The Origins and Characteristics of the Threshold Voltage Variability of Quasi-Ballistic Single-Walled Carbon Nanotube Field-Effect Transistors

Ultra-scaled transistors based on single-walled carbon nanotubes are identified as one of the top candidates for future microprocessor chips as they provide significantly better device performance and scaling properties than conventional silicon technologies.  From the perspective of the chip performance, the device variability is as important as the device performance for practical applications.  Here we presents a systematic investigation on the origins and characteristics of the threshold voltage (V_T) variability of scaled quasi-ballistic nanotube transistors.   Analysis of experimental results from variable temperature measurement as well as gate oxide thickness scaling studies shows that the random variation from fixed charges present on the oxide surface close to nanotubes dominates the V_T variability of nanotube transistors.  The V_T variability of single-tube transistors has a figure of merit that is quantitatively comparable with that of current silicon devices; and it could be reduced with the adoption of improved device passivation schemes, which might be necessary  for practical devices incorporating multiple nanotubes, whose area normalized V_T variability becomes worse due to the synergic effects from the limited surface coverage of nanotubes and the nonlinearity of the device off-state leakage current, as predicted by the Monte Carlo simulation.