MEMS Anchor Structure for External Shear Force Rejection
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Solution Overview
Problem
MEMS sensors experience inaccuracies in force measurement due to deviations from expected relative locations of movable proof masses and fixed electrodes caused by manufacturing tolerances, wear, or external stresses, leading to inaccurate measurements.
Innovation Solution
A MEMS sensor design featuring anchors extending into the MEMS layer with a suspended spring-mass system and compliant springs that rotate about orthogonal axes to absorb shear forces, coupled with stiffening springs for shock absorption, maintaining the proof mass's position relative to fixed electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the MEMS sensor uses a rigid anchor structure to maintain fixed positions, then manufacturing precision is improved, but the sensor cannot compensate for external stresses and shear forces
Solution Approach 1:
The patent applies the dynamics principle by replacing rigid anchor structures with compliant springs that can dynamically adjust and rotate. The compliant springs are designed to rotate about orthogonal axes in response to shear forces, allowing the anchor structure to adapt to external stresses while maintaining the proof mass's relative position accuracy. This dynamic capability resolves the contradiction between manufacturing precision and adaptability to external forces.
Solution Approach 2:
The patent employs parameter changes by utilizing the rotational degrees of freedom of the compliant springs. The springs change their angular orientation parameters in response to applied shear forces, allowing the system to compensate for external stresses. This parameter change mechanism enables the sensor to maintain position accuracy despite variations in external conditions, resolving the contradiction between precision and adaptability.
2Device complexity
If the MEMS sensor structure is simplified without compliant springs, then device complexity is reduced, but measurement precision deteriorates due to tilt and position deviations
Solution Approach 1:
The patent introduces dynamic elements (compliant springs with rotational capability) to the otherwise static anchor structure. This dynamic addition allows the system to automatically compensate for shear forces and maintain the proof mass's expected relative location with electrodes, thereby improving measurement precision without requiring complex active control systems.
Solution Approach 2:
The compliant springs provide self-service compensation for external stresses through their inherent rotational compliance. The springs automatically rotate to counteract shear forces, eliminating the need for external correction mechanisms or complex active control systems, thus improving measurement precision while keeping the overall device structure relatively simple.
3Object-affected harmful factors
If the compliant springs are made more compliant to better absorb shear forces, then rejection of external stresses is improved, but the spring-mass system becomes more susceptible to vibration and shock
Solution Approach 1:
The patent applies dynamics by designing the compliant springs with specific rotational characteristics that provide shear force rejection while maintaining structural integrity. The springs are configured to rotate about orthogonal axes, creating a dynamic response that selectively resists shear forces while maintaining stiffness against vibrational and shock loads through the mass of the spring-mass system itself.
Solution Approach 2:
The patent utilizes parameter changes in the spring-mass system's natural frequency and damping characteristics. By carefully selecting the mass and spring constants, the system achieves optimal performance where the compliant springs can reject shear forces effectively while the overall system mass provides sufficient resistance to vibration and shock, resolving the contradiction between compliance and strength.
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 design effectively rejects shear forces and external stresses, preventing tilt and maintaining accurate measurement of forces by keeping the proof mass parallel to electrodes, enhancing measurement precision.
Implementation Method 1
a first compliant spring connected between the at least one anchor and the suspended spring-mass system, wherein the first compliant spring rotates about a first axis that extends in the first direction in response to a shear force along the second direction
Implementation Method 2
a second compliant spring connected between the at least one anchor and the suspended spring-mass system, wherein the second compliant spring rotates about a second axis that extends the second direction in response to a shear force along the first direction
Implementation Method 3
stiffening springs for shock absorption
Data Source
AI summary
A MEMS sensor includes at least one anchor that extends into a MEMS layer and a proof mass suspended from the at least one anchor. Each anchor is coupled to the proof mass via two compliant springs that are oriented perpendicular to each other and attached to a respective anchor. The compliant springs absorb non-measured external forces such as shear forces that are applied to the sensor packaging, preventing these forces from modifying the relative location and operation of the proof mass.