Single Proof Mass MEMS Accelerometer Cross-Axis Error Reduction
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Solution Overview
Problem
MEMS accelerometers face challenges in achieving high accuracy and low noise due to cross-axis errors and susceptibility to noise from smaller proof masses, especially in multi-axis sensing where individual proof masses for each axis are required for high accuracy but result in reduced size and increased noise susceptibility.
Innovation Solution
A two-axis MEMS accelerometer design using a larger single proof mass with a novel arrangement of comb capacitors that passively eliminates cross-axis errors by mirroring the comb capacitors about an axis of reflection, allowing independent measurement of acceleration along both axes while minimizing noise through increased inertial mass and robust signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If individual proof masses are used for each sense axis to reduce cross-axis interference, then measurement precision is improved, but device complexity and size increase
Solution Approach 1:
The patent combines multiple proof masses into a single integrated proof mass structure that senses acceleration along multiple orthogonal axes simultaneously. This merging approach maintains the ability to independently measure each axis while reducing the total number of separate proof masses, thereby decreasing device complexity and size while preserving measurement precision across all axes
2Device complexity
If a single proof mass is used for multiple axes to reduce device complexity, then device complexity is reduced, but cross-axis error increases
Solution Approach 1:
The patent employs asymmetric spring structures with different stiffness characteristics along orthogonal directions to enable a single proof mass to independently sense acceleration along multiple axes. The asymmetric design creates directionally selective mechanical coupling that allows the proof mass to respond to acceleration along one axis without being significantly affected by acceleration along perpendicular axes, thereby reducing cross-axis error while maintaining low device complexity
3Volume of moving object
If smaller proof masses are used to reduce device size, then device size is reduced, but noise susceptibility increases
Solution Approach 1:
By merging multiple proof masses into a single larger integrated proof mass that senses multiple axes simultaneously, the patent increases the total inertial mass used for sensing. This larger combined mass provides better noise immunity and more stable measurements compared to using multiple smaller separate proof masses, while still achieving compact device dimensions through the integrated structure
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 significantly improves noise performance and accuracy by using a single proof mass for both axes, reducing cross-axis errors and thermal noise, while maintaining robust signal-to-noise ratio and minimizing the effects of parasitic modes of movement.
Implementation Method 1
MEMS accelerometers often use capacitive sensors to measure the change in distance between proof mass and support structures. In such a capacitive sensor, electrodes on the support and the proof mass are electrically insulated from each other, and their capacitance is measured. As the distance between the electrodes on the support and proof mass decreases, the capacitance increases.
Implementation Method 2
The basic elements of a MEMS accelerometer are a proof mass, surrounding support structures and a spring connecting the proof mass to the support structures. When the MEMS accelerometer experiences an external acceleration, the proof mass is also forced to accelerate due to the spring coupling. However, since the spring is not perfectly stiff, the spring deflects and the distance between the support and the proof mass changes.
Implementation Method 3
When the MEMS accelerometer experiences an external acceleration, the proof mass is also forced to accelerate due to the spring coupling. The dimensions of the inertial proof mass are important because they typically determine the range of sensitivity of the detection.
Data Source
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AI summary
The present invention provides a high-accuracy low-noise MEMS accelerometer by using a larger, single proof mass to measure acceleration along two orthogonal axes. A novel arrangement of electrodes passively prevents cross axis error in the acceleration measurements. Novel arrangements of springs and a novel proof mass layout provide further noise reduction.