Flexible Travel Stops for MEMS Shock Robustness
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Solution Overview
Problem
MEMS devices face harsh accelerations in low-pressure environments, leading to severe impact forces and potential damage due to the inadequacy of existing rigid travel stops in mitigating vertical displacement, which can cause unstable behavior and failure modes such as chipping and increased adhesion forces.
Innovation Solution
The implementation of flexible travel stops within the MEMS device, featuring a contact lever and torsion springs that allow elastic deformation, increasing deceleration time and mitigating impact forces by distributing them through a bumper on the substrate, thereby reducing the risk of stiction-induced failure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rigid travel stops are used to limit vertical displacement, then the device structure is simple, but severe impact forces occur during harsh acceleration causing damage and failure
Solution Approach 1:
The patent applies beforehand cushioning by introducing compliant travel stop structures that deform elastically during impact events. The travel stop includes a bumper portion and a compliant portion that can deform to absorb impact energy, thereby cushioning the proof mass against severe impact forces before damage occurs. This resolves the contradiction by maintaining structural simplicity while reducing impact forces through pre-designed compliant elements.
Solution Approach 2:
The patent changes the mechanical parameters of the travel stop structure by making it compliant rather than rigid. The compliant portion has controlled stiffness that allows elastic deformation, changing the force-displacement characteristics of the travel stop. This parameter change enables the travel stop to mitigate impact forces while still limiting vertical displacement, resolving the contradiction between strength and impact force.
2Reliability
If compliant travel stop structures are used to reduce impact forces, then shock robustness is improved, but device complexity increases
Solution Approach 1:
The patent merges the travel stop structure with existing device components. The compliant travel stop is integrated into the proof mass or substrate structure, combining multiple functions into unified elements. The bumper portion and compliant portion are formed as integrated structures rather than separate components, thereby improving shock robustness while minimizing increases in device complexity.
Solution Approach 2:
The patent employs flexible and compliant portions that function as thin-film elastic structures. These compliant portions are fabricated using standard MEMS thin-film deposition and patterning techniques, allowing complex compliant geometries to be created with simple fabrication processes. This approach improves reliability through compliant impact mitigation while avoiding significant increases in device complexity.
3Measurement precision
If the proof mass is allowed to move freely during acceleration, then measurement sensitivity is maintained, but impact forces increase causing chipping and adhesion failure
Solution Approach 1:
The patent introduces compliant travel stop structures as intermediary elements between the proof mass and the substrate. These compliant structures act as mediators that limit the proof mass displacement during harsh acceleration, preventing direct impact and associated damage such as chipping and adhesion failure. The compliance of the intermediary structure allows it to deform and absorb impact energy while still providing effective displacement limitation.
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 flexible travel stop structure effectively reduces impact forces by up to 75% and enhances restoring forces, minimizing the risk of device failure by distributing load and counteracting adhesion forces, thus improving the shock robustness of MEMS devices.
Implementation Method 1
featuring a contact lever and torsion springs that allow elastic deformation, increasing deceleration time and mitigating impact forces
Data Source
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AI summary
A microelectromechanical systems (MEMS) device is provided, which includes a substrate; a proof mass positioned in space above a surface of the substrate, where the proof mass is configured to move relative to the substrate; a flexible travel stop structure formed within the proof mass, where the flexible travel stop structure includes a contact lever connected to the proof mass via flexible elements; and a bumper formed on the surface of the substrate, where the contact lever is aligned to make contact with the bumper when the proof mass moves toward the substrate.