A Miniaturised, Fully Integrated NDIR CO₂ Sensor On-Chip

Area of Science:

• Optoelectronics
• Integrated Photonics
• Gas Sensing Technology

Background:

• Accurate carbon dioxide (CO2) monitoring is crucial for environmental and industrial applications.
• Existing NDIR sensors often lack miniaturization and cost-effectiveness.
• Silicon photonics offers a platform for integrated optical sensing solutions.

Purpose of the Study:

• To develop and characterize a fully integrated NDIR CO2 sensor on a silicon chip.
• To assess the sensor's performance, including limit of detection and cross-sensitivity.
• To explore the potential for low-cost, miniaturized NDIR CO2 sensing.

Main Methods:

• Fabrication of an NDIR CO2 sensor using wafer bonding of silicon substrates.
• Integration of a mid-infrared (mid-IR) LED and two photodiodes.
• Utilizing an integrating cylinder with access waveguides for optical path.
• Experimental and numerical analysis of CO2 detection and water vapor cross-sensitivity.

Main Results:

• Achieved a limit of detection of approximately 750 ppm for CO2.
• Observed no significant water vapor interference in experimental tests.
• Numerical simulations confirmed negligible impact of water vapor absorption.
• Identified temperature fluctuations as a factor affecting long-term stability.

Conclusions:

• The integrated silicon NDIR CO2 sensor shows promising performance for gas detection.
• The design minimizes water vapor interference, enhancing reliability.
• Wafer-level fabrication and use of bare chip components suggest potential for low-cost, high-volume production.
• Further optimization is needed to address temperature-dependent stability for enhanced long-term performance.