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The gate-controlled quantum capacitance and the channel resistance play an important role in the performance of graphene field-effect transistors (GFETs). This paper experimentally verifies that the output phase of the graphene field-effect transistor changes under the influence of quantum capacitance and the channel resistance, which are controlled by the gate voltage. This phenomenon is theoretically analyzed, and a model is established to simulate the phase shift. The obtained simulation results of the model are in good agreement with the experimental results. This work reveals the influence of gate voltage variation on the phase characteristics of GFETs and provides a research basis for the application of GFETs in phase shifter and the establishment of the small-signal model.

This paper presents an improved white light-emitting-diode (LED) wireless transmitter for the Joint Illumination and Communication (JIC) System, which consists of two parts: the driver circuit and the pre-emphasis circuit. The main purpose of the driver circuit part is to solve the problem of dissipated power when sweeping the remaining carriers during the signal modulation of the high-efficiency, high-power and high-speed white LED driver. A push-pull structure driver with a current conduction angle less than 180 degrees is proposed, which is analogous to a Class C power amplification driver, thus avoiding the simultaneous existence of voltage and current on the driver circuit when the remaining carriers are swept out, and improves the efficiency of the LED driver. On this basis, the pre-emphasis circuit part adopts the phase shift technology to improve the data transmission rate, and the system efficiency has also been improved. Then, an improved class C push-pull structure white LED driver with phase shift pre-emphasis technology is formed. This novel driver and pre-emphasis technology achieve a system efficiency of 95.73% with a 10 W LED. The test results show that the system communication -3 dB bandwidth expanded from the original 8.3 MHz to 13.67 MHz, and the best-obtained transceiver baud rate is 25 Mbps at a distance of 1.3 m with BER of 1.63 × 10-4. The test result verifies that the LED driver proposed in this paper is currently the highest figure of merit (FoM) for high power JIC systems.

This paper proposes a theoretical model of photo-controlled quantum capacitors in double-gated graphene-insulator-graphene (DGGIG) structure for terahertz (THz) frequency and phase modulations. In the model, the current-voltage characteristics of each segment of the DGGIG structure are controlled by different gate voltages. Using the different voltages, the DGGIG structure can be used to either generate plasma oscillation waves or shift phase in the terahertz band. Not only has the DGGIG structure various electrical properties, but also the optical properties are also excellent. Photoexcitation alters carrier concentration in DGGIG channel, and thus causes the change of the quantum capacitors. We propose a photo-controlled quantum capacitor model to quantify this phenomenon. The model shows that the quantum capacitors and photoexcitation have a sublinear dependence. An example of a device based on the model is given to describe the application of photo-controlled quantum capacitors in terahertz frequency and phase modulations. The modelled device shows that photoexcitation can change the frequency and phase of the plasma oscillation waves.

For the further integration of receivers in multi-color visible light communication systems, a novel color photodetector (PD) was designed and fabricated by using a 40 nm standard complementary metal oxide semiconductor (CMOS) process without any process modifications. The PD consists of CMOS photodiode and two-dimensional (2D) polysilicon subwavelength grating above the photodiode. The 2D polysilicon grating is controlled in structural parameters to realize color filtering, based on guided-mode resonance, for the first time in a standard CMOS process. Here three kinds of color PDs were designed to respond to the three primary colors. The measured results demonstrate that the color PDs exhibit wavelength selectivity in the visible range (400-700 nm) and the maximum peaks in the spectral response curves of them are at 660 nm (red), 585 nm (green) and 465 nm (blue), respectively. In addition, the added 2D polysilicon grating almost does not reduce the responsivity of the photodiodes.

A metal-catalyst-free method for the direct growth of patterned graphene on an insulating substrate is reported in this paper. Parylene N is used as the carbon source. The surface molecule layer of...

The data rate for visible light communication (VLC) with commercial phosphorescent white light-emitting diodes (LEDs) is very limited because the $-$ 3 dB modulation-bandwidth of these LEDs is only a few megahertz. To increase the modulation bandwidth, a new, fully integrated driver circuit is proposed in this paper. The integrated circuit chip consists of a pre-emphasis circuit unit, an adjustable remaining carrier-sweep-out circuit, and a power-MOSFET driver. Using this chip, the $-$ 3 dB bandwidth of phosphorescent white LED transmitters can be extended from 3 to 80 MHz. The best obtained transceiver baud rate is 112 Mbit/s for a distance of 1.5 m, and the bit-error-ratio is ${\text{1.04}}\,\times \,10^{-3}$ , which meets the data-rate requirement for IEEE 802.3 100BASE-TX. The LED-driver circuit is manufactured in an UMC ${\text{0.18}}\,{\mu }\text{m}$ CMOS process, and the chip area is ${\text{1052}}\ \times\ {\text{762}}\ {\mu }\text{m}^2$ . This driver chip can be used in VLC systems with the following advantages: low cost, low power-consumption, compatible with standard CMOS technology, and high integration-density.

This paper theoretically explores photocontrolled terahertz amplified modulator in electron plasma wave optically switched resonant tunneling diode (ORTD) gate high-electron mobility transistor. We present a developed distributed circuit model based on the Khmyrova model. Photoexcitation causes ORTD operating state between negative differential conductivity and positive differential conductivity, which power gain of the device can be control by photoexcitation. Numerical and analytical results show that photoexcitation enabling amplified modulator can realize much larger modulation depth (>95%) than what has been reported in photocontrolled modulator. Our results show the potential of this device in several fields of terahertz technology, such as photocontrolled modulator, mixer, and other two port networks.

Optical receivers with potentially high operation bandwidth and low cost have received considerable interest due to rapidly growing data traffic and potential Tb/s optical interconnect requirements. Experimental realization of 65 GHz optical signal detection and 262 GHz intrinsic operation speed reveals the significance role of graphene photodetectors (PDs) in optical interconnect domains. In this work, a novel complementary metal oxide semiconductor post-backend process has been developed for integrating graphene PDs onto silicon integrated circuit chips. A prototype monolithic optoelectronic integrated optical receiver has been successfully demonstrated for the first time. Moreover, this is a firstly reported broadband optical receiver benefiting from natural broadband light absorption features of graphene material. This work is a perfect exhibition of the concept of monolithic optoelectronic integration and will pave way to monolithically integrated graphene optoelectronic devices with silicon ICs for three-dimensional optoelectronic integrated circuit chips.

This paper presents the frequency and output power characteristics of oscillators in the graphene tunneling FETs (GTFET) technology. In order to acquire these characteristics, the practical operating conditions of GTFET oscillators are carefully analyzed, and then, the device parameters are simplified to an equivalent circuit and the I/V large signal model is approximated by a compact form. Expressions for the maximum oscillation frequency, maximum output power, and the relationship between frequency and power are given combing the equivalent circuit and the simplified model. In addition, the key device parameters that can be used to improve the performance of a GTFET oscillator are also discussed.

Bipolar phototransistors have higher optical responsivity than photodiodes and play an important role in the field of photoelectric conversion. Two-dimensional materials offer a good optical responsivity and have the potential advantages of heterogeneous integration, but mass-production is difficult. In this study, a bipolar phototransistor is presented based on a vertical Au/graphene/ MoS 2 van der Waals heterojunction that can be mass-produced with a silicon semiconductor process using a simple photolithography process. Au is used as the emitter, which is a functional material used not just for the electrodes, MoS 2 is used for the collector, and graphene in used for the base of the bipolar phototransistor. In the bipolar phototransistor, the electric field of the dipole formed by the Au and graphene contact is in the same direction as the external electric field and thus enhances the photocurrent, and a maximum photocurrent gain of 18 is demonstrated. A mechanism for enhancing the photocurrent of the graphene/ MoS 2 photodiode by contacting Au with graphene is also described. Additionally, the maximum responsivity is calculated to be 16,458 A/W, and the generation speed of the photocurrent is 1.48 × 10 − 4 A/s.

Complementary metal–oxide–semiconductor (CMOS) compatible silicon (Si)-based light sources are attracting more and more attention for the potential to realizing on-chip optical interconnection ultimately. Annealed noble metal nanoparticles (NPs) are often used to enhance the emission efficiency of low-efficiency light emitters due to the surface plasmon (SP) effects. Compared with silver NPs (Ag NPs) and gold NPs (Au NPs) show excellent stability in the air environment. However, Au NPs are not always chosen to enhance the emission efficiency of light-emitting diodes (LEDs) due to the high annealing temperature and CMOS incompatible. Here, we report the first study of enhancing emission from CMOS compatible Si-based LEDs by transferring annealed Au NPs onto the device surfaces. A 4.3-fold total enhancement integrated across the electroluminescence spectrum and an eightfold enhancement at 900 nm are ultimately achieved. The enhancement is attributed to electrical performances improvement of the Si-based LEDs and enhanced scattering by Au NPs due to the coupling between the SP modes of Au NPs and the waveguide modes of Si slab waveguide.

An experimental demonstration of backend monolithic integration of Si3N4 microring filter with bulk complementary metal–oxide–semiconductor (CMOS) integrated circuit (IC) is accomplished using CMOS postbackend process. Si3N4 photonic layer is integrated on the top surface of CMOS IC die which is manufactured in commercial CMOS foundry. The Si3N4 microring filters in photonic layer are fabricated using CMOS postbackend process with only two additional lithography steps. The filters can be thermally tuned by microheaters integrated in CMOS circuits, which are controlled by transmission gates. A measured optical transmission spectrum and a dynamic characteristic of the integrated filter are provided.

Benefit from exceptional electrical transport properties, graphene receives worldwide attentions, especially in the domain of high frequency electronics. Due to absence of effective bandgap causing off-state the device, graphene material is extraordinarily suitable for analog circuits rather than digital applications. With this unique ambipolar behavior, graphene can be exploited and utilized to achieve high performance for frequency multipliers. Here, dual-gated graphene field-effect transistors have been firstly used to achieve frequency quadrupling. Two Dirac points in the transfer curves of the designed GFETs can be observed by tuning top-gate voltages, which is essential to generate the fourth harmonic. By applying 200 kHz sinusoid input, arround 50% of the output signal radio frequency power is concentrated at the desired frequency of 800 kHz. Additionally, in suitable operation areas, our devices can work as high performance frequency doublers and frequency triplers. Considered both simple device structure and potential superhigh carrier mobility of graphene material, graphene-based frequency quadruplers may have lots of superiorities in regards to ultrahigh frequency electronic applications in near future. Moreover, versatility of carbon material system is far-reaching for realization of complementary metal-oxide-semiconductor compatible electrically active devices.

This paper reports a high-speed OOK-NRZ visible light communication system using red, green and blue LDs, data rates of 1940Mb/s, 2660Mb/s and 2670Mb/s are obtained over distance of ∼1.5m. All the BERs are below 10-9.

Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni&ndash, Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni&ndash, Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni&ndash, Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2/Si substrate at a low temperature (~600 &deg, C).

This letter proposes a graphene field-effect transistor (GFET) device with double top-gates and double feedback. An intuitive explanation of the device is provided and its performance is verified by numerical solution of the GFET large signal model in the p- and n-type regions. Simulation shows that the device can provide full current saturation within a large voltage range using a typical GFET’s structure. The saturation current can be adjusted using a control voltage and other circuit parameters, which makes it a voltage-controlled current source suitable for analog and flexible circuit applications.

We present optoelectronic mixing phenomenon in graphene FET (GFET) and give a brief analysis for the first time. Demonstrated by a measurement system, two operating modes of optoelectronic mixer (OE-mixer) circuits are proposed, either of them mixing optical and electrical signals directly using a single GFET. Optoelectronic conversion losses of 24 and 35 dB are obtained in a 50-Ω impedance system, respectively. GFET OE-mixer might be of strong importance for radio over fiber systems, millimeter wave, and terahertz frequencies applications.

In this paper, an adaptive impedance tracking front end for inductively powered body sensor node is presented. By implementing a novel impedance matching network with digitally tunable capacitor array in an inductively powered energy hsarvester chip, the system can adaptively maintain impedance match with the coil under influences from nearby human body or metal object, deformation and in homogeneity from manufacture. The experiment demonstrates that the system can effectively maintain resonant frequency of the receiver antenna, boost resonance amplitude of coil and rectifier output significantly compared with fixed matching networks in on-body application.

We have demonstrated a graphene photodetector with tunable photoresponse via electrostatic doping with split local back-gates formed by heavily doped silicon for the first time. A tunable photocurrent from 0 nA to 250 nA is obtained.

The integration of optical devices and electronic integrated circuits (IC) is a main issue for optoelectronic convergence. In this work, a CMOS post-backend process flow is proposed to potentially achieve a 3-D monolithic optoelectronic integrated chip. The proposed integrated chip is composed of an IC die as electronic layer and a waveguide device layer as photonic layer above electronic layer. The photonic layer is fabricated by CMOS post-backend process with a temperature blow 450 oC, which would do no harm to the performance of the CMOS ICs. We also fabricated Si3N4 mircoring add-drop filters on a bulk Si wafer. The cross-section of the waveguide is 400 nm × 1 μm, and the radius of microring is 30μm. Measured results match well with numerical simulations.

In this letter, the chemical vapor deposition grown single-layer graphene with micrometer scale graphene flakes interspersed on the surface has been first used to implement field-effect transistors (FETs) for the purpose of frequency tripling. Two Dirac points can be observed in the transfer curves of the designed FETs, which are essential to generate pure third harmonic with ambipolar graphene. With an input of 1 kHz, more than 94% of the output signal RF power is concentrated at 3 kHz. To the best of our knowledge, it is the highest output spectral purity for reported frequency triplers. The excellent spectral purity, combined with the superhigh carrier mobility of graphene, makes this graphene-based frequency tripler a very promising candidate for the ultrahigh-frequency electronic applications.