MEMS Sensor Z-Axis Electrode Parasitic Capacitance Reduction
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Solution Overview
Problem
Commercial MEMS accelerometers measuring z-axis movement face reliability issues due to parasitic capacitance between electrodes and the substrate, affecting the accuracy of capacitance measurements.
Innovation Solution
A MEMS sensor design featuring a movable sensing element with a z-axis MEMS electrode and a reference electrode, where the reference structure is radially outward and coplanar with the MEMS structure, minimizing parasitic capacitance by balancing electrostatic forces and using a cap to encapsulate the structures, thereby reducing noise and increasing measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an electrode is positioned under the inertial mass to measure z-axis movement, then z-axis motion detection capability is improved, but parasitic capacitance between the electrode and substrate increases, degrading measurement reliability
Solution Approach 1:
The patent transitions from a planar electrode configuration to a three-dimensional arrangement by positioning the sensing electrode laterally adjacent to the inertial mass rather than directly beneath it. This spatial reconfiguration in another dimension reduces parasitic capacitance coupling between the electrode and substrate while preserving z-axis motion sensing capability through capacitive coupling between the electrode and the movable inertial mass.
Solution Approach 2:
The patent introduces the movable inertial mass as an intermediary element between the sensing electrode and the substrate. The electrode senses z-axis motion through capacitive coupling with the inertial mass, which acts as a mediator that transmits motion information to the electrode without requiring direct electrode-substrate contact, thereby minimizing parasitic capacitance effects.
2Measurement precision
If the movable sensing element is positioned close to the substrate for sensitive detection, then measurement sensitivity is improved, but parasitic capacitance and environmental noise increase, degrading signal quality
Solution Approach 1:
The patent segments the sensing system into distinct functional components: the inertial mass for motion experience, the sensing electrode for signal detection, and the substrate for structural support. This segmentation allows the electrode to be positioned optimally for sensitivity while maintaining electrical isolation from the substrate through the inertial mass, thereby reducing parasitic capacitance and environmental noise interference.
Solution Approach 2:
The patent employs composite material structures including conductive layers, dielectric layers, and sacrificial material layers in a multi-layer configuration. These composite structures enable precise control of capacitive coupling characteristics, allowing the sensing element to maintain high sensitivity to z-axis motion while minimizing parasitic capacitance through carefully engineered dielectric barriers and conductive pathways.
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
The design enhances the accuracy of z-axis movement measurements by minimizing parasitic capacitance and environmental noise, ensuring reliable and precise sensing of z-axis motion while maintaining the integrity of the MEMS structure.
Implementation Method 1
The movable structure and the fixed structures form a capacitor having a capacitance that changes when the movable structure moves relative to the fixed structures
Implementation Method 2
minimizing parasitic capacitance by balancing electrostatic forces
Data Source
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AI summary
A MEMS sensor includes a substrate and a MEMS structure coupled to the substrate. The MEMS structure has a mass movable with respect to the substrate. The MEMS sensor also includes a reference structure positioned radially outward from the MEMS structure. The reference structure is used to provide a reference to offset any environmental changes that may affect the MEMS sensor in order to increase the accuracy of its measurement.