MEMS Two-Stage Motion Limit Structure for Shock Robustness
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Solution Overview
Problem
MEMS inertial sensors are prone to failure due to high acceleration forces, as their spring suspension designs are not robust enough to withstand shock events, leading to device damage and stiction issues.
Innovation Solution
A two-stage motion limit structure is implemented, comprising a compliant primary stop feature and a rigid secondary stop feature, which reduces contact forces between movable and stationary structures, mitigating stiction and damage by allowing the energy used to compress the primary stop to push apart the secondary stop, thereby enhancing robustness and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spring suspension design is used to suspend the movable mass, then the device can sense acceleration effectively, but the device becomes vulnerable to damage during high acceleration shock events
Solution Approach 1:
A motion limit structure is provided that includes a compliant stop feature positioned to engage with the movable mass before it can reach positions that would cause damage. The compliant nature of the stop feature allows it to deform and absorb impact energy, cushioning the movable mass during shock events and preventing catastrophic failure while maintaining normal sensing operation during regular use
2Reliability
If the movable mass is constrained to prevent excessive motion, then device reliability improves, but stiction and contact damage occur due to high contact forces
Solution Approach 1:
The stop feature is designed with compliant properties that change its mechanical characteristics based on operating conditions. During normal operation, the stop feature maintains a configuration that minimizes contact. During shock events, it deforms to absorb energy, and the compliance reduces peak contact forces, preventing stiction and contact damage while still providing necessary motion 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 two-stage motion limit structure effectively reduces the risk of damage and stiction during high-g shock events, maintaining the integrity of the MEMS device by managing contact forces and ensuring the movable structures return to their initial position.
Implementation Method 1
the energy used to compress the primary stop to push apart the secondary stop
Implementation Method 2
a compliant primary stop feature and a rigid secondary stop feature
Data Source
AI summary
A MEMS device includes a substrate, a proof mass capable of moving relative to the substrate, and a motion limit structure. The motion limit structure includes an arm structure flexibly coupled to the proof mass or the substrate. The arm structure has a first contact region and a second contact region. In response to a shock force that causes the proof mass to move, the first contact region contacts a first stop region on the other one of the proof mass and the substrate. Following contact of the first contact region with the first stop region and upon continuation of the shock force, the second contact region contacts a second stop region on the other one of the proof mass and the substrate such that the contact between the second contact and stop regions reduces a contact force between the first contact and stop regions.