Facile quantification and identification for reducing gases over a wide concentration range

Abstract

Two dedicated methods for quantification and identification for metal oxide semiconductor gas sensors with a specific temperature cycled operation (TCO) are presented. Both are giving an estimate for a certain parameter of the sensor relaxation caused by a step from high to low temperature. In this relaxation a highly oxidized sensor surface is gradually reduced by gas. The relaxation parameter is evaluated by calculating the slope of the logarithmic conductance over time for small gas concentration or by an estimation of the relaxation time constant for high concentrations respectively. A linear calibration curve between the relaxation parameter and the gas concentration is found for carbon monoxide, hydrogen and ammonia in the concentration range from 10 ppb to 100 ppm. For benzene the relaxation depends in form of a power law (exponent 0.4-0.5) with the gas concentration. The results can be interpreted within the framework of a general model for TCO MOS sensors.