MEMS Resonator Anisotropic Stiffness Compensation
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Solution Overview
Problem
MEMS gyroscope and accelerometer devices face challenges due to anisotropic stiffness in their resonant members, leading to energy losses and false zero-rate output (ZRO) indications caused by fabrication imperfections and asymmetries, which affect their accuracy and reliability.
Innovation Solution
The resonant member is designed with a main body made of a single-crystal solid, featuring varying material stiffness in different radial directions, with optimized geometry to mimic isotropic behavior, and electrodes are arranged within apertures to compensate for anisotropic stiffness, ensuring minimal net momentum force and symmetrical capacitive channels to prevent ZRO effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resonant member is made using conventional fabrication processes, then manufacturing is easier and cost is reduced, but anisotropic stiffness and fabrication imperfections cause energy losses and false zero-rate output indications
Solution Approach 1:
The resonant member is intentionally designed with asymmetric geometry to compensate for the anisotropic stiffness of single-crystal silicon. By strategically placing apertures and varying the thickness distribution, the overall component stiffness becomes substantially isotropic, counteracting the inherent material anisotropy and eliminating false ZRO signals caused by asymmetric stress distribution.
Solution Approach 2:
The patent modifies the geometric parameters of the resonant member (aperture size, shape, and position; thickness variations) to change the stress distribution and stiffness characteristics. These parameter adjustments transform the anisotropic single-crystal material into an effectively isotropic component, resolving the ZRO accuracy issue while maintaining compatibility with conventional MEMS fabrication processes.
2Measurement precision
If electrodes are positioned closer to the resonant member to improve sensing capability, then measurement precision improves, but capacitive coupling asymmetries increase causing false ZRO indications
Solution Approach 1:
Apertures are extracted from the resonant member body at strategic locations to accommodate electrodes. This creates symmetrical capacitive coupling paths between the electrodes and the resonant member, ensuring that electrostatic forces are evenly distributed and preventing false ZRO indications while maintaining close electrode-resonant member spacing for high sensing precision.
3Reliability
If the resonant member geometry is optimized to compensate for anisotropic stiffness, then component stiffness becomes isotropic and ZRO accuracy improves, but device complexity increases
Solution Approach 1:
The resonant member incorporates apertures (porous structure) within its body to adjust the stress distribution and stiffness characteristics. These apertures are strategically positioned to counterbalance the anisotropic stiffness of the single-crystal silicon, creating an effectively isotropic component without requiring complex external structures or 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 design minimizes energy losses and false indications of rotation, enhancing the accuracy and reliability of MEMS devices by making their component stiffness substantially isotropic and reducing the impact of fabrication imperfections.
Implementation Method 1
If the resonant member 112 is rotated, the Coriolis Effect will transfer energy from the drive mode to the sense mode and cause the resonant member 112 to vibrate in the sense mode
Implementation Method 2
Each electrode 118 is capacitively coupled to the resonant member 112. More specifically, the resonant member 112 has a plurality of capacitive surface portions 122 that each face and are capacitively coupled to an associated capacitive surface portion 128 of an electrode 118. A capacitive channel 130 is thereby defined between the resonant member 112 and each electrode 118.
Data Source
AI summary
A sensing device includes an anchor having a central axis that defines a first radial direction and a second radial direction, and a resonant member flexibly supported by the anchor that includes a main body made of a single-crystal solid. The main body has a first material stiffness in the first radial direction and a second material stiffness in the second radial direction that is less than the first material stiffness. Moreover, the main body has a first component stiffness in the first radial direction and a second component stiffness in the second radial direction that is substantially similar to the first component stiffness. Another sensing device includes a resonant member having a main body that defines an aperture extending through the main body, and an electrode located in the aperture such that a capacitive channel is defined between the electrode and the main body that circumscribes the electrode.