Influence of Phonon Scattering on the Performance of p-i-n Band-to-Band-Tunneling Transistors

Power dissipation has become a major obstacle in performance scaling of modern integrated circuits, and has spurred the search for devices operating at lower voltage swing. In this letter, we study p-i-n band-to-band tunneling field effect transistors (TFET) taking semiconducting carbon nanotubes as the channel material. The on-current of these devices is mainly limited by the tunneling barrier properties, and phonon scattering has only a moderate effect. We show, however, that the off-current is limited by phonon absorption assisted tunneling, and thus is strongly temperature-dependent. Subthreshold swings below the 60mV/decade conventional limit can be readily achieved even at room temperature. Interestingly, although subthreshold swing degrades due to the effects of phonon scattering, it remains low under practical biasing conditions.Comment: 14 pages, 3 figure

Scalability of Atomic-Thin-Body (ATB) Transistors Based on Graphene Nanoribbons

A general solution for the electrostatic potential in an atomic-thin-body (ATB) field-effect transistor geometry is presented. The effective electrostatic scaling length, {\lambda}eff, is extracted from the analytical model, which cannot be approximated by the lowest order eigenmode as traditionally done in SOI-MOSFETs. An empirical equation for the scaling length that depends on the geometry parameters is proposed. It is shown that even for a thick SiO2 back oxide {\lambda}eff can be improved efficiently by thinner top oxide thickness, and to some extent, with high-k dielectrics. The model is then applied to self-consistent simulation of graphene nanoribbon (GNR) Schottky-barrier field-effect transistors (SB-FETs) at the ballistic limit. In the case of GNR SB-FETs, for large {\lambda}eff, the scaling is limited by the conventional electrostatic short channel effects (SCEs). On the other hand, for small {\lambda}eff, the scaling is limited by direct source-to-drain tunneling. A subthreshold swing below 100mV/dec is still possible with a sub-10nm gate length in GNR SB-FETs.Comment: 4 figures, accepted by ED

Simulation of phonon-assisted band-to-band tunneling in carbon nanotube field-effect transistors

Electronic transport in a carbon nanotube (CNT) metal-oxide-semiconductor field effect transistor (MOSFET) is simulated using the non-equilibrium Green's functions method with the account of electron-phonon scattering. For MOSFETs, ambipolar conduction is explained via phonon-assisted band-to-band (Landau-Zener) tunneling. In comparison to the ballistic case, we show that the phonon scattering shifts the onset of ambipolar conduction to more positive gate voltage (thereby increasing the off current). It is found that the subthreshold swing in ambipolar conduction can be made as steep as 40mV/decade despite the effect of phonon scattering.Comment: 13 pages, 4 figure

Ballisticity of nanotube FETs: Role of phonon energy and gate bias

We investigate the role of electron-phonon scattering and gate bias in degrading the drive current of nanotube MOSFETs. Our central results are: (i) Optical phonon scattering significantly decreases the drive current only when gate voltage is higher than a well-defined threshold. It means that elastic scattering mechanisms are most detrimental to nanotube MOSFETs. (ii) For comparable mean free paths, a lower phonon energy leads to a larger degradation of drive current. Thus for semiconducting nanowire FETs, the drive current will be more sensitive than carbon nanotube FETs because of the smaller phonon energies in semiconductors. (iii) Radial breathing mode phonons cause an appreciable reduction in drive current.Comment: 16 pages, 1 table, 4 figure

On the possibility of obtaining MOSFET-like performance and sub-60 mV/decade swing in 1D broken-gap tunnel transistors

Tunneling field-effect transistors (TFETs) have gained a great deal of recent interest due to their potential to reduce power dissipation in integrated circuits. One major challenge for TFETs so far has been achieving high drive currents, which is a prerequisite for high-performance operation. In this paper we explore the performance potential of a 1D TFET with a broken-gap heterojunction source injector using dissipative quantum transport simulations based on the nonequilibrium Green's function formalism, and the carbon nanotube bandstructure as the model 1D material system. We provide detailed insights into broken-gap TFET (BG-TFET) operation, and show that it can indeed produce less than 60mV/decade subthreshold swing at room temperature even in the presence of electron-phonon scattering. The 1D geometry is recognized to be uniquely favorable due to its superior electrostatic control, reduced carrier thermalization rate, and beneficial quantum confinement effects that reduce the off-state leakage below the thermionic limit. Because of higher source injection compared to staggered-gap and homojunction geometries, BG-TFET delivers superior performance that is comparable to MOSFET's. BG-TFET even exceeds the MOSFET performance at lower supply voltages (VDD), showing promise for low-power/high-performance applications.Comment: 34 pages, 11 figure

Factors Influencing Public Perception of Science

Our literature review identified factors influencing public perception of science within the context of science communication. We analyzed 40 studies using an integrative literature review method and found that most research about public perception of science was conducted in developed countries’ contexts. We identified five categories of factors that influence public perception: Type of science, audience beliefs, socio-demographics, source of communication, and environment. We observed the type of science is the fundamental factor that determines the influence of other factors. Audience belief factors are the most influential factor theme. We also noticed that factors act as confounding and/or mediating variables that cannot separate them as a single factor to identify individual influence. To show the factors and their degree of influence on public perception of science, we developed a conceptual framework called the “ring of public perception of science.” The framework highlights the need for a holistic approach to examining the influence of factors affecting public perception of science. The proposed framework is based on a qualitative approach; further research is needed to validate relationships among these factors. Specifically, we recommend further research on context-specific factors because context is important to science communication, emerging environmental factors because of the changing landscape of science communication, and the use of social media to disseminate scientific information

Ballisticity of nanotube field-effect transistors: Role of phonon energy and gate bias

We investigate the role of electron-phonon scattering and gate bias in degrading the drive current of nanotube field-effect transistors FETs. Optical phonon scattering significantly decreases the drive current only when gate voltage is higher than a well-defined threshold. For comparable electron-phonon coupling, a lower phonon energy leads to a larger degradation of drive current. Thus in semiconductor nanowire FETs, the drive current will be more sensitive than in carbon nanotube FETs because of the smaller phonon energies in semiconductors. Acoustic phonons and other elastic scattering mechanisms are most detrimental to nanotube FETs irrespective of biasing conditions

Performance comparison between p-i-n tunneling transistors and conventional MOSFETs

Field-effect transistors based on band-to-band tunneling (BTBT) have gained a lot of recent interest due to their potential for reducing power dissipation in integrated circuits. In this paper we present a detailed performance comparison between conventional n-i-n MOSFET transistors, and BTBT transistors based on the p-i-n geometry (p-i-n TFET), using semiconducting carbon nanotubes as the model channel material. Quantum transport simulations are performed using the nonequilibrium Green's function formalism including realistic phonon scattering. We find that the TFET can indeed produce subthreshold swings below the conventional MOSFET limit of 60mV/decade at room temperature leading to smaller off-currents and standby power dissipation. Phonon assisted tunneling, however, limits the off-state performance benefits that could have been achieved otherwise. Under on-state conditions the drive current and the intrinsic device delay of the TFET are mainly governed by the tunneling barrier properties. On the other hand, the switching energy for the TFET is observed to be fundamentally smaller than that for the MOSFET, reducing the dynamic power dissipation. Aforementioned reasons make the p-i-n geometry well suited for low power applications.Comment: 37 pages, 12 figure

Influence of phonon scattering on the performance of p-i-np-i-n band-to-band tunneling transistors

Power dissipation has become a major obstacle in performance scaling of modern integrated circuits and has spurred the search for devices operating at lower voltage swing. In this letter, we study p-i-n band-to-band tunneling field effect transistors taking semiconducting carbon nanotubes as the channel material. The on current of these devices is mainly limited by the tunneling barrier properties, and phonon-scattering has only a moderate effect.We show, however, that the off current is limited by phonon absorption assisted tunneling, and thus is strongly temperature dependent. Subthreshold swings below the 60 mV/decade conventional limit can be readily achieved even at room temperature. Interestingly, although subthreshold swing degrades due to the effects of phonon scattering, it remains low under practical biasing conditions