Patterned multiwall carbon nanotube films as materials of NO2 gas sensors

Multiwall carbon nanotube (MWNT) films grown by thermal chemical vapor deposition on a micromachined substrate with a chrome heater and a diaphragm have been investigated as sensing materials of resistive gas sensors for nitrogen dioxide (NO2). We fabricated the aligned MWNT films, which grew into mesh and serpentine shapes by photolithography. Photolithography patterned the cobalt catalyst layer. MWNT films showed a p-type electrical resistivity with decreasing electrical resistance upon exposure to NO2. The sensor exhibited a reversible response at a thermal treatment temperature of 130 °C for a time constant of a few minutes. The resistance change to NO2 of the mesh-shaped MWNT films was found to be larger than that of the serpentine-shaped MWNT films.