Capacitive Sensor Beam Stress Moderation
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Solution Overview
Problem
Capacitive sensors face challenges in reducing stress in beams, maintaining mass balance, and preventing deficits or sticking due to device size increases and movable electrode movement, especially when using single crystal silicon substrates for enhanced detection sensitivity.
Innovation Solution
The capacitive sensor incorporates a stress moderating unit at the ends of the beam connected to the fixed and movable electrodes, and employs vertical etching of single crystal silicon to form a uniform cross-section, ensuring reduced stress and improved detection sensitivity while avoiding member deficits and sticking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a thin and long beam is provided to make the sensor compact or set an appropriate spring constant, then the device size is reduced and spring constant is optimized, but the stress generated in the beam becomes great
Solution Approach 1:
The patent applies local quality by providing a stress moderating unit only at specific locations (ends of the beam) where stress concentration occurs, rather than uniformly throughout the entire beam structure. This localized intervention reduces beam stress while maintaining the thin and long beam design for compactness.
Solution Approach 2:
The stress moderating unit acts as an intermediary element between the beam structure and the stress concentrations at its ends. This intermediate component absorbs or redistributes the stress, protecting the beam from excessive stress while maintaining the desired compact dimensions.
2Manufacturing precision
If crystal anisotropy etching is used to form the sensor structure, then fine working can be achieved, but various portions such as anchor portion become tapered and deficits or sticking occur
Solution Approach 1:
The patent applies preliminary action by forming the stress moderating unit before final assembly and operation. This pre-formed structural feature prevents tapering and sticking issues from occurring during subsequent movements, ensuring structural integrity while maintaining the precision benefits of crystal anisotropy etching.
3Stress or pressure
If device size is increased to reduce stress, then beam stress is reduced, but deficits or sticking of members are generated
Solution Approach 1:
The patent applies dimensionality change by introducing the stress moderating unit as an additional structural dimension at the beam ends, rather than simply increasing the overall device size. This allows stress reduction through structural modification in a localized dimension while maintaining compact overall dimensions and preventing member deficits or sticking.
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 approach effectively reduces beam stress, enhances detection sensitivity, and prevents member deficits and sticking, allowing for precise and reliable physical value detection.
Implementation Method 1
a movable electrode that is movably supported by a fixed portion of a semiconductor layer through a beam
Implementation Method 2
a capacitance between these electrodes is detected, thereby detecting various physical values
Data Source
AI summary
A capacitive sensor includes a fixed electrode and a movable electrode that is movably supported by an anchor portion through a beam portion. The fixed electrode and the movable electrode are opposed to each other with a gap interposed therebetween, thereby constituting a detecting unit. A capacitance suitable for a size of the gap is detected to detect a predetermined physical value. At least one of an end of the beam portion connected to the anchor portion and an end of the beam portion connected to the movable electrode is provided with a stress moderating unit that moderates a stress.