Novel flexible resistive-type humidity sensor

A novel flexible resistive-type humidity sensor was fabricated through in situ co-polymerization of methyl methacrylate (MMA) and [3-(methacrylamino)propyl] trimethyl ammonium chloride (MAPTAC) copolymer on a polyester (PET) substrate. The activation energy for conduction and the copolymer/substrate interface were used to explain the differences of humidity sensing characteristics of the sensors fabricated on a PET substrate, in comparison with those fabricated on an alumina substrate.The humidity sensing characteristics of the flexible humidity sensor could be comparable with the sensor fabricated on an alumina substrate. The flexible humidity sensor showed acceptable linearity (Y = −0.0327X + 5.9345; R2 = 0.9351) between logarithmic impedance (log Z) and RH in the range of 10–90%RH, low hysteresis (within 6.1%RH), good response (45 s) and recovery time (150 s), and long-term stability (120 days at least), measured at 1 V, 1 kHz and 25 °C.