MEMS Anchoring Region Design for Shear Force Rejection
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Solution Overview
Problem
MEMS sensors face inaccuracies due to manufacturing tolerances, wear, or applied forces, which cause the proof masses to depart from expected relative locations, leading to incorrect force measurements.
Innovation Solution
A MEMS sensor design featuring an anchoring region with dual-anchored and single-anchored portions connected by isolation and compliant springs, which maintains the proof mass's position within the MEMS plane despite undesired forces, preventing tilting and ensuring accurate measurements by keeping the proof mass aligned with the base substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the MEMS sensor uses conventional anchoring structures, then the device complexity is reduced, but the measurement precision deteriorates due to manufacturing tolerances and applied forces causing proof mass displacement
Solution Approach 1:
The anchoring region is divided into multiple portions (first portion, second portion, third portion) with different anchoring configurations. The first portion is rigidly coupled to the cover substrate, the second portion is rigidly coupled to both cover and base substrates, and the third portion connects to the proof mass via springs. This segmentation allows each portion to perform its specific function in maintaining proof mass position while managing overall structural complexity.
Solution Approach 2:
Springs are introduced as intermediary elements connecting the anchoring portions to the proof mass. These springs (first spring connecting first portion to second portion, second spring connecting first portion to third portion) act as compliant intermediaries that maintain the proof mass's expected location relative to the base substrate even when external forces are applied, while isolating the proof mass from direct mechanical stress.
2Measurement precision
If the proof mass is rigidly anchored to maintain position, then the measurement precision improves, but the reliability deteriorates due to stress concentration and potential structural failure under applied forces
Solution Approach 1:
Different portions of the anchoring region have different coupling characteristics. The first and second portions use rigid coupling to the substrates for stability, while the connection to the proof mass uses compliant spring coupling. This local differentiation allows the structure to maintain position stability where needed while providing stress relief where required.
Solution Approach 2:
The springs are pre-installed as compliant elements that cushion and absorb stress before it can cause damage to the proof mass or rigid anchoring structures. The first spring connects the first portion to the second portion, and the second spring connects the first portion to the third portion, creating a compliant pathway that prevents stress concentration at critical interfaces.
3Manufacturing precision
If the MEMS layer components are tightly coupled to maintain alignment, then the manufacturing precision improves, but the ease of manufacture deteriorates due to tighter tolerance requirements
Solution Approach 1:
The springs serve as intermediary elements that accommodate manufacturing tolerances and alignment variations between different components. Instead of requiring tight mechanical coupling between the anchoring portions and the proof mass, the springs provide compliant connections that maintain functional alignment while being more forgiving of manufacturing variations.
Solution Approach 2:
The anchoring structure transitions from a static rigid connection to a dynamic compliant connection using springs. This allows the structure to adapt to minor misalignments and manufacturing variations while maintaining the expected functional relationship between components, thereby easing manufacturing requirements.
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 solution effectively cancels residual linear offsets, maintaining consistent capacitance between electrodes and preventing inaccurate sensor outputs, ensuring the MEMS sensor meets strict offset limits and provides accurate force measurements.
Implementation Method 1
a first spring connecting the first portion to the second portion
Implementation Method 2
a second spring connecting the first portion to the third portion
Implementation Method 3
movement of the movable proof masses within the MEMS layer (in-plane movement) relative to the fixed electrodes, which form capacitors for sensing the movement
Data Source
AI summary
A MEMS sensor includes a central anchoring region that maintains the relative position of an attached proof mass relative to sense electrodes in the presence of undesired forces and stresses. The central anchoring region includes one or more first anchors that rigidly couple to a cover substrate and a base substrate. One or more second anchors are rigidly coupled to only the cover substrate and are connected to the one or more first anchors within the MEMS layer via an isolation spring. The proof mass in turn is connected to the one or more second anchors via one or more compliant springs.