Does carrier velocity saturation help to enhance fmax in graphene field-effect transistors?
Artikel i vetenskaplig tidskrift, 2020

It has been argued that current saturation in graphene field-effect transistors (GFETs) is needed to get optimal maximum oscillation frequency (f(max)). This paper investigates whether velocity saturation can help to get better current saturation and if that correlates with enhancedf(max). We have fabricated 500 nm GFETs with high extrinsicf(max)(37 GHz), and later simulated with a drift-diffusion model augmented with the relevant factors that influence carrier velocity, namely: short-channel electrostatics, saturation velocity effect, graphene/dielectric interface traps, and self-heating effects. Crucially, the model provides microscopic details of channel parameters such as carrier concentration, drift and saturation velocities, allowing us to correlate the observed macroscopic behavior with the local magnitudes. When biasing the GFET so all carriers in the channel are of the same sign resulting in highly concentrated unipolar channel, we find that the larger the drain bias is, both closer the carrier velocity to its saturation value and the higher thef(max)are. However, the highestf(max)can be achieved at biases where there exists a depletion of carriers near source or drain. In such a situation, the highestf(max)is not found in the velocity saturation regime, but where carrier velocity is far below its saturated value and the contribution of the diffusion mechanism to the current is comparable to the drift mechanism. The position and magnitude of the highestf(max)depend on the carrier concentration and total velocity, which are interdependent and are also affected by the self-heating. Importantly, this effect was found to severely limit radio-frequency performance, reducing the highestf(max)from similar to 60 to similar to 40 GHz.


Pedro C. Feijoo

Universitat Autonoma de Barcelona (UAB)

Francisco Pasadas

Universitat Autonoma de Barcelona (UAB)

Marlene Bonmann

Chalmers, Mikroteknologi och nanovetenskap, Terahertz- och millimetervågsteknik

Muhammad Asad

Chalmers, Mikroteknologi och nanovetenskap, Terahertz- och millimetervågsteknik

Xinxin Yang

Chalmers, Mikroteknologi och nanovetenskap, Terahertz- och millimetervågsteknik

Andrey Generalov


Andrei Vorobiev

Chalmers, Mikroteknologi och nanovetenskap, Terahertz- och millimetervågsteknik

Luca Banszerus

RWTH Aachen University

Christoph Stampfer

RWTH Aachen University

Martin Otto

Advanced Microelectronic Center Aachen (AMICA)

Daniel Neumaier

Advanced Microelectronic Center Aachen (AMICA)

Jan Stake

Chalmers, Mikroteknologi och nanovetenskap, Terahertz- och millimetervågsteknik

David Jiménez

Universitat Autonoma de Barcelona (UAB)

Nanoscale Advances

25160230 (eISSN)

Vol. 2 9 4179-4186

Flexibla terahertz detektorer i grafen

Vetenskapsrådet (VR) (2017-04504), 2018-01-01 -- 2021-12-31.

Graphene Core Project 2 (Graphene Flagship)

Europeiska kommissionen (EU) (EC/H2020/785219), 2018-04-01 -- 2020-03-31.


Informations- och kommunikationsteknik

Nanovetenskap och nanoteknik (SO 2010-2017, EI 2018-)






Annan elektroteknik och elektronik



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