Electronic current transport in CNT-FETs for operation in ballistic region

Abstract

Carbon nanotubes have exhibited excellent molecular adsorption properties and their dimensions are comparable to typical bio-molecules such as the DNA. Carbon nanotube field effect transistors (CNT-FETs) and integrated circuits are being explored for electrical sensing of bio-materials and gases. The adsorbed molecules by the carbon nanotube and the CNT-FET result in a change of the CNT conductance and electronic properties of the CNT-FET which can be easily monitored. It thus becomes very important to better understand electronic transport and model its behavior in relation to bio- and chemical sensing. Some of the recently developed compact analytical models for current transport in CNT-FETs are compatible with EDA tools for analysis and design of CNT-FET based integrated circuits but these are limited to applications in non-ballistic region. Since applications requiring a large number of bio-sensing using CNT-FETs are in 2- 20 nm range, in this work, the current transport model of CNT-FETs has been suitably modified for operation in the ballistic region for use in integrated circuit design and sensing applications. The surface potentials in a CNT-FET have been coupled with the current transport equations to obtain compact electronic current transport models for operation in the ballistic region. A p-type CNT-FET is considered for the analysis which can be easily applied in n-type CNT-FETs. The work is also compared with other electronic transport models and experimental measurements. A close agreement establishes the validity of our electronic transport model of the transistor operation in the ballistic region. It is also shown that two subbands in the valance band of CNT are sufficient for computation of current in CNT-FETs. The current transport model characterizing CNT-FET in the ballistic region is simple and compatible with EDA tools for bio-sensing chip design.