Potential Stable Low-Permeation Rate Standard Based on Micro-machined Silicon

Area of Science:

• Materials Science
• Chemical Engineering
• Metrology

Background:

• Developing accurate low-permeation-rate standard artifacts is crucial for precise environmental monitoring and material characterization.
• Polymer-based standards often suffer from long-term stability issues and reproducibility challenges.
• Micro-machined silicon wafers present a potential alternative due to their inherent material properties.

Purpose of the Study:

• To evaluate the suitability of micro-machined silicon wafers as standard artifacts for low permeation rate measurements.
• To assess the accuracy, stability, and reliability of silicon wafers in quantifying permeation.
• To compare the performance of silicon wafer standards against traditional polymer standards.

Main Methods:

• Two independent experimental techniques were employed: a chilled mirror hygrometer and a mass loss method.
• Silicon wafers with precisely engineered micro-machined holes were fabricated and tested.
• The relationship between hole area and water partial pressure was analyzed for both measurement techniques.

Main Results:

• A clear linear correlation was observed between the hole area of silicon wafers and the resulting water partial pressure, confirmed by both measurement methods.
• The mass loss technique showed a consistent offset compared to the chilled mirror hygrometer, attributed to O-ring seal leakage.
• Silicon wafers demonstrated superior long-term reproducibility in permeation rates compared to polymer standards.
• A significant drawback was the high fragility of the silicon wafers, leading to cracking during testing.

Conclusions:

• Micro-machined silicon wafers offer a stable and reproducible alternative for low permeation rate measurements, outperforming polymer standards in this regard.
• Despite their promising metrological properties, the inherent fragility of silicon wafers poses a significant challenge for their widespread adoption as standard artifacts.
• Further research into enhancing the mechanical robustness of silicon wafer standards is recommended to overcome their practical limitations.