No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Generic Graphene Based Components and Circuits for Millimeter Wave High Data-rate Communication Systems
Abstract
We are developing millimeter wave (mm-wave) components and circuits based on hydrogen-intercalated graphene. The development covers epitaxial graphene growth, device fabrication, modelling, integrated circuit design and fabrication, and circuit characterizations. The focus of our work is to utilize the distinctive graphene properties and realize new components that can overcome some of the main challenges of existing mm-wave technologies in term of linearity.
We put forward and numerically analyze a D-shaped surface plasmon resonance fiber sensor with high figure of merit (FOM), within the detection range of 1.33–1.41. The sensing area is coated with platinum (Pt) grating, aluminum oxide (Al2O3) nanofilm, and graphene film. Plasmonic resonance of Pt grating can be excited by the core mode of the D-shaped fiber, so as to detect the change of refractive index (RI). The addition of graphene and Al2O3 layers is to enhance the nearfield electric intensity of the Pt grating, thus improving the sensing performance. Especially, the FOM of the designed sensor can be consumedly improved by the Al2O3/graphene/Pt grating hybrid nanostructure, up to 432 RIU−1, with a high RI sensitivity of 11,252 nm/RIU in near-infrared region. The influence of the three nanolayers on the sensing performance is carefully calculated and analyzed. The designed sensor would be a candidate for biological applications, environmental monitoring, and medical diagnostics.
In recent years, the demand for high data rate wireless communications has increased dramatically, which requires larger bandwidth to sustain multi-user accessibility and quality of services. This can be achieved at millimeter wave frequencies. Graphene is a promising material for the development of millimeter-wave electronics because of its outstanding electron transport properties. Up to now, due to the lack of high quality material and process technology, the operating frequency of demonstrated circuits has been far below the potential of graphene. Here, we present monolithic integrated circuits based on epitaxial graphene operating at unprecedented high frequencies (80–100 GHz). The demonstrated circuits are capable of encoding/decoding of multi-gigabit-per-second information into/from the amplitude or phase of the carrier signal. The developed fabrication process is scalable to large wafer sizes.
The transport properties of quasi-free-standing (QFS) bilayer graphene on SiC depend on a range of scattering mechanisms. Most of them are isotropic in nature. However, the SiC substrate morphology marked by a distinctive pattern of the terraces gives rise to an anisotropy in graphene's sheet resistance, which may be considered an additional scattering mechanism. At a technological level, the growth-preceding in situ etching of the SiC surface promotes step bunching which results in macro steps ∼10 nm in height. In this report, we study the qualitative and quantitative effects of SiC steps edges on the resistance of epitaxial graphene grown by chemical vapor deposition. We experimentally determine the value of step edge resistivity in hydrogen-intercalated QFS-bilayer graphene to be ∼190 Ωμm for step height hS = 10 nm and provide proof that it cannot originate from mechanical deformation of graphene but is likely to arise from lowered carrier concentration in the step area. Our results are confronted with the previously reported values of the step edge resistivity in monolayer graphene over SiC atomic steps. In our analysis, we focus on large-scale, statistical properties to foster the scalable technology of industrial graphene for electronics and sensor applications.
The recent discovery of graphene has led to many advances in two-dimensional physics and devices. The graphene devices fabricated so far have relied on SiO(2) back gating. Electrochemical top gating is widely used for polymer transistors, and has also been successfully applied to carbon nanotubes. Here we demonstrate a top-gated graphene transistor that is able to reach doping levels of up to 5x1013 cm-2, which is much higher than those previously reported. Such high doping levels are possible because the nanometre-thick Debye layer in the solid polymer electrolyte gate provides a much higher gate capacitance than the commonly used SiO(2) back gate, which is usually about 300 nm thick. In situ Raman measurements monitor the doping. The G peak stiffens and sharpens for both electron and hole doping, but the 2D peak shows a different response to holes and electrons. The ratio of the intensities of the G and 2D peaks shows a strong dependence on doping, making it a sensitive parameter to monitor the doping.
A wafer-scale graphene circuit was demonstrated in which all circuit components, including graphene field-effect transistor
and inductors, were monolithically integrated on a single silicon carbide wafer. The integrated circuit operates as a broadband
radio-frequency mixer at frequencies up to 10 gigahertz. These graphene circuits exhibit outstanding thermal stability with
little reduction in performance (less than 1 decibel) between 300 and 400 kelvin. These results open up possibilities of achieving
practical graphene technology with more complex functionality and performance.
We uncover the constitutive relation of graphene and probe the physics of its optical phonons by studying its Raman spectrum as a function of uniaxial strain. We find that the doubly degenerate E[subscript 2g] optical mode splits in two components: one polarized along the strain and the other perpendicular. This splits the G peak into two bands, which we call G+ and G−, by analogy with the effect of curvature on the nanotube G peak. Both peaks redshift with increasing strain and their splitting increases, in excellent agreement with first-principles calculations. Their relative intensities are found to depend on light polarization, which provides a useful tool to probe the graphene crystallographic orientation with respect to the strain. The 2D and 2D′ bands also redshift but do not split for small strains. We study the Grüneisen parameters for the phonons responsible for the G, D, and D′ peaks. These can be used to measure the amount of uniaxial or biaxial strain, providing a fundamental tool for nanoelectronics, where strain monitoring is of paramount importance University of Palermo Sultan Qaboos University MITRE Interconnect Focus Center European Research Council Royal Society
Graphene is the two-dimensional building block for carbon allotropes of every other dimensionality. We show that its electronic structure is captured in its Raman spectrum that clearly evolves with the number of layers. The D peak second order changes in shape, width, and position for an increasing number of layers, reflecting the change in the electron bands via a double resonant Raman process. The G peak slightly down-shifts. This allows unambiguous, high-throughput, nondestructive identification of graphene layers, which is critically lacking in this emerging research area.
This article reviews the basic theoretical aspects of graphene, a one atom thick allotrope of carbon, with unusual two-dimensional Dirac-like electronic excitations. The Dirac electrons can be controlled by application of external electric and magnetic fields, or by altering sample geometry and/or topology. We show that the Dirac electrons behave in unusual ways in tunneling, confinement, and integer quantum Hall effect. We discuss the electronic properties of graphene stacks and show that they vary with stacking order and number of layers. Edge (surface) states in graphene are strongly dependent on the edge termination (zigzag or armchair) and affect the physical properties of nanoribbons. We also discuss how different types of disorder modify the Dirac equation leading to unusual spectroscopic and transport properties. The effects of electron-electron and electron-phonon interactions in single layer and multilayer graphene are also presented.
This letter presents the design, fabrication and characterization of the first graphene based monolithic microwave integrated circuit (MMIC) in microstrip technology operating in W-band. The circuit is a resistive mixer in a 250 nm graphene field effect transistor (G-FET) technology on a SiC substrate. A conversion loss of 18 dB is achieved which is limited by the available local oscillator (LO) power. The mixer exhibits a flat response over radio frequency (RF) range of 90-100 GHz. The RF bandwidth is also limited by the measurement setup.
Low-noise amplifier is one of the most attractive applications of graphene transistors in the RF area. In this letter, a graphene amplifier MMIC is fabricated on the quasi-free-standing bilayer epitaxial graphene grown on SiC (0001) substrate. In order to realize both the high gain and low return loss, Au matching lines are designed as the input and output impedance match networks. The fabricated graphene amplifier MMIC shows a small-signal power gain of 3.4 dB at 14.3 GHz and a minimum noise figure of 6.2 dB. This letter is a significant step forward for graphene electronics in low-noise amplifier and demonstrates graphene's potential in RF applications for future high-speed electronics.
We report on the interface between graphene and 4H-SiC0001 as investigated by scanning tunneling microscopy STM and low energy electron diffraction LEED. It is characterized by the so-called 6 3 6 3R30° reconstruction, whose structural properties are still controversially discussed but at the same time are crucial for the controlled growth of homogeneous high-quality large-terrace graphene surfaces. We discuss the role of three observed phases with periodicities 6 3 6 3R30°, 6 6, and 5 5. Their LEED inten-sity levels and spectra strongly depend on the surface preparation procedure applied. The graphitization process imprints distinct features in the STM images as well as in the LEED spectra. The latter have the potential for an easy and practicable determination of the number of graphene layers by means of LEED.
We demonstrate the growth of high quality graphene layers by chemical vapor deposition (CVD) on insulating and conductive SiC substrates. This method provides key advantages over the well-developed epitaxial graphene growth by Si sublimation that has been known for decades. (1) CVD growth is much less sensitive to SiC surface defects resulting in high electron mobilities of ∼1800 cm(2)/(V s) and enables the controlled synthesis of a determined number of graphene layers with a defined doping level. The high quality of graphene is evidenced by a unique combination of angle-resolved photoemission spectroscopy, Raman spectroscopy, transport measurements, scanning tunneling microscopy and ellipsometry. Our measurements indicate that CVD grown graphene is under less compressive strain than its epitaxial counterpart and confirms the existence of an electronic energy band gap. These features are essential for future applications of graphene electronics based on wafer scale graphene growth.