Shaahin G. Shirazi

This work compares the changes in performance of a carbon nanotube CNT-based n-i-n metal-oxide-semiconductor MOSFET and p-i-n tunnel field effect transistor TFET based on different dielectric values of gate κ_c and source/drain regions κ_sd. The results prove that at a constant κ_sd a higher κ_c improves transconductance g_m, output conductance g_d, ON-state current, subthreshold swing SS and may lower the threshold voltage V_T. However, at a constant κ_c for an n-i-n MOSFET the performance does not change significantly with κ_sd, but g_d increases. For the p-i-n TFET g_m, g_d and ON-state current degrade prominently while the minimum current declines and SS may improve. Also two different dielectrics for source κ_s and drain κ_d could provide TFET with a lower power-higher performance characteristic. The results are given based on certified NEGF formalism and are explained based on semiclassical discussion with respect to energy band diagram concept. This method simplifies the realization of device's performance optimization. Due to 1D transport properties of CNTs the results could be applied to any device with 1D electronic transport characteristics.

For a carbon nanotube field effect transistor (CNTFET) the ballistic I-V characteristics have been investigated theoretically with respect to ambient temperature for both the p-i-n tunnel FET (TFET) and n-i-n metal-oxide-semiconductor FET (MOSFET). The performance stability of a TFET at higher temperatures, especially in subthreshold regime in which the n-i-n device exhibits a devastating characteristic, is appreciable. Alongside very low subthreshold swing even at a temperature beyond 300 K, a p-i-n tunnel FET could be a more reliable choice for operating in a wide range of temperatures. The subthreshold swing, transconductance, output conductance, saturation mechanism and on/off current ratio are also considered with respect to CNT diameter as well. A lower diameter lessens some negative effects of operating at a high temperature. All the results can be realized based on the energy band diagram of the device and the Fermi functions of source and drain. This trend gives a valuable insight into exploring the changes in 1D device characteristics.

Carbon nanotube (CNT) could be exploited as a channel or source/drain region in field effect transistors (FETs). We theoretically investigate the impact of CNT doping level on a coaxially gated CNTFET's performance in the ballistic regime. The results show that the transconductance and subthreshold swing are independent of the CNT doping value. But threshold voltage and output conductance strongly depend on the channel doping level. It seems that the most important impact of CNT doping is the change in off-state current values resulting in a shift in the transfer characteristics of the device. However, it is possible to choose an optimal value of CNT doping to obtain the highest performance.

Choosing a suitable doping level of channel relevant to channel diameter is considered for determining the carbon nanotube field effect transistors' performance which seem to be the best substitute of current transistor technology. For low diameter values of channel the ratio of on/off current declines by increasing the doping level. But for higher diameter values there is an optimum point of doping level in obtaining the highest on/off current ratio. For further verification, the variations of performance are justified by electron distribution function's changes on energy band diagram of these devices. The results are compared at two different gate fields.

Choosing a suitable doping level of channel relevant to channel diameter is considered for determining the carbon nanotube field effect transistors’ performance which seem to be the best substitute of current transistor technology. For low diameter values of channel, the ratio of on/off current declines by increasing the doping level. But for higher diameter values, there is an optimum point of doping level in obtaining the highest on/off current ratio. For further verification, the variations of performance are justified by electron distribution function’s changes on energy band diagram of these devices. The results are compared at two different gate fields.

Carbon nanotubes are known as an interesting material to be used in the next generations of electronic technology, especially at nano regime. Nowadays, carbon nanotube field effect transistor or CNTFET is one of the promising devices for future electronic applications. A CNTFET which uses carbon nanotube as channel or source/drain region is the most promising candidate for replacing the current silicon transistor technology. The study of modern manufacturing approach and impact of device parameters on its performance is one of the important research fields in nanoelectronics. In this paper we study some aspects of changes in gate parameters at different channel diameters. This paper shows that for small values of diameter, increasing the dielectric constant of gate insulator doesn't help to improve the performance as value of dielectric constant of gate insulator reaches a certain amount. Also, increasing the oxide thickness of gate insulator doesn't always decrease transistor performance. For high diameter values, increasing the thickness up to a certain value improves the transistor performance.

Carbon nanotube field effect transistors are the most promising candidate for replacing of current silicon transistor technology. Choosing a suitable dielectric constant for a specific temperature range is important in determining device performance. For higher dielectric constant, rising up the temperature causes current ratio to diminish, while at lower dielectric constants the current ratio increases. An interesting case is observed for transistors with dielectric constants in the middle range which exhibit an approximately constant current ratio for all ambient temperatures considered.

Nowadays carbon nanotube field effect transistor or CNTFET is one of the promising devices for future electronic applications. These transistors are frequently simulated using non-equilibrium Green's function (NEGF) formalism. In this paper we study aspects of changes in gate parameters at different channel diameter which have not been known before. We find that in small values of diameter, increasing the dielectric constant of gate insulator doesn't help to improve the performance as value of dielectric constant reaches a certain amount. We also find that increasing the oxide thickness doesn't always decrease transistor performance. For high diameter values, increasing the thickness upto a certain value, improves the transistor performance.