Amine-Functionalized Capacitive Carbon Dioxide Sensor Performance as a Function of Temperature and Sensing Film Thickness

This paper systematically investigates sensor performance of amine-functionalized, microfabricated capacitive carbon dioxide (CO
₂
) sensors as a function of sensor temperature and sensing film thickness. The sensor comprises a 1 mm by 1 mm interdigitated electrode structure with
$2~\mu \text{m}$
line width and
$2~\mu \text{m}$
line spacing, surrounded by a resistive temperature sensor and a resistive heater. A mixture of 3-aminopropyltrimethoxysilane and propyltrimethoxysilane was spray-coated onto the sensors and the CO
₂
response was measured in a gas mixing system. Using a 100 nm thick sensing film, a maximum sensor sensitivity of −1.2%/1,000ppm CO
₂
concentration was obtained with response times of 5-10 minutes at a sensor temperature of 85°C. The sensor sensitivity decreases for higher and lower temperatures while the sensor response time monotonically decreases with increasing sensor temperature. Thicker sensing films improve sensor sensitivity at the expense of a longer response time.