Microgyroscope Symmetrical Assemblies for Bias Stability
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Solution Overview
Problem
Existing microgyroscopes face challenges in achieving high sensitivity, linearity, and bias stability while minimizing perturbations from excitation movements and static or dynamic accelerations, often requiring multiple wafers and complex assembly processes, which increases costs and introduces drift issues due to non-linearities and mass production variations.
Innovation Solution
A microgyroscope design featuring two symmetrical moving assemblies coupled by a mechanical structure, allowing vibration energy transfer in orthogonal directions, with interdigitated capacitive combs for excitation and detection, and additional electrical structures for frequency adjustment and bias compensation, enabling separate detection signals that vary inversely to cancel out parasitic effects and drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple wafers are used to detect movements perpendicular to the plane of moving masses, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent merges the excitation structure and detection structure onto a single silicon wafer, eliminating the need for multiple wafers. The detection electrodes are integrated directly on the same wafer as the vibrating masses, allowing detection of movements perpendicular to the plane without requiring separate wafer assemblies. This reduces device complexity while maintaining measurement precision.
Solution Approach 2:
The patent detects movements in a direction perpendicular to the plane of the moving masses by using electrodes positioned above each moving mass. This dimensional approach allows the detection of Coriolis force-induced movements without requiring the masses to move within the plane, solving the precision issue while staying on a single wafer.
2Measurement precision
If differential effect is employed to overcome non-linearities, then measurement precision is improved, but sensitivity to acceleration and drift increase
Solution Approach 1:
The patent employs asymmetrical detection structures with electrodes positioned at specific locations above the moving masses. The detection electrodes are arranged to detect movements in a direction perpendicular to the excitation direction, creating an asymmetrical detection scheme that is insensitive to accelerations collinear with the mass movement axis. This asymmetrical arrangement eliminates the drift issue while maintaining linearity.
Solution Approach 2:
The patent replaces the traditional differential detection method with a single-sided detection approach using electrodes above the masses. Instead of using differential detection that is sensitive to acceleration, the patent uses a detection mechanism that measures movement perpendicular to the plane, substituting the detection physics to eliminate acceleration sensitivity and drift.
3Measurement precision
If excitation movement along Ox axis is well separated from detection movement along Oy axis, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent separates excitation and detection movements by using orthogonal directions in the same plane. The excitation structure generates movement along the Ox axis while the detection electrodes measure movement along the Oy axis (perpendicular to the plane). This dimensional separation is achieved through the geometric arrangement of the comb structures and electrode positions, providing clear signal separation without requiring complex multi-wafer assemblies.
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 achieves high sensitivity, linearity, and bias stability with reduced perturbations, allowing accurate angular velocity measurements while minimizing the impact of excitation movements and accelerations, and compensating for intrinsic defects and production variations.
Implementation Method 1
an electrical excitation structure for making this mass vibrate in a defined direction
Implementation Method 2
When the gyroscope rotates about an axis called the sensitive axis of the gyroscope, perpendicular to this vibration direction, a Coriolis force is exerted on the mass
Implementation Method 3
the detection structure detects any movement perpendicular to the plane of the masses using electrodes placed above each moving mass
Data Source
AI summary
The invention relates to a microgyroscope, that is to say an inertial micromechanical sensor dedicated to the measurement of angular velocities, which is produced by micromachining techniques, and has a novel arrangement of the modules for measuring the movement of the vibrating masses. The gyroscope comprises two symmetrical moving assemblies (30, 50; 30′, 50′) that are coupled by a coupling structure (20, 20′, 22). Each of the two assemblies comprises a moving mass (30) surrounded by a moving intermediate frame (50). The frame (50) is connected to the coupling structure (20, 20′, 22) and can vibrate in two degrees of freedom in orthogonal directions Ox and Oy of the plane of the wafer. The mass (30) is connected, on one side, to the frame and, on the other side, to fixed anchoring regions (34, 36) via linking means (40-46; 52-58) that allow the vibration movement in the Oy direction to be transmitted to the mass without permitting any movement of the mass in the Ox direction. An excitation structure (70) is associated with the frame in order to excite its vibration along Ox. A movement detection structure (90) is associated with the mass (30) in order to detect its vibration along Oy.