Showing papers by "Jing Guo published in 2005"

High performance n-type carbon nanotube field-effect transistors with chemically doped contacts.

Abstract: Short channel (80 nm) n-type single-walled carbon nanotube (SWNT) field-effect transistors (FETs) with potassium (K) doped source and drain regions and high-K gate dielectrics (ALD HfO2) are obtained. For nanotubes with diameter 1.6 nm and band gap 0.55 eV, we obtain n-MOSFET-like devices exhibiting high on-currents due to chemically suppressed Schottky barriers at the contacts, subthreshold swing of 70 mV/decade, negligible ambipolar conduction, and high on/off ratios up to 106 at a bias voltage of 0.5 V. The results compare favorably with the state-of-the-art silicon n-MOSFETs and demonstrate the potential of SWNTs for future complementary electronics. The effects of doping level on the electrical characteristics of the nanotube devices are discussed. Single-walled carbon nanotubes (SWNTs) are promising for future high performance electronics such as field effect transistors (FETs) owing to their various unique properties including ballistic transport with relatively long mean free paths and high compatibility with high- dielectrics imparted by their unique chemical bonding and surface stability. 1-12 While much has been done to achieve high performance p-type nanotube FETs through contact optimization, dielectric integration and lateral scaling, progress on n-FETs has been slow partly due to the difficulty in affording low Schottky (SB) contacts for high on-states and at the same time achieving high on/off ratios with small diameter (or large band gap) tubes. 7 Here, by invoking chemical doping, high- dielectrics, and new device design, we demonstrate n-type SWNT FETs with performance matching or approaching the best p-type nanotube FETs and surpassing the state-of-the-art Si n-MOSFET.

Nanoscale Transistors: Device Physics, Modeling and Simulation

Abstract: Basic Concepts.- Devices, Circuits, and Systems.- The Ballistic Nanotransistor.- Scattering Theory of the MOSFET.- Nanowire Field-Effect Transistors.- Transistors at the Molecular Scale.

Assessment of high-frequency performance potential of carbon nanotube transistors

Abstract: Self-consistent quantum simulations are used to explore the high-frequency performance potential of carbon nantube field-effect transistors (CNTFETs). The cutoff frequency expected for a recently reported CNT Schottky-barrier FET is well below the performance limit, due to the large parasitic capacitance between electrodes. We show that using an array of parallel nanotubes as the transistor channel reduces parasitic capacitance per tube. Increasing tube density gives a large improvement of high-frequency performance when tubes are widely spaced and parasitic capacitance dominates but only a small improvement when the tube spacing is small and intrinsic gate capacitance dominates. Alternatively, using quasi-one-dimensional nanowires as source and drain contacts should significantly reduce parasitic capacitance and improve high-frequency performance. Ballistic CNTFETs should outperform ballistic Si MOSFETs in terms of the high-frequency performance limit because of their larger band-structure-limited velocity.

Role of phonon scattering in carbon nanotube field-effect transistors

Abstract: The role of phonon scattering in carbon nanotube field-effect transistors (CNTFETs) is explored by solving the Boltzmann transport equation using the Monte Carlo method. The results show that elastic scattering in a short-channel CNTFET has a small effect on the source-drain current due to the long elastic mean-free path (mfp) (∼1μm). If elastic scattering with a short mfp were to exist in a CNTFET, the on current would be severely degraded due to the one-dimensional channel geometry. At high drain bias, optical phonon scattering, which has a much shorter mfp (∼10nm), is expected to dominate, even in a short-channel CNTFET. We find, however, that inelastic optical scattering has a small effect in CNTFETs under modest gate bias.

A quantum-mechanical treatment of phonon scattering in carbon nanotube transistors

Abstract: Phonon scattering in carbon nanotube field-effect transistors (CNTFETs) is treated using the nonequilibrium Green’s function formalism with the self-consistent Born approximation. The treatment simultaneously captures the essential physics of phonon scattering and important quantum effects. For a one-dimensional channel, it is computationally as efficient as and physically more rigorous than the so-called “Buttiker probe” approach [Phys. Rev. Lett. 57, 1761 (1986)], which has been widely used in mesoscopic physics. The non-self-consistent simulation results confirm that the short mean-free-path optical phonon (OP) scattering, though expected to dominate even in a short channel CNTFET, essentially has no direct effect on the dc on current under modest gate biases. The self-consistent simulation results indicate that OP scattering, however, can have an indirect effect on the on current through self-consistent electrostatics. Using a high-κ gate insulator suppresses the indirect effect and leads to a dc on c...

Carrier transport and light-spot movement in carbon-nanotube infrared emitters

Abstract: Infrared emission from a carbon-nanotube (CNT) field-effect transistor, with the position of the light spot controlled by applied bias, was recently reported. In this letter, a self-consistent simulation, which couples a quantum treatment of the metal–CNT contacts to a semiclassical treatment of the channel, is performed to understand carrier transport and light emission in a CNT infrared emitter. The results show that when the channel is long, light emission significantly affects carrier transport, and reduces the source–drain current by a factor of 2 in ambipolar transport regime. The experimentally observed light-spot movement along the channel can be mostly understood and explained by a simple, semiclassical picture.

Performance assessment of sub-percolating nanobundle network transistors by an analytical model

Abstract: Nanobundle network transistors (NBTs) have emerged as a viable, higher performance alternative to poly-silicon and organic transistors with possible applications in macroelectronic displays, chemical/biological sensors, and photovoltaics. A simple analytical model for I-V characteristics of NBTs (below the percolation limit) is proposed and validated by numerical simulation and experimental data. The physics-based predictive model provides a simple relation between transistor characteristics and design parameters which can be used for optimization of NBTs. The model provides important insights into the recent experiments on NBT characteristics and electrical purification of nanobundle networks

Design of a novel three-valued static memory using Schottky barrier carbon nanotube FETs

Abstract: This paper proposes a novel three-state memory using scaled Schottky-barrier carbon nanotube field effect transistors (SB CNFETs). The design utilizes the inherent ambipolar device characteristics of the SB CNFET. Simulation results show /spl sim/37% area reduction and /spl sim/30% reduction of total power in a 64 KB memory array.

Carbon nanotube-based non-volatile memory and charge sensors

Abstract: Beyond 65 nm node, the ultra-narrow channel memory device serves as a possible technology for further scaling. A self-assembled carbon nanotube (CNT) channel with self aligned metal nanocrystals is proposed as an alternative to Si based ultra-narrow channel memory. The device demonstrates large memory window and single-electron sensitivity. The analysis of the transport in the CNT channel using non-equilibrium Green's function (NEGF) formalism confirms single electron sensitivity quantitatively at room temperature. The CNT channel conductance exhibits sensitivity to position of the charge along the channel. The NEGF based analysis is easily extended to the application of CNTFET as a charge sensor. The electrostatics of the CNT-nanocrystal memory was analyzed for transport between nanocrystal and CNT. Despite the nanocrystal being in close proximity of the CNT, it is strongly coupled to the gate electrode electrostatically. This effect is not observed in the planar 2D Si- based nanocrystal memory. It obviates a major trade-off in memory design of scaling the control dielectric to decrease operational voltage, while ensuring low gate leakage and should allow ultra-low voltage operations. Large tunneling current should also enhance write times. Large electric field asymmetry should enable a better write/retention ratio.