Towards RF graphene devices: A review

Graphene has been targeted for a wide variety of applications due to its characteristics. It is a zero-bandgap material, has high conductivity, and high carrier mobility, which makes it a promising material for radiofrequency applications. This review examines the applications of graphene in the design of radiofrequency building blocks, their performance, and current hurdles. Initially, graphene passive devices (inductors, capacitors, antennas, and waveguides) are analyzed, as well as their current modelling techniques. Then, radiofrequency transistors and their modelling are reported and discussed. An insight on the current state of radiofrequency devices is provided which more specifically targets graphene oscillators, multipliers, and mixers. Finally, the current fabrication issues and techniques are analyzed and discussed, providing a global overview on the application of graphene for radiofrequency electronics.Work supported by PTDC/EEI-TEL/29670/2017 - (POCI-01-0145-FEDER-029670), co-financed by the European Regional Development Fund (ERDF), through COMPETE 2020, grant SFRH/BD/141462/2018, grant SFRH/BD/137529/2018, grant UIDB/04436/2020, grant UIDP/04436/2020, and grant UIDB/04650/2020

Chemical vapour deposition of hexagonal boron nitride for two dimensional electronics

Hexagonal boron nitride (h-BN) has potential applications in protective coatings, single photon emitters and as substrate for graphene electronics. In this paper, we report on the growth of h-BN by chemical vapor deposition (CVD) using ammonia borane as the precursor. Use of CVD allows controlled synthesis over large areas defined by process parameters, e.g. temperature, time, process chamber pressure and gas partial pressures. Furthermore, independently grown graphene and h-BN layers are put together to realize enhancement in electronic properties of graphene.info:eu-repo/semantics/publishedVersio

Programmable graphene-based microfluidic sensor for DNA detection

This study presents the development of a lab-on-a-chip (LoC) by integrating a graphene field-effect transistor (FET) chip with a programmable microfluidic device for DNA detection. The real-time biochemical events on the graphene FET chip were monitored through Dirac voltage shift data from the portable graphene curve reader with changes dependent on the fluidic flow into the sensing interface by a fully automated programmable microfluidic system. High sensitivity with high reliability can be obtained with a nine-graphene sensor layout on a single chip. The portable graphene curve reader also provides a tunable electrical parameter setup and straightforward data acquisition. Fluidic control was performed through a multi-position valve, allowing sequential commands for liquid injection into the polydimethylsiloxane (PDMS) flow cell mounted on the sensing chip. The flow cell design with impinging jet geometry and the microfluidic system packaging offer high precision and portability as a less laborious and low-cost sensing setup. The merged system allows for various functionalities, including probe DNA (pDNA) immobilization, a blocking step, and DNA hybridization with stable signal output autonomously, even in a long-run experimental setup. As a DNA sensor, the proposed prototype has demonstrated a high sensitivity of ~44 mV/decade of target DNA concentration, with an outstanding limit of detection (LoD) of ~0.642 aM, making it one of the most sensitive sensors reported up to date. The programmable device has demonstrated essential versatilities for biomolecular detection in a fully portable and automated platform.This research is supported by PORTGRAPHE-Control of Port and Douro Wines authenticity using graphene DNA sensors project co-funded by Fundação para a Ciência e a Tecnologia (FCT) Portugal (PTDC/BIA-MOL/31069/2017) and the ERDF through COMPETE2020 (POCI-01–0145-FEDER-031069). One of the authors (Telma Domingues) acknowledges a Ph.D. grant from Fundação para a Ciência e a Tecnologia (FCT) Portugal (SFRH/BD/08181/2020). FCT partially supported University of Minho´s research in the Strategic Funding UIDB/04650/2020

Attomolar label-free detection of DNA hybridization with electrolyte-gated Graphene field-effect transistors

In this work, we develop a field-effect transistor with a two-dimensional channel made of a single graphene layer to achieve label-free detection of DNA hybridization down to attomolar concentration, while being able to discriminate a single nucleotide polymorphism (SNP). The SNP-level target specificity is achieved by immobilization of probe DNA on the graphene surface through a pyrene-derivative heterobifunctional linker. Biorecognition events result in a positive gate voltage shift of the graphene charge neutrality point. The graphene transistor biosensor displays a sensitivity of 24 mV/dec with a detection limit of 25 aM: the lowest target DNA concentration for which the sensor can discriminate between a perfect-match target sequence and SNP-containing one.Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2013 and project POCI01-0145-FEDER-031069 (PORTGRAPHE). G. Machado Jr. acknowledges a PhD grant (no. 237630/2012–5) from CNPq– Brazil. J.B. acknowledges European funding from NBFS project under contract NORTE-01-0145-FEDER-00001

Ultrasensitive dopamine detection with graphene aptasensor multitransistor arrays

Detecting physiological levels of neurotransmitters in biological samples can advance our understanding of brain disorders and lead to improved diagnostics and therapeutics. However, neurotransmitter sensors for real-world applications must reliably detect low concentrations of target analytes from small volume working samples. Herein, a platform for robust and ultrasensitive detection of dopamine, an essential neurotransmitter that underlies several brain disorders, based on graphene multitransistor arrays (gMTAs) functionalized with a selective DNA aptamer is presented. High-yield scalable methodologies optimized at the wafer level were employed to integrate multiple graphene transistors on small-size chips (4.5 × 4.5 mm). The multiple sensor array configuration permits independent and simultaneous replicate measurements of the same sample that produce robust average data, reducing sources of measurement variability. This procedure allowed sensitive and reproducible dopamine detection in ultra-low concentrations from small volume samples across physiological buffers and high ionic strength complex biological samples. The obtained limit-of-detection was 1 aM (10-18) with dynamic detection ranges spanning 10 orders of magnitude up to 100 µM (10-8), and a 22 mV/decade peak sensitivity in artificial cerebral spinal fluid. Dopamine detection in dopamine-depleted brain homogenates spiked with dopamine was also possible with a LOD of 1 aM, overcoming sensitivity losses typically observed in ion-sensitive sensors in complex biological samples. Furthermore, we show that our gMTAs platform can detect minimal changes in dopamine concentrations in small working volume samples (2 µL) of cerebral spinal fluid samples obtained from a mouse model of Parkinson's Disease. The platform presented in this work can lead the way to graphene-based neurotransmitter sensors suitable for real-world academic and pre-clinical pharmaceutical research as well as clinical diagnosis.This work was funded by: "la Caixa" Banking Foundation under grant agree ment LCF/PR/HR21-00410; national funds, through the Foundation for Science and Technology (FCT)—projects UIDB/50026/2020, UIDP/50026/2020, and UIDB/04650/2020; by FCT project PTDC/MED-NEU/28073/2017 (POCI-01-307 0145-FEDER-028073); by The Branco Weiss fellowship—Society in Science (ETH Zurich); and by FCT Ph.D. fellowships SFRH/BD/14536/2022 (M.A.), SFRH/BD/08181/2020 (T.D.), and PD/BD/127823/2016 (D.R.)

Influence of the electrolyte salt concentration on DNA detection with graphene transistors

Liquid-gated Graphene Field-Effect Transistors (GFET) are ultrasensitive bio-detection platforms carrying out the graphene’s exceptional intrinsic functionalities. Buffer and dilution factor are prevalent strategies towards the optimum performance of the GFETs. However, beyond the Debye length (λD), the role of the graphene-electrolytes’ ionic species interactions on the DNA behavior at the nanoscale interface is complicated. We studied the characteristics of the GFETs under different ionic strength, pH, and electrolyte type, e.g., phosphate buffer (PB), and phosphate buffer saline (PBS), in an automatic portable built-in system. The electrostatic gating and charge transfer phenomena were inferred from the field-effect measurements of the Dirac point position in single-layer graphene (SLG) transistors transfer curves. Results denote that λD is not the main factor governing the effective nanoscale screening environment. We observed that the longer λD was not the determining characteristic for sensitivity increment and limit of detection (LoD) as demonstrated by different types and ionic strengths of measuring buffers. In the DNA hybridization study, our findings show the role of the additional salts present in PBS, as compared to PB, in increasing graphene electron mobility, electrostatic shielding, intermolecular forces and DNA adsorption kinetics leading to an improved sensitivity.This research is supported by PORTGRAPHE-Control of Port and DouroWines authenticity using graphene DNA sensors project co-funded by FCT (PTDC/BIA-MOL/31069/2017) and the ERDF through COMPETE2020 (POCI-01-0145-FEDER-031069)

Optimizing PMMA solutions to suppress contamination in the transfer of CVD graphene for batch production

Mass production and commercial adoption of graphene-based devices are held back by a few crucial technical challenges related to quality control. In the case of graphene produced by chemical vapor deposition, the transfer process represents a delicate step that can compromise device performance and reliability, thus hindering industrial production. In this context, the impact of poly(methyl methacrylate) (PMMA), the most common support material for transferring graphene from the Cu substrate to any target surface, can be decisive in obtaining reproducible sample batches. Although effective in mechanically supporting graphene during the transfer, PMMA solutions needs to be efficiently designed, deposited, and post-treated to serve their purpose while minimizing potential contaminations. Here, we prepared and tested PMMA solutions with different average molecular weight (AMW) and weight concentration in anisole, to be deposited by spin coating. Optical microscopy and Raman spectroscopy showed that the amount of PMMA residues on transferred graphene is proportional to the AMW and concentration in the solvent. At the same time, the mechanical strength of the PMMA layer is proportional to the AMW. These tests served to design an optimized PMMA solution made of a mixture of 550,000 (550k) and 15,000 (15k) AMW PMMA in anisole at 3% concentration. In this design, PMMA550k provided suitable mechanical strength against breakage during the transfer cycles, while PMMA-15k promoted depolymerization, which allowed for a complete removal of PMMA residues without the need for any post-treatment. An XPS analysis confirmed the cleanness of the optimized process. We validated the impact of the optimized PMMA solution on the mass fabrication of arrays of electrolyte-gated graphene field-effect transistors operating as biosensors. On average, the transistor channel resistance decreased from 1860 to 690 Ω when using the optimized PMMA. Even more importantly, the vast majority of these resistance values are distributed within a narrow range (only ca. 300 Ω wide), in evident contrast with the scattered values obtained in non-optimized devices (about 30% of which showed values above 1 MΩ). These results prove that the optimized PMMA solution unlock the production of reproducible electronic devices at the batch scale, which is the key to industrial productionproject "GEMIS – Graphene-enhanced Electro-Magnetic Interference Shielding", with the reference POCI-01-0247-FEDER-045939, co-funded by COMPETE 2020 – Operational Programme for Competitiveness and Internationalization and the Portuguese Foundation for Science and Technology (FCT), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (ERDF) and the FCT via the Strategic Funding UIDB/04650/2020. C. D. Liao acknowledges a Marie Skłodowska-Curie COFUND Fellowship (H2020-MSCA-COFUND 2015). T. Queirós acknowledges a PhD grant from FCT with reference SFRH/BD/150646/2020 in the framework of the Quantum Portugal Initiative. T. Domingues acknowledges a PhD grant from FCT with reference SFRH/BD/08181/202

Reductive nanometric patterning of graphene oxide paper using electron beam lithography

Electron beam lithography (EBL) was used for preparing nanostructured reduced patterns on the GO paper surface, while preserving its mechanical resistance and flexibility. Different EBL parameters, like dose and time of exposure for patterning were tested. SEM analysis showed the consequent increase of contrast of the reduced stripes on the patterned regions due to the increase of electron beam doses. Moreover, surface potential microscopy experiments also exhibited a clear contrast between the patterned and non-patterned regions. Structural analysis of the patterned paper through X-ray diffraction and nanoindentation showed that the interlayer distance between GO sheets decreases after reduction allowing the increase of the Hardness and Young modulus that makes this material able to be manipulated and integrated on different devices. Furthermore, we also observe that exposed areas to electron beam reduction process show an increase in the electrical conductivity up to 3 × 104 times. The developed flexible GO films can have interesting applications such as biosensors or templates for inducing tissue regeneration, by providing a surface with differently patterned cues with contrasting electron mobility. Preliminary in vitro studies with L929 fibroblasts support the cytocompatible nature of this patterned GO paper.Gil Gonçalves thanks the Fundação para a Ciência e a Tecnologia for the PostDoc grant (SFRH/BDP/84419/2012). P.A.A.P.M. acknowledge the FCT/MCTES for a research contract under the Program Investigator 2013 (IF/00917/2013/CP1162/CT0016) and TEMA – Centre for Mechanical Technology and Automation (UID/EMS/00481/2013), financed by national funds through the FCT/MEC. I.B. wish to acknowledge the Portuguese Foundation for Science and Technology for the financial support (grant IF/00582/2015). H·I·S.N. acknowledges CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. The biological studies of this work have been funded by the Ministerio de Economía y Competitividad and the Fondo Europeo de Desarrollo Regional (MAT2016-78857-R, MINECO/FEDER, UE). AGM and MCS acknowledge ISCIII-MINECO-FEDER for respective contracts. Authors would like to thank Dr M. Teresa Portolés from the Biochemistry and Molecular Biology Department at Universidad Complutense de Madrid for the generous supply of L929 fibroblasts. Dr José Ángel Rodríguez and Dr Javier Mazarío from the Service of Microscopy and Image Analysis at the Hospital Nacional de Parapléjicos are acknowledged for assistance with CLSM studies and Dr Enrique Rodríguez from the Servicio Interdepartamental de Investigación at the Universidad Autónoma de Madrid for SEM studies.info:eu-repo/semantics/acceptedVersio

Clean-Room lithographical processes for the fabrication of Graphene biosensors

This work is on developing clean-room processes for the fabrication of electrolyte-gate graphene field-effect transistors at the wafer scale for biosensing applications. Our fabrication process overcomes two main issues: removing surface residues after graphene patterning and the dielectric passivation of metallic contacts. A graphene residue-free transfer process is achieved by using a pre-transfer, sacrificial metallic mask that protects the entire wafer except the areas around the channel, source, and drain, onto which the graphene film is transferred and later patterned. After the dissolution of the mask, clean gate electrodes are obtained. The multilayer SiO2/SiNx dielectric passivation takes advantage of the excellent adhesion of SiO2 to graphene and the substrate materials and the superior impermeability of SiNx. It hinders native nucleation centers and breaks the propagation of defects through the layers, protecting from prolonged exposition to all common solvents found in biochemistry work, contrary to commonly used polymeric passivation. Since wet etch does not allow the required level of control over the lithographic process, a reactive ion etching process using a sacrificial metallic stopping layer is developed and used for patterning the passivation layer. The process achieves devices with high reproducibility at the wafer scale.Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UIDB/04650/2020, UIDP/00013/2020, and Operational Program Competitiveness and Internationalization (POCI) under project POCI-01-0145-FEDER-031069 (PORTGRAPHE). This work was partially supported by E.U. Horizon 2020 Research and Innovation Programme, under project MULTIMAL (grant #777222). P.D. Cabral acknowledges the Ph.D. grant (SFRH/BD/128579/2017) from the FC