Time-dependent simulation of particle and displacement currents in THz graphene transistors

Zhan, Zhen; Colomés, Enrique; Benali, A.; Marian, Damiano; Oriols, X.

doi:10.1088/1742-5468/2016/05/054019

Cited by 8 publications

(12 citation statements)

References 35 publications

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“…Second, in fact, the discrete nature of electrons alone is not enough to understand the electrical current at THz frequencies. The relevant total current is the sum of the conduction (flux of particles) plus the displacement (time-derivative of the electric field) components [14][15][16][17] . The displacement current on a surface is different from zero whenever electrons are able to modify the electric field on it (independently on how far the electrons are from the surface).…”

Section: Total (Displacement Plus Particle) Current and Noise In Quanmentioning

confidence: 99%

“…From Eqs. (16) and (1), with f n = 1/T SNR 0 , we can straightforwardly obtain the ratio between f n and f τ as:…”

Section: Total (Displacement Plus Particle) Current and Noise In Quanmentioning

confidence: 99%

“…( 6 ) is now a closed surface enclosing an arbitrary volume and is a mathematical vector field defined in Ref. 16 . It can be proven that in a two terminal device, the instantaneous time current assigned to a k -th electron while crossing the device with velocity in the x direction can be written as (see Refs.…”

Section: Total (Displacement Plus Particle) Current and Noise In Quanmentioning

confidence: 99%

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Noise and charge discreteness as ultimate limit for the THz operation of ultra-small electronic devices

Colomés

Matéos

González

et al. 2020

Sci Rep

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To manufacture faster electron devices, the industry has entered into the nanoscale dimensions and Terahertz (THz) working frequencies. The discrete nature of the few electrons present simultaneously in the active region of ultra-small devices generate unavoidable fluctuations of the current at THz frequencies. The consequences of this noise remain unnoticed in the scientific community because its accurate understanding requires dealing with consecutive multi-time quantum measurements. Here, a modeling of the quantum measurement of the current at THz frequencies is introduced in terms of quantum (Bohmian) trajectories. With this new understanding, we develop an analytic model for THz noise as a function of the electron transit time and the sampling integration time, which finally determine the maximum device working frequency for digital applications. The model is confirmed by either semi-classical or full- quantum time-dependent Monte Carlo simulations. All these results show that intrinsic THz noise increases unlimitedly when the volume of the active region decreases. All attempts to minimize the low signal-to-noise ratio of these ultra-small devices to get effective THz working frequencies are incompatible with the basic elements of the scaling strategy. One can develop THz electron devices, but they cannot have ultra-small dimensions. Or, one can fabricate ultra-small electron devices, but they cannot be used for THz working frequencies.

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Section: Total (Displacement Plus Particle) Current and Noise In Quanmentioning

confidence: 99%

“…From Eqs. (16) and (1), with f n = 1/T SNR 0 , we can straightforwardly obtain the ratio between f n and f τ as:…”

Section: Total (Displacement Plus Particle) Current and Noise In Quanmentioning

confidence: 99%

Section: Total (Displacement Plus Particle) Current and Noise In Quanmentioning

confidence: 99%

See 1 more Smart Citation

Noise and charge discreteness as ultimate limit for the THz operation of ultra-small electronic devices

Colomés

Matéos

González

et al. 2020

Sci Rep

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“…The time-dependent total currents in equation ( 1) are computed with the BITLLES simulator [21] from self-consistent Monte Carlo solutions of the Boltzmann and Poisson equations. The temporal step of the simulations is ∆t = 7×10 −16 s. Finally, we notice that all the transient simulations have been repeated many times and the results properly averaged in order to minimize the presence of physical noise [22] (random fluctuations) in the current values.…”

Section: A Device Structure and Time-dependent Simulationsmentioning

confidence: 99%

Limitations of the Intrinsic Cutoff Frequency to Correctly Quantify the Speed of Nanoscale Transistors

Zhan

Colomés

Oriols

2017

IEEE Trans. Electron Devices

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Abstract-The definition of the intrinsic cut-off frequency (fT ) based on the current gain equals to one (0 dB) is critically analyzed. A condition for the validity of the quasi-static estimation of fT is established in terms of the temporal variations of the electric charge and electric flux on the drain, source and gate terminals. Due to the displacement current, an electron traversing the channel length generates a current pulse of finite temporal width. For electron devices where the intrinsic delay time of the current after a transient perturbation is comparable to such width, the displacement currents cannot be neglected and the quasi-static approximation becomes inaccurate. We provide numerical results for some ballistic transistors where the estimation of fT under the quasi-static approximation can be one order of magnitude larger than predictions obtained from a time-dependent numerical simulations of the intrinsic delay time (including particle and displacement currents). In other ballistic transistors, we show that the gate current phasor can be smaller than the drain one at all frequencies, giving no finite value for fT .

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“…At such timescales and length scales, a full quantum treatment of the electrical current is mandatory. Furthermore, the total current at such frequencies is the sum of the conduction (flux of particles) plus the displacement (time derivative of the electric field) components [53,[69][70][71].…”

Section: The Quantum Noise At High Frequenciesmentioning

confidence: 99%

Identifying weak values with intrinsic dynamical properties in modal theories

et al. 2021

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The so-called eigenvalue-eigenstate link states that no property can be associated to a quantum system unless it is in an eigenstate of the corresponding operator. This precludes the assignation of properties to unmeasured quantum systems in general. This arbitrary limitation of orthodox quantum mechanics generates many puzzling situations such as for example the impossibility to uniquely define a work distribution, an essential building block of quantum thermodynamics. Alternatively, modal theories (e.g., Bohmian mechanics) provide an ontology that always allows one to define intrinsic properties, i.e., properties of quantum systems that are detached from any possible measuring context. We prove here that Aharonov, Albert, and Vaidman's notion of a weak value can always be identified with an intrinsic dynamical property of a quantum system defined in a certain modal theory. Furthermore, the fact that weak values are experimentally accessible (as an ensemble average of weak measurements which are postselected by a strong measurement) strengthens the idea that understanding the intrinsic (unperturbed) dynamics of quantum systems is possible and useful in a given modal theory. As examples of the physical soundness of these intrinsic properties, we discuss three intrinsic Bohmian properties, viz., the dwell time, the work distribution, and the quantum noise at high frequencies.

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Time-dependent simulation of particle and displacement currents in THz graphene transistors

Cited by 8 publications

References 35 publications

Noise and charge discreteness as ultimate limit for the THz operation of ultra-small electronic devices

Noise and charge discreteness as ultimate limit for the THz operation of ultra-small electronic devices

Limitations of the Intrinsic Cutoff Frequency to Correctly Quantify the Speed of Nanoscale Transistors

Identifying weak values with intrinsic dynamical properties in modal theories

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