Detecting Volatile Organic Compounds in the ppb Range With Gas Sensitive Platinum Gate SiC-Field Effect Transistors

In this paper, the use of a platinum gate gas-sensitive SiC field-effect transistor (SiC-FET) was studied for the detection of low concentrations of hazardous volatile organic compounds (VOCs). For this purpose, a new gas mixing system was realized providing VOCs down to sub-parts per billion levels with permeation ovens and gas predilution. Benzene, naphthalene, and formaldehyde were chosen as major indoor air pollutants and their characteristics are briefly reviewed. Measurements have shown that the selected VOCs can be detected by the SiC-FET in the parts per billion range and indicate a detection limit of ~1 ppb for benzene and naphthalene and ~10 ppb for formaldehyde in humid atmospheres. For 10-ppb naphthalene at 20% r.h., the sensor response is high with 12 mV, respectively, a relative response of 1.4%. Even in a background of 2-ppm ethanol, the relative response is still 0.3%. Quantification independent of the humidity level can be achieved using temperature cycled operation combined with pattern recognition, here linear discriminant analysis. Discrimination of benzene, naphthalene, and formaldehyde is also possible.