A Vertically Aligned Multiwall Carbon Nanotube-Based Humidity Sensor with Fast Response, Low Hysteresis, and High Repeatability

We present a vertically aligned multiwall carbon nanotube (VA-MWCNT) based humidity sensor with low cost and simple fabrication method compatible with mass production. The VA-MWCNT is well aligned and possesses an interconnect topography. Initially, the VA-MWCNT showed superhydrophobic characteristics, which are not suitable for humidity sensing. Therefore, to protect the topography of the material and make the surface more hydrophilic, a low cost and easy handling treatment method was adopted with O2 plasma surface functionalization. The fabricated device showed good linearity at the range of 40% RH-90% RH, low hysteresis (H = 1.5%RH), fast response (3.3 s), high stability (Cv < 0.04%), and high repeatability (Rr_max <0.6%), demonstrating excellent performance in both static and dynamic measurements. The high performance and low-cost fabrication methods make the VA-MWCNT-based sensor a promising candidate for the application of humidity sensing. Moreover, benefiting from the simple fabrication process, it can be easily extended to resistive sensing fusion with the integration of the temperature sensor and flow sensor for more complex applications.