1,720,966 research outputs found
Modeling and Simulation of Graphene-Based Devices for RF Applications
Full text linkThe first experimental preparation and characterization of a monolayer graphene in 2004 has triggered the interest of the scientific community because of the peculiar graphene properties (e.g. structural, electrical). The two-dimensional (2D) structure with monoatomic thickness and the incredible high carrier mobility of graphene have created widespread expectations that it could be the perfect material for future nanoelectronic devices. Graphene-Field-Effect-Transistors (GFETs) have been extensively investigated, but the absence of an energy bandgap in monolayer graphene (which heavily hampers its use in digital electronics which requires high Ion/Ioff ratios) leads to non-saturated output characteristics, hence in poor intrinsic voltage gains. For this reason, vertical graphene-based architectures, as the Graphene-Base-Transistor (GBT), have been proposed as alternative solution for THz RF electronics. Unluckily, the technological difficulties related to the fabrication processes have slowed-down the improvement of these transistor concepts. Because of the early stage of the technology, the modeling and simulations play a major role, in order to understand the physical mechanisms involved in the graphene-based device operation and to provide useful guidelines to support the design of optimized devices.
This thesis is positioned in this framework, and it is focused on the development of physics-based models and simulators for GFETs and GBTs, with the aim to support the design of fast transistors and to reliably predict the device performance limits. Concerning GFETs, in this work we mostly focused on the drawbacks related to the series resistances associated to the metal/graphene contact, both from modeling and experimental perspectives. For GBTs, instead, we developed an electrical model and a single-particle Monte Carlo simulator able to predict the RF performance and the impact of electron scattering on the device operation, respectively.
The developed simulators represent an important set of tools to support future investigations on the use in electronic devices of graphene and other 2D materials, e.g. semiconducting transition metal dichalcogenides, which show properties that can overcome the limits of graphene
Backscattering and common-base current gain of the Graphene Base Transistor (GBT)
Full text linkIn this paper, we investigate electron transport and electron scattering in the insulators of the Graphene Base Transistor (GBT) by means of a Monte Carlo transport model. We focus on electron backscattering in the base-collector insulator as the possible root cause of the large experimental base current and small measured common-base current gain (αF) of GBTs. Different GBT structures have been simulated and the impact of the scattering parameters on the base current is analyzed. Simulated backscattering-limited αF values are found to be much higher than available experimental data, suggesting that state-of-the-art technology is still far from being optimized. However, those simulated αF values can be low enough to limit the maximum achievable GBT performance
Simulation Study of the Graphene Base Transistor
No full textThe Graphene Base Transistor (GBT) has been recently proposed to possibly overcome the THz limit for RF circuits. We developed a modelling framework to explore the GBT design space, the device optimization and the prediction of its RF performance. Via a proper scaling of the EBI and BCI thicknesses, the THz operation is achievable both in terms of fT and fmax. In this latter case, a very low RCONT value is required, thus it is necessary to improve the metal-graphene interface beyond state of the art graphene technology
Graphene base transistors with bilayer tunnel barriers: Performance evaluation and design guidelines
No full textGraphene-based capacitors and Graphene base transistors (GBTs) featuring innovative engineered tunnel barriers are characterized in DC and the data are thoroughly analyzed by means of an electrical model and a Monte Carlo transport simulator. Following model calibration on experiments, we then propose strategies to improve the DC common-base current gain and the cutoff frequency of GBTs. The DC and RF performance of optimized GBT structures based on realistic technology data are analyzed in detail to highlight advantages and potential limits of this device concept
Simulation of DC and RF Performance of the Graphene Base Transistor
No full textWe examined the DC and RF performance of the graphene base transistor (GBT) in the ideal limit of unity common base current gain. To this purpose, we developed a model to calculate the current–voltage characteristics of GBTs with semiconductor or metal emitter taking into account space charge effects in the emitter–base and base–collector dielectrics that distort the potential profile and limit the upper value of fT.
Model predictions are compared with available experiments. We show that, in spite of space charge high current effects, optimized GBT designs still hold the promise to achieve intrinsic cutoff frequency in the terahertz region, provided that an appropriate set of dielectric and emitter materials is chosen
Dependability Assessment of Transfer Length Method to Extract the Metal–Graphene Contact Resistance
Full text linkThe measurement of the contact resistance (RC) in semiconductor devices relies on the well–established Transfer Length Method (TLM). However, an in–depth investigation on its applicability to characterize the metal–graphene contacts is still missing. In this work, a dependability analysis on the RC values extracted from several metal–graphene stacks is performed, also devising strategies to limit the large observed statistical errors and to obtain dependable results. In particular, artifacts due to an incorrect application of TLM, e.g., negative resistance values, can be eliminated. Finally, a simulation study is proposed to quantify the contribution to RC of the so–called junction resistance at the edge of the contact, that some authors in the literature invoke to explain the observed artifacts
On the Adequacy of the Transmission Line Model to Describe the Graphene-Metal Contact Resistance
Full text linkThe contact-end-resistance (CER) method is applied to transfer length method structures to characterize in-depth the graphene-metal contact and its dependence on the back-gate bias. Parameters describing the graphene-metal stack resistance are extracted through the widely used transmission line model. The results show inconsistencies which highlight application limits of the model underlying the extraction method. These limits are attributed to the additional resistance associated with the p-p+ junction located at the contact edge, that is not part of the conventional transmission line model. Useful guidelines for a correct application of the extraction technique are provided, identifying the bias range in which this additional resistance is negligible. Finally, the CER method and the transmission line model are exploited to characterize the graphene-metal contacts featuring different metals. © 2012 IEEE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
State-of-the-art semi-classical Monte Carlo method for carrier transport in nanoscale transistors
No full textWe review the Monte Carlo method to model
semi-classical carrier transport in advanced semiconductor
devices. We report examples of the use of the Multi-
Subband Monte Carlo method to simulate MOSFETs with
III-V compound semiconductor channel. Monte Carlo
transport modeling of graphene-based transistors is also
addressed
- …
