2D Electronics Based on Graphene Field Effect Transistors: Tutorial for Modelling and Simulation

Modular Fabrication of Microfluidic Graphene FET for Nucleic Acids Biosensing

Graphene field-effect transistors (GFETs) are widely used in biosensing due to their excellent properties in biomolecular signal amplification, exhibiting great potential for high-sensitivity and point-of-care testing in clinical diagnosis. However, difficulties in complicated fabrication steps are the main limitations for the further studies and applications of GFETs. In this study, a modular fabrication technique is introduced to construct microfluidic GFET biosensors within 3 independent steps. The low-melting metal electrodes and intricate flow channels are incorporated to maintain the structural integrity of graphene and facilitate subsequent sensing operations. The as-fabricated GFET biosensor demonstrates excellent long-term stability, and performs effectively in various ion environments. It also exhibits high sensitivity and selectivity for detecting single-stranded nucleic acids at a 10 fm concentration. Furthermore, when combined with the CRISPR/Cas12a system, it facilitates amplification-free and rapid detection of nucleic acids at a concentration of 1 fm. Thus, it is believed that this modular-fabricated microfluidic GFET may shed light on further development of FET-based biosensors in various applications.

The design of a point of care FET biosensor to detect and screen COVID-19

Graphene field effect transistor (FET) biosensors have attracted huge attention in the point-of-care and accurate detection. With the recent spread of the new emerging severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the need for rapid, and accurate detection & screening tools is arising. Employing these easy-to-handle sensors can offer cheap, rapid, and accurate detection. Herein, we propose the design of a reduced graphene oxide (rGO) FET biosensor for the detection of SARS-CoV-2. The main objective of this work is to detect the SARS-CoV-2 spike protein antigen on spot selectively and rapidly. The sensor consists of rGO channel, a pair of golden electrodes, and a gate underneath the channel. The channel is functionalized with COVID-19 spike protein antibodies to achieve selectivity, and with metal nanoparticles (MNPs) such as copper and silver to enhance the bio-sensing performance. The designed sensor successfully detects the SARS-CoV-2 spike protein and shows singular electrical behavior for detection. The semi-empirical modeling approach combined with none-equilibrium Green's function were used to study the electronic transport properties of the rGO-FET biosensor before and after the addition of the target molecules. The sensor's selectivity is also tested against other viruses. This study provides a promising guide for future practical fabrication.

Extraction of Graphene's RF Impedance through Thru-Reflect-Line Calibration

Graphene has unique properties that can be exploited for radiofrequency applications. Its characterization is key for the development of new graphene devices, circuits, and systems. Due to the two-dimensional nature of graphene, there are challenges in the methodology to extract relevant characteristics that are necessary for device design. In this work, the Thru-Reflect-Line (TRL) calibration was evaluated as a solution to extract graphene's electrical characteristics from 1 GHz to 65 GHz, where the calibration structures' requirements were analyzed. It was demonstrated that thick metallic contacts, a low-loss substrate, and a short and thin contact are necessary to characterize graphene. Furthermore, since graphene's properties are dependent on the polarization voltage applied, a backgate has to be included so that graphene can be characterized for different chemical potentials. Such characterization is mandatory for the design of graphene RF electronics and can be used to extract characteristics such as graphene's resistance, quantum capacitance, and kinetic inductance. Finally, the proposed structure was characterized, and graphene's resistance and quantum capacitance were extracted.

Graphene-Based Microwave Circuits: A Review

Over the past two decades, research on 2D materials has received much interest. Graphene is the most promising candidate regarding high-frequency applications thus far due to is high carrier mobility. Here, the research about the employment of graphene in micro- and millimeter-wave circuits is reviewed. The review starts with the different methodologies to grow and transfer graphene, before discussing the way graphene-based field-effect-transistors (GFETs) and diodes are built. A review on different approaches for realizing these devices is provided before discussing the employment of both GFETs and graphene diodes in different micro- and millimeter-wave circuits, showing the possibilities but also the limitations of this 2D material for high-frequency applications.

Numerical Evaluation of the Effect of Geometric Tolerances on the High-Frequency Performance of Graphene Field-Effect Transistors

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-related tolerance; to understand to which extent an increase of the accuracy of the GFET layout patterning process steps can improve the performance uniformity, their impact on the GFET performance variability should be considered and compared to that of the channel length. In this work, we assess the impact of the fabrication-related tolerances of GFET-base amplifier geometrical parameters on the RF performance, in terms of the amplifier transit frequency and maximum oscillation frequency, by using a design-of-experiments approach.