Coaxial Gate Research Articles

A novel band-to-band tunneling junctionless carbon nanotube field-effect transistor with lightly doped pocket: Proposal, assessment, and quantum transport analysis

Overcoming the performance limits encountered with the conventional nanoscale transistors while simplifying the fabrication process is an objective that can give a new impulses to the modern nanoelectronics. A novel band-to-band tunneling junctionless carbon nanotube field-effect transistor, endowed with a lightly doped pocket underneath the coaxial gate, is computationally proposed herein. The quantum simulation based on the non-equilibrium Green's function formalism is used in the investigation while considering the self-consistent electrostatics and ballistic transport conditions. The proposed nanodevice switches via the modulation of band-to-band tunneling in the absence of thermionic emission mechanism. The pocket-induced barrier is employed to mitigate the ambiploar behavior attributed to the thermionic current and to improve the nanodevice performance. The simulations show that the proposed device exhibits improved leakage current, ambipolar behavior, subthermionic subthreshold swing, and current ratio in comparison to those provided by its conventional counterpart uniformly doped. In addition, the role of the pocket length in boosting the performance of the proposed band-to-band tunneling device is investigated, where the optimal length of lightly doped pocket is revealed. Note that the obtained enhancements have been thoroughly analyzed using the energy-position-resolved charge density and current spectrum. The recorded improvements, namely subthermionic subthreshold swing and high ION/IOFF current ratio, together with the merits of junctionless paradigm, make the proposed pocket-based technique, as an intriguing strategy that can be used to boost the performance of similar nanoscale band-to-band tunneling junctionless field-effect transistors for high-performance and low-power applications.

Improved performance of nanoscale junctionless carbon nanotube tunneling FETs using dual-material source gate design: A quantum simulation study

This paper proposes a novel technique based on dual-material source gate (DMSG) design to enhance the performance of a junctionless carbon nanotube tunneling field-effect transistor (JL CNTTFET) endowed with ultrascaled coaxial gate. The nanodevice is computationally investigated by quantum transport simulations, which treat the ballistic transport via the non-equilibrium Green's function (NEGF) formalism while considering the self-consistent nanodevice electrostatics. The dual-material source gate design aims to reduce the ultrascaled gate effects on the performance of the CNTTFET while maintaining the junctionless benefits. It has been found that the engineered source-gate work function based on the dual-material strategy can greatly improve the performance of the JL CNTTFET with 5-nm coaxial-gate length, namely the subthreshold and switching characteristics. The record of steeper swing factor, high current ratio, and enhanced ambipolar and leakage current in an ultrascaled regime has explicitly confirmed the efficacy of the proposed DMSG-based improvement technique while making it a promising and viable technique for high-performance ultrascaled junctionless tunnel nanotransistors.

Improving the performance of a junctionless carbon nanotube field-effect transistor using a split-gate

In this paper, a novel junctionless carbon nanotube field-effect transistor (JL-CNTFET) endowed with a split coaxial gate (SCG) is proposed through a rigorous self-consistent simulation. This latter is based on solving self-consistently the Schrödinger and Poisson equations using the non-equilibrium Green's function (NEGF) formalism and the finite difference method (FDM), respectively. It has been found that the suggested SCG JL-CNTFET can exhibit significantly improved switching performance including the off-current, current ratio, intrinsic delay and power-delay product, due to the decreasing of band-to-band tunneling via the split-gate strategy. The obtained results indicate that the proposed SCG JL-CNTFET can be considered as a promising device for the futuristic high-performance integrated circuits intended for low-power and high-speed applications.

Performance Assessment of a New Radiation Dosimeter Based on Carbon Nanotube Field-Effect Transistor: A Quantum Simulation Study

In this paper, the performance of a new nanoscale radiation sensitive field-effect transistor (RADFET) based on carbon nanotube (CNT) is investigated using an atomistic simulation approach. The proposed radiation nanosensor uses the radiation-induced interface trapped charges as a sensing mechanism, and it is endowed with the coaxial gate and the CNT-based sensitive channel. The quantum simulations are carried out using the non-equilibrium Green’s function formalism with self-consistent electrostatics assuming a ballistic transport. The threshold voltage shift is considered as a sensing metric. A comprehensive RADFET simulation that includes the electrostatic potential, charge density, $I_{\mathrm {DS}}$ – $V_{\mathrm {GS}}$ characteristics, and sensitivity behavior, has been performed. In addition, a parametric study has been done in order to explore the impact of change in the dosimeter geometrical parameters on the RADFET sensitivity. It has been found that the proposed radiation sensor is effective and its sensitivity can be further improved using thicker silicon dioxide layer and longer CNT diameters. The obtained results make the proposed CNT-based RADFET as a promising candidate for high-performance radiation sensing applications, especially for in vivo dosimetry, where the development of new nanodosimeters is in dire need.

Quantum simulation of a junctionless carbon nanotube field-effect transistor with binary metal alloy gate electrode

In this paper, a quantum simulation study that highlights the role of linearly graded binary metal alloy (LGBMA) gate in improving the performance of coaxially gated junctionless carbon nanotube field-effect transistor (JL CNTFET) is presented. The computational approach is based on solving the Schrödinger equation using the non-equilibrium Green's function (NEGF) formalism self-consistently coupled with the Poisson equation in the ballistic limit. The proposed device is called junctionless work function engineered gate carbon nanotube field-effect transistor (JL WFEG CNTFET). The simulation results reveal that the proposed design improves the ambipolar property, tunneling leakage current, and subthreshold swing in comparison to the conventional structure. It has also been found that the proposed JL WFEG CNTFET exhibits an improved switching behavior than that of the conventional JL CNTFET, where an enhancement in terms of on-state to off-state current ratio, intrinsic delay, and power-delay product has been recorded. The obtained results make the JL CNTFET with coaxial LGBMA gate as a promising candidate for futuristic ultra-scaled, high-speed, and low-power applications.

Design and Fabrication of Carbon Nanotube Field‐Emission Cathode with Coaxial Gate and Ballast Resistor

A low density vertically aligned carbon nanotube-based field-emission cathode with a ballast resistor and coaxial gate is designed and fabricated. The ballast resistor can overcome the non-uniformity of the local field-enhancement factor at the emitter apex. The self-aligned fabrication process of the coaxial gate can avoid the effects of emitter tip misalignment and height non-uniformity.

Focusing properties of dual-gate field emitters

Field emitters are used as distributed electron sources in applications such as field emission displays (FEDs). Reducing the angular aperture of the electron beam increases the resolution and luminance of the FED. This study comparatively analyzes the focusing properties of several kinds of dual-gate emitter structures. The configurations considered are the coplanar and coaxial gate types, and also the coaxial gates structure with protruding emitter, considered for the first time in this context. The simulation work was performed using the SIMION 3D 7.0 software package. Several conclusions are drawn concerning the suitability of double-gated emitter structures for electron beam focusing.

Fractional Millimicrosecond Electrical Stroboscope

A simple electrical stroboscope having a rise time of 6 × 10-11 seconds and a 6-db bandwidth of 5.5 kmc is described. Oscillograms showing 160-mc square waves and 640 million pulses per second are shown. These waveforms display rise times as fast as 2 × 10-10 seconds. Instrumentation includes a strobe-pulse generator, a coaxial gate using a gallium-arsenide point-contact crystal, suitable wide-band coaxial attenuators, a low-pass integrating filter and a low-frequency oscilloscope.