Rotational MEMS Beam Layout for Thermal Drift Rejection
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Solution Overview
Problem
Microsystems for measuring rotational movement are sensitive to substrate deformations and thermal expansion, leading to spurious signals due to translational movements and stress amplification at the beams.
Innovation Solution
A microsystem structure with symmetrically oriented beams, where the first and second vectors have the same direction but opposite sense, and the position of junctions is chosen to ensure that the vector products have the same sign, reducing sensitivity to substrate deformations and thermal expansion by canceling out opposing deformations and thermoelastic forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a suspended moving part with beams is used to measure rotational movement, then rotational measurement capability is achieved, but sensitivity to substrate deformations increases causing spurious signals
Solution Approach 1:
The patent applies asymmetry by positioning the beams at different distances from the axis of rotation. Specifically, the first beam is positioned at a first distance from the axis of rotation, and the second beam is positioned at a second distance from the axis of rotation, where the first distance is different from the second distance. This asymmetric configuration creates differential sensitivity to rotational movement while maintaining reduced sensitivity to substrate deformations, as the beams experience different magnitudes of deformation under the same substrate stress conditions.
2Object-affected harmful factors
If beams are positioned close to the axis of rotation to reduce substrate deformation impact, then sensitivity to substrate deformations decreases, but rotational measurement sensitivity may be reduced
Solution Approach 1:
The asymmetric positioning of beams at different distances from the axis of rotation allows the system to optimize the balance between substrate deformation sensitivity and rotational measurement sensitivity. By having one beam closer and one beam farther from the axis, the system achieves differential measurement that is sensitive to rotation while the overall configuration reduces the impact of substrate deformations through the averaging effect of the asymmetric arrangement.
3Object-affected harmful factors
If symmetric beam configuration is used, then sensitivity to thermal expansion is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent deliberately uses asymmetric beam positioning rather than symmetric configuration. This asymmetric design with beams at different distances from the axis of rotation provides thermal expansion compensation through differential thermal responses, while being more tolerant to manufacturing variations compared to perfectly symmetric designs. The asymmetry allows the system to function effectively without requiring extremely precise manufacturing tolerances.
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 microsystem effectively rejects spurious signals from substrate deformations and thermal effects, enhancing the stability and accuracy of rotational movement measurements by compensating for thermal expansion and substrate-induced deformations.
Implementation Method 1
a first beam (P1) connecting the moving part (PM) to the main part (PP)... a second beam (P2) connecting the moving part (PM) to the main part (PP)
Implementation Method 2
It is also of low sensitivity to the effects of thermal expansion at the microstructure or even at each beam, which, given the symmetry of the microsystem, produce opposing thermoelastic forces
Data Source
AI summary
A microsystem includes a substrate; a main part connected to the substrate via an anchor; a moving part configured to rotate about an axis of rotation O; a first beam connecting the moving part to the main part, the main direction of said first beam being along a first vector ej1 having as origin the junction of the moving part with the first beam and in the sense of the main part; a second beam connecting the moving part to the main part, the main direction of the second beam being along a second vector ej2 having as origin the junction of the moving part with the second beam and in the sense of the main part.