Orange Dye Thin Film Resistive Hygrometers

S.A. Moiz1, H.S. Karimov2, N.D. Gohar1

1GIK Institute of Engineering Sciences and Technology, Topi 23460, NWFP, Pakistan

2Physical Technical Institute, Aini St. 299/1, Dushanbe, 734063, Tajikistan


An investigation on electrical properties of organic semiconductor, Orange Dye (OD), C17H17N5O2, resistive hygrometers was made in present study. Organic thin films were deposited on substrate by different thin film deposition methods, such as by vacuum evaporation method (Aluminum/Orange Dye/Aluminum), by spin-coater method from solution (Gold/Orange Dye/Gold), and in normal gravity condition by placing drops of OD solutions over the surface of tissue paper (Tin metal/Orange Dye in tissue paper/Net metal). As OD is also temperature sensitive, that is why to compensate temperature effect for the measurement of humidity dependent electrical properties, special arrangement was provided over the same substrate, but encapsulated from humidity environment.

The AC (frequency of 10 Hz) and DC resistances were evaluated from current-voltage characteristics of all samples of resistive hygrometers, measured in the temperature interval range of 20-70C and relative humidity range of 30-80%. It was observed that the resistance of the OD decreases with a rise in temperature. Similarly, OD resistance is observed to decrease with increase in humidity level. The relative resistance ratio to relative humidity was found 30 and 12 for the samples deposited by vacuum evaporation and from solution by spin coater respectively. Humidity dependent on electrical properties of these resistive hygrometer make them attractive for use in development of industrial humidity meters.