Movable Body Opening Reduces Electrostatic Sticking in Capacitive Sensors
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Solution Overview
Problem
Existing electrostatic capacitive sensors face issues with movable electrodes sticking to the substrate due to electrostatic forces, particularly during the manufacturing process when a potential difference occurs between the movable electrode and the support substrate.
Innovation Solution
The design incorporates a movable body with an opening that faces the substrate between fixed electrode portions, reducing the electrostatic force and potential difference, and includes dummy electrode portions electrically connected to the movable body to further suppress sticking. Additionally, slit portions are used to reduce damping and increase detection sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a stopper is provided on the movable electrode to prevent sticking, then direct contact with the substrate is avoided, but the exposed region of the substrate still causes electrostatic attraction leading to sticking
Solution Approach 1:
A dummy electrode is introduced as an intermediary between the movable electrode and the exposed substrate region. The dummy electrode is electrically connected to the movable electrode and positioned to face the exposed substrate region, thereby mediating the electrostatic interaction and preventing direct attraction between the movable electrode and substrate
Solution Approach 2:
The exposed substrate region, which originally causes harmful electrostatic attraction, is converted into a useful component by facing it with a dummy electrode. The electrostatic force is redirected to act between the dummy electrode and substrate, while the movable electrode remains free from direct attraction, thus converting the harmful exposed region into a beneficial element for the overall system
2Measurement precision
If the movable electrode is kept close to the substrate for high sensitivity, then detection precision improves, but electrostatic force increases causing sticking
Solution Approach 1:
The electrode system is segmented into the movable electrode and the dummy electrode. The movable electrode maintains close proximity to the substrate for high detection sensitivity, while the dummy electrode is positioned to face the exposed substrate region and bear the electrostatic force, thus segmenting the functional roles and separating the sensitivity requirement from the force problem
3Object-affected harmful factors
If the exposed region of the substrate is reduced, then electrostatic force is reduced, but manufacturing complexity increases
Solution Approach 1:
The dummy electrode serves multiple functions simultaneously: it faces the exposed substrate region to manage electrostatic force, it is electrically connected to the movable electrode to maintain potential relationships, and it utilizes the existing exposed substrate region without requiring additional substrate modifications, thus achieving self-service and avoiding increased manufacturing complexity
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 the sticking of the movable body to the substrate, enhances detection sensitivity, and simplifies the manufacturing process by minimizing electrostatic forces, while maintaining high reliability in the functional element and its applications.
Implementation Method 1
a movable body that includes a movable electrode portion; a support portion that supports the movable body so as to be displaceable about a first axis
Implementation Method 2
The first fixed electrode portion is disposed between the second fixed electrode portion and the third fixed electrode portion in a plan view, an opening that faces a region of the substrate between the first fixed electrode portion and the third fixed electrode portion is provided in the movable body
Implementation Method 3
an opening that faces a region of the substrate between the first fixed electrode portion and the third fixed electrode portion is provided in the movable body, and the width of the opening is equal to or more than the width of the region
Data Source
AI summary
A functional element includes: a substrate; a movable body that includes a movable electrode portion; a support portion that supports the movable body; a first fixed electrode portion that is disposed on the substrate and a portion of which faces a first portion as one of portions of the movable body; a second fixed electrode portion that is disposed on the substrate and a portion of which faces a second portion as the other portion of the movable body; and a third fixed electrode portion that is disposed on the substrate and a portion of which faces the first portion. An opening that faces a region of the substrate between the first fixed electrode portion and the third fixed electrode portion is provided in the movable body, and the width of the opening is equal to or more than the width of the region.