MEMS Piston-Tube Capacitive Accelerometer
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current MEMS capacitive accelerometers face challenges in reducing Brownian Noise Equivalent Acceleration (BNEA) due to solid proof mass structures causing squeeze thin film damping and limited capacitive sensitivity, which increases Circuit Noise Equivalent Acceleration (CNEA), hindering their ability to measure micro/nano-g acceleration effectively.
Innovation Solution
The implementation of a piston-tube electrode configuration in MEMS capacitive accelerometers, which distributes the proof mass around tubes with through holes, reducing squeeze thin film damping and enhancing capacitive sensitivity, thereby lowering BNEA and CNEA, and allowing for high-linearity and low off-axis sensitivity measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a solid proof mass structure is used, then the accelerometer structure is simple, but squeeze thin film damping increases Brownian noise
Solution Approach 1:
The solid proof mass is segmented into multiple discrete masses positioned around the tubes. This segmentation eliminates the squeeze thin film damping effect while maintaining structural simplicity, thereby reducing Brownian noise without significantly complicating the device structure.
2Measurement precision
If the proof mass size is increased to reduce Brownian noise, then Brownian noise decreases, but the device size increases
Solution Approach 1:
Instead of increasing the proof mass size in a conventional manner, the invention positions multiple discrete proof masses around the tubes in a distributed configuration. This dimensional redistribution allows for effective Brownian noise reduction while maintaining a compact device footprint.
3Measurement precision
If parallel plate electrodes are used, then capacitive sensitivity is large, but squeeze thin film damping increases and travel range is limited
Solution Approach 1:
Instead of using conventional parallel plate electrodes that cause squeeze thin film damping, the invention inverts the approach by using piston-tube electrodes where the proof masses are positioned around the tubes. This inverted configuration maintains high capacitive sensitivity while eliminating the harmful damping effect.
4Stability of the object's composition
If comb-drive electrodes are used, then linearity is improved, but capacitive sensitivity is small
Solution Approach 1:
The invention merges the advantages of both parallel plate and comb-drive electrode configurations into a unified piston-tube electrode structure. This combined approach achieves both high capacitive sensitivity and good measurement linearity, overcoming the limitations of either configuration used alone.
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 design achieves a high quality factor, reducing Brownian noise and increasing capacitive sensitivity, enabling the detection of tens of nano-g accelerations at low frequencies, making MEMS capacitive accelerometers competitive with geophones and seismometers.
Implementation Method 1
squeeze thin film damping is present between the proof mass and substrate which greatly reduces the quality factor of the accelerometers
Implementation Method 2
The moving mass around the tubes forms the proof mass, and they are suspended by three or more supporting springs
Implementation Method 3
suspended by three or more supporting springs to return the accelerometer proof mass to its initial position
Data Source
AI summary
A novel high resolution, low noise MEMS capacitive accelerometer is disclosed. The accelerometer utilizes a piston-tube electrode configuration that enables the use of a wide area for the electrodes. Therefore, a high capacitive sensitivity is achieved. The accelerometer consists of two structures: upper and lower. The lower structure contains a plurality of fixed electrodes that are attached to the base and have a piston-style shape (teeth). Those pistons form the sensing electrodes of the accelerometer. The upper structure contains a plurality of moving electrodes that have a tube-style shape (through holes), and they are attached to a substrate via restoring mechanical springs. The proof mass of the accelerometer is distributed around these tubes to reduce squeeze thin film damping in the system. The accelerometer is able to sense linear acceleration along the z-axis and/or the angular acceleration about the in-plane axes (x and y).