Contact and sheet resisstances of carbon nanotube forest in gas sensing applications

Here we report a systematic study on the contact and sheet resistances of vertically aligned carbon nanotube (CNT) forest in gas sensing applications. Four different methods: (1) transfer length method (TLM), (2) contact chain method, (3) Kelvin method and (4) four-point probe method have been implemented. Experimental results show prototype CNT forest with the stripe-shape of 100 μm in height and 100 μm in width has a sheet resistance of 100 Ω/□ and contact resistance of less than 50 Ω for an area of 100×100 μm². Consistent measurement results from the four methods validate the reliability of this study. When such CNT samples were tested as resistor-based gas sensors, results show 0.5 ppm of NH₃ gas sensing resolution with a detection response time of one minute.