Printed Carbon Nanotube-Based Humidity Sensors Deployable on Surfaces of Widely Varying Curvatures

In this paper, we demonstrate the humidity-sensing ability and the robustness of our syringe-printed single-walled carbon nanotube- graphene oxide (SWCNT-GO) traces on adhesive and flexible poly(ethylene terephthalate) (PET) thin films. The printed traces, which exhibited humidity sensing by undergoing a change in resistance with the relative humidity, showed a high humidity sensitivity (S, where S can be as high as 1.5%). At the same time, the flexible and adhesive nature of thin PET films ensures that these traces are deployable on surfaces with different curvatures. The humidity sensitivity of our SWCNT-GO traces is over 2 times greater than the pure SWCNT networks: we propose that the hygroscopic swelling of GO flakes under humid conditions is responsible for this enhanced humidity sensitivity. Furthermore, the printed traces demonstrated that even after being subjected to hundreds of hours of long-term stability tests, their humidity -sensing capabilities remained intact. Furthermore, these traces withstood over 2200 cycles of temperature cycling reliability tests without any failures or significant degradation in their electrical performances. Therefore, these SWCNT-GO traces printed on thin, flexible, and adhesive PET films demonstrate excellent potential for being used as highly reliable humidity sensors, which are ultrathin, sensitive, and can be on surfaces of various curvatures.