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A method for designing carbon nanotube field-effect transistors (CNTFETs) with optimized oxide thickness is proposed herein. The optimum oxide thickness that provides the maximum current ratio (on/off ratio) is calculated for each design. The effect of oxide thickness on the on/off ratio is investigated by treating it as the independent variable and calculating the on-state and off-state currents. Particle swarm optimization is used to determine the exact optimum oxide thickness to achieve the maximum current ratio, which is one of the most important parameters in switching applications. The optimum insulator thickness is calculated for CNTFETs with different chiral vectors, insulator types, channel lengths and source/drain doping levels. For further study of the CNTFETs, performance parameters including cutoff frequency and transconductance of the devices are also calculated and investigated. The results show that CNTFET designers should select the oxide thickness very carefully, not simply based on reported values in other works. Each design requires its own optimum oxide thickness which provides the maximum on/off current ratio only for that design. [ABSTRACT FROM AUTHOR]

A new structure with a Gaussian doping distribution along the channel region is proposed to improve the performance of tunneling carbon nanotube field-effect transistors (T-CNTFETs). The new structure involves a Gaussian doping distribution in the channel region with a low level of doping at the sides that gradually increases towards the middle of the channel. The source doping is p-type, while the doping in the drain and channel regions is n-type. The doping distribution is uniform in the drain/source regions. To simulate the behavior of T-CNTFETs, the Poisson and Schrödinger equations are solved self-consistently using the nonequilibrium Green's function formalism. The simulation results show that the proposed structure exhibits increased saturation current but decreased OFF-state current compared with the conventional structure (C-T-CNTFET), yielding a ~ 104 times higher current ratio for a gate length of 20 nm. The proposed structure also shows improvements in parameters such as the transconductance, gate capacitance, cutoff frequency, and delay compared with the conventional structure and can be considered to be a more appropriate option for different applications. [ABSTRACT FROM AUTHOR]

To enhance their performance, various designs of carbon nanotube (CNT) interconnects were analyzed and compared with conventional copper interconnects. To ameliorate the propagation delay of very long interconnect lines, smart buffers are inserted as repeaters along the lines. The existing buffer designs discussed here, including the conventional, LECTOR, Schmitt, and current-mode logic (CML) types, were implemented using both CNT and metal–oxide–semiconductor (MOS) technology for comparison in different combinations, viz. MOS repeater–Cu interconnect and CNT repeater–CNT interconnect. Furthermore, the proposed buffer designs use power gating techniques and an automated toggling approach to reduce the delay, besides mitigating the average power consumption. Compared with the aforementioned existing buffers, the proposed design 1 offers a 98 % saving in the dynamic power with a 64 % reduction in the propagation delay, but at the cost of higher leakage power consumption. The proposed design 2 offers a 99.86 % saving in the dynamic power with an 88 % reduction in the leakage power, reducing the delay by 52 %. The proposed design 3 results in a 99.94 % saving in the dynamic power and 93 % in the leakage power, but with a delay penalty. The results of the analysis of their electrothermal performance at temperatures ranging from 200 to 450 K revealed that the increases in the delay and power with rise in temperature were relatively greater for the MOS repeater–Cu interconnect combination compared with the CNT repeater–CNT interconnect combination. Simulations at the 32-nm technology node were carried out using HSPICE by considering a section of a long interconnect line as a driver interconnect load (DIL) system, using the Stanford SPICE model for CNT and the Berkeley Short-Channel IGFET Model (BSIM)4 Predictive Technology Model (PTM) for MOS. [ABSTRACT FROM AUTHOR]

With advantages such as low sub-threshold swing, low OFF-state current and the ability to attain a higher ON-OFF ratio, the tunnel CNTFET is one of the most comprehensively investigated devices for low-power application. The problems associated with this device are fabrication issues since conventional doping is not possible in CNTs. Therefore, a doping-less tunnel CNTFET is proposed which is free from problems associated with a conventional tunnel CNTFET. A mathematical model is developed for an electrostatically doped tunnel CNTFET, and to validate the model accuracy and the equation set, the simulation results are compared with NanoTCAD ViDES results. Finally, the developed model is deployed in an inverter design to verify the suitability of the model for circuit applications. [ABSTRACT FROM AUTHOR]

Aggressive technology scaling as per Moore’s law has led to elevated power dissipation levels owing to an exponential increase in subthreshold leakage power. Short channel effects (SCEs) due to channel length reduction, gate insulator thickness change, application of high-k gate insulator, and temperature change in a double-gate metal-oxide-semiconductor field-effect transistor (DG MOSFET) and carbon nanotube field-effect transistor (CNTFET) were investigated in this work. Computational simulations were performed to investigate SCEs, viz. the threshold voltage (Vth) roll-off, subthreshold swing (SS), and Ion/Ioff ratio, in the DG MOSFET and CNTFET while reducing the channel length. The CNTFET showed better performance than the DG MOSFET, including near-zero SCEs due to its pure ballistic transport mechanism. We also examined the threshold voltage (Vth), subthreshold swing (SS), and Ion/Ioff ratio of the DG MOSFET and CNTFET with varying gate insulator thickness, gate insulator material, and temperature. Finally, we handpicked almost similar parameters for both the CNTFET and DG MOSFET and carried out performance analysis based on the simulation results. Comparative analysis of the results showed that the CNTFET provides 47.8 times more Ion/Ioff ratio than the DG MOSFET. Its better control over the threshold voltage, near-zero SCEs, high on-current, low leakage power consumption, and ability to operate at high temperature make the CNTFET a viable option for use in enhanced switching applications and low-voltage digital applications in nanoelectronics. [ABSTRACT FROM AUTHOR]

In this paper, we comprehensively study the effects of gate and channel engineering on the performances of surrounding-gate CNTFETs using a quantum kinetic model, which is based on two-dimensional non-equilibrium Green functions (NEGF) solved self-consistently with Poisson's equations. The iterative approach between Poisson equation and NEGF has been discussed. For the first time, the influences of double-material-gate and linear doping structures on the CNTFETs have been investigated. The calculated results show that double-material-gate CNTFETs with conventional doping (DMG-CNTFETs) can effectively suppress the drain-induced barrier lowering (DIBL), short-channel effects (SCEs), and achieve better sub-threshold property as compared with single-material-gate CNTFETs with conventional doping (SMG-CNTFETs). Compared with conventional doping, linear doping presents lower leakage current, higher I/ I ratio, and lower sub-threshold swing, which means a better ability of gate controlling. In addition, we present a detailed discussion of the performances of scaling down, and conclude that DMG structure can meet the ITRS'10 requirements better than SMG, especially that the I/ I ratio is two orders of magnitude higher than that of ITRS'10 requirements. [ABSTRACT FROM AUTHOR]

We report density-functional theory (DFT), atomistic simulations of the screening properties of carbon nanotube (CNT) field-effect transistors (FETs). Our attention has been focused on recently demonstrated [1, 2] bulk-modulated CNTFETs. Our calculations have been intended to explore, at an atomistic level, the effect of the one-dimensional screening properties on the physical mechanisms which govern the channel conductance modulation in these new devices. We find that in order to correctly describe charge response mechanisms in a small-diameter nanotube, a calculation including electron-electron interaction effects is necessary. Many-body effects tied to the attractive nature of the exchange interaction can produce an unconventional charge response which manifests itself in a negative quantum capacitance. [ABSTRACT FROM AUTHOR]