Micro-mirror Electrode Spacer for Stiffness and Curvature Control
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Solution Overview
Problem
Conventional MEMS micro-mirror devices face limitations in stiffness and curvature control due to residual stresses in the reflective coating, which affect optical performance and reliability, and the uniform thickness of the mirror platform and hinge restricts the improvement of stiffness and electrode gap compensation.
Innovation Solution
The introduction of an electrode spacer allows for independent variation of the electrode gap and hinge thickness, enabling additional mirror stiffness while maintaining compensation, through a design with a tilting platform, stiffening ribs, and a two-step etching process to form the mirror platform and hinge separately.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the mirror platform has uniform thickness to simplify manufacturing, then the manufacturing process is easier, but the stiffness and curvature control are limited
Solution Approach 1:
The mirror platform transitions from uniform thickness to non-uniform thickness with localized thickening. Stiffening ribs are added at specific locations (edges and corners) to increase local stiffness where needed for curvature control, while the center remains thin to reduce mass and maintain manufacturability. This local quality change resolves the contradiction by providing enhanced stiffness only where structurally necessary.
Solution Approach 2:
The mirror platform is segmented into regions of different thicknesses rather than maintaining uniform thickness. The structure is divided into a thin central region and thicker peripheral regions with stiffening ribs, allowing independent optimization of each region's properties for stiffness, mass, and manufacturability.
2Strength
If the hinge thickness is increased to improve stiffness, then the mirror platform stiffness improves, but the electrode gap compensation is affected
Solution Approach 1:
The hinge and mirror platform are formed in separate etching steps rather than as a single uniform structure. This segmentation allows independent control of hinge thickness (for stiffness) and mirror platform thickness (for electrode gap compensation), resolving the contradiction by decoupling the two parameters that were previously linked.
Solution Approach 2:
The design allows dynamic adjustment of hinge thickness independently from the mirror platform thickness through separate etching processes. The hinge can be optimized for maximum stiffness while the mirror platform thickness is optimized for electrode gap compensation, with each parameter可调 through process control.
3Force
If the electrode gap is reduced to increase electrostatic force, then the driving torque increases, but the mirror swing space is constrained
Solution Approach 1:
The stiffening ribs extend downward below the mirror platform level, utilizing the vertical dimension to provide structural support without occupying horizontal swing space. This allows the mirror to achieve full swing amplitude while the ribs provide the necessary stiffness, effectively adding a third dimension to the stiffening strategy.
Solution Approach 2:
The stiffening function is copied from the mirror platform structure to separate downward-extending ribs. These ribs replicate the stiffening effect without interfering with the mirror's rotational motion, as they are positioned in a different spatial location (below the platform level) rather than adding mass to the rotating portion.
4Strength
If stiffening structures are added to control mirror curvature, then the mirror stiffness improves, but the device complexity increases
Solution Approach 1:
The stiffening ribs are merged with the hinge structure and formed in the same etching step, eliminating the need for separate manufacturing processes. This integration reduces device complexity by combining multiple functions (stiffening and hinge support) into a single structural element created through a unified process.
Solution Approach 2:
The etching process itself creates the stiffening structures as a byproduct of defining the hinge geometry. The same chemical etching step that forms the hinge automatically creates the downward-extending stiffening ribs, allowing the structure to stiffen itself without additional manufacturing steps or complex tooling.
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 design enhances the stiffness and reduces curvature of the mirror platform, decouples the driving torque from etch depth tolerance, and provides a larger swing space independent of the electrode gap, improving the angular motion and optical performance of the micro-mirror device.
Implementation Method 1
a first hot electrode on the first spacer below the first thin section defining an electrode gap for pivoting the tilting platform about the tilting axis
Data Source
AI summary
A micro-mirror includes stiffer end sections for limiting curvature, and thin middle sections forming ground electrodes and a hinge. Spacers arc provided beneath the thin middle sections of the micro-mirror for supporting hot electrodes, which attract the ground electrodes for rotating the micro-mirror about a tilt axis. The spacers enable the gap between the hot electrode and the micro-mirror to be designed separately from the thickness of the micro-mirror, and the gap between the ends of the micro-mirror and the substrate.