MEMS Accelerometer Electrode Layout for Capacitance Offset Reduction
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Solution Overview
Problem
Existing physical quantity sensors, such as those using MEMS techniques, face challenges in reducing capacitance offset due to wiring and other sensor influences, which affects accuracy in detecting acceleration.
Innovation Solution
The sensor design includes a movable body, fixed electrodes, and dummy electrodes strategically positioned to form capacitances that reduce offset, with the third fixed electrode not overlapping the movable body and being electrically connected to either the first or second fixed electrode, and a dummy electrode at the same potential as the movable body to enhance capacitance formation and minimize sticking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dummy electrode is provided to prevent sticking and reduce capacitance offset, then sticking prevention is improved, but capacitance offset reduction is insufficient due to wiring and other sensor influences
Solution Approach 1:
The sensor is divided into multiple independent detection units, each with its own fixed electrode, movable body portion, and dummy electrode. This segmentation allows each unit to independently compensate for its own wiring and structural influences, achieving more effective capacitance offset reduction while maintaining sticking prevention
Solution Approach 2:
Dummy electrodes are strategically positioned adjacent to each fixed electrode to create localized capacitance compensation zones. Each dummy electrode specifically counteracts the capacitance influence of its corresponding fixed electrode and associated wiring, providing targeted offset reduction while maintaining the anti-sticking function
2Measurement precision
If multiple fixed electrodes and dummy electrodes are added to reduce capacitance offset, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The dummy electrode structure is merged with the overall sensor substrate layout, sharing common electrical connections and support structures with the fixed electrodes. This integration reduces the number of separate components and simplifies the manufacturing process while maintaining the capacitance compensation function
Solution Approach 2:
The dummy electrodes serve multiple functions simultaneously: they compensate for capacitance offset by creating balanced capacitive divisions, prevent electrode sticking through electrostatic repulsion, and provide reference potentials for signal conditioning. This multi-functionality reduces the need for additional separate components
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 capacitance offset and prevents sticking, allowing for accurate detection of acceleration by differential detection, even when multiple axes are involved.
Implementation Method 1
a first capacitance detected using the first pad and the second pad, and a second capacitance detected using the first pad and the third pad
Implementation Method 2
a first dummy electrode that is fixed to the substrate, is provided next to the third fixed electrode, and is at the same potential as the movable body
Data Source
AI summary
A physical quantity sensor includes: a movable body; a support that supports the movable body via a coupler; a substrate that is disposed so as to overlap the movable body in a plan view and is provided with a first fixed electrode and a second fixed electrode thereon along a first direction orthogonal to a longitudinal direction of the coupler; a third fixed electrode that does not overlap the movable body in the plan view, is electrically connected with any one of the first fixed electrode and the second fixed electrode, and is provided on the substrate; and a first dummy electrode that is disposed next to the third fixed electrode in the plan view, is at the same potential as the movable body, and is provided on the substrate.