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In this work, we investigated on microwave parameters geometry dependence in Graphene Field Effect Transistors (GFETs). A DC and RF characterization of the fabricated GFETs has been performed. The parametric analysis was carried out on 24 GFET families fabricated on the same chip and differing only for the channel length (Δ) and the gate length (Lg). In order to obtain a statistical average, each family included ten devices with the same geometry.Our study demonstrates that the output resistance and the cut-off frequency depend on both Δ and Lg. As expected, Rout increases with the graphene channel surface thus confirming the good quality of the fabrication procedures. An optimum region which maximizes the cut-off frequency has been found.

Graphene is a relatively new material whose unique properties have attracted significant interest for its use in electronic and photonic applications. In particular, field effect has been proved in graphene samples and the observed high carrier mobility makes graphene an interesting solution for high frequency electronics. In this work, we focused on the analysis of microwave parameters dependence on geometries in Graphene Field Effect Transistors (GFETs). In particular, a statistical, experimental investigation of the cut-off frequency (fT) and of the output impedance (Zout) dependency on both the gate-drain/source distance (Δ) and the gate length (Lg) was carried out. 24 GFET families were fabricated on the same chip, each one made of 10 identical (same geometry) devices. The analysis of the measured data shows that fT and Zout are both Δ and Lg dependent, and that there exists a region in Δ and Lg design space where fT is optimized.

Graphene is a relatively new material whose unique properties have attracted significant interest for its use in electronic and photonic applications. In particular, field effect has been proved in graphene samples and this feature, together with the high carrier mobility observed, makes graphene an interesting solution for high frequency electronics. In our work, we performed a statistical analysis in order to evaluate the microwave parameters dependence on Graphene Field Effect Transistors (GFETs) dimensions. In more detail, for the first time, we studied the behavior of the cut-off frequency (ft) and of the output impedance (Zout) at varying both the gate-drain/gate-source distance (Δ) and the gate length (Lg). In order to perform the abovementioned statistical analysis, we fabricated 24 GFETs families on the same chip. Each family is composed of 10 equal devices, with the same Δ and Lg values. After their fabrication, the GFETs were characterized in both DC and RF regimes. DC measurements allowed us to obtain the transconductance curves (Id vs Vgs) and, hence, to evaluate the static transconductance (gm), whose value deeply influences the cut-off frequency. The scattering parameters were then measured, in the region where gm shows its highest value, by using a vector network analyzer. This allowed us to evaluate the short circuit current gain (h21), ft and Zout.

In this work we focused on the analysis of Graphene Field Effect Transistor (GFET) microwave parameters dependence on geometries. In particular, a statistical, experimental investigation of the cut-off frequency (ft) dependency on both the gate-drain/source distance (Δ) and the gate length (Lg) was carried out. 24 GFET families on the same chip were fabricated, each one made of 10 identical (same geometry) devices. The analysis of the measured data shows that ft is both Δ and Lg dependent, and that there exists an optimal region in Δ and Lg design space.

In this work, we focused on the study of Graphene Field Effect Transistors (GFETs) photoelectrical response due to the combination of photovoltaic and photo-thermoelectric effects. The technological steps for the transistors fabrication together with their electro-optic response will be presented. Measurements were performed by using a 405 nm laser diode with AM modulation at 1.33 KHz shined onto the sample under test. GFETs electrical output signals were measured by using a lock-in amplifier synchronized to the same reference frequency of the laser driver. This gave us the possibility to evaluate the optical characteristics as a function of both the incident laser power and the static polarization of the device. We found that the optical response of our devices depends on the static polarization of the gate-source voltage and it shows a linear trend as a function of the incident laser power.

The aim of this study is to understand the photoresponse of a Ruthenium-complex/graphene heterostructure. Early work demonstrated that light detection by graphene field effect devices was enhanced by dropcasting Ruthenium Complex molecules. Here we proposed to fabricate a new class of devices where the Ruthenium-complex molecules are embedded between two layer of CVD monolayer graphene.

The aim of this study is to understand the photoresponse of a Ruthenium-complex/graphene heterostructure. Early work demonstrated that light detection by graphene field effect devices was enhanced by dropcasting Ruthenium Complex molecules. Here we proposed to fabricate a new class of devices where the Ruthenium-complex molecules are embedded between two layer of CVD monolayer graphene.

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice. This peculiarity is responsible of extraordinary physical properties. Graphene exhibits a strong ambipolar field effect and thanks to its huge charge carrier mobility, graphene is a suitable material for high frequency Electronics. Graphene field effect transistors (GFET) for high frequency applications have recently received much attention and significant progress has been achieved in this area. GFETs have been already made by using pre-patterned metal or graphene nanoribbon (GNR) back-gates and hexagonal boron nitride as a dielectric spacer. Among the most employed techniques for the graphene transfer, i.e. mechanical exfoliation, chemical exfoliation and chemical vapor deposition (CVD) growth, the latter has the advantage to produce several devices on the same chip with a very high yield. In this work, we focus on the characterization of a novel generation of GFETs, in which a graphene sheet, grown via CVD, is used as channel material.

We report compact, scalable, high-performance, waveguide integrated graphene-based photodetectors (GPDs) for telecom and datacom applications, not affected by dark current. To exploit the photothermoelectric (PTE) effect, our devices rely on a graphene/polymer/graphene stack with static top split gates. The polymeric dielectric, poly(vinyl alcohol) (PVA), allows us to preserve graphene quality and to generate a controllable p-n junction. Both graphene layers are fabricated using aligned single-crystal graphene arrays grown by chemical vapor deposition. The use of PVA yields a low charge inhomogeneity ∼8 × 1010 cm-2 at the charge neutrality point, and a large Seebeck coefficient ∼140 μV K-1, enhancing the PTE effect. Our devices are the fastest GPDs operating with zero dark current, showing a flat frequency response up to 67 GHz without roll-off. This performance is achieved on a passive, low-cost, photonic platform, and does not rely on nanoscale plasmonic structures. This, combined with scalability and ease of integration, makes our GPDs a promising building block for next-generation optical communication devices.

We present a micrometer-scale, on-chip integrated, plasmonic enhanced graphene photodetector (GPD) for telecom wavelengths operating at zero dark current. The GPD is designed to directly generate a photovoltage by the photothermoelectric effect. It is made of chemical vapor deposited single layer graphene, and has an external responsivity ∼12.2 V/W with a 3 dB bandwidth ∼42 GHz. We utilize Au split-gates to electrostatically create a p-n-junction and simultaneously guide a surface plasmon polariton gap-mode. This increases the light-graphene interaction and optical absorption and results in an increased electronic temperature and steeper temperature gradient across the GPD channel. This paves the way to compact, on-chip integrated, power-efficient graphene based photodetectors for receivers in tele- and datacom modules.

In this work, we report on a comparison among graphene field-effect transistors (GFETs) employing different dielectrics as gate layers to evaluate their microwave response. In particular, aluminum oxide (Al$_{2}$O$_{3}$), titanium oxide (TiO$_{2}$), and hafnium oxide (HfO$_{2}$) have been tested. GFETs have been fabricated on a single chip and a statistical analysis has been performed on a set of 24 devices for each type of oxide. Direct current and microwave measurements have been carried out on such GFETs and short circuit current gain and maximum available gain have been chosen as quality factors to evaluate their microwave performance. Our results show that all of the devices belonging to a specific group (i.e., with the same oxide) have a well-defined performance curve and that the choice of hafnium oxide represents the best trade-off in terms of dielectric properties. Graphene transistors employing HfO$_{2}$ as the dielectric layer, in fact, exhibit the best performance in terms of both the cutoff frequency and the maximum frequency of oscillation.

In this work, we report on the design, fabrication and characterization of Metal-Oxide Graphene Field-effect Transistors (MOGFETs) exploiting novel clamped gate geometries aimed at enhancing the device transconductance. The fabricated devices employ clamped metal contacts also for source and drain, as well as an optimized graphene meandered pattern for source contacting, in order to reduce parasitic resistance. Our experimental results demonstrate that MOGFETs with the proposed structure show improved high frequency performance, in terms of maximum available gain and transition frequency values, as a consequence of the higher equivalent transconductance obtained.

We report compact, scalable, high-performance, waveguide integrated graphene-based photodetectors (GPDs) for telecom and datacom applications, not affected by dark current. To exploit the photothermoelectric (PTE) effect, our devices rely on a graphene-polymer-graphene stack with static top split gates. The polymeric dielectric, poly(vinyl alcohol) (PVA), allows us to preserve graphene quality and to generate a controllable p-n junction. Both graphene layers are fabricated using aligned single-crystal graphene arrays grown by chemical vapor deposition. The use of PVA yields a low charge inhomogeneity 8 x 10$^{10}$ $cm^{-2}$ at the charge neutrality point, and a large Seebeck coefficient 140 ${\mu}$V K$^{-1}$, enhancing the PTE effect. Our devices are the fastest GPDs operating with zero dark current, showing a flat frequency response up to 67 GHz without roll-off. This performance is achieved on a passive, low-cost, photonic platform, and does not rely on nanoscale plasmonic structures. This, combined with scalability and ease of integration, makes our GPDs a promising building block for next-generation optical communication devices., Comment: 15 pages, 11 figures. Published under ACS AuthorChoice license

In this work, we investigate the possibility of employing graphene field effect transistors, specifically designed for microwave applications, as infrared detectors for telecom applications. Our devices have been fabricated on a sapphire substrate employing CVD-grown transferred graphene. The roles of both the gate dielectric and the DC bias conditions have been evaluated in order to maximize the infrared generated signal through an experimental investigation of the signal-to-noise ratio dependence on the transistor operating point.

Phase change materials (PCMs) are highly attractive for nonvolatile electrical and all-optical memory applications because of unique features such as ultrafast and reversible phase transitions, long-term endurance, and high scalability to nanoscale dimensions. Understanding their transient characteristics upon phase transition in both the electrical and the optical domains is essential for using PCMs in future multifunctional optoelectronic circuits. Here, we use a PCM nanowire embedded into a nanophotonic circuit to study switching dynamics in mixed-mode operation. Evanescent coupling between light traveling along waveguides and a phase-change nanowire enables reversible phase transition between amorphous and crystalline states. We perform time-resolved measurements of the transient change in both the optical transmission and resistance of the nanowire and show reversible switching operations in both the optical and the electrical domains. Our results pave the way toward on-chip multifunctional optoelectronic integrated devices, waveguide integrated memories, and hybrid processing applications.

Graphene and related materials can lead to disruptive advances in next generation photonics and optoelectronics. The challenge is to devise growth, transfer and fabrication protocols providing high (>5,000 cm2 V-1 s-1) mobility devices with reliable performance at the wafer scale. Here, we present a flow for the integration of graphene in photonics circuits. This relies on chemical vapour deposition (CVD) of single layer graphene (SLG) matrices comprising up to ~12000 individual single crystals (SCs), grown to match the geometrical configuration of the devices in the photonic circuit. This is followed by a transfer approach which guarantees coverage over ~80% of the device area, and integrity for up to 150 mm wafers, with room temperature mobility ~5000 cm2 V-1 s-1. We use this process flow to demonstrate double SLG electro-absorption modulators with modulation efficiency ~0.25, 0.45, 0.75, 1 dB V-1 for device lengths ~30, 60, 90, 120 {\mu}m. The data rate is up to 20 Gbps. Encapsulation with single-layer hBN is used to protected SLG during plasma-enhanced CVD of Si3N4, ensuring reproducible device performance. Our full process flow (from growth to device fabrication) enables the commercial implementation of graphene-based photonic devices., Comment: 30 pages, 9 Figures