Preparation of flexible resistive micro-humidity sensors and their humidity-sensing properties

A novel resistive-type micro-humidity sensor was constructed from an interdigitated micro-electrode on a flexible polyimide substrate of size 2.0 mm × 3.0 mm. The humidity-sensing film was composed of a thermal curable epoxy resin and photocurable polyelectrolyte and fabricated by screen printing process, followed by thermal and photocuring reaction. The humidity sensing characteristics of the flexible micro-humidity sensor were comparable with a sensor fabricated on a commercial alumina substrate. The micro-humidity sensor was found to have a sensitivity of 0.046 log Ω/%RH, a linearity of R2 = 0.990, a hysteresis of 1.48%RH, a response time of 65 s, and a temperature coefficient of 0.50%RH/°C. Bode diagrams and Nyquist plots for two samples (the micro-humidity sensor and the typical alumina-based sensor) were investigated to demonstrate the effect of sensor size and different substrates on humidity-sensing characteristics.