Sandwich MEMS Mirror with Cellular Core for Low Curvature
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional MEMS mirrors face challenges in achieving high mirror resonance frequency while minimizing stress-induced curvature, as thin mirrors result in excessive curvature and thick mirrors lower resonant frequency, and existing stiffening methods are limited to small mirrors and compromise optical performance.
Innovation Solution
A micro-mirror device with a sandwich structure featuring a closed cellular core and smooth, solid outer skins, which allows for a thick core to provide high bending resistance and low curvature, while maintaining a thin profile for high resonance frequency, achieved through semiconductor on insulator structures and deep reactive ion etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the mirror is made thin to achieve high resonance frequency, then the resonance frequency is improved, but excessive curvature is induced by stresses resulting in excessive optical coupling losses
Solution Approach 1:
The patent employs a composite sandwich structure consisting of two thin outer skin layers and a thick core layer. The outer skins provide a smooth reflective surface with minimal stress-induced curvature, while the thick core provides structural support and high bending resistance. This composite construction allows the mirror to maintain both high resonance frequency (due to overall thin profile) and low curvature (due to the stiffening effect of the sandwich structure).
Solution Approach 2:
The sandwich structure distributes different functional properties to different parts of the mirror: the outer skin layers are made thin and smooth to minimize curvature and optimize optical performance, while the core layer is made thick to provide structural support and increase resonance frequency. Each layer has optimized local properties that contribute to the overall performance.
2Shape
If the mirror is made thick to reduce stress-induced curvature, then the curvature is improved, but the resonant frequency is lowered due to increased mass
Solution Approach 1:
The sandwich composite structure resolves this contradiction by combining thin outer layers with a thick lightweight core. The core provides the necessary bending resistance and structural support without adding excessive mass, while the thin outer layers maintain low curvature. This achieves both goals of reducing curvature and maintaining high resonance frequency simultaneously.
Solution Approach 2:
The core layer employs a cellular or porous structure that provides high structural stiffness and bending resistance relative to its mass. This cellular architecture allows the core to act as an efficient stiffening element that increases resonance frequency while keeping the overall mirror thickness optimized for low curvature and minimal mass.
3Speed
If hinge stiffness is increased to compensate for heavy mirror, then the resonance frequency is improved, but too high voltage is required to drive the mirror electro-statically
Solution Approach 1:
The sandwich structure provides high bending stiffness and moment of inertia with relatively low mass, achieving high resonance frequency without requiring excessive hinge stiffness. This reduces the electrostatic drive voltage requirement compared to a solid thick mirror that would require much stiffer hinges to achieve the same resonance frequency.
Solution Approach 2:
By changing the structural parameters from a solid thick mirror to a sandwich construction with cellular core, the patent achieves high resonance frequency through optimized mass distribution and structural efficiency rather than through increased hinge stiffness, thereby reducing the required drive voltage.
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 solution effectively minimizes curvature and maximizes resonance frequency, enabling large area mirrors to tilt to high angles with reduced optical coupling losses and acceptable voltage requirements, enhancing the performance of MEMS devices.
Implementation Method 1
Conventional MEMs mirrors for use in optical switches, such as the one disclosed in U.S. Pat. No. 6,535,319 issued Mar. 18, 2003 to Buzzetta et al, redirect beams of light to one of a plurality of output ports, and include an electro-statically controlled mirror pivotable about a single axis.
Implementation Method 2
A micro-mirror device with a sandwich structure featuring a closed cellular core and smooth, solid outer skins, which allows for a thick core to provide high bending resistance and low curvature, while maintaining a thin profile for high resonance frequency
Implementation Method 3
attracting means for rotating the mirrored platform about the axis of rotation
Data Source
AI summary
A large micro-mirror, e.g. 3 mm by 4 mm, in accordance with the present invention has sufficient rigidity to ensure a low mirror curvature, e.g. a radius of curvature greater than 5 meters, and a low mass in order to ensure a high oscillation frequency, e.g. greater than 1000 Hz. A method of making the micro-mirror utilizes bulk micro-machining technology, which enables the manufacture of a honeycomb structure sandwiched between two solid and smooth silicon layers without any indentations or holes. The honeycomb sandwich structure provides the rigidity and low mass needed to obtain a micro-mirror with a low mirror curvature and high resonant frequency.