Multi-Stage MEMS Stopper Design for Shock and Stiction Control
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Solution Overview
Problem
MEMS devices face issues with movable masses contacting fixed structures due to electrostatic attraction and excessive shock, leading to device failure, structural damage, and stiction, which can render sensors inoperative.
Innovation Solution
Implementing a controlled contact system with staged, flexible beams that absorb impact forces and reduce stiction by providing a gradual, progressive reaction to shocks, using multiple contact surfaces and beams configured to flex and rotate, thereby mitigating wear and preventing component damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If fixed rigid stoppers are used to prevent contact during shock events, then the movable mass is protected from contacting other components, but the stoppers wear out and cause stiction or electrostatic capture failures due to continuous shock
Solution Approach 1:
The patent replaces fixed rigid stoppers with a movable stopper that can dynamically adjust its position and compliance level. The stopper includes a movable portion that can shift between engaged and disengaged states, allowing the system to adapt to different shock intensities and reduce continuous contact wear.
Solution Approach 2:
The patent changes the mechanical parameters of the stopper by introducing a compliant portion with controlled elasticity. This allows the stopper to deform under shock loads, absorbing energy and reducing the severity of impacts on both the movable mass and the stopper structure itself.
2Reliability
If fixed rigid stoppers are used to prevent contact during shock events, then component contact is prevented, but excessive shock generates large impact forces that break MEMS structures or dislocate particles
Solution Approach 1:
The patent incorporates a compliant portion in the stopper that acts as a cushioning element before contact occurs. This compliant section deforms under impact, absorbing shock energy and preventing the transmission of high impact forces to the fragile MEMS structures and particles.
Solution Approach 2:
The movable stopper with compliant portion serves as an intermediary between the movable mass and the fixed stopper structure. This intermediary absorbs and distributes impact forces, preventing direct transmission of excessive shock to the sensitive components.
3Duration of action of stationary object
If continuous shock keeps the mass contacting the stopper, then the stoppers wear out and cause stiction, but reducing contact prevents protection during shock events
Solution Approach 1:
The movable stopper dynamically adjusts its engagement level based on shock conditions. During normal operation, it maintains minimal contact to reduce wear. During shock events, it engages fully to provide protection, then disengages to minimize continuous contact and prevent stiction.
Solution Approach 2:
The stopper engages periodically during shock events rather than maintaining continuous contact. This periodic engagement provides protection when needed while allowing recovery and reduced wear during normal operation, preventing the accumulation of stiction forces.
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 controlled contact system effectively absorbs impact forces, reduces stiction, and minimizes wear on components, ensuring the sensor's functionality and longevity by preventing contact between movable and fixed structures.
Implementation Method 1
a first beam flexed upon impact when a first stage contact surface of the first beam impacts a first opposing surface within the gap
Implementation Method 2
reduces stiction by providing a gradual, progressive reaction to shocks
Data Source
AI summary
Devices and associated method are shown that include a mass movably coupled over a substrate. In selected configurations, a controlled contact system is coupled between the mass and the at least one stopper. Examples are also shown where the controlled contact system includes a first stage contact coupled to a flexible beam and a second stage contact.