Capacitive humidity sensors based on zinc oxide nanorods grown on silicon nanowires arrays at room temperature

Silicon nanowires (SiNWs) with a length of about 8 μm and zinc oxide nanorods (ZnONRs) with a length of about 200 nm were prepared by wet chemical etching and chemical bath deposition, respectively. Capacitive humidity sensors based on ZnONRs/SiNWs were fabricated and their humidity sensing properties were examined at room temperature (∼25°C). The largest response range of the sensors is 2.40-64.40 nF when the relative humidity (RH) changes from 11.30 to 97.69%. The sensitivity is 0.69 nF/% RH. The longest response and recovery time is ∼26 and 7 s, respectively, which corresponding to 97.69% RH. The sensors are proven to have long-term stability, with a maximum relative standard deviation (RSD) of 2.93% corresponding to 11.30% RH during about one month at room temperature in air. ZnONRs/SiNWs are a better ideal capacitive humidity sensing material compared to those we previously reported. It might be easy to miniaturize and compatible with traditional integrated circuit (IC) process.