Carbon nanotube-enhanced capillary condensation for a capacitive humidity sensor

A capacitive humidity sensor is presented for moisture detection at room temperature. The sensor is fabricated by depositing multi-wall carbon nanotubes (MWCNTs) on one of the stainless-steel substrates. When compared to a sensor without CNTs, a CNT-enhanced sensor has an increase of 60-200% in capacitance response when the humidity is under 70% relative humidity (RH), and 300-3000% if the RH level goes over 70%. The performance is comparable to a commercial sensor from Honeywell, which is used as a benchmark throughout the experiments. Our results demonstrate that nano-materials like MWCNTs can naturally form networks of porous nano-structures, which can potentially realize a miniature capacitive humidity sensor with a higher sensitivity. The gain in performance is attributed to the capillary condensation effect.