Transparent MEMS Resonators via Ultrafast Laser Wet Etching
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Solution Overview
Problem
Existing methods for fabricating MEMS resonators, such as plasma etching, face limitations including complex processes, limited aspect ratios, and thermal stress issues due to heat generation and mismatched thermal characteristics with other materials.
Innovation Solution
The use of laser micromachining, specifically ultrafast-laser-induced modification followed by wet etching, to fabricate MEMS resonators from bulk optically transparent materials like fused silica, enabling the creation of resonators with ultra-high aspect ratios and improved thermal and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If plasma etching is used to fabricate MEMS resonators, then anisotropic etching with controlled etch profile is achieved, but device complexity increases due to multiple process steps and thermal stress issues arise from heat generation
Solution Approach 1:
The fabrication process is segmented into distinct functional modules: laser inscription unit, wet etching unit, and release unit. Each module performs a specific function independently, simplifying the overall process control while maintaining precision. The laser inscription creates precise 3D patterns, wet etching selectively removes material along predefined paths, and release separates the resonator from the substrate.
Solution Approach 2:
The patent replaces the plasma-based mechanical etching system with a laser-assisted wet chemical etching system. The ultrafast laser inscribes the resonator structure by modifying the material properties locally, and subsequent wet etching follows the inscribed paths. This substitution eliminates the complex plasma generation and control systems while achieving comparable or superior etching precision with reduced thermal stress.
2Manufacturing precision
If plasma etching is used to achieve high aspect ratios, then etch rate control is improved, but the maximum achievable aspect ratio is limited to below 10:1
Solution Approach 1:
The ultrafast laser performs preliminary action by inscribing the resonator structure and creating chemically modified pathways before the wet etching process. This pre-defined path guidance allows the wet etchant to follow precise trajectories deep into the substrate, achieving aspect ratios exceeding 10:1 without losing etch rate control. The laser inscription acts as a template that directs the subsequent chemical etching process.
Solution Approach 2:
The patent changes the fundamental parameters of the etching process by transitioning from plasma-phase to liquid-phase chemistry. Wet etching with appropriate chemical solutions provides different etching kinetics that are better suited for high aspect ratio structures. The laser-inscribed pathways modify the local chemical environment, enhancing etchant penetration depth and maintaining controlled etching rates throughout the entire etch depth, thereby achieving aspect ratios greater than 10:1.
3Ease of manufacture
If conventional laser micromachining is used on fused silica, then material processing is achieved, but surface damage occurs due to laser-induced cracks and material redeposition
Solution Approach 1:
The patent employs periodic pulsed laser action with carefully controlled duty cycles and pulse durations. The ultrafast laser delivers energy in short, intense pulses that allow the material to respond linearly and reversibly between pulses. This periodic delivery method prevents excessive heat accumulation and avoids the nonlinear optical effects that lead to cracking and redeposition. The间歇性 (intermittent) nature of the pulsing allows heat diffusion and stress relaxation between pulses.
Solution Approach 2:
The patent fundamentally changes the laser processing parameters by using ultrafast pulse durations (femtosecond to picosecond range) instead of continuous or long-pulse operation. This parameter change transforms the heating mechanism from thermal diffusion-dominated to localized nonlinear absorption. The ultrafast pulses deposit energy faster than heat can diffuse, creating highly localized modifications without significant thermal damage zones. This parameter transformation enables clean material processing without surface cracks or redeposition.
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 allows for the fabrication of MEMS resonators with high aspect ratios and low energy loss, enhancing their sensitivity and accuracy for applications in inertial sensing, time referencing, bio-sensing, and acoustic sensing, while avoiding thermal stress and surface damage issues.
Implementation Method 1
Femtosecond Laser-Induced Chemical Etching (FLICE) technology
Implementation Method 2
The resonator structure may then be subsequently defined and released through selective wet etching of the laser-modified areas
Data Source
AI summary
Systems, processes and devices are provided for laser-based manufacturing of resonators and MEMS devices from bulk material including optically transparent material. Processes include digital marking of resonator structures in bulk material through non-linear interaction of ultrafast laser beam inscribing and material. The resonator structure may be defined and released through selective wet etching of the laser-modified areas, utilizing a combination of basic and acidic aqueous solutions. Processes can also include hydrofluoric thinning prior to wet etching to prevent laser surface damages. Systems and processes can pattern and fabricate resonator structures and concentricring structures. Embodiments provide miniaturized vibratory sensors from low loss material, such as fused silica and quartz, with an improved resolution and accuracy of measurements for inertial sensing, time referencing, bio-sensing and acoustic sensing.