Dimensional Field Effect Transistor Research Articles

Small-Signal Model for 2D-Material Based FETs Targeting Radio-Frequency Applications: The Importance of Considering Nonreciprocal Capacitances

A small-signal equivalent circuit of 2D-material based field-effect transistors is presented. Charge conservation and non-reciprocal capacitances have been assumed so the model can be used to make reliable predictions at both device and circuit levels. In this context, explicit and exact analytical expressions of the main radio-frequency figures of merit of these devices are given. Moreover, a direct parameter extraction methodology is provided based on S-parameter measurements. In addition to the intrinsic capacitances, transconductance and output conductance, our approach allows extracting the series combination of drain/source metal contact and access resistances. Accounting for these extrinsic resistances is of upmost importance when dealing with low dimensional field-effect transistors.

Low-frequency noise in MoSe2 field effect transistors

One of the important performance metrics of emerging nanoelectronic devices, including low dimensional Field Effect Transistors (FETs), is the magnitude of the low-frequency noise. Atomically thin 2D semiconductor channel materials such as MoX2 (X ≡ S, Se) have shown promising transistor characteristics such as ION/IOFF ratio exceeding 106 and low IOFF, making them attractive as channel materials for next generation nanoelectronic devices. However, MoS2 FETs demonstrated to date exhibit high noise levels under ambient conditions. In this letter, we report at least two orders of magnitude smaller values of Hooge parameter in a back-gated MoSe2 FET (10 atomic layers) with nickel S/D contacts and measured at atmospheric pressure and temperature. The channel dominated regime of noise was extracted from the total noise spectrum and is shown to follow a mobility fluctuation model with 1/f dependence. The low noise in MoSe2 FETs is comparable to other 1D nanoelectronic devices such as carbon nanotube FETs (CNT-FETs) and paves the way for use in future applications in precision sensing and communications.

Suppressed and enhanced shot noise in one dimensional field-effect transistors

Landauer---Buttiker shot noise formula only considers the impact of Pauli exclusion principle on noise, but not the impact of Coulomb repulsion among carriers. A theory recently derived by the authors is able to include also the impact of Coulomb repulsion, and provides a computational methodology to obtain noise properties on a more complete physical basis. We review recent results from the application of this methodology with the use of in-house developed computational electronics tools. We show that in a one-dimensional FET, electrostatic repulsion among charge carriers in the channel can be responsible for strongly suppressed or enhanced shot noise with respect to the Poissonian Noise, or to the noise level provided by Landauer---Buttiker formula. This is very relevant for device and circuit design, since current semiconductor technology evolution has brought nanoscale FETs very close to the limit of one-dimensional FETs.

Liquid gated three dimensional graphene network transistor

In this paper, a novel three dimensional field effect transistor (FET) is presented. The transistor is made of graphene foam, which is a complex three dimensional network of single to double layer graphene that is immersed in the ionic liquid. The electrolytic double layer capacitance at the ionic liquid graphene interface provides all-around three dimensional liquid gating of the transistor. The high surface area of the graphene foam results in providing higher current carrying capacity than a two dimensional graphene transistor. Moreover, the nanometer thick electrolytic double layer formed at the high surface area liquid-graphene interface results in large gate capacitance that allows for low voltage operation. Owing to its all carbonaceous form and all around liquid gating, the presented three dimensional graphene transistor may lead the way for real electronic interfaces with the biological world and for biochemical sensing.

Analytical Model of Nanowire FETs in a Partially Ballistic or Dissipative Transport Regime

The intermediate transport regime in nanoscale transistors between the fully ballistic case and the quasi equilibrium case described by the drift-diffusion model is still an open modeling issue. Analytical approaches to the problem have been proposed, based on the introduction of a backscattering coefficient, or numerical approaches consisting in the MonteCarlo solution of the Boltzmann transport equation or in the introduction of dissipation in quantum transport descriptions. In this paper we propose a very simple analytical model to seamlessly cover the whole range of transport regimes in generic quasi-one dimensional field-effect transistors, and apply it to silicon nanowire transistors. The model is based on describing a generic transistor as a chain of ballistic nanowire transistors in series, or as the series of a ballistic transistor and a drift-diffusion transistor operating in the triode region. As an additional result, we find a relation between the mobility and the mean free path, that has deep consequences on the understanding of transport in nanoscale devices.