Miniaturized CO₂ Gas Sensor Using 20% ScAlN-Based Pyroelectric Detector

Area of Science:

• Materials Science
• Sensor Technology
• Infrared Spectroscopy

Background:

• Non-dispersive infrared (NDIR) CO2 sensors previously achieved detection limits of 25 ppm.
• Existing sensors utilized 10-cm gas channels and 12% ScAlN pyroelectric detectors.
• Miniaturization and cost reduction are key goals for widespread CO2 monitoring.

Purpose of the Study:

• To develop a more compact and cost-effective CO2 gas sensor.
• To investigate the performance of 20% ScAlN pyroelectric detectors in miniaturized NDIR sensors.
• To assess the sensor's response time, detection limits, and selectivity.

Main Methods:

• Fabrication of CMOS-compatible 20% ScAlN pyroelectric detectors on 8-in. wafers.
• Miniaturization of the gas channel to 4 cm length and 1 mm diameter (approx. 65x volume reduction).
• Characterization of detector properties including pyroelectric coefficient and optical absorption at 4.26 μm.
• Testing of CO2 gas response, detection limits, and selectivity against nitrogen and sulfur hexafluoride.

Main Results:

• The 20% ScAlN detectors exhibited abnormally oriented grains and higher pyroelectric coefficients compared to 12% ScAlN.
• The miniaturized sensor detected CO2 concentrations from 5000 ppm down to 100 ppm with a response time of ~5 s.
• High selectivity was demonstrated, with minimal signal change (<0.4%) when exposed to nitrogen or sulfur hexafluoride.

Conclusions:

• The developed miniaturized CO2 gas sensor shows potential for practical applications, including real-time air quality monitoring.
• The use of 20% ScAlN pyroelectric detectors and semiconductor manufacturing techniques enables cost reduction.
• Integration with consumer electronics for widespread environmental monitoring is a promising future direction.