Characterizations of contact and sheet resistances of vertically aligned carbon nanotube forests with intrinsic bottom contacts

Comprehensive studies on the sheet and contact resistances of vertically aligned carbon nanotube (CNT) forests with as-grown bottom contacts to the metal layer have been conducted. Using microfabrication and four distinct methods: (1) the transfer length method (TLM), (2) the contact chain method, (3) the Kelvin method, and (4) the four point probe method, we have designed multiple testing devices to characterize the resistances of CNT-forest-based devices. Experimental results show that devices based on stripe-shaped CNT forests 100 μm in height and 100 μm in width have a sheet resistance of approximately 100Ω/□. The corresponding specific contact resistance to the molybdenum layer is roughly 5 x 104 Ω μm2. Consistency of the results from the four different methods validates the study. After two months of storage of the CNT forest samples in open air, less than 0.9% deviations in the resistance values were observed. We further demonstrated one application of CNT forests as an NH3 gas sensor and measured 0.5 ppm of sensing resolution with a detection response time of 1 min.