Inertial Sensor Stopping Electrode Equipotential Design
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Solution Overview
Problem
Inertial sensors face challenges in achieving high sensitivity while preventing the 'sticking' phenomenon caused by electrostatic attraction between the moving element and the stopper, which affects the accuracy of acceleration detection.
Innovation Solution
The inertial sensor design includes a substrate with a moving element that seesaws about a swing axis, a detection electrode, an exposure part, protrusions that act as stoppers, and a covered electrode with the same electric potential as the moving element, preventing electrostatic attraction and allowing for accurate acceleration detection without reducing the detection area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protrusion-like stopper is provided at the substrate and configured to come into contact with the moving element, then the moving element's displacement is regulated, but electrostatic attraction causes the moving element to stick to the substrate
Solution Approach 1:
The patent applies equipotentiality by providing a covered electrode with the same electric potential as the moving element at the top of the protrusion. This creates an equipotential region that eliminates the electrostatic potential difference between the stopper and moving element, thereby preventing electrostatic attraction and sticking while maintaining the displacement regulation function.
Solution Approach 2:
The covered electrode acts as an intermediary between the protrusion (stopper) and the moving element. It mediates the interaction by providing the same electric potential as the moving element, thus preventing direct electrostatic attraction between the differently-potentialled protrusion and moving element while still enabling mechanical contact for displacement regulation.
2Object-generated harmful factors
If a dummy electrode having the same electric potential as the moving element is arranged at the substrate, then electrostatic attraction is restrained, but the detection electrode area is reduced and sensitivity drops
Solution Approach 1:
The patent resolves the area conflict by transitioning from a two-dimensional planar dummy electrode to a three-dimensional structure. The covered electrode is positioned at the top of the protrusion in the Z-direction, allowing it to provide electrostatic protection without occupying lateral space that would reduce the detection electrode area, thereby maintaining sensitivity.
Solution Approach 2:
The patent segments the dummy electrode function from the detection electrode function. The covered electrode is separated and positioned at the protrusion top, while the detection electrode maintains its full area on the substrate. This segmentation allows both functions to operate independently without compromising the detection electrode's area and sensitivity.
3Reliability
If the stopper is covered with detection electrodes having different electric potential, then the stopper can regulate displacement, but electrostatic attraction occurs between the moving element and stopper
Solution Approach 1:
The patent applies local quality by differentiating the electric potential characteristics at different locations. The detection electrode on the substrate maintains its different electric potential for displacement regulation, while the covered electrode at the protrusion top has the same electric potential as the moving element to prevent electrostatic attraction. This local differentiation resolves the contradiction between regulation and sticking prevention.
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 enables high sensitivity in detecting acceleration while effectively preventing the sticking of the moving element, ensuring accurate and reliable inertial measurements.
Implementation Method 1
forming an electrostatic capacitance with the moving element
Implementation Method 2
having a same electric potential as the moving element, preventing electrostatic attraction
Data Source
AI summary
An inertial sensor includes: a substrate; a moving element swinging about a swing axis along a Y-axis; a detection electrode provided at the substrate, overlapping the moving element as viewed in a plan view from a Z-axis direction orthogonal to the Y-axis, and forming an electrostatic capacitance with the moving element; an exposure part provided at an inner side of the detection electrode and exposing a surface facing the moving element, of the substrate; a protrusion overlapping the moving element as viewed in a plan view from the Z-axis direction and protruding toward the moving element from the exposure part of the substrate; and a covered electrode provided at a top of the protrusion and having a same electric potential as the moving element.