Nonlinearity, Scaling Trends of Quasi-Ballistic Graphene Field Effect Transistors Targeting RF Applications (original) (raw)
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RF DEVICE CHARACTERIZATION OF GRAPHENE TRANSISTORS
ProQuest, 2023
Radio Frequency performance of field-effect transistors has been explored in depth, experimented and industrially in use since a long time. Whenever one thinks of transistors which could take us to the regime of more than 1 THz in frequency it would always be the High Electron Mobility Transistors (HEMTS) as the perfect solution to that. The Graphene transistors have been very much in research from 2010 and promise equal results due to their huge potential in mobility. In the Semiconductor Manufacturing And Fabrication Laboratory at the Rochester Institute Of Technology our research group has been designing, fabricating and characterizing the graphene transistors of top-gated and back- gated varieties of which the former has been more explored and characterized because of its potential in high frequency performance. In this thesis characterization of both the top-gated and the back-gated varieties will be discussed in intricate detail with different permutation and combinations in experiments in order to depict the efficiency of these transistors in terms of their frequency characteristics and the possible ways to optimize the mobility and transconductance, thereby changing the hysteresis behaviours of the top-gated transistors. The maximum oscillation frequency has been explored for the top- gated variant where it can be estimated how they are in performance and exhibit unique nature compared to that of the PMOS and the NMOS devices along with this distinctive hysteresis behaviours by application of a polymer on GFETs has been investigated.
RF performance of short channel graphene field-effect transistor
2010
Introduction: Graphene, a two dimensional single sheet of carbon atoms with excellent electronic properties, has attracted tremendous research efforts because of its high carrier mobility and velocity . While the lack of a bandgap in graphene makes its use challenging for digital applications, significant progress has been made on graphene analog devices for radio-frequency (RF) applications, where a high on/off ratio is not necessarily required. Recently, graphene RF transistors [6-7] with a cut-off frequency as high as 100 GHz have been demonstrated . Future advances in the RF performance would rely on the proper scaling of the graphene channel. Despite extensive theoretical efforts, a systematic experimental scaling study has been largely lacking. In this paper, we present experimental studies on transport characteristics of graphene FETs with channel lengths down to 70 nm. The factors limiting the performance of short channel graphene devices are discussed. RF performance of a sub-100 nm graphene transistor fabricated on epitaxial graphene grown on a SiC substrate is also presented. A cut-off frequency as high as 170 GHz is achieved in a 90 nm graphene FET using a scalable top-down fabrication processes. Our results indicate that further improvement of RF performance of graphene FETs can be enabled by channel length scaling with structure optimization and contact resistance reduction. Experiments: 20nm Pd/30nm Au by e-beam evaporation is used as the contact metal. NFC/HfO2 is used as the top gate dielectric for top-gated RF devices . Results and discussion: The carrier density dependence of the total resistance of a 1µm and a 70 nm device at V ds =10 mV at room temperature is shown in . The mobility can be extracted by model fitting . The quantum capacitance and the impact of gate field on contact resistance are not considered here. and show the output characteristics of the 1µm and 70 nm device at room temperature and low temperature. summarizes the temperature-dependent transfer characteristics for the 70 nm device. The transconductance is increased by almost 40% when measured at low temperature as shown in summarizes the temperature dependence of carrier mobility. The decrease of effective mobility as the channel gets shorter is a strong signature of quasi-ballistic transport. . summarizes the temperature dependent contact resistance of the three different devices. The reduction of contact resistance would greatly benefit the DC and RF performance, especially for short channel devices. In order to evaluate the performance of short channel graphene devices for RF applications, a "virtual source" model, which was originally developed for Si MOSFET [9], is adopted here after incorporating the effect of residual doping at the Dirac point, drain-induced doping effect
IEEE Transactions on Electron Devices, 2011
We present a compact physics-based model of the current-voltage characteristics of graphene field-effect transistors, of especial interest for analog and radio-frequency applications where bandgap engineering of graphene could be not needed. The physical framework is a field-effect model and drift-diffusion carrier transport. Explicit closed-form expressions have been derived for the drain current. The model has been benchmarked with measured prototype devices, demonstrating accuracy and predictive behavior.
2013
We present an analytical model for the I-V characteristics of Grephene Nanoribbon Field Effect Transistors (GNRFETs) based on effective mass approximation and semiclassical ballistic transport. The model incorporates the effects of edge bond relaxation and third nearest neighbor (3NN) interaction as well as thermal broadening. Several performance metrics of double-gate GNR-FETs, operating close to quantum capacitance limit, are calculated. Numerical results show that AGNRs with widths of about 3-4 nm at most are required in order to obtain optimum high frequency and switching performance.
Impact of channel length and width for charge transportation of graphene field effect transistor
Chinese Journal of Chemical Physics, 2020
The effect of channel length and width on the large and small-signal parameters of the graphene field effect transistor (GFET) have been explored using an analytical approach. In the case of faster saturation as well as extremely high transit frequency, GFET shows outstanding performance. From the transfer curve, it is observed that there is a positive shift of Dirac point from the voltage of 0.15 V to 0.35 V because of reducing channel length from 440 nm to 20 nm and this curve depicts that graphene shows ambipolar behavior. Besides, it is found that because of widening channel the drain current increases and the maximum current is found approximately 2.4 mA and 6 mA for channel width 2 µm and 5 µm respectively. Furthermore, an approximate symmetrical capacitance-voltage (C-V) characteristic of GFET is obtained and the capacitance reduces when the channel length decreases but the capacitance can be increased by raising the channel width. In addition, a high transconductance, that demands high-speed radio frequency (RF) applications, of 6.4 mS at channel length 20 nm and 4.45 mS at channel width 5 µm along with a high transit frequency of 3.95 THz have been found that demands high-speed radio frequency applications.
IEEE Journal of the Electron Devices Society
This paper addresses the high-frequency performance limitations of graphene field-effect transistors (GFETs) caused by material imperfections. To understand these limitations, we performed a comprehensive study of the relationship between the quality of graphene and surrounding materials and the high-frequency performance of GFETs fabricated on a silicon chip. We measured the transit frequency (f T) and the maximum frequency of oscillation (f max) for a set of GFETs across the chip, and as a measure of the material quality, we chose low-field carrier mobility. The low-field mobility varied across the chip from 600 cm 2 /Vs to 2000 cm 2 /Vs, while the f T and f max frequencies varied from 20 GHz to 37 GHz. The relationship between these frequencies and the low-field mobility was observed experimentally and explained using a methodology based on a small-signal equivalent circuit model with parameters extracted from the drain resistance model and the charge-carrier velocity saturation model. Sensitivity analysis clarified the effects of equivalent-circuit parameters on the f T and f max frequencies. To improve the GFET high-frequency performance, the transconductance was the most critical parameter, which could be improved by increasing the charge-carrier saturation velocity by selecting adjacent dielectric materials with optical phonon energies higher than that of SiO 2. INDEX TERMS Graphene, field-effect transistors, high frequency, transit frequency, maximum frequency of oscillation, microwave electronics, contact resistances, transconductance.
RF Performance Projections of Graphene FETs vs. Silicon MOSFETs
2011
A graphene field-effect-transistor (GFET) model calibrated with extracted device parameters and a commercial 65 nm silicon MOSFET model are compared with respect to their radio frequency behavior. GFETs slightly lag behind CMOS in terms of speed despite their higher mobility. This is counterintuitive, but can be explained by the effect of a strongly nonlinear voltage-dependent gate capacitance. GFETs achieve their maximum performance only for narrow ranges of V DS and I DS , which must be carefully considered for circuit design. For our parameter set, GFETs require at least µ=3000 cm 2 V -1 s -1 to achieve the same performance as 65nm silicon MOSFETs.
Nanomaterials
The interest in graphene-based electronics is due to graphene’s great carrier mobility, atomic thickness, resistance to radiation, and tolerance to extreme temperatures. These characteristics enable the development of extremely miniaturized high-performing electronic devices for next-generation radiofrequency (RF) communication systems. The main building block of graphene-based electronics is the graphene-field effect transistor (GFET). An important issue hindering the diffusion of GFET-based circuits on a commercial level is the repeatability of the fabrication process, which affects the uncertainty of both the device geometry and the graphene quality. Concerning the GFET geometrical parameters, it is well known that the channel length is the main factor that determines the high-frequency limitations of a field-effect transistor, and is therefore the parameter that should be better controlled during the fabrication. Nevertheless, other parameters are affected by a fabrication-relat...
Current transport in graphene tunnel field effect transistor for RF integrated circuits
In this work, an analytical model of Graphene Nanoribbon (GNR) T Transistor (T-FET) is presented conside voltage (V DS ), gate source voltage (V GS ), c and top gate dielectric (t OX ). For a GNR 0.275eV band gap, ON current of 1605 µ with a very high ON/OFF current ratio o slope of 7.07mV/decade is calculated fr characteristics. Current saturation is o voltage, V GS of 0.28V and beyond for v Performance of the proposed model is c earlier published work and the proj MOSFET requirements and it is found proper device geometry and input voltage demonstrate seven times lower power dis times higher intrinsic speed in the upper conventional CMOS technology.
IEEE Transactions on Electron Devices, 2000
The analytical model of the small-signal current and capacitance characteristics of RF graphene FET is presented. The model is based on explicit distributions of chemical potential in graphene channels (including ambipolar conductivity at high source-drain bias) obtained in the framework of drift-diffusion current continuity equation solution. Small-signal transconductance and output conductance characteristics are modeled taking into account the two modes of drain current saturation including drift velocity saturation or electrostatic pinch-off. Analytical closed expression for the complex current gain and the cutoff frequency of high-frequency GFETs are obtained. The model allows describe an impact of parasitic resistances, capacitances, interface traps on extrinsic current gain and cut-off frequency.