Modelling a CNTFET with Undeposited CNT Defects

The Carbon NanoTube Field Effect Transistor (CNTFET) is a promising device to supersede the MOSFET at the end of the technology roadmap of CMOS. When designing and manufacturing a CNTFET, additional features such as pitch, number and position of the CNTs must be considered to assess its performance. One of the defect types that can occur when fabricating a CNTFET, is the absence of some CNTs following the deposition/growth step. As result of this type of defect, a CNTFET will show a change in operational characteristics because drain current, gate capacitance, and delay will be affected due to the lower number of CNTs present in the channel of the transistor. This paper presents a new model by which the drain current, the gate capacitance and the delay can be found when not all CNTs are deposited on the substrate. This results in an uneven CNT spacing, new equations are derived and shown to be applicable to both defective and defect-free CNTFETs. The proposed model has been implemented in MATLAB and has been extensively simulated to show that defects due to undeposited CNTs have a significant impact on the operation of a CNTFET. Degradation in performance is related to both the number and position of the defects.