Reduced-Height Alignment Electrodes for MEMS Gyroscope Mode Alignment
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Solution Overview
Problem
Bulk Acoustic Wave (BAW) vibratory planar gyroscopes face challenges in aligning nodes and antinodes due to non-degenerate in-plane and out-of-plane resonance modes, leading to quadrature errors that are difficult to compensate for using existing methods.
Innovation Solution
A novel in-plane electrode configuration with alignment electrodes of reduced height, typically half the height of the resonant body, is used to align both in-plane and out-of-plane modes, allowing for electrostatic force application at a 45° angle to simultaneously affect both modes, simplifying the fabrication process and improving alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional full-height electrodes are used for mode alignment, then the alignment mechanism works for degenerate modes, but it cannot effectively align non-degenerate in-plane and out-of-plane modes in BAW vibratory planar gyroscopes
Solution Approach 1:
The patent applies local quality by using electrodes of different heights tailored to specific functional requirements. Full-height electrodes (extending through the resonant body thickness) are used for in-plane mode actuation and sensing, while reduced-height electrodes (not extending through the full thickness) are used for out-of-plane mode actuation. This differential electrode height configuration enables selective coupling to different vibration modes, allowing effective mode alignment in non-degenerate BAW vibratory planar gyroscopes where traditional uniform electrodes fail.
2Measurement precision
If compensatory mechanisms are used to align nodes and antinodes, then quadrature error is reduced, but the fabrication process becomes more complex and difficult to implement
Solution Approach 1:
The patent implements preliminary action by pre-aligning the major axes of the in-plane and out-of-plane modes during the fabrication process itself, rather than requiring post-fabrication compensatory adjustments. The reduced-height electrodes are strategically positioned and dimensioned during manufacturing to automatically correct for misalignment between modes. This built-in alignment mechanism eliminates the need for complex external compensatory mechanisms and simplifies the overall fabrication process while achieving low quadrature error.
3Manufacturing precision
If smaller reduced-height electrodes are used for mode alignment, then alignment precision improves, but the drive amplitude is limited
Solution Approach 1:
The patent applies segmentation by dividing the electrode system into distinct functional groups with different heights: full-height electrodes for in-plane mode actuation and reduced-height electrodes for out-of-plane mode actuation. This segmented configuration allows each electrode type to be optimized for its specific function - the reduced-height electrodes provide precise alignment control for out-of-plane modes, while the full-height electrodes deliver the necessary drive amplitude for in-plane modes. The synergistic combination of these segmented electrode structures resolves the trade-off between alignment precision and drive amplitude.
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 effectively reduces quadrature errors, enabling better performance and higher yields by aligning resonance modes and allowing for larger drive amplitudes in BAW vibratory planar gyroscopes.
Implementation Method 1
alignment of in-plane electrodes is achieved by utilizing alignment electrodes that have a height less than the full height of the gyroscope resonant body. Similar to tilted 45° electrodes, such electrodes can apply a force component along 45° to the gyroscope that can affect modes with both in-plane and out-of-plane movements
Data Source
AI summary
A MEMS BAW vibratory planar gyroscope having an in-plane electrode configuration for mode-alignment by utilizing alignment electrodes that have a height less than a full height of the gyroscope resonant body. Such alignment electrodes apply a force component that affects modes with both in-plane and out-of-plane movements. The gyroscope includes a resonant body having a height and a perimeter surface and electrodes disposed adjacent the exterior perimeter surface of the resonant body. At least one of the electrodes is an alignment electrode and has a height less than the height of the resonant body.