MEMS Accelerometer Overtravel Stop with Sub-Etch Gap
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Solution Overview
Problem
Existing MEMS accelerometers face damage from harsh accelerations due to proof mass movement beyond a desired range, limited by the minimum etch size of the stop gap, leading to chipping or damage of the proof mass and overtravel stop.
Innovation Solution
A compliant spring structure with extensions that move oppositely to the proof mass motion, allowing a stop gap smaller than the minimum etch size, controlled without altering the semiconductor process, to prevent excessive velocity and contact damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the stop gap is made smaller to prevent proof mass damage, then the proof mass is protected from chipping, but the manufacturing precision is limited by the minimum etch size
Solution Approach 1:
The patent transitions from a single static stop structure to a dynamic system where the stop gap dimension changes during operation. The compliant spring structure allows the stop gap to be larger in the fabricated state (meeting minimum etch size requirements) and smaller during operation (protecting the proof mass). This dimensional transformation in the time domain resolves the contradiction between manufacturing constraints and protection requirements.
Solution Approach 2:
The patent introduces dynamic behavior to the stop mechanism through the compliant spring structure. Instead of a fixed stop gap, the system dynamically adjusts the gap size as the proof mass moves. The spring compliance allows the stop to approach the proof mass gradually, reducing impact velocity and preventing chipping while maintaining manufacturable dimensions.
2Ease of manufacture
If the stop gap is made larger to ease manufacturing, then the minimum etch size constraint is satisfied, but the proof mass may experience excessive velocity and contact damage
Solution Approach 1:
The compliant spring structure acts as a cushioning element that is engaged before the hard stop contact. As the proof mass approaches the stop, the compliant spring deforms first, absorbing kinetic energy and reducing the velocity at which the proof mass contacts the hard stop. This beforehand cushioning prevents chipping while allowing a larger, manufacturable stop gap dimension.
Solution Approach 2:
The patent changes the physical state and mechanical properties of the stop mechanism by introducing compliance through the spring structure. This transforms the stop from a rigid, static feature to a dynamic system with energy absorption capabilities. The parameter change in mechanical compliance allows the system to tolerate larger gap dimensions while still preventing damage through controlled energy dissipation.
3Reliability
If traditional over travel stops are used, then the proof mass movement is limited, but the stop gap must be at least the minimum etch size causing potential damage
Solution Approach 1:
The patent resolves the contradiction by introducing temporal dimensionality to the stop gap measurement. The gap is larger during fabrication (satisfying minimum etch size) and effectively smaller during operation (protecting the proof mass). The compliant spring structure enables this dimensional transformation, allowing the same physical structure to serve both manufacturing and protection functions.
Solution Approach 2:
The system transitions from a static stop gap to a dynamic one where the effective gap size changes with the motion state of the proof mass. The compliant spring structure enables this dynamic behavior, allowing the stop mechanism to adapt its effective gap size during operation to prevent damage while maintaining manufacturable 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
Reduces the risk of chipping or damage by controlling the stop gap to less than the minimum etch size, maintaining higher resolution and reducing stiction, while ensuring the proof mass stops before significant contact occurs.
Implementation Method 1
A compliant spring structure with extensions that move oppositely to the proof mass motion
Implementation Method 2
ensuring the proof mass stops before significant contact occurs
Data Source
Figure 1A~1B
Figure 2
Figure 3~4
AI summary
A microelectromechanical systems (MEMS) accelerometer comprises a compliant spring structure with a first beam, a second beam, and a rigid structure. One end of the first beam and one end of the second beam are coupled to the rigid structure and a proof mass is coupled to another end of the second beam. Further, a spring anchor is coupled to another end of the first beam. In response to the proof mass moving, an extension coupled to the rigid structure moves in an opposite direction to motion of the proof mass to contact the proof mass and stop the movement of the proof mass.