Fabrication of humidity sensors by multi-walled carbon nanotubes

Abstract

Humidity sensors have multi-walled carbon nanotubes (MWNTs) as the sensing material is demonstrated. The sensor was fabricated on a silicon dioxide coated silicon wafer with metal electrodes. MWNTs were deposited and interlinked with the electrodes by means of the dielectrophoresis technique. The sensing device has the function of a hygrometer when measuring resistance variations to the local relative humidity percentage (RH%) through MWNTs. By measuring the MWNT resistances, we find that higher RH% results in a decrease of conductivity. The results indicate that electron transports in MWNTs are affected by water molecules adsorption on the outermost nanotube surface. A miniature thermocouple sensor was also fabricated and integrated with the humidity sensor. This allowed us to simultaneously sense environmental humidity and temperature. Hence, accurate humidity measurements were achieved with this prototype by calibrating the electrical resistance and temperature levels to carry out the tests with the humidity percentages.