Capacitive Acceleration Sensor Electrostatic Attraction Reduction
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Solution Overview
Problem
Capacitance type sensors, such as acceleration sensors, face issues with electrostatic attraction between the movable body and the insulating substrate, leading to inhibited rocking motion and reduced sensing accuracy due to charge buildup on the glass substrate, causing the sensor body to stick or rock inaccurately.
Innovation Solution
The sensor device incorporates a substrate with recessed portions and insulating regions positioned to increase the gap between the insulating portion and the movable body, using a dummy electrode and extension electrodes to reduce electrostatic attraction, and includes connecting portions with narrower widths and groove features to minimize facing areas, thereby enhancing the stability and accuracy of the movable body's rocking motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the insulating portion is provided between the fixed electrode and the dummy electrode on the exposed base substrate surface, then the electrical insulation is improved, but the electrostatic attraction between the insulating portion and the movable body increases significantly
Solution Approach 1:
The patent transitions from a two-dimensional planar arrangement to a three-dimensional structure by providing a recessed portion in the base substrate. The insulating portion is placed within this recessed portion, effectively moving it away from the movable body in the vertical dimension. This spatial reconfiguration reduces the electrostatic attraction between the insulating portion and the movable body while maintaining the necessary electrical insulation between the fixed electrode and the dummy electrode.
2Reliability
If the insulating portion is charged, then the electrical insulation function is maintained, but the sensor portion becomes stuck to the base substrate or rocking is inhibited
Solution Approach 1:
The patent applies the beforehand cushioning principle by pre-configuring a recessed portion in the base substrate where the insulating portion will be placed. This recessed structure acts as a cushioning measure that anticipates and prevents the harmful effect of electrostatic attraction. When the insulating portion becomes charged, the recessed structure ensures that the movable body does not stick to the base substrate, as the insulating portion is already positioned in a recessed area away from the movable body's path, thus preserving the rocking motion functionality.
3Reliability
If the base substrate is made of glass or insulating material, then the electrical insulation and structural stability are improved, but the substrate is easily charged leading to electrostatic attraction
Solution Approach 1:
The patent extracts the insulating portion from the exposed surface of the base substrate and places it within a recessed portion. This extraction removes the problematic interaction between the insulating portion and the movable body. By taking out the insulating portion from the surface level and positioning it in the recessed area, the patent eliminates the source of electrostatic attraction while maintaining the electrical insulation properties of the glass or insulating material base substrate.
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 configuration effectively reduces electrostatic attraction, allowing for accurate rocking of the movable body and improved sensing accuracy by increasing the distance between the insulating portion and the movable body, thus preventing sticking and ensuring reliable measurements.
Implementation Method 1
there is a concern that electrostatic attraction is significantly generated between the sensor portion (movable body) and the insulating portion in which the base substrate is exposed
Implementation Method 2
capacitance type sensor in which a structure that a movable electrode is supported by a fixing portion through an elastic element such as a torsion spring is formed, and which is capable of measuring various physical quantities such as an acceleration rate and an angular velocity by detecting a change of electrostatic capacitance between electrodes
Data Source
AI summary
An acceleration sensor (sensor device) includes a substrate that includes a recessed portion (second recessed portion), a fixed electrode, and a dummy electrode juxtaposed with an insulating portion, and a movable body that is supported to be rockable by the substrate, in which the movable body includes a first region facing the fixed electrode, a second region facing a part of the dummy electrode, and a connecting portion connecting the first region and the second region to each other, the fixed electrode is provided with an extension electrode portion extending to a position facing the connecting portion, in a plan view of the movable body, at least a part of the extension electrode portion faces the connecting portion, and the insulating portion between the extension electrode portion and the dummy electrode faces the connecting portion inside the recessed portion.