Stefano Venica

Simulation of DC and RF Performance of the Graphene Base Transistor

We 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.

Going ballistic: Graphene hot electron transistors

This paper reviews the experimental and theoretical state of the art in ballistic hot electron transistors that utilize two-dimensional base contacts made from graphene, i.e. graphene base transist ...

Graphene base transistors with optimized emitter and dielectrics

The Graphene Base Transistor (GBT) is a very promising device concept for analog applications. The device operates similar to the hot electron transistor and exploits the high carrier mobility of graphene to reduce the base resistance that limits the unity power gain frequency (fmax) and the noise figure (NF) of RF devices. Although the DC functionality of the GBT has been experimentally demonstrated, at present RF performance can be investigated by simulations only. In this paper, we predict the DC current and the cutoff frequency of different GBT designs (including dimensions and various materials), with the aim to optimize the GBT structure and to achieve THz operation. In particular, optimized emitter/dielectrics combinations are proposed to maximize RF figures of merit.

Detailed characterization and critical discussion of series resistance in graphene-metal contacts

We apply the contact-end resistance method to TLM structures in order to characterize the graphene-metal contact resistance. A critical analysis of the experimental results shows that the commonly used transmission line model fails to accurately describe the graphene-metal contact under specific biasing conditions. The experiments suggest the presence of an additional resistance contribution associated to the p-p+ junction induced in the graphene in the proximity of the contact. This voltage dependent resistance limits the range of applicability of the extraction technique. However, for carefully chosen bias conditions that reduce this additional resistance to small values, the technique provides reliable results, useful to investigate the graphene-metal contact properties and their technology dependence.

Modeling electrostatic doping and series resistance in graphene-FETs

We model the source/drain series resistance and the electrostatic doping effects associated to the source and drain metals in graphene FETs using a Monte Carlo transport simulator. We compare the new model to simulations assuming chemical doping in the source/drain regions. A procedure to include the series resistance as part of the self-consistent Monte Carlo loop is proposed and verified against the widely employed method based on look-up tables.

State-of-the-art semi-classical Monte Carlo method for carrier transport in nanoscale transistors

We 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.

On the Adequacy of the Transmission Line Model to Describe the Graphene–Metal Contact Resistance

The 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.

Graphene Base Transistors With Bilayer Tunnel Barriers: Performance Evaluation and Design Guidelines

Graphene-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.