Capacitive Inertial Sensor Structure for High Sensitivity and Low Damping
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Solution Overview
Problem
Existing physical quantity sensors face challenges in achieving both high sensitivity and low damping simultaneously due to uniform thickness and gap distances between electrodes, leading to limitations in frequency bandwidth and sensitivity.
Innovation Solution
A physical quantity sensor design with a movable body that includes regions with varying gap distances and through-hole depths, allowing for a movable body that swings about a rotation axis, featuring steps and through-holes to reduce damping while maintaining sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform thickness movable body with uniform through-hole depth is used, then the structure is simple to manufacture, but hole damping becomes large and frequency bandwidth is limited
Solution Approach 1:
The movable body is divided into multiple regions with different through-hole depths. Regions closer to the rotation axis have smaller through-hole depths, while regions farther away have larger through-hole depths. This local differentiation optimizes damping characteristics in different areas, reducing overall hole damping and expanding frequency bandwidth without compromising manufacturing feasibility.
2Device complexity
If a constant gap distance between electrodes is maintained, then the structure is simple, but sensitivity cannot be further increased
Solution Approach 1:
The gap distance between the movable body and fixed electrode is varied across different regions. Regions closer to the rotation axis have smaller gap distances to enhance sensitivity where displacement is smaller, while regions farther away have larger gap distances. This non-uniform gap distribution optimizes overall sensitivity without requiring complex structural changes.
3Reliability
If the movable body thickness is reduced to lower damping, then sensitivity improves, but impact resistance deteriorates and breaking risk increases
Solution Approach 1:
Instead of uniformly reducing the movable body thickness, the patent implements region-specific through-hole depths. This allows damping to be reduced locally in non-critical areas while maintaining sufficient thickness in regions requiring high strength and impact resistance, thus balancing damping performance with mechanical strength.
4Ease of manufacture
If uniform through-hole depth is used, then manufacturing is easier, but damping reduction is insufficient
Solution Approach 1:
The patent implements a multi-region through-hole structure where each region has optimized depth. This can be manufactured using sequential etching processes or by combining different etching techniques, achieving superior damping reduction while maintaining reasonable manufacturing complexity through systematic process design.
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 design achieves high sensitivity and low damping, enabling operation in a wider frequency range with improved impact resistance and reduced risk of sticking, while maintaining rigidity.
Implementation Method 1
a movable body that has a first mass portion facing the first fixed electrode in a Z axis direction along the Z axis and is configured to swing with respect to the substrate about a rotation axis along the Y axis
Implementation Method 2
the first surface of the first mass portion is provided with a step or a slope such that a first gap distance in the Z axis direction of a first gap that is a gap between the first mass portion and the first fixed electrode in the first region is smaller than a second gap distance in the Z axis direction of a second gap that is a gap between the first mass portion and the first fixed electrode in the second region
Implementation Method 3
a depth in the Z axis direction of through-holes of a first through-hole group and a second through-hole group is smaller than a maximum thickness in the Z axis direction of the movable body
Data Source
AI summary
A physical quantity sensor includes a substrate that has a first fixed electrode and a movable body that has a first mass portion facing the first fixed electrode. The first mass portion includes a first region, and a second region farther from the rotation axis than the first region, a first through-hole group is provided in the first region, and a second through-hole group is provided in the second region, and the movable body has a first surface on a substrate side, and a second surface. The first surface of the first mass portion is provided with a step or a slope such that a first gap distance of a first gap between the first mass portion and the first fixed electrode in the first region is smaller than a second gap distance of a second gap between the first mass portion and the first fixed electrode in the second region. A depth of through-holes of the first through-hole group and the second through-hole group is smaller than a maximum thickness of the movable body.