MEMS Flexure with Protrusion Elements for Torsional Stiffness
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Solution Overview
Problem
MEMS accelerometers face challenges in reducing size while maintaining sensitivity, linearity, and reliability, particularly due to insufficient restoring force from smaller movable structures, making them vulnerable to high impact loads and difficult to sense motion along multiple axes effectively.
Innovation Solution
The design incorporates a flexure with enhanced torsional stiffness, achieved by using protrusion elements that break up the elongated beam into shorter lengths, allowing for independent adjustment of axial and in-plane rotational spring constants, enabling a single proof mass to sense acceleration in three orthogonal directions with improved linearity and restoring force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the size of movable structures is reduced to shrink device size, then device size is reduced, but restoring force becomes insufficient and vulnerability to high impact loads increases
Solution Approach 1:
The flexure is segmented into multiple beam segments (first beam segment, second beam segment, third beam segment) connected by rotational joints. This segmentation allows each segment to contribute to the overall restoring force while maintaining compact device size, resolving the contradiction between small size and sufficient restoring force.
Solution Approach 2:
The flexure employs a composite structure combining multiple beam segments with different geometric properties and material characteristics. The first beam segment has different dimensions than the second and third segments, creating a composite system that optimizes both size and restoring force through the combined mechanical properties of its components.
2Adaptability or versatility
If multiple movable structures are used to sense motion along multiple axes, then sensing capability along multiple axes is improved, but collective size of movable structures increases
Solution Approach 1:
The single proof mass serves multiple sensing functions by detecting acceleration along three orthogonal axes (X, Y, and Z directions) through different beam segments. This multi-functional design eliminates the need for separate movable structures for each axis, reducing collective size while maintaining multi-axis sensing capability.
Solution Approach 2:
The invention adds the Z-axis (vertical dimension) sensing capability to the traditional planar X-Y axis sensing. The first beam segment sensing acceleration in the Z-direction perpendicular to the substrate plane, while the second and third segments sense X and Y directions, creates a three-dimensional sensing system from a single proof mass.
3Volume of moving object
If the length of elongated beam flexure is increased to reduce device size, then device size is reduced, but torsional stiffness decreases
Solution Approach 1:
The flexure is divided into multiple beam segments connected by rotational joints, which breaks the continuous beam into discrete sections. This segmentation allows the system to achieve compact size through folded geometry while the joints provide torsional stiffness through their rotational resistance, resolving the contradiction between small size and torsional stiffness.
Solution Approach 2:
The composite structure of multiple beam segments with different lengths and cross-sections creates a flexure system where torsional stiffness is distributed across all segments. The first beam segment with length L1 and width W1, second segment with length L2 and width W2, and third segment with length L3 and width W3 work together to provide overall torsional stiffness while maintaining compact 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
This configuration enhances the MEMS accelerometer's ability to detect acceleration in three axes with increased torsional stiffness, improved linearity, and enhanced resistance to high impact loads, while reducing device size and maintaining sensitivity.
Implementation Method 1
The design incorporates a flexure with enhanced torsional stiffness, achieved by using protrusion elements that break up the elongated beam into shorter lengths
Implementation Method 2
a first spring system including first and second flexures interconnected between a first beam and a second beam, respectively, of the movable element
Implementation Method 3
The movement of the movable structure changes capacitance, and an electrical circuit connected to the MEMS accelerometer structure measures the change in capacitance to determine the acceleration forces
Data Source
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Figure 7~8
AI summary
A flexure for a MEMS device includes an elongated beam and a protrusion element extending outwardly from a sidewall of the elongated beam. A MEMS inertial sensor includes a movable element spaced apart from a surface of a substrate, an anchor attached to the substrate, and a spring system. The spring system includes first and second beams, a center flexure between the first and second beams, a first end flexure interconnected between an end of the first beam and the anchor, and a second end flexure interconnected between an end of the second beam and the movable element. Each of the end flexures includes the elongated beam having first and second ends, and the sidewall defining a longitudinal dimension of the elongated beam, and the protrusion element extending from the sidewall of the elongated beam, the protrusion element being displaced away from the first and second ends of the beam.