, allowing the mirrors to tilt freely without substrate contact while maintaining structural integrity at reduced pitch dimensions
3Reliability
If the fill factor is increased to reduce distance between mirrors, then the optical efficiency is improved, but stiction effects occur
Solution Approach 1:
The continuous support surface is segmented into discrete regions with individual spring elements for each mirror, allowing high fill factor configuration while maintaining separation between mirrors and substrate through elastic suspension
4Loss of time
If stiction effects occur, then the switching time increases, but the mirror array reliability decreases
Solution Approach 1:
Spring elements serve as intermediary components that eliminate stiction effects through elastic deformation, enabling rapid mirror switching while maintaining system reliability through consistent mechanical coupling
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 mirror system enhances switching speed and reduces energy required for actuation, improves image contrast by efficiently deflecting stray light, and maintains high reliability and optical efficiency.
Implementation Method 1
each of the plurality of mirrors comprises a spring element on an underside of the mirror
Implementation Method 2
stiction effects can occur if a tilted mirror is in physical contact to an underlying substrate
Implementation Method 3
each mirror in the first tilting position is arranged to reflect a light beam that is emitted from the light source onto the aperture
Implementation Method 4
less force, i.e. less energy, is required to actuate the movement of the mirrors
Data Source
Figure 1
Figure 2
Figure 3a~3b
AI summary
The invention relates to a mirror system (10) for a projection apparatus (60), wherein the projection apparatus (60) comprises a light source (61) and an aperture (62), wherein the mirror system (10) comprises a support surface (11); and a plurality of mirrors (12) arranged on the support surface (11); wherein each of the plurality of mirrors (12) is arranged tiltable between a first and a second tilting position, wherein the first and the second tilting position are discrete positions; wherein each mirror (12) in the first tilting position is arranged to reflect a light beam (63) that is emitted from the light source (61) onto the aperture (62); wherein each mirror (12) in the second tilting position is arranged to reflect the light beam (63) that is emitted from the light source (61) away from the aperture (62); and wherein each of the plurality of mirrors (12) comprises a spring element (31) on an underside of the mirror (12).