Self-Aligned Mask Patterning for Humidity-Protected MEMS Mirrors
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Solution Overview
Problem
Piezoelectric actuators in laser MEMS scanners degrade in humid environments due to elemental migration and electrochemical activity, leading to cracking and resonance frequency shifts, while protective coatings reduce reflectivity and affect resonant frequency.
Innovation Solution
A self-aligned mask using reactive ion etching (RIE) is employed to selectively remove protective coatings from mirrors, utilizing a cover as a shadow mask and openings aligned with the mirror, maintaining reflectivity and resonant frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective coating is applied to piezoelectric components, then reliability is improved by protecting from humid environment degradation, but mirror reflectivity deteriorates and resonant frequency changes
Solution Approach 1:
The protective coating is segmented into two regions: the mirror surface remains uncovered to maintain reflectivity, while the piezoelectric components are coated for protection. This is achieved through selective coating application or selective removal processes that divide the treatment area into protected and unprotected zones.
Solution Approach 2:
Different regions of the device receive different treatments: the mirror surface maintains its original reflective properties while the piezoelectric components receive protective coating. This local differentiation allows each component to have the specific properties it needs for optimal performance.
2Reliability
If a protective coating is applied to piezoelectric components, then reliability is improved by protecting from humid environment degradation, but resonant frequency deteriorates due to mass loading
Solution Approach 1:
The protective coating is segmented to exclude the mirror surface, preventing mass loading on the resonating structure. Only the piezoelectric components receive coating, thereby protecting them from humidity while maintaining the mirror's resonant frequency stability.
Solution Approach 2:
The protective coating is applied locally only where needed for humidity protection, avoiding areas where it would affect resonant frequency. This selective application ensures that the mirror's mechanical properties remain unchanged while still providing protection to vulnerable components.
3Manufacturing precision
If selective removal of protective coating is performed, then manufacturing precision is improved by self-aligned mask, but device complexity increases
Solution Approach 1:
The mask structure is merged with the device housing or cover, combining two separate components into one. This self-aligned mask approach eliminates the need for separate alignment steps and reduces overall process complexity while maintaining high manufacturing precision.
Solution Approach 2:
The mask structure serves dual purposes: it acts as both the device cover/housing and the alignment mask for selective coating removal. This self-service approach eliminates the need for external alignment tools or complex positioning mechanisms, simplifying the overall manufacturing process.
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
Protects piezoelectric components from humid environments without affecting mirror reflectivity or resonant frequency, ensuring accurate display performance.
Implementation Method 1
One or more piezoelectric components are used to actuate the oscillation of the mirror at a desired frequency and amplitude
Implementation Method 2
Etching is performed through the top scanning opening to remove the protective film from a top of the mirror
Data Source
AI summary
A method includes forming a mirror assembly for a scanning device that includes a mirror rotationally supported by flexible beams, the mirror assembly also including a piezoelectric material. The mirror is encased with a cover having a top scanning opening aligned with the mirror to form a scanning assembly. An interior of the scanning assembly is coated with a protective film. Etching is performed through the top scanning opening to remove the protective film from a top of the mirror.