Depression of a capacitive-type humidity sensor’s drift by introducing a cross-linked structure in the sensing polymer

A capacitive-type humidity sensor based on a poly(methyl methacrylate) (PMMA) cross-linked with divinylbenzene (DVB) was fabricated. We examined the influence of introducing a cross-linked structure in the sensing polymer on the long-term stability of the sensor in a hot and humid atmosphere. As the DVB content increased, the irreversible increase in the water sorption ability of the cross-linked PMMA by long-term aging in a 40 °C and 90% RH atmosphere was depressed. This was because the irreversible increase in volume of the sensing polymer caused by swelling in such atmosphere was prevented due to the rigid cross-linked structure. The depression of the drift of the water sorption ability resulted in the depression of the drift of the sensor capacitance.