Ultra-Thin SiC Resonator Fabrication Without Voids or Delamination
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Solution Overview
Problem
Current methods for fabricating MEMS resonators from single-crystalline silicon carbide (SiC) face challenges in achieving high-quality, ultra-thin resonators due to issues like void formation during annealing and delamination of thin metal films, which hinder the production of high-performance devices for applications such as phononic gyroscopes and RF technology.
Innovation Solution
The method involves grinding and polishing a bulk single-crystalline SiC wafer to an ultra-thin thickness, suspending it with an interposer film comprising plasma-enhanced chemical vapor deposition (PECVD) and thermal oxides to prevent void formation and delamination, and patterning thin metal films on both sides for actuation, while using specific etching techniques to maintain the integrity of the resonator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional fabrication methods are used to create ultra-thin SiC resonators, then thin metal films can be deposited, but void formation and delamination occur during annealing
Solution Approach 1:
A suspended membrane structure is introduced as an intermediary between the SiC layer and the substrate. This membrane prevents direct contact between the thin metal films and the substrate during annealing, eliminating the thermal stress that causes void formation and delamination while still allowing the resonator to function.
Solution Approach 2:
The structure is segmented into distinct functional layers: the SiC resonator layer, the suspended membrane support structure, and the substrate. This segmentation allows the membrane to independently accommodate thermal expansion differences between layers during annealing, preventing stress-induced defects.
2Speed
If bulk SiC wafers are thinned to ultra-thin dimensions, then high-frequency performance is achieved, but yield decreases due to fabrication defects
Solution Approach 1:
The suspended membrane structure is prepared in advance during fabrication, creating a protective framework before the thinning and annealing processes. This preliminary structure prevents defect formation during subsequent high-frequency optimization steps, maintaining both performance and yield.
3Ease of operation
If thin metal films are patterned on both sides of the SiC resonator, then actuation performance is improved, but delamination risk increases
Solution Approach 1:
The suspended membrane acts as an intermediary support structure that bears the mechanical stress of thin metal film deposition on both sides of the SiC resonator. This prevents direct stress concentration at the metal-SiC interfaces, eliminating delamination while preserving actuation performance.
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 approach enables the production of high-quality, ultra-thin SiC resonators with improved yield and performance, capable of achieving navigation-grade performance in gyroscopes and high-frequency stability in RF applications, overcoming previous barriers in MEMS resonator fabrication.
Implementation Method 1
suspending it with an interposer film comprising plasma-enhanced chemical vapor deposition (PECVD) and thermal oxides
Implementation Method 2
suspending it with an interposer film comprising plasma-enhanced chemical vapor deposition (PECVD) and thermal oxides
Implementation Method 3
grinding and polishing a bulk single-crystalline SiC wafer to an ultra-thin thickness
Data Source
AI summary
A method of making a SiC resonator includes forming a layer of an oxide material on a relatively thick wafer of SiC; bonding the layer of oxide material on the relatively thick wafer of SiC to a handle wafer having at least an oxide exterior surface, the resulting bond being substantially free of voids; planarizing the relatively thick wafer of SiC to a desired thickness; forming top and bottom electrodes on the wafer of SiC wafer to define a SiC wafer resonator portion; and forming a trench around the top and bottom electrodes, the tench completely penetrating the planarized wafer of SiC around a majority of a distance surrounding said top and bottom electrodes, except for one or more tether regions of the planarized wafer of SiC which remain physically coupled a remaining portion the SiC wafer resonator portion which defines a frame formed of the planarized wafer of SiC surrounding the SiC wafer resonator portion.