On-chip integrated NDIR CO₂ gas sensor

Area of Science:

• Microelectromechanical systems (MEMS)
• Infrared spectroscopy
• Sensor technology

Background:

• Portable CO2 monitoring requires miniaturized, rapid-response sensors.
• Conventional NDIR sensors face limitations in size, response time, and stability due to discrete components.

Purpose of the Study:

• To develop an on-chip integrated NDIR CO2 sensor with enhanced performance for portable applications.
• To overcome the trade-offs associated with conventional NDIR sensor designs.

Main Methods:

• Monolithic integration of a MEMS infrared emitter and thermopile detector on a silicon substrate.
• Co-optimization of optical chamber and device layout using radiative transfer and thermal coupling principles.
• Adoption of an orthogonal optical-gas path configuration.

Main Results:

• Achieved an effective optical path length of 11 mm with 91.8% optical coupling efficiency.
• Developed a highly compact sensor module (< 21mm x 10mm x 5mm).
• Demonstrated a response time of ~3s, power consumption of 31mW, and a detection limit of 146 ppm.
• Maintained stable performance across wide temperature and humidity ranges.

Conclusions:

• The on-chip integration approach significantly reduces sensor footprint without sacrificing performance.
• This technology offers a promising solution for advanced portable CO2 monitoring systems.
• Enables applications in wearable respiratory monitoring and environmental sensing.