MEMS Mirror Comb Electrode Area Expansion
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Solution Overview
Problem
Existing MEMS mirrors face limitations in increasing the total area between movable and fixed comb electrodes, which restricts the drive force and accuracy in detecting the movement of a moving member.
Innovation Solution
A semiconductor device with a tilting portion and a base, featuring alternately arranged electrode fingers of movable and fixed comb electrodes, where some electrode fingers are provided on a body and others on an extension, allowing for increased surface area without size or number increments, using a silicon-on-insulator substrate and specific etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the area of each comb electrode is increased to increase total facing area, then drive force and detection accuracy are improved, but device size increases
Solution Approach 1:
The patent extends the comb electrodes in the depth direction (third dimension) by forming them on both the front surface and back surface of the movable portion, allowing increased total facing area without increasing the planar footprint of the device
Solution Approach 2:
The patent arranges fixed comb electrodes and movable comb electrodes in an alternating pattern, with fixed electrodes on the base and movable electrodes on the movable portion, creating a nested interdigitated structure that maximizes facing area within compact dimensions
2Measurement precision
If the number of comb electrodes is increased to increase total facing area, then drive force and detection accuracy are improved, but device complexity increases
Solution Approach 1:
The patent divides the comb electrodes into multiple fingers arranged in an interdigitated pattern, where fixed comb electrodes and movable comb electrodes are segmented into multiple alternating elements, increasing total facing area and detection precision while maintaining manageable structural complexity
Solution Approach 2:
The comb electrode structure serves dual functions: it provides electrostatic drive force for actuation and simultaneously serves as a capacitive sensor for detecting the position of the movable portion, eliminating the need for separate actuation and sensing mechanisms
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
Enhances the total area between comb electrodes, improving drive force and detection accuracy while maintaining compact dimensions, thus overcoming size and number limitations.
Implementation Method 1
the mirror is driven by electrostatic force generated between the movable comb electrode and the fixed comb electrode
Implementation Method 2
the amount of movement of the moving member is detected based on a change in the electrostatic capacitance between the movable comb electrode and the fixed comb electrode
Data Source
AI summary
A mirror device includes a frame body, a mirror configured to tilt about a Y-axis with respect to the frame body, a fixed inner comb electrode including a plurality of electrode fingers arranged in the arrangement direction along the Y-axis and provided at the frame body, and a movable inner comb electrode including a plurality of electrode fingers arranged in the arrangement direction and provided at the mirror, the electrodes fingers of the fixed inner comb electrode and the movable inner comb electrode being alternately arranged. The mirror includes a mirror body and an extension extending from the mirror body. Some of the electrode fingers of the movable inner comb electrode are provided at the mirror body, and another electrode fingers of the movable inner comb electrode are provided at the extension.