MEMS Spring Member Asymmetry for Vertical Stiffness
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Solution Overview
Problem
Folded spring members in MEMS sensors are prone to twisting under high vertical loads, leading to reduced vertical stiffness and potential failure due to excessive vertical displacement of the movable element, which can stick to the substrate.
Innovation Solution
The design incorporates symmetrically disposed spring members with a support structure that bridges the beams, preventing twisting by increasing torsional stiffness and maintaining vertical stiffness, thereby limiting vertical movement of the movable element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If folded spring members are used to achieve low lateral stiffness, then the movable element can move freely in the intended direction, but the spring members become prone to twisting under high vertical loads, reducing vertical stiffness and causing excessive vertical displacement
Solution Approach 1:
The spring member design employs asymmetric geometry where the first and second portions have different configurations relative to the neutral axis. The first portion extends in a first direction while the second portion extends in a second direction, creating an asymmetric structure that provides different stiffness characteristics in different directions - compliant laterally but stiff vertically under high loads
Solution Approach 2:
The spring member transitions from a planar folded structure to a three-dimensional configuration by extending portions in different directions (first direction and second direction) relative to the neutral axis. This dimensional change allows the structure to resist twisting moments and vertical loads more effectively while maintaining lateral compliance
2Measurement precision
If folded spring members are used to reduce lateral stiffness, then the sensor can detect lateral acceleration accurately, but the movable element may contact and stick to the substrate under mechanical shock, causing sensor failure
Solution Approach 1:
The asymmetric spring member design preemptively counteracts the twisting effect that would occur under vertical shock loads. By designing the first and second portions to extend in different directions, the structure creates inherent resistance to twisting moments before they occur, preventing the chain reaction that would lead to substrate contact and sensor failure
Solution Approach 2:
The spring member functions as a composite structural element combining features of both compliant and stiff structures. The asymmetric configuration with portions extending in different directions creates a hybrid behavior - compliant in the lateral measurement direction but stiff in the vertical direction under high loads, effectively combining the benefits of both folded and straight spring designs
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 vertical stiffness of the spring members, preventing the movable element from sticking to the substrate and mitigating sensor failure under mechanical shock, making the MEMS sensor more reliable in high-load conditions.
Implementation Method 1
Movement of the movable element deforms the compliant members, storing potential energy therein. The stored potential energy tends to return the movable element to its neutral position once the force is removed.
Data Source
AI summary
A device (96) includes a microelectromechanical (MEMS) sensor (40). The sensor (40) includes a movable element (42) adapted for motion in a direction (44) and an anchor (46) coupled to a substrate (48). The MEMS sensor (40) further includes spring members (50) interconnected between the movable element (42) and the anchor (46). Each of the spring members (50) includes beams (56, 58, 60) arranged in substantially parallel alignment, with the beam (60) positioned between the other beams (56, 58). Each of the beams (56, 58) is coupled to the anchor (46) and the beam (60) is coupled to the movable element (42). Each of the spring members (50) further includes a support structure (64) joined with the beams (56, 58) to provide vertical stiffness to the beams (56, 58) of the spring member (50).