Bifilar Flexure Laser Thinning for Precise Accelerometer Hinges
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Solution Overview
Problem
The existing wet etch process for fabricating accelerometer proof mass hinges is challenging due to variability in etch rate, temperature, and contamination, making it difficult to achieve consistent results.
Innovation Solution
A femtosecond laser-based ablation process is used to thin the bifilar flexure regions, allowing for precise control of laser power and raster pattern, minimizing damage and ensuring reproducibility and high controllability in achieving the desired hinge thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wet etch process is used to thin the proof mass hinges, then the etch rate is high, but the manufacturing precision deteriorates due to variability in etch rate, temperature, and contamination
Solution Approach 1:
The patent replaces the chemical wet etch process with a laser ablation process. The laser beam directly ablates the quartz material to thin the hinges, eliminating the need for chemical etchants and photoresist processing. This substitution of chemical-mechanical process with a direct energy-based process provides precise control over material removal, achieving both high productivity and manufacturing precision.
Solution Approach 2:
The patent changes the fundamental process parameter from chemical etching to laser ablation. By controlling laser power, pulse duration, and scanning speed, the process achieves precise control over hinge thickness. The laser parameters can be dynamically adjusted to maintain consistent etching rates without the variability inherent in wet etch processes, directly addressing the manufacturing precision issue.
2Device complexity
If wet etch process is used, then the process is simple, but the reliability deteriorates due to difficulty in stopping at optimum hinge thickness
Solution Approach 1:
The laser ablation process replaces the multi-step wet etch process (photoresist coating, exposure, development, etching, stripping) with a direct material removal process. The laser system provides real-time control over the etching depth through programmable scanning patterns and power modulation, eliminating the reliability issues associated with determining the optimal stop point in wet etching.
Solution Approach 2:
The laser ablation process incorporates feedback mechanisms through programmable control systems that monitor and adjust laser parameters during the thinning process. The translation stage and laser scanning system can be controlled to achieve precise thickness reduction based on pre-programmed paths, ensuring consistent results and reliable stopping at the desired hinge thickness.
3Productivity
If high laser power is applied to thin the flexure arms quickly, then the productivity is high, but the harmful factors increase due to laser damage to surrounding areas
Solution Approach 1:
The patent employs periodic pulsed laser action rather than continuous high-power irradiation. By using short laser pulses with appropriate duty cycles, the process removes material efficiently while allowing thermal diffusion between pulses, preventing heat accumulation and damage to surrounding areas. This periodic action maintains high productivity while minimizing harmful thermal effects.
Solution Approach 2:
The laser beam is focused to a small spot size and scanned along precise paths only where material removal is needed. The translation stage positions the sample so that the laser acts locally on the flexure arm surfaces requiring thinning, leaving surrounding areas unaffected. This localized processing achieves high productivity in the target zones without causing damage to other regions.
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 laser ablation process replaces the wet etch process, providing highly reproducible and controlled thinning of proof mass hinges, reducing damage to surrounding areas and achieving strong, precise hinges with minimal variability, thereby improving the fabrication of accelerometer proof masses.
Implementation Method 1
a femtosecond laser optically coupled to the translation stage with focusing optics, the femtosecond laser applying a laser beam on the flexure arms over a plurality of passes to gradually thin the bifilar flexure regions
Data Source
AI summary
A system for producing a proof-mass assembly includes a translation stage to receive a flapper hingedly supported by a bifilar flexure that extends radially inwardly from a support ring, wherein the bifilar flexure comprises a pair of flexure arms spaced apart by an opening or window; and a femtosecond laser optically coupled to the translation stage with focusing optics, the femtosecond laser applying a laser beam on the flexure arms over a plurality of passes to gradually thin the bifilar flexure regions, the laser periodically reducing a laser output to minimize damage from laser scanning and maximize bifilar flexure strength until the bifilar flexure reaches a predetermined thickness.