MEMS Cavity Electrode Structure for Precise Frequency Tuning
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Solution Overview
Problem
Existing MEMS gyroscope designs face challenges in precise frequency adjustment due to the bulkiness and imprecision of parallel plate combs and additional processing steps required for metal electrodes, leading to susceptibility to external forces and variations in electrostatic forces needed for frequency tuning.
Innovation Solution
The introduction of cavity electrodes within a supporting structure wafer, such as the handle wafer, allows for stable and precise frequency adjustment of oscillation frequencies in microelectromechanical devices, reducing susceptibility to packaging distortions and enabling precise control of resonance frequencies without increasing silicon area or requiring additional processing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If parallel plate combs are used for frequency adjustment, then frequency tuning capability is provided, but the device becomes bulky and imprecise
Solution Approach 1:
The patent transitions from planar parallel plate combs to three-dimensional cavity electrodes formed within the handle wafer substrate. This vertical integration into the substrate dimension allows frequency adjustment functionality to be embedded without increasing the device's planar footprint, resolving the contradiction between precision tuning capability and compact size.
Solution Approach 2:
The cavity electrodes are nested within the handle wafer substrate, with cavities formed inside the substrate volume and electrodes positioned within these cavities. This nesting approach embeds the frequency adjustment mechanism within the existing device structure, eliminating the need for additional external components and reducing overall device volume while maintaining tuning precision.
2Manufacturing precision
If metal electrodes are added to the cap wafer, then frequency adjustment is enabled, but additional processing steps are required
Solution Approach 1:
The frequency adjustment electrodes are merged with the handle wafer substrate by forming cavities and electrodes directly within the substrate material using existing semiconductor processing techniques. This integration eliminates the need for separate metal electrode deposition and bonding steps on the cap wafer, reducing manufacturing process complexity while maintaining frequency tuning capability.
Solution Approach 2:
The handle wafer substrate serves dual functions: providing mechanical support and housing the frequency adjustment electrodes within its cavities. This self-service approach allows the substrate to provide its own frequency tuning functionality without requiring additional external components or complex assembly processes, simplifying manufacturing.
3Force
If traditional frequency adjustment methods are used, then electrostatic force can be applied, but susceptibility to external forces increases
Solution Approach 1:
The electrostatic force application is moved from the planar cap wafer interface to the vertical cavity structure within the handle wafer. This three-dimensional configuration provides mechanical shielding and structural rigidity that reduces susceptibility to external forces and packaging distortions, while maintaining the electrostatic force mechanism for frequency adjustment.
Solution Approach 2:
The cavity structure within the handle wafer provides mechanical cushioning and isolation for the frequency adjustment electrodes before external forces are applied. This pre-established protective structure reduces the impact of external forces and packaging distortions on the electrostatic force application, improving reliability.
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 enhances the quality factor of out-of-plane motion and prevents unwanted contacts between electrodes, allowing for precise frequency adjustment and improved sensitivity in MEMS gyroscope designs.
Implementation Method 1
The cavity electrode, when having a different electrical potential than the movable electrode, applies an electrostatic force to the movable electrode, which frequency adjusts an oscillation frequency of the functional element
Data Source
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AI summary
A microelectromechanical device structure comprises a supporting structure wafer (310). A cavity electrode (130) 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 (300), 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.