Fused Quartz Dual-Shell Resonator for Shock-Stable Gyroscopes
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Solution Overview
Problem
Conventional MEMS gyroscopes face issues with microcracks and fracture in high-stress environments due to mechanical stresses during high-spin and shock events, leading to reduced dynamic pull-in stability and snap-down of resonant structures.
Innovation Solution
A dual-shell resonator structure with a co-fabricated outer cap shell and inner device shell, sharing a common stem, is formed using triple-stacked wafers and high-temperature glassblowing, providing a fixed-fixed anchor for improved shock survivability and vibration resistance, with capacitive excitation and detection capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional resonator structures are used in high-performance applications, then the device can operate in dynamic environments, but mechanical stresses during high-spin and shock events cause microcracks and fracture in high-stress concentration locations
Solution Approach 1:
The resonator is divided into two separate shells (inner device shell and outer cap shell) that are co-fabricated but structurally distinct. This segmentation allows each shell to independently handle stress loads, preventing stress concentration at single critical points and eliminating the microcrack propagation paths found in conventional single-shell structures.
Solution Approach 2:
The dual-shell structure creates a composite mechanical system where the inner and outer shells work together to distribute and manage mechanical stresses. The configuration provides fixed-fixed anchoring that creates a more robust stress distribution pattern, reducing peak stress concentrations that lead to fracture in conventional resonators.
2Ease of operation
If conventional resonator structures are used, then the device can function in dynamic environments, but external shocks and vibrations reduce the threshold of dynamic pull-in stability and cause snap-down of the resonant structure
Solution Approach 1:
By separating the resonating mass (inner shell) from the protective enclosure (outer shell), the structure isolates the resonant elements from direct shock loads. The segmentation allows the inner shell to maintain its vibrational integrity while the outer shell absorbs and distributes external mechanical disturbances, preventing snap-down.
Solution Approach 2:
The outer cap shell acts as a protective cushion that absorbs and dissipates shock energy before it can reach the inner resonant structure. This prior cushioning effect raises the threshold for dynamic pull-in events by pre-absorbing mechanical energy that would otherwise cause instability.
3Ease of manufacture
If limited bonding surfaces are used in resonator configuration, then the fabrication process is simplified, but weak points are created that reduce structural integrity
Solution Approach 1:
The co-fabrication process merges the formation of inner and outer shells into a single integrated manufacturing step using triple-stacked wafers. This combining of operations maintains fabrication simplicity while the resulting dual-shell structure provides enhanced structural integrity through multiple bonding interfaces distributed throughout the device.
Solution Approach 2:
The triple-stacked wafer configuration adds a vertical dimension to the fabrication process, stacking multiple wafer layers before bonding. This dimensional approach allows multiple bonding surfaces to be created simultaneously during a single fabrication sequence, maintaining ease of manufacture while significantly improving structural integrity through distributed bonding.
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 dual-shell resonator structure enhances mechanical integrity and reduces vibration sensitivity, enabling operation in harsh environments with improved shock survivability and maintaining sensor stability.
Implementation Method 1
The outer cap shell, inner device shell and common stem are formed by triple stacked wafers with concentric cavities... The outer cap shell, inner device shell and stem are co-fabricated by high-temperature glassblowing of the triple-stacked wafers
Implementation Method 2
The inner device shell includes a portion configured to vibrate within the outer cap shell... the inner device shell is configured to operate using at least one of capacitive excitation and detection relative to the substrate layer
Implementation Method 3
The outer rim of the cap shell and a base of the inner stem are each configured to be fixed to a substrate layer and to provide an anchor for the inner device shell
Data Source
AI summary
A dual-shell architecture and methods of fabrication of fused quartz resonators is disclosed. The architecture may include two encapsulated and concentric cavities using plasma-activated wafer bonding followed by the high-temperature glassblowing. The dual-shell architecture can provide a protective shield as well as a “fixed-fixed” anchor for the sensing element of the resonators. Structures can be instrumented to operate as a resonator, a gyroscope, or other vibratory sensor and for precision operation in a harsh environment. Methods for fabricating a dual-shell resonator structure can include pre-etching cavities on a cap wafer, pre-etching cavities on a device wafer, bonding the device wafer to a substrate wafer to form a substrate pair and aligning and bonding the cap wafer to the substrate pair to form a wafer stack with aligned cavities including a cap cavity and a device cavity. The wafer stack may be glassblown to form a dual-shell structure.