MEMS Sensor Cross-Axis Sensitivity Reduction
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Solution Overview
Problem
Prior MEMS sensors with a teeter-totter configuration are susceptible to cross-axis sensitivity, leading to errors and stiction-related failures under multi-directional overload conditions due to lateral accelerations, which increase adhesion forces and cause device failure.
Innovation Solution
A MEMS sensor design featuring a single central anchor, multi-segment folded torsion springs positioned far from the central anchor, and rigid beams connecting them, with wider spring ends and a higher aspect ratio of width to length, increasing stiffness in both X- and Y-directions to reduce cross-axis sensitivity and prevent stiction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional teeter-totter configuration is used, then device complexity is reduced, but cross-axis sensitivity increases causing measurement errors
Solution Approach 1:
The suspension structure is divided into multiple segments including folded torsion springs with multiple sections, rigid beams, and anchor points distributed throughout the movable element. This segmentation allows each component to be optimized for specific functions, reducing cross-axis sensitivity while maintaining manufacturability
Solution Approach 2:
The design employs asymmetric placement of anchor points and non-uniform spring configurations to counterbalance cross-axis forces. The folded torsion springs have different section arrangements on opposite sides, creating asymmetric stiffness distribution that compensates for lateral acceleration effects
2Measurement precision
If lateral stiffness is increased to reduce cross-axis sensitivity, then measurement precision improves, but stiction risk increases under overload conditions
Solution Approach 1:
The suspension system uses flexible folded torsion springs that provide dynamic response to lateral forces. Under normal operation, the springs maintain high stiffness for precision, but under overload conditions, the flexible nature allows controlled deformation that prevents stiction, enabling the system to survive multi-directional overloads
Solution Approach 2:
The design changes the stiffness parameter through the folded spring geometry, where the effective stiffness varies with the state of the system. The spring configuration provides high stiffness for precision measurement while maintaining enough flexibility under extreme conditions to prevent permanent adhesion
3Measurement precision
If folded torsion springs are positioned far from central anchor, then cross-axis sensitivity reduces, but manufacturing precision requirements increase
Solution Approach 1:
The folded torsion springs are divided into multiple sections with anchor points distributed at different locations. This segmentation allows the system to achieve the benefits of distant spring placement while using multiple smaller, more easily manufactured components with relaxed alignment tolerances
Solution Approach 2:
Multiple folded spring structures are combined with rigid beams and distributed anchor points to create a composite suspension system. This merging allows the system to achieve high precision through the collective effect of multiple components rather than relying on single critical dimensions
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 effectively reduces cross-axis sensitivity and stiction-induced failures by enhancing stiffness, improving accuracy and reliability, and allowing for cost-effective manufacturing using existing MEMS fabrication processes.
Implementation Method 1
multi-segment folded torsion springs positioned as far away from the central suspension anchor as possible
Implementation Method 2
increasing stiffness in both the X- and Y- directions
Implementation Method 3
Capacitive accelerometers sense a change in electrical capacitance, with respect to acceleration, to vary the output of an energized circuit
Data Source
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AI summary
A MEMS sensor includes a movable element positioned in spaced apart relationship above a surface of a substrate and a single centrally located suspension anchor formed on the surface of the substrate. First and second rigid beams are coupled to opposing sides of the suspension anchor and are suspended above the surface of the substrate. A first torsion spring is interconnected between the movable element and the first rigid beam, and a second torsion spring is interconnected between the movable element and the first rigid beam. The rigid beams and the torsion springs are stiff in a lateral direction relative to the surface of the substrate so as to limit slide displacement of the movable element under the condition of a multi-directional overload situation.