MEMS Gyroscope Anchorage Structure for Drift-Stable Sensing Gaps
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Solution Overview
Problem
Micromechanical detection structures in MEMS multi-axis gyroscopes are prone to measurement errors due to substrate deformations caused by thermal variations, mechanical stresses, and humidity, leading to drifts in electrical parameters such as static offset and sensitivity.
Innovation Solution
The micromechanical structure incorporates a coupling assembly with rigid elements and elastic decoupling elements that anchor the driven mass to the substrate at multiple points near the sensing electrodes, minimizing the effect of substrate deformations on the gaps between the sensing mass and electrodes, thereby reducing capacitive variations and maintaining sensitivity and offset stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the sensing mass is anchored to the substrate at a central point, then the structure is simple and easy to manufacture, but the substrate deformations cause significant drift in electrical parameters
Solution Approach 1:
The central anchorage element is segmented into multiple anchorage points distributed across the substrate. Instead of a single central anchor, the sensing mass is supported by multiple discrete anchorage elements positioned at strategic locations, which distributes the mechanical stress and reduces the impact of substrate deformations on any single anchor point.
Solution Approach 2:
Elastic anchorage elements are introduced as intermediary components between the sensing mass and the substrate. These elastic elements act as mediators that decouple the sensing mass from direct substrate deformations, allowing the mass to maintain its position relative to the fixed electrodes even when the substrate deforms thermally or mechanically.
2Measurement precision
If the sensing mass is positioned close to the fixed electrodes to increase sensitivity, then the detection capability is improved, but substrate deformations cause larger variations in gap distances
Solution Approach 1:
Elastic anchorage elements serve as intermediaries that compensate for substrate deformations. When the substrate deforms, these elastic elements deform accordingly, maintaining a consistent gap distance between the sensing mass and the fixed electrodes. This allows the sensing mass to remain close to the electrodes for high sensitivity while protecting against gap variations caused by substrate deformations.
Solution Approach 2:
The mechanical properties of the anchorage elements are specifically designed to change their stiffness characteristics. The elastic anchorage elements have tailored mechanical properties that allow them to flex under substrate deformation while maintaining the positional relationship between the sensing mass and electrodes, effectively decoupling the gap distance from substrate deformation parameters.
3Reliability
If multiple anchorage points are used to reduce substrate deformation effects, then the stability of electrical parameters is improved, but the device complexity increases
Solution Approach 1:
Multiple anchorage points are merged into an integrated anchorage structure that is formed as a single piece or closely coupled components. The multiple anchorage elements are positioned and connected in a way that creates a unified mechanical support system, reducing assembly complexity while maintaining the stability benefits of distributed anchoring.
Solution Approach 2:
The anchorage structure is designed to perform multiple functions simultaneously: it provides mechanical support for the sensing mass, compensates for substrate deformations, and maintains electrical isolation. This multi-functionality reduces the need for additional components and simplifies the overall device architecture while achieving the desired electrical parameter stability.
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 configuration effectively reduces the mean variation of gaps and inclination of the driven mass relative to the substrate, minimizing undesired variations in electrical detection parameters and maintaining accurate sensitivity and offset values even under deformation conditions.
Implementation Method 1
The elastic anchorage elements 8a, 8b are configured to be compliant to torsion about their direction of extension, thus enabling rotation of the sensing mass 3 out of the horizontal plane xy
Implementation Method 2
The first and second fixed electrodes 5a, 5b define, together with the sensing mass 3, a first sensing capacitor and a second sensing capacitor with plane and parallel faces, which are designated as a whole by C1, C2
Data Source
AI summary
A multi-axis MEMS gyroscope includes a micromechanical detection structure having a substrate, a driving-mass arrangement, a driven-mass arrangement with a central window, and a sensing-mass arrangement which undergoes sensing movements in the presence of angular velocities about a first horizontal axis and a second horizontal axis. A sensing-electrode arrangement is fixed with respect to the substrate and is set underneath the sensing-mass arrangement. An anchorage assembly is set within the central window for constraining the driven-mass arrangement to the substrate at anchorage elements. The anchorage assembly includes a rigid structure suspended above the substrate that is elastically coupled to the driven mass by elastic connection elements at a central portion, and is coupled to the anchorage elements by elastic decoupling elements at end portions thereof.