Model For Graphene Field-effect Transistors Research Articles

The Behavioural Model of Graphene Field-effect Transistor

The behavioural model of a graphene field-effect transistor (GFET) is proposed. In this approach the GFET element is treated as a “black box” with only external terminals available and without considering the physical phenomena directly. The presented circuit model was constructed to reflect steady-states characteristics taking also into account GFET capacitances. The authors’ model is defined by a relatively small number of equations which are not nested and all the parameters can be easily extracted. It was demonstrated that the proposed model allows to simulate the steady-state characteristics with the accuracy approximately as high as in the case of the physical model. The presented compact GFET model can be used for circuit or system-level simulations in the future.

Ring oscillators based on monolayer Graphene FET

A ring oscillator is an important circuit used to evaluate the performance limits of any digital technology. The advantages of Graphene field effect transistor (GFET) over current CMOS technologies make it a prominent candidate for future high-performance electronics. In this paper, a GFET model is implemented in Verilog-A, and GFET design and analysis of a ring oscillator are performed using advanced design system (ADS) tool. By using GFET ring oscillator, the designed circuit is simulated using a 0.18 µm GFET process in ADS environment. The results show that the power consumption is 9.98 mW, while the VCO generates 24.12 GHz at 1 V. The effect of Graphene channel length variations on the frequency span, power dissipation and phase noise of GFET ring oscillators are studied. The main performance characteristics of the ring oscillator are compared with CMOS technology. It is shown that a GFET ring oscillator gives a higher oscillation frequency and has more power dissipation.

Empirical Drain Current Model of Graphene Field-Effect Transistor for Application as a Circuit Simulation Tool

In this paper, an empirical model of dual gate graphene field-effect transistor (GFET) has been developed. The explicit form of drain current expression has been established analytically based on a drift-diffusion approach. The channel sheet charge density helps us to determine the quantum capacitance more accurately. The channel potential has been derived from the equivalent circuit. The improvement of carrier mobility has been included. The closed form expression is obtained with a few fitting parameters to explore the model characteristics. The model is also valid for single gate technology. The model has been verified against some pioneering experimental results reported in literatures. Model simulation agrees well with existing experimental data. We have also compared the results of the model obtained from NANOHUB online simulator for further verification. The characteristics of small signal parameters of this GFET model have been observed and cut-off frequency has been determined. The developed analytical GFET model is also found to be computationally efficient. It is observed that with ± 10% variation in top gate oxide thickness, maximum drain current and peak transconductance vary by (−11.53%/ + 14%) and (−25%/+31.25%), respectively. The double gate bilayer GFET model is implemented in Verilog-A and verified for a voltage amplifier in SPICE environment.

Distributed Amplifier Based on Monolayer Graphene Field Effect Transistor

Due to the ultra-high carrier mobility and ultralow resistivity of Graphene channel, a Graphene field effect transistor (GFET) is an interesting candidate for future RF and microwave electronics. In this paper, the introduction and review of existing compact circuit-level model of GFETs are presented. A compact GFET model based on drift-diffusion transport theory is then implemented in Verilog-A for RF/microwave circuit analysis. Finally, the GFET model is used to design a GFET-based distributed amplifier (DA) using advanced design system (ADS) tools. The simulation results demonstrate a gain of 8[Formula: see text]dB, an input/output return loss less than [Formula: see text]10[Formula: see text]dB, [Formula: see text]3[Formula: see text]dB bandwidth from DC up to 5[Formula: see text]GHz and a dissipation of about 60.45[Formula: see text]mW for a 1.5[Formula: see text]V power supply. The main performance characteristics of the distributed amplifier are compared with 0.18[Formula: see text][Formula: see text]m CMOS technology.

A model of carrier density and drain current for monolayer graphene field-effect transistors

A model of carrier density and drain current for monolayer graphene field-effect transistors (GFET) is proposed in this paper. In general, the carrier density is the numerical integration of the density of states (DOS) and Fermi-Dirac distribution. To avoid numerical solution, a physical-based and analytical calculation for carrier density and quantum capacitance is presented. Due to the intrinsic physical mechanism, the interface trap density is taken into account in the drain current model of GFET. Through the comparisons between model results and numerical iterations or experimental data, the validity of the proposed models is supported. The clear physical conception and simplicity of algorithm make our scheme suitable for compact modelling.

Device and Compact Circuit-Level Modeling of Graphene Field-Effect Transistors for RF and Microwave Applications

Graphene field-effect transistors (GFETs) are promising candidates for future nano-electronic circuitry with excellent radio frequency (RF) and microwave performance due to the ultra-high carrier mobility, large saturation velocity, and good electrical conductivity of the graphene channel. In this paper, a compact circuit-level model of GFETs is proposed for RF and microwave high-frequency applications. An improved double-gate monolayer short channel GFET with an agate length of 150 nm was first designed and fabricated by self-aligned gate processing, enabled by optimized organic, contamination-free graphene transfer, for realizing high working frequency up to 40 GHz. A compact, precise circuit-level model, including the linear and nonlinear operation of GFETs, is then proposed with model parameters extracted based on the test data from the fabricated GFETs. The proposed model is capable of precisely simulating the ambipolar status of GFETs working up to microwave frequency. The calculated errors of the S-parameters, the reflection coefficient, the gain, (all in decibel), and the I–V data (in decimal) are less than 3.5%, 4.1%, 3.1%, and 2.4%, respectively. By defining as the symbolically defined device module, the GFET model with gate dimensional scalability can be easily embedded in the common commercial simulators for RF and microwave circuit and system level designs.

A Unified Scalable Quasi-Ballistic Transport Model of GFET for Circuit Simulations

A unified quasi-ballistic transport model is developed for single- and double-gate graphene field-effect transistors (GFETs) using the McKelvey flux theory approach. The proposed model is compact, scalable, and compatible for the simulation of I-V characteristics of GFET for all regions of device operation. The drain current equation (IDS) incorporates the formulation of quasithermal velocity, quasi-ballistic mobility of charge carrier (describe the carrier transport of 2-D material like graphene), and source/drain backscattering coefficient. This model is also capable to describe the mobility of graphene material in degenerate and nondegenerate states. The GFET with different channel lengths, widths, and oxide thicknesses is simulated using this model for single- and double-gate devices. The proposed model synchronized with experimental results and explains the peculiar transport characteristics of GFET with normalized root-mean-square error less than 9%.

Intrinsic carrier mobility extraction based on a new quasi-analytical model for graphene field-effect transistors

The most common method of mobility extraction for graphene field-effect transistors is proposed by Kim. Kim’s method assumes a constant mobility independent of carrier density and gets the mobility by fitting the transfer curves. However, carrier mobility changes with the carrier density, leading to the inaccuracy of Kim’s method. In our paper, a new and more accurate method is proposed to extract mobility by fitting the output curves at a constant gate voltage. The output curves are fitted using several kinds of current–voltage models. Besides the models in the literature, we present a modified model, which takes into account not only the quantum capacitance, contact resistance, but also a modified drift velocity-field relationship. Comparing with the other models, this new model can fit better with our experimental data. The dependence of carrier intrinsic mobility on carrier density is obtained based on this model.

Large-Signal Model of Graphene Field-Effect Transistors—Part I: Compact Modeling of GFET Intrinsic Capacitances

We present a circuit-compatible compact model of the intrinsic capacitances of graphene field-effect transistors (GFETs). Together with a compact drain current model, a large-signal model of GFETs is developed combining both models as a tool for simulating the electrical behavior of graphene-based integrated circuits, dealing with the DC, transient behavior, and frequency response of the circuit. The drain current model is based in a drift-diffusion mechanism for the carrier transport coupled with an appropriate field-effect approach. The intrinsic capacitance model consists of a 16-capacitance matrix including self-capacitances and transcapacitances of a four-terminal GFET. To guarantee charge conservation, a Ward-Dutton linear charge partition scheme has been used. The large-signal model has been implemented in Verilog-A, being compatible with conventional circuit simulators and serving as a starting point toward the complete GFET device model that could incorporate additional non-idealities.

Graphene Field-Effect Transistor Model With Improved Carrier Mobility Analysis

This paper presents a SPICE-like graphene field-effect transistor (GFET) model with an improved carrier mobility analysis. The model considers the mobility difference between the electrons and the holes in graphene, as well as the mobility variation against the carrier density. Closed-form analytical solutions have been derived, and the model has been implemented in Verilog-A language. This was compiled into an advanced design system. The proposed model gives excellent agreement between the simulation results and the measurement data for both the hole and electron conduction simultaneously. The model is suitable for the exploration of GFET-based applications, especially for those using the ambipolar transfer property of GFET.

Empirical Modeling of a Graphene Field-Effect Transistor Sensor

This theoretical nanoscience work explore the empirical method of extracting experimental radiation sensor data from published work and project the performance limit of the sensor in term of back gate voltage, resistance and radiation flux. We demonstrate an empirical regression modeling of an X-ray radiation sensor based on a graphene field effect transistor (GFET). The experimental data obtained from published work only showed the values of resistance, R versus back gate voltage, Vbg for X-ray flux, E of 0 kV, 30 kV and 40 kV. Least Squares Estimation (LSE) in nonlinear regression model is utilized to obtain the individual polynomial regression model of resistance versus back gate voltage model for each of the 3 X-ray flux. LSE with multiple nonlinear regression incorporating with Nimmo and Atkinsmethod is employ to get a unified polynomial regression based on the individual model. The model is simulated in MATLAB and provide fast execution time. The unified model for is able to predict the resistance versus back gate voltage for various X-ray radiation flux beyond these three values given values. In addition to that, we are able to find the limit of X-ray flux based on the initial characteristic. Moreover, our technique enable one to visualize the interrelationship between R, Vbg and E variables and perform multivariate analysis. The empirical regression model of GFET is shown to have good agreement with experimental data and theoretical prediction for multivariate such as back gate voltage, resistance and X-ray flux.

Semianalytical quantum model for graphene field-effect transistors

We develop a semianalytical model for monolayer graphene field-effect transistors in the ballistic limit. Two types of devices are considered: in the first device, the source and drain regions are doped by charge transfer with Schottky contacts, while, in the second device, the source and drain regions are doped electrostatically by a back gate. The model captures two important effects that influence the operation of both devices: (i) the finite density of states in the source and drain regions, which limits the number of states available for transport and can be responsible for negative output differential resistance effects, and (ii) quantum tunneling across the potential steps at the source-channel and drain-channel interfaces. By comparison with a self-consistent non-equilibrium Green's function solver, we show that our model provides very accurate results for both types of devices, in the bias region of quasi-saturation as well as in that of negative differential resistance.

An Accurate and Verilog-A Compatible Compact Model for Graphene Field-Effect Transistors

The present paper provides an accurate drift-diffusion model of the graphene field-effect transistor (GFET). A precise yet mathematically simple current-voltage relation is derived by focusing on device physics at energy levels close to the Dirac point. With respect to previous work, our approach extends modeling accuracy to the low-voltage biasing regime and improves the prediction of current saturation. These advantages are highlighted by a comparison study of the drain current, transconductance, output conductance, and intrinsic gain. The model has been implemented in Verilog-A and is compatible with conventional circuit simulators. It is provided as a tool for the exploration of GFET-based integrated circuit design. The model shows good agreement with measurement data from GFET prototypes.

A quantum statistical model for graphene FETs on SiC

We present a quantum statistical model for nanoscale graphene field-effect transistors (FETs) on a SiC substrate. In the model, the scattering events as well as ballistic transport are taken into account. The channel charge and current are calculated with the Keldysh non-equilibrium Green's function technique. The model, which is meant for the design of the graphene FETs, is semianalytical, but it is easy to reduce the model to a simple fully analytical one, which then can be applied to the design of the integrated circuits made of graphene. It is shown that the neglect of the scattering would lead to too large values for the saturation current. The calculated transconductance and the on-off ratio for the saturation current are in agreement with the experimental results.

Explicit Drain Current, Charge and Capacitance Model of Graphene Field-Effect Transistors

This paper presents a compact physics-based model of the drain current, charge, and capacitance of graphene field-effect transistors, which is of relevance for the exploration of dc, ac, and transient behavior of graphene-based circuits. The physical framework is a field-effect model and drift-diffusion carrier transport incorporating saturation velocity effects. First, an explicit model has been derived for the drain current. Using it as a basis, explicit closed-form expressions for the charge and capacitances based on the Ward-Dutton partition scheme were derived, covering continuously all the operation regions. The model is of special interest for analog and radio-frequency applications where bandgap engineering of graphene is not needed.