MEMS Sense Linkage Structure for Common-Mode Motion Rejection
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Solution Overview
Problem
Existing MEMS rotation sensors face challenges in reliability, accuracy, and sensitivity due to the inability to effectively distinguish between desired rotational motion and undesired common mode motion of proof masses, leading to spurious signals.
Innovation Solution
The use of coupled proof masses with out-of-phase motion and specialized linkages, such as inner and outer sense linkages, that exhibit significantly higher stiffness in response to undesired in-phase motion compared to desired out-of-phase motion, thereby enhancing the sensor's ability to resist spurious signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple proof masses are coupled together and driven in out-of-phase motion, then measurement precision and common mode rejection are improved, but device complexity increases due to additional masses and linkages
Solution Approach 1:
The device is divided into multiple proof masses (first, second, third, and fourth masses) that are coupled together through sense linkages. Each mass can be independently controlled to move in out-of-phase motion, allowing differential capacitance measurements that reject common mode signals while detecting rotational motion with high precision.
Solution Approach 2:
Multiple proof masses are merged into a single integrated structure where the first mass is coupled to the third mass via a first inner sense linkage and the second mass is coupled to the fourth mass via a second inner sense linkage. This combined structure enables simultaneous out-of-phase motion of multiple masses, improving measurement precision while maintaining a unified device architecture.
2Reliability
If sense linkages are designed to exhibit high stiffness for in-phase motion, then reliability and accuracy improve by reducing spurious signals, but manufacturing precision requirements increase
Solution Approach 1:
The sense linkages are designed with non-uniform cross-sectional areas along their lengths. Specifically, the linkages have regions of varying thickness that create localized stiffness characteristics. This allows the linkages to exhibit high stiffness for in-phase motion (rejecting spurious signals) while maintaining appropriate flexibility for out-of-phase motion (enabling rotational detection), thereby improving reliability without excessively tightening manufacturing precision requirements.
3Area of stationary object
If proof masses are suspended closer together to reduce device area, then area of stationary object decreases, but mechanical stress and susceptibility to common mode motion increase
Solution Approach 1:
The sense linkages utilize vertical dimension variations through non-uniform cross-sectional areas. By varying the thickness and geometry of the linkages in the vertical direction, the design achieves compact horizontal spacing between masses while compensating for increased mechanical stress through optimized structural geometry. This dimensional approach allows reduced device area without proportionally increasing stress or susceptibility to common mode motion.
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
This configuration improves the reliability and accuracy of MEMS rotation sensors by significantly increasing stiffness in response to undesired in-phase motion, reducing mechanical stress, and enhancing the sensor's ability to detect rotational motion accurately.
Implementation Method 1
A first torsion spring is coupled between the upper portion of the inner sense linkage and the lower portion of the inner sense linkage
Implementation Method 2
Each inner sense linkage includes an upper portion, a lower portion, and a central torsion flexure
Implementation Method 3
When the substrate (along with the proof mass) experiences rotation, the motion of the proof mass will deviate from a straight path due to an apparent Coriolis force in a direction perpendicular to the axis of oscillation of the proof mass
Implementation Method 4
One approach to angular rate sensing in microelectromechanical systems (MEMS) involves causing a proof mass coupled to a substrate by one or more springs to oscillate along a chosen axis
Data Source
AI summary
A MEMS device and method of forming the same includes paired masses suspended above a substrate includes linkages that couple pairs of masses to each other. Inner sense linkages couple interior edges of adjacent masses to each other. The inner sense linkages are configured to exhibit a first stiffness when the adjacent masses coupled to each inner sense linkage move out-of-phase relative to each other along a preferred axis of the inner sense linkages and to exhibit a second, increased stiffness in response to in-phase motion of the adjacent masses coupled to each inner sense linkage.