MEMS Sensor Dual Proof Masses Thermal Stress
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Solution Overview
Problem
Microelectromechanical Systems (MEMS) sensors face challenges in reducing size and sensitivity to temperature-induced errors, particularly due to thermally induced stress, which affects measurement accuracy and can lead to strain and deformation in the substrate and suspension anchors.
Innovation Solution
The use of dual proof masses arranged in rotational symmetry, allowing them to fit together in a nested configuration, minimizes measurement errors caused by thermally induced stress and optimizes substrate area, while maintaining accuracy and compact size through existing MEMS fabrication processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If dual proof masses are used to reduce sensitivity to temperature-induced errors, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The patent applies asymmetry by arranging the two proof masses in a non-symmetric configuration relative to the substrate center. Specifically, the first proof mass is positioned at a first location and the second proof mass is positioned at a second location, where their positions are deliberately asymmetric to create differential responses to thermal stress. This asymmetric arrangement allows the masses to experience different thermal deformations, enabling the system to measure and compensate for temperature-induced errors while maintaining a relatively simple single-substrate structure.
Solution Approach 2:
The patent implements nesting by integrating multiple functional elements within a compact substrate area. The dual proof masses are positioned in spaced-apart relationship above the substrate, utilizing vertical spacing and horizontal positioning to pack the sensor structure efficiently. This nested arrangement allows the complex dual-mass configuration to occupy minimal substrate area, reducing device complexity while maintaining the measurement accuracy benefits of having two proof masses.
2Measurement precision
If proof masses are positioned in spaced-apart relationship to reduce thermal stress effects, then measurement accuracy improves, but substrate area increases
Solution Approach 1:
The patent resolves the area conflict by transitioning from a two-dimensional planar arrangement to a three-dimensional configuration. The proof masses are positioned in spaced-apart relationship both horizontally and vertically above the substrate. This vertical spacing (z-dimension) allows the masses to be separated enough to reduce thermal stress coupling while occupying minimal substrate footprint. The spaced-apart positioning exploits the third dimension to achieve thermal decoupling without proportionally increasing the substrate area.
Solution Approach 2:
The patent implements nesting by integrating multiple functional elements within a compact substrate area. The dual proof masses are positioned in spaced-apart relationship above the substrate, utilizing vertical spacing and horizontal positioning to pack the sensor structure efficiently. This nested arrangement allows the complex dual-mass configuration to occupy minimal substrate area, reducing device complexity while maintaining the measurement accuracy benefits of having two proof masses.
3Measurement precision
If dual proof masses are used with rotational symmetry to minimize thermal stress errors, then measurement accuracy improves, but manufacturing complexity increases
Solution Approach 1:
The patent applies asymmetry by arranging the two proof masses in a non-symmetric configuration relative to the substrate center. Specifically, the first proof mass is positioned at a first location and the second proof mass is positioned at a second location, where their positions are deliberately asymmetric to create differential responses to thermal stress. This asymmetric arrangement allows the masses to experience different thermal deformations, enabling the system to measure and compensate for temperature-induced errors while maintaining a relatively simple single-substrate structure.
Solution Approach 2:
The patent employs parameter changes by utilizing the spaced-apart positioning of the proof masses to alter the thermal stress distribution parameters. By controlling the distance and spatial relationship between the masses, the system changes the thermal response parameters to minimize measurement errors. This parameter optimization allows standard MEMS fabrication processes to produce the sensor with acceptable precision without requiring complex additional manufacturing steps.
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 achieves high sensitivity to z-axis acceleration with reduced measurement inaccuracies due to thermal stress, enabling cost-effective manufacturing and compact size, while maintaining high accuracy and sensitivity.
Implementation Method 1
A first movable element, referred to herein as a first proof mass, and a second movable element, referred to herein as a second proof mass, are positioned in spaced apart relationship above planar surface 28 of substrate 26
Implementation Method 2
Capacitive accelerometers sense a change in electrical capacitance, with respect to acceleration, to vary the output of an energized circuit
Data Source
Figure 1~2
Figure 3~4
AI summary
A microelectromechanical systems (MEMS) sensor (20) includes a substrate (26) and suspension anchors (34, 36) formed on a planar surface (28) of the substrate (26). The MEMS sensor (20) further includes a first movable element (38) and a second movable element (40) suspended above the substrate (26). Compliant members (42, 44) interconnect the first movable element (38) with the suspension anchor 34 and compliant members (46, 48) interconnect the second movable element (40) with the suspension anchor (36). The movable elements (38, 40) have an equivalent shape. The movable elements may be generally rectangular movable elements (38, 40) or L-shaped movable elements (108, 110) in a nested configuration. The movable elements (38, 40) are oriented relative to one another in rotational symmetry about a point location (94) on the substrate (26).