Graphene Field-effect Transistors Research Articles

A Lightweight, Zero-Power Intermodulation Sensor Based on the Graphene Oscillator

Wireless sensor networks (WSNs) require a massive number of sensor nodes for data collection and storage, for which the power management and area efficiency of battery-powered sensors may be an issue. In this article, we propose and numerically study a fully passive and lightweight intermodulation sensor based on the reconfigurable graphene field-effect transistors (GFETs) oscillator and passive frequency mixer. The output frequency of the self-powered GFET-based oscillator can be sensitive to the surface doping effect caused by charged surface absorbates, reactive gases, contaminations, or aqueous solutions. In the intermodulation sensor, the low-frequency signals generated by GFET oscillator are mixed with the incident radio frequency (RF) waves, forming the retransmitted and the RF intermodulation signals. Since the intermodulation products do not mess up with the reception signal, the unwanted clutters, self-jamming, and interferences can be effectively suppressed. Our results show that the output frequency of the GFET oscillator can sensitively respond to charged molecules, and such information can be encoded in the backscatter intermodulation signal. We believe that our GFET-based intermodulation sensor may be beneficial for a variety of the Internet of Things (IoTs), remote sensing, and environment monitoring applications.

Optimization of 14 nm double gate Bi-GFET for lower leakage current

In recent years, breakthroughs in electronics technology have resulted in upgrades in the physical properties of the metal oxide semiconductor field effect transistor (MOSFET) toward smaller sizes and improvements in both quality and performance. Hence, the growth field effect transistor (GFET) is being promoted as one of the worthy contenders due to its superior material characteristics. A 14 nm horizontal double-gate bilayer graphene FET with a high-k/metal gate is proposed, which is composed of hafnium dioxide (HfO 2 ) and tungsten silicide (WSi x ) respectively . It is simulated and modelled using silvaco ATHENA and ATLAS technology computer-aided design (TCAD) tools, as well as the Taguchi L9 orthogonal array (OA). The threshold voltage (V TH ) adjustment implant dose, V TH adjustment implant energy, source/drain (S/D) implant dose, and S/D implant energy have all been investigated as process parameters. While the V TH adjustment tilt angle and the S/D implant tilt angle have both been investigated as noise factors. When compared to the initial findings before optimization, the I OFF has a value of 29.579 nA/µm, indicating a significant improvement. Findings from the optimization technique demonstrate excellent device performance with an I OFF of 28.564 nA/µm, which is closer to the international technology roadmap semiconductor (ITRS) 2013 target than before.

Low-Temperature Direct Growth of Amorphous Boron Nitride Films for High-Performance Nanoelectronic Device Applications.

We successfully demonstrated the improvement and stabilization of the electrical properties of a graphene field effect transistor by fabricating a sandwiched amorphous boron nitride (a-BN)/graphene (Gr)/a-BN using a directly grown a-BN film. The a-BN film was grown via low-pressure chemical vapor deposition (LPCVD) at a low growth temperature of 250 °C and applied as a protection layer in the sandwiched structure. Both structural and chemical states of the as-grown a-BN were verified by various spectroscopic and microscopic analyses. We analyzed the Raman spectra of Gr/SiO2 and a-BN/Gr/a-BN structures to determine the stability of the device under exposure to ambient air. Following exposure, the intensity of the 2D/G-peak ratio of Gr/SiO2 decreased and the position of the G and 2D peaks red-shifted due to the degradation of graphene. In contrast, the peak position of encapsulated graphene is almost unchanged. We also confirmed that the mobility of a-BN/Gr/a-BN structure is 17,941 cm2/Vs. This synthetic strategy could provide a facile way to synthesize uniform a-BN film for encapsulating various van der Waals materials, which is beneficial for future applications in nanoelectronics.

High-Performance Device to Detect Interleukin-13 Based on Graphene Field-Effect Transistor

High-Performance Device to Detect Interleukin-13 Based on Graphene Field-Effect Transistor

Femtomolar Level-Specific Detection of Lead Ions in Aqueous Environments, Using Aptamer-Derivatized Graphene Field-Effect Transistors

The detection of lead ion (Pb2+) contamination in aqueous media is relevant for preventing endemic health issues as well as damage to cognitive and physical health. Existing home kit tests are unable to achieve clinically relevant sensitivity and specificity. Here, a label-free graphene field-effect transistor sensor for detecting Pb2+ at the femtomolar (fM) level, discriminating between confounding ions, is reported. The sensing principle is based on electrically monitoring Pb2+-binding-mediated conformational changes of a specific aptamer tethered to graphene, modeled through the Hills–Langmuir mechanism. A record sensitivity─through a limit of detection of ∼61 fM, for Pb2+ was demonstrated. For model verification, specific discrimination of Pb2+ from other ions at the 1 picomolar (pM) level was shown. The reported work provides motivation for development of portable, label-free, point-of-care devices with both high specificity and sensitivity.

Seed layer engineering for crack-free sol–gel Alumina deposition on GFETs

Low-cost and low thermal budget-based spin-coated sol–gel Alumina was explored as a dielectric/passivation layer for graphene field effect transistor (GFET). Post thermal annealing, the crack was observed in the sol–gel Alumina layer exactly above the graphene channel. The possible mechanism of crack could be graphene lateral restoring movement due to (i) the Thermal Expansion Coefficient (TEC) difference between graphene and adjacent layers and (ii) shrinkage stress generated during the solvent removal process. Based on the crack formation phenomenon, a combination of different annealing schemes (low thermal budget deep ultraviolet (DUV) annealing) and seed layer engineering (thickness and different deposition schemes) were carried out. Finally, a novel two-step seed layer deposition method with DUV annealing was proposed and demonstrated to resolve the crack issue successfully and also able to retain the Dirac point in the electrical characteristics.

Integrated Approach from Sample-to-Answer for Grapevine Varietal Identification on a Portable Graphene Sensor Chip.

Identifying grape varieties in wine, related products, and raw materials is of great interest for enology and to ensure its authenticity. However, these matrices' complexity and low DNA content make this analysis particularly challenging. Integrating DNA analysis with 2D materials, such as graphene, offers an advantageous pathway toward ultrasensitive DNA detection. Here, we show that monolayer graphene provides an optimal test bed for nucleic acid detection with single-base resolution. Graphene's ultrathinness creates a large surface area with quantum confinement in the perpendicular direction that, upon functionalization, provides multiple sites for DNA immobilization and efficient detection. Its highly conjugated electronic structure, high carrier mobility, zero-energy band gap with the associated gating effect, and chemical inertness explain graphene's superior performance. For the first time, we present a DNA-based analytic tool for grapevine varietal discrimination using an integrated portable biosensor based on a monolayer graphene field-effect transistor array. The system comprises a wafer-scale fabricated graphene chip operated under liquid gating and connected to a miniaturized electronic readout. The platform can distinguish closely related grapevine varieties, thanks to specific DNA probes immobilized on the sensor, demonstrating high specificity even for discriminating single-nucleotide polymorphisms, which is hard to achieve with a classical end-point polymerase chain reaction or quantitative polymerase chain reaction. The sensor was operated in ultralow DNA concentrations, with a dynamic range of 1 aM to 0.1 nM and an attomolar detection limit of ∼0.19 aM. The reported biosensor provides a promising way toward developing decentralized analytical tools for tracking wine authenticity at different points of the food value chain, enabling data transmission and contributing to the digitalization of the agro-food industry.

Real-time monitoring of cyanobacterial harmful algal blooms by graphene field-effect transistor

Demands for clean water are increasing due to factors such as population growth, global warming, and environmental degradation. One of the main obstacles to achieving this purpose is the cyanobacterial blooms, which are the overgrowth of cyanobacteria well known as blue–green algae. Since many cyanobacteria strains are reported to produce geosmin (GSM) or 2-methylisoborneol (MIB) as metabolites, monitoring the level of those two odor compounds is available to the detection of cyanobacterial bloom. The limit of detection (LOD) of the pre-developed equipment is high to detect the initial proliferation of cyanobacteria. To overcome the limitation, we fabricated graphene field-effect transistors (GFETs) based bioelectronic nose which use human olfactory receptors (hORs) 51S1 and 3A4 as bioprobe. The hOR51S1 and 3A4 were reconstituted to nanodiscs (NDs) due to their stable, sensitive, and selective interaction with GSM and MIB, respectively. The LOD (10 fM) of the fabricated device was the lowest among previously developed detection platforms. In addition, the device demonstrated high selectivity for GSM and MIB with other odor compounds, such as IBMP and IPMP. To evaluate sensing properties of the bioelectronic nose, the real samples from river water containing GSM and MIB were prepared and monitored by bioelectronics nose to measure its sensitivity and selectivity. Furthermore, the developed platform, a bioelectronic nose mimicking the human sense of smell, can be applied to detect other harmful compounds in environmental areas by using various bioprobes.

Chemiresistive Hydrogen Sensing with Size-Limited Palladium Nanoparticles in Iptycene-Containing Poly(arylene ether)s

Metal nanoparticles have been widely employed in chemical sensing due to their high reactivity toward various gases. The size of the metal nanoparticles often dictates their reactivity and hence their performance as chemiresistive sensors. Herein, we report that iptycene-containing poly(arylene ether)s (PAEs) have been shown to limit the growth of palladium nanoparticles (Pd NPs) and stabilize the Pd NPs dispersion. These porous PAEs also facilitate the efficient transport of analytes. Single-walled carbon nanotube (SWCNT)-based chemiresistors and graphene field-effect transistors (GFETs) using these PAE-supported small Pd NPs are sensitive, selective, and robust sensory materials for hydrogen gas under ambient conditions. Generalizable strategies including presorting SWCNTs with pentiptycene-containing poly(p-phenylene ethynylene)s (PPEs) and thermal annealing demonstrated significant improvements in the chemiresistive performance. The polymer:NP colloids produced in this study are readily synthesized and solution processable, and these methods are of general utility.

Graphene FETs with high and low mobilities have universal temperature-dependent properties

We use phenomenological modelling and detailed experimental studies of charge carrier transport to investigate the dependence of the electrical resistivity, ρ, on gate voltage, V g , for a series of monolayer graphene field effect transistors with mobilities, μ, ranging between 5000 and 250 000 cm2 V−1 s−1 at low-temperature. Our measurements over a wide range of temperatures from 4 to 400 K can be fitted by the universal relation for all devices, where is the resistivity maximum at the neutrality point and δn is an ‘uncertainty’ in the bipolar carrier density, given by the full width at half maximum of the resistivity peak expressed in terms of carrier density, n. This relation is consistent with thermal broadening of the carrier distribution and the presence of the disordered potential landscape consisting of so-called electron–hole puddles near the Dirac point. To demonstrate its utility, we combine this relation with temperature-dependent linearised Boltzmann transport calculations that include the effect of optical phonon scattering. This approach demonstrates the similarity in the temperature-dependent behaviour of carriers in different types of single layer graphene transistors with widely differing carrier mobilities. It can also account for the relative stability, over a wide temperature range, of the measured carrier mobility of each device.

Capacitive NO2 Detection Using CVD Graphene-Based Device.

A graphene-based capacitive NO2 sensing device was developed by utilizing the quantum capacitance effect. We have used a graphene field-effect transistor (G-FET) device whose geometrical capacitance is enhanced by incorporating an aluminum back-gate electrode with a naturally oxidized aluminum surface as an insulating layer. When the graphene, the top-side of the device, is exposed to NO2, the quantum capacitance of graphene and, thus, the measured capacitance of the device, changed in accordance with NO2 concentrations ranging from 1-100 parts per million (ppm). The operational principle of the proposed system is also explained with the changes in gate voltage-dependent capacitance of the G-FET exposed to various concentrations of NO2. Further analyses regarding carrier density changes and potential variances under various concentrations of NO2 are also presented to strengthen the argument. The results demonstrate the feasibility of capacitive NO2 sensing using graphene and the operational principle of capacitive NO2 sensing.

Covalent functionalisation controlled by molecular design for the aptameric recognition of serotonin in graphene-based field-effect transistors.

In the last decade, solution-gated graphene field effect transistors (GFETs) showed their versatility in the development of a miniaturized multiplexed platform for electrophysiological recordings and sensing. Due to their working mechanism, the surface functionalisation and immobilisation of receptors are pivotal to ensure the proper functioning of devices. Herein, we present a controlled covalent functionalisation strategy based on molecular design and electrochemical triggering, which provide a monolayer-like functionalisation of micro-GFET arrays retaining the electronic properties of graphenes. The functionalisation layer as a receptor was then employed as the linker for serotonin aptamer conjugation. The micro-GFET arrays display sensitivity toward the target analyte in the micromolar range in a physiological buffer (PBS 10 mM). The sensor allows the in-flow real-time monitoring of serotonin transient concentrations with fast and reversible responses.

Ultrasensitive detection of SARS-CoV-2 spike protein by graphene field-effect transistors.

COVID-19, caused by the severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2), originated a global health crisis, causing over 2 million casualties and altering human daily life all over the world. This pandemic emergency revealed the limitations of current diagnostic tests, highlighting the urgency to develop faster, more precise and sensitive sensors. Graphene field effect transistors (GFET) are analytical platforms that enclose all these requirements. However, the design of a sensitive and robust GFET is not a straightforward objective. In this work, we report a GFET array biosensor for the detection of SARS-CoV-2 spike protein using the human membrane protein involved in the virus internalisation: angiotensin-converting enzyme 2 (ACE2). By finely controlling the graphene functionalisation, by tuning the Debye length, and by deeply characterising the ACE2-spike protein interactions, we have been able to detect the target protein with an extremely low limit of detection (2.94 aM). This work set the basis for a new class of analytical platforms, based on human membrane proteins, with the potential to detect a broad variety of pathogens, even before their isolation, being a powerful tool in the fight against future pandemics.

Low Power Consumption and High Sensitivity Temperature Sensor Chip Based on Monolayer Suspended Graphene Field Effect Transistor

Low Power Consumption and High Sensitivity Temperature Sensor Chip Based on Monolayer Suspended Graphene Field Effect Transistor

Direct observation of infrared electroluminescence of high mobility graphene field-effect transistors

In this presentation we will discuss our efforts based on high sensitivity infrared microscopy and spectroscopy to unravel the origin of super-incandescent emission of high-mobility graphene transistors.

Laser-induced tuning of graphene field-effect transistors for pH sensing.

Here we demonstrate, using pulsed femtosecond laser-induced two-photon oxidation (2PO), a novel method of locally tuning the sensitivity of solution gated graphene field-effect transistors (GFETs) without sacrificing the integrity of the carbon network of chemical vapor deposition (CVD) grown graphene. The achieved sensitivity with 2PO was (25 ± 2) mV pH-1 in BIS-TRIS propane HCl (BTPH) buffer solution, when the oxidation level corresponded to the Raman peak intensity ratio I(D)/I(G) of 3.58. Sensitivity of non-oxidized, residual PMMA contaminated GFETs was 20-22 mV pH-1. The sensitivity decreased initially by 2PO to (19 ± 2) mV pH-1 (I(D)/I(G) = 0.64), presumably due to PMMA residue removal by laser irradiation. 2PO results in local control of functionalization of the CVD-grown graphene with oxygen-containing chemical groups enhancing the performance of the GFET devices. The GFET devices were made HDMI compatible to enable easy coupling with external devices for enhancing their applicability.

A Smart Measurement System for the Combined Nanoscale and Device Level Characterization of Electron Devices: Implementation Using Ink-Jet Printing Technologies

In this article, the integration into a single measurement system of device level and nanoscale measurement equipment is presented and applied to the electrical characterization of emerging electron devices. This system is a smart solution to simplify the test procedure, since it allows a fast switching between measurement modes (device or nanoscale level), also featuring an enlarged testing capability. Key in the system is a custom-made inkjet-printed circuit board (I-PCB) that connects the device terminals to the proper instrumentation. The flexibility offered by inkjet-printing technologies is a clear advantage, since many kinds of devices can be tested, without the need of expensive hardware modifications. As a particular case of study, the proposed strategy is demonstrated by implementing a system that alternates between standard electrical measurements with a Semiconductor Parameter Analyzer (SPA) and Conductive Atomic Force Microscopy (CAFM) nanoscale measurements on back-gate graphene field-effect transistors.

A sprayed graphene transistor platform for rapid and low-cost chemical sensing.

We demonstrate a novel and versatile sensing platform, based on electrolyte-gated graphene field-effect transistors, for easy, low-cost and scalable production of chemical sensor test strips. The Lab-on-PCB platform is enabled by low-boiling, low-surface-tension sprayable graphene ink deposited on a substrate manufactured using a commercial printed circuit board process. We demonstrate the versatility of the platform by sensing pH and Na+ concentrations in an aqueous solution, achieving a sensitivity of 143 ± 4 μA per pH and 131 ± 5 μA per log10Na+, respectively, in line with state-of-the-art graphene chemical sensing performance.

Preparation and Electrical Testing of Double Top Gate Graphene Field-Effect Transistor

In this paper, we prepare and test a graphene field-effect transistor with two top gates. The Fermi energy level of graphene can be adjusted by applying positive and negative voltages to the two top gates, and N-type and P-type graphene are formed in the channel region, thus inducing a graphene p-n junction. The current model is established using the gradual channel approximation (GCA) method, and the current and p-n junction characteristics of the device were obtained by formula simulations. Based on the principle of p-n junction luminescence, this device with graphene p-n junction is expected to achieve terahertz wave radiation with an appropriate optical resonant cavity.

Electrolyte-Gated Graphene Field Effect Transistor-Based Ca2+ Detection Aided by Machine Learning.

Flexible electrolyte-gated graphene field effect transistors (Eg-GFETs) are widely developed as sensors because of fast response, versatility and low-cost. However, their sensitivities and responding ranges are often altered by different gate voltages. These bias-voltage-induced uncertainties are an obstacle in the development of Eg-GFETs. To shield from this risk, a machine-learning-algorithm-based LgGFETs' data analyzing method is studied in this work by using Ca2+ detection as a proof-of-concept. For the as-prepared Eg-GFET-Ca2+ sensors, their transfer and output features are first measured. Then, eight regression models are trained with the use of different machine learning algorithms, including linear regression, support vector machine, decision tree and random forest, etc. Then, the optimized model is obtained with the random-forest-method-treated transfer curves. Finally, the proposed method is applied to determine Ca2+ concentration in a calibration-free way, and it is found that the relation between the estimated and real Ca2+ concentrations is close-to y = x. Accordingly, we think the proposed method may not only provide an accurate result but also simplify the traditional calibration step in using Eg-GFET sensors.