MEMS Out-of-Plane Sensor Surface Variation
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Solution Overview
Problem
Microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) with out-of-plane movement using capacitive means face challenges such as limited resolution, sensitivity, and mechanical noise due to the non-linearity of transduction processes and the risk of parasitic capacitances, especially in inertial sensors where reduced dimensions increase mechanical noise and reduce static capacitance.
Innovation Solution
A MEMS/NEMS device with out-of-plane movement utilizing capacitive means with surface variation, where all electrodes participate in detection regardless of displacement direction, allowing for high capacitive density and improved linearity and sensitivity, and enabling the device to function as both a sensor and actuator with reduced size and increased inertial mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive means with air gap variation are used for out-of-plane detection, then the device can detect movement, but the resolution and sensitivity are limited due to non-linearity of the transduction process
Solution Approach 1:
The patent changes the detection parameter from air gap variation to surface area variation. By making the comb fingers move parallel to their surface rather than perpendicular, the capacitance variation is caused by the variation of the surfaces of the facing fingers instead of the air gap, resulting in a more linear transduction process and improved detection resolution.
Solution Approach 2:
The patent transitions from one-dimensional air gap variation detection to two-dimensional surface area variation detection. The comb fingers are designed to move in a direction parallel to their surface, utilizing the surface area change between facing fingers to detect out-of-plane movement, thereby achieving better linearity and sensitivity.
2Measurement precision
If capacitive means with air gap variation are used, then the device can detect movement, but the damping coefficient is high due to air layer crushing, resulting in mechanical noise
Solution Approach 1:
The patent changes the detection mechanism from air gap compression to surface area variation. By making the comb fingers move parallel to their surface, the air layer between fingers is not crushed during operation, eliminating the high damping coefficient and associated mechanical noise while maintaining detection capability.
3Measurement precision
If capacitive means with air gap variation are used, then the device can detect movement, but the facing surfaces may stick together due to the pull-in phenomenon
Solution Approach 1:
The patent changes the movement direction of comb fingers from perpendicular to parallel relative to their surface. This prevents the facing surfaces from moving closer in the air gap direction, eliminating the pull-in phenomenon and associated sticking risk while maintaining the ability to detect out-of-plane movement through surface area variation.
4Productivity
If the dimensions of MEMS devices are reduced for mass production, then integration requirements are met, but the inertial mass is reduced causing increased mechanical noise from Brownian forces
Solution Approach 1:
The patent changes the detection parameter to surface area variation, which provides higher sensitivity and signal-to-noise ratio. This allows for reduced device dimensions suitable for mass production while maintaining sufficient detection capability despite reduced inertial mass, as the improved linearity and sensitivity compensate for the lower mass.
5Productivity
If the dimensions of MEMS devices are reduced, then integration requirements are met, but the static capacitance is reduced making the device more sensitive to parasitic capacitances
Solution Approach 1:
The patent changes from air gap variation detection to surface area variation detection, which provides a more linear transduction process with higher sensitivity. This approach maintains adequate static capacitance levels even in miniaturized devices, reducing the relative impact of parasitic capacitances and improving overall measurement reliability in integrated systems.
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 solution enhances sensitivity and linearity, reduces mechanical noise, and allows for compact design while maintaining performance, enabling the device to detect direction and apply forces effectively in both sensing and actuation applications.
Implementation Method 1
the relative movement of the combs can be air gap variation or area variation. In the case of a surface variation, the fingers move in a direction parallel to the plane of their surface and the capacitance variation is due to the variation of the surfaces of the facing fingers
Implementation Method 2
Capacitive devices with air gap variation have several drawbacks... They have limited resolution and sensitivity due to the non-linearity of the transduction process
Data Source
Figure 1A~1B
Figure 2~3B
Figure 4A~4B
AI summary
Microelectromechanical sensor comprising a fixed part (2) and a movable part (4) suspended from the fixed part (2) such that the movable part (4) is capable of moving at least in one out-of-plane direction of movement (Z), the fixed part (2) comprising at least first electrodes (8) extending parallel to the direction of movement (Z) of the movable part (4), the movable part (4) comprising a seismic mass (18) and at least second electrodes (20) extending parallel to the out-of-plane direction of movement (Z), the first electrodes (8) and the second electrodes (20) being arranged relative to each other so as to be interdigitated, wherein the second electrodes (20) are directly connected to the inertial mass (18) and only a part of the face of each movable electrode (20) is opposite a stationary fixed electrode (8).