Cavity Electrode Structure for Precise MEMS Gyroscope Frequency Tuning
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Solution Overview
Problem
Existing microelectromechanical gyroscope designs face challenges in accurately adjusting oscillation frequencies due to non-ideal manufacturing processes, leading to deviations in primary and secondary oscillation frequencies, which affects sensitivity and precision, and current methods like parallel plate combs and metal electrodes are bulky, imprecise, and susceptible to external distortions.
Innovation Solution
The introduction of cavity electrodes within a supporting structure wafer, which are electrically connected and adjustable, allowing for precise frequency adjustment of mechanical oscillations in microelectromechanical devices by changing the electrical potential between the cavity electrodes and movable electrodes, thereby improving the quality factor of out-of-plane motion and reducing the risk of electrode contact or sticking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If parallel plate combs or metal electrodes are used for frequency adjustment, then frequency adjustment capability is provided, but the device becomes bulky and imprecise
Solution Approach 1:
The cavity electrode is nested within the supporting structure wafer, utilizing the existing wafer volume to house the electrode structure. This eliminates the need for external bulky electrodes while maintaining frequency adjustment capability through the cavity design that fits within the wafer's internal space.
Solution Approach 2:
The invention transitions from planar electrode arrangements to a three-dimensional cavity structure within the wafer. By utilizing the vertical dimension and creating a cavity that extends into the wafer thickness, the design achieves precise frequency adjustment without increasing the device's planar footprint.
2Adaptability or versatility
If metal electrodes are placed on the cap wafer, then frequency adjustment is enabled, but the structure becomes susceptible to packaging distortions
Solution Approach 1:
The cavity electrode is merged with the supporting structure wafer, forming an integrated structure where the electrode is part of the wafer itself rather than a separate component. This integration ensures that the electrode moves with the wafer during packaging, eliminating relative motion and susceptibility to packaging-induced distortions.
Solution Approach 2:
The cavity structure acts as an intermediary between the frequency adjustment function and the external environment. By providing a controlled internal cavity space, the design isolates the electrode from external packaging stresses while maintaining the ability to adjust frequency through electrical potential changes.
3Adaptability or versatility
If frequency adjustment is implemented using conventional methods, then oscillation frequency can be modified, but the quality factor of out-of-plane motion decreases
Solution Approach 1:
The cavity electrode is positioned to create a localized electrostatic field that specifically affects the out-of-plane motion mode. By concentrating the frequency adjustment influence on the desired motion mode while minimizing interference with other modes, the design maintains high quality factor for out-of-plane motion while achieving frequency adjustability.
4Device complexity
If functional elements are placed close to the supporting structure wafer, then device integration is improved, but the risk of electrode contact or sticking increases
Solution Approach 1:
The cavity structure is pre-formed in the supporting structure wafer before final assembly, establishing a fixed geometric relationship between the cavity electrode and the functional layer. This preliminary structuring ensures adequate clearance is maintained throughout operation, preventing contact or sticking while achieving high integration.
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 solution provides a stable and precise frequency adjustment mechanism that is less susceptible to packaging distortions, enhances the quality factor of out-of-plane motion, and allows for flexible placement of functional elements without electrical contact, improving the overall performance and reliability of microelectromechanical sensors like gyroscopes.
Implementation Method 1
The cavity electrode and the movable electrode form together a parallel plate capacitor. The electrostatic force between the capacitor electrodes is primarily in the direction of the mode of oscillation that is to be adjusted.
Data Source
AI summary
A microelectromechanical device structure comprises a supporting structure wafer. A cavity electrode is formed within a cavity in the supporting structure wafer. The cavity electrode forms a protruding structure from a base of the cavity towards the functional layer, and the cavity electrode is connected to a defined electrical potential. The cavity electrode comprises a silicon column within the cavity in the supporting structure wafer, which is partially or entirely surrounded by a cavity. One or more cavity electrodes may be utilized for adjusting a frequency of an oscillation occurring within the functional layer.