Bianca Adiaconita

In the actual microelectronics context, transistors with alternative semiconductor materials, using elements from the fourth group, other than silicon or germanium—for example, carbon—have become materials of extreme interest in overcoming certain limitations experienced by traditional MOSFETs. Therefore, graphene field-effect transistors (GFETs) offer the advantage of ambipolar conduction, providing static transfer characteristics dominated by ON current, I_ON, both at positive gate bias for the electron accumulation channel and at negative gate bias for the hole accumulation channel. Between these two ON states, a Dirac point arises as a minimum current, representing the moment of compensation between electron and hole currents, which essentially defines the OFF current, I_OFF. Due to this future development of GFET transistors, it is necessary to propose simulation techniques for optimizing these electronic devices. GFET simulations are present in the literature, but further calibrations are necessary, since graphene does not exist as a defined semiconductor material in the usual Technology Computer-Aided Design (TCAD) libraries. In addition, the properties of each graphene material differ from one experimental realization to another, depending on the technology applied by each author. This article starts with some experimental transfer characteristics measured for two types of fabricated GFET devices. Then, this study presents a few calibration techniques to simulate the graphene layer within GFET, aiming to fit the experimental transfer characteristics with the simulated curves while keeping some optimized technological sizes. The final goal of this article is to establish a list of GFET device parameters linked to the material properties and to estimate them through successive simulations, using empirical calibrations, for each type of experimental graphene material. This algorithm is not a validated procedure; instead, it indicates a set of sensitive GFET parameters, which allow for the adjustment of the shape and order of magnitude of the simulated current with the experimental one for given static characteristics.

Biosensing performance in graphene-derived field-effect transistors (BioFETs) is widely attributed to surface chemistry, yet the role of the underlying charge transport mechanism remains poorly understood. This work establishes a direct correlation between disorder-driven transport and biosensing transduction in vertical graphene (VG) and nanocrystalline graphite (NCG) FET devices. Temperature-dependent electrical characterization (15–500 K) reveals a hybrid transport regime: three-dimensional Mott variable-range hopping below 240 K, transitioning to thermally activated Arrhenius-type conduction above 240 K. The extracted VRH parameters characteristic temperature T₀, localization length ξ, and density of states N(E_F) quantify fundamentally distinct disorder landscapes: VG operates in a strongly localized, edge-dominated regime, while NCG forms a continuous percolative network with greater transport stability. Surface functionalization via PASE and amine-terminated ssDNA probes, followed by DNA hybridization across four nucleobase systems, demonstrates that the sequence-dependent electrical response is mechanistically interpretable within the VRH–transconductance framework. NCG transduces biomolecular binding through direct charge transfer and hopping pathway perturbation, whereas VG responds through interfacial electrostatic reorganization. These results introduce a unified VRH–transconductance–sensing framework, providing a rational physical basis for next-generation graphene BioFET design.

This study investigates the interfacial interactions between two organic semiconductors (tetrathiafulvalene (TTF) and hexaazatriphenylene-hexacarbonitrile (HAT-CN)) and graphene-based materials (nanocrystalline graphite and vertically aligned graphene) used in Field-Effect Transistors (FETs). The interaction mechanisms, including π–π stacking, charge transfer, and dipole–dipole interactions, were explored through SEM imaging, Raman and FTIR spectroscopy, and FET transfer characteristics. Spectroscopic data confirmed strong π–π and charge-transfer interactions, with distinct modifications in graphene structural and electronic features. Electrical measurements revealed significant modulation of channel conductivity, confirming effective surface functionalization. These findings provide a framework for engineering high-performance organic/graphene hybrid interfaces in electronic devices and biosensors. Importantly, the results demonstrate that molecular design and interfacial control at the nanoscale can be strategically used to modulate charge transport in graphene-based FETs. This approach opens new pathways for developing tunable, molecule-specific biosensors and nanoelectronic platforms with enhanced sensitivity and selectivity.

In recent years, field-effect transistors (FETs) based on graphene have attracted significant interest due to their unique electrical properties and their potential for biosensing and molecular detection applications. This study uses FETs with a nanocrystalline graphite (NCG) channel to detect DNA nucleobases. The exceptional electronic properties of NCG, and its high surface area, enable strong π–π stacking interactions with DNA nucleobases, promoting efficient adsorption and stabilization of the biomolecules. The direct attachment of nucleobases to the NCG channel leads to substantial changes in the device’s electrical characteristics, which can be measured in real time to assess DNA binding and sequence recognition. This method enables highly sensitive, label-free DNA detection, opening up new possibilities for rapid genetic analysis and diagnostics. Understanding the interactions between DNA nucleobases and graphene-based materials is crucial for advancing genetic research and biotechnology, paving the way for more accurate and efficient diagnostic tools.

Electrochemical sensors based on vertically oriented graphene (VG) have gained attention in recent years due to the unique properties of VG, such as its large surface area, biocompatibility, and high electrical conductivity. In this paper, we studied an electrochemical sensor with interdigitated electrodes modified with VG as an essential interface for the identification of two types of human colon adenocarcinoma cells: SW403 (high invasiveness) and HT29 (low invasiveness). Both cell lines have epithelial morphology, and we tested the electrochemical sensor on different concentrations of SW403 and HT29 cells. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used for morphological characterization of VG deposited on the working interdigitated electrodes, Raman spectroscopy was used to evaluate the graphitic nature of the VG growth on electrodes, and atomic force microscopy (AFM) was used to study the rugosity of the VG. Fourier-transform infrared spectrometry (FTIR) was used to study the configurations of the chemical bonds in the VG used for the working electrode of the electrochemical sensor. Vertically oriented graphene improves the sensor’s response on the cell lines, as evaluated by electrochemical impedance spectroscopy (EIS).

This paper explores the synthesis methods and properties of vertically aligned graphene nanosheets (VG) and their applications. VG is obtained using the plasma-enhanced chemical vapor deposition (PECVD) method, and different VG types with other properties can be obtained by changing the process parameters. VG is part of the graphene family; properties such as excellent electrical conductivity, thermal conductivity, chemical stability, and a large, specific surface area make it suitable for biomedical applications. Examples of biomedical applications in which VG is used are biosensors, electrochemical sensors, modified surfaces for bone growth, regeneration, and for antimicrobial effects. First, VG’s properties are reviewed in this review article, and then the most recent progress in its applications and related sciences and technologies are discussed.

In recent research, 3D printing has become a powerful technique and has been applied in the last few years to carbon-based materials. A new generation of 3D-printed electrodes, more affordable and easier to obtain due to rapid prototyping techniques, has emerged. We propose a customizable fabrication process for flexible (and rigid) carbon-based biosensors, from biosensor design to printable conductive inks. The electrochemical biosensors were obtained on a 50 µm Kapton^® (polyimide) substrate and transferred to a 500 µm PDMS substrate, using a 3D-extrusion-based printing method. The main features of our fabrication process consist of short-time customization implementation, fast small-to-medium batch production, ease of electrochemical spectroscopy measurements, and very good resolution for an extrusion-based printing method (100 µm). The sensors were designed for future integration into a smart wound dressing for wound monitoring and other biomedical applications. We increased their sensibility with electro-deposited gold nanoparticles. To assess the biosensors’ functionality, we performed surface functionalization with specific anti-N-protein antibodies for SARS-CoV 2 virus, with promising preliminary results.

This study proposes a feasible approach for the rapid, sensitive, and label-free identification of cancerous cells based on dielectrophoretic (DEP) manipulation and electrical characterization. In this method, the concentration of target cells at the level of customized microelectrodes via DEP is first determined, followed by an electrical impedance evaluation. The study demonstrates the capacity of the methodology to electrically differentiate HT-29 cancer cells from healthy blood cells based on their impedance spectra. Within a higher frequency domain, the electrical impedance of trapped cancer cells was significantly lower compared with the normal ones. In order to evaluate the functionality and reproducibility of the proposed method, the influence of the DEP and EIS (electrical impedance spectroscopy) operating voltages on the electrical characterization of trapped HT-29 cells was analyzed.