Microheater-integrated single gas sensor array chip fabricated on flexible polyimide substrate

A microheater-integrated sensor substrate for the single 16-channel sensor array chip was prepared from a polyimide film by modifying the fabrication processes used in the flexible printed circuit technology. Conductive copper layers were patterned to form interdigitated detection electrodes and a resistive heating line at front and backsides, respectively. The microheater was found to have the power consumption of 1.35 mW mm−2 at an operation temperature of 40 °C and was possible to act as a thermometer, simultaneously, possessing the temperature coefficient of resistance of 37 × 10−4 °C−1. Vapor-sensing materials were deposited on the detection electrodes by casting of carbon black–polymer composite solutions. Their ethanol-sensing characteristics have been investigated carefully as a function of the analyte concentration and the operation temperature. The response magnitude linearly intensified with increasing the ethanol concentration in the wide range of 60–8000 ppm in air and generally decreased as the operation temperature goes from 22 to 60 °C. This temperature dependence could be explained with the variation in analyte solubility induced by the thermodynamic enthalpy change during the sensing process. By using the sensor array chip and the principal component analysis, classification was successfully made among the three different volatile organic compounds of ethanol, toluene and benzene.