3D MEMS Accelerometer with Offset Proof Masses
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Solution Overview
Problem
MEMS accelerometers have limitations in minimum size, detection limit, sensitivity, and power efficiency due to existing fabrication methods, and they are not well-suited for 3-dimensional capacitive sensing and simultaneous measurement of acceleration in three dimensions.
Innovation Solution
A 3-dimensional capacitive accelerometer is fabricated using a single process on a double silicon oxide layer substrate with static and dynamic electrodes, torsion beams, and a proof mass, allowing for capacitive sensing in multiple axes with minimal size and maximum sensitivity, and can be combined for three-dimensional acceleration measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional MEMS fabrication methods are used, then devices can be manufactured with standard processes, but minimum size, detection limit, sensitivity and power efficiency are limited
Solution Approach 1:
The patent combines multiple accelerometer elements (X, Y, and Z-axis sensors) into a single integrated device structure. The Z-axis accelerometer is integrated with X-Y accelerometers on the same substrate, merging multiple sensing functions into one compact unit. This integration improves detection capability while managing fabrication complexity through unified design.
Solution Approach 2:
The patent transitions from planar 2D accelerometer structures to 3D capacitive sensing by positioning proof masses below the substrate plane and using vertical capacitor configurations. The Z-axis accelerometer utilizes the third dimension (depth below substrate) to achieve capacitive sensing, enabling three-dimensional acceleration measurement and improving detection limits through volumetric rather than just surface-area-based sensing.
2Volume of moving object
If accelerometer size is reduced for compact applications, then packaging size decreases, but sensitivity and detection limit deteriorate
Solution Approach 1:
The patent embeds the proof mass structure within the substrate architecture, with proof masses positioned below the substrate plane and integrated into the overall device footprint. The Z-axis accelerometer components are nested within the same packaging envelope as the X-Y accelerometers, achieving compact integration without sacrificing sensing capability.
Solution Approach 2:
The patent employs a composite structure with double-sided silicon oxide layers, metal interconnects, and suspended proof masses integrated into a unified device. This composite construction allows optimized capacitive sensing geometry within minimal volume, maintaining high sensitivity through carefully engineered material combinations and structural configurations.
3Use of energy by moving object
If power consumption is minimized for efficient operation, then energy efficiency improves, but detection limit and sensitivity may be compromised
Solution Approach 1:
The patent replaces mechanical deflection measurement methods with capacitive sensing. Instead of measuring physical displacement of proof masses through mechanical means, the invention uses electrical capacitance changes between stationary and moving electrodes to detect acceleration. This substitution enables lower power consumption since capacitive sensing requires minimal actuation energy compared to mechanical measurement systems, while maintaining high detection sensitivity through electrical field interactions.
4Adaptability or versatility
If 3-dimensional capacitive sensing is implemented, then simultaneous measurement in three dimensions is achieved, but device complexity and fabrication difficulty increase
Solution Approach 1:
The patent uses a universal substrate structure and fabrication process that serves multiple sensing functions. The same double-sided silicon oxide layer architecture, electrode patterning techniques, and proof mass release processes are used for both Z-axis and X-Y axis accelerometers. This universal approach enables 3D capacitive sensing capability while managing fabrication complexity through process reuse and standardized manufacturing steps.
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 enables highly efficient 3D acceleration measurement with minimal power consumption, achieving high sensitivity and response, and can be integrated into compact structures like catheters for cardiovascular applications.
Implementation Method 1
at least one capacitive sensing circuit is defined by the electrical communication between said static electrode plate and said dynamic electrode plate
Implementation Method 2
at least one dynamic electrode plate disposed below said one or more first electrode and supported by at least one torsion beam that spans the aperture
Data Source
AI summary
A 3-dimensional MEMS accelerometer fabricated on a single planar substrate deploys three co-planar sensor elements. Each sensor element is a capacitive device deploying a static electrode plate and a parallel dynamic electrode plate supported by a torsion beam. The dynamic electrode plate also includes a proof mass portion that displaces the center of gravity to below the plane of the plate. Two of the sensor elements are identical and rotated by 90 degrees on the planar substrate. The third capacitive sensor has two pairs of adjacent capacitive plates, each one having a dynamic electrode plate is suspended by a torsion beam. The proof mass on each dynamic electrode plates however is offset laterally from the torsion axis in opposite directions from the other plates to cancel the their respective capacitance charges induced by in-plane acceleration. However, this arrangement also adds the capacitive change induced by acceleration orthogonal to the planar substrate.