We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

This Review covers the state-of-the-art technologies on photonics-based terahertz communications, which are compared with competing technologies based on electronics and free-space optical communications. Future prospects and challenges are also discussed. Almost 15 years have passed since the initial demonstrations of terahertz (THz) wireless communications were made using both pulsed and continuous waves. THz technologies are attracting great interest and are expected to meet the ever-increasing demand for high-capacity wireless communications. Here, we review the latest trends in THz communications research, focusing on how photonics technologies have played a key role in the development of first-age THz communication systems. We also provide a comparison with other competitive technologies, such as THz transceivers enabled by electronic devices as well as free-space lightwave communications.

/pdf/advances-in-terahertz-communications-accelerated-by-t151adrqkd.pdf

Advances in terahertz communications accelerated by photonics

http://www.acsu.buffalo.edu/~jmjornet/papers/2014/j1.pdf

Full length article: Terahertz band: Next frontier for wireless communications

Recent changes in how people consume multimedia services are causing an explosive increase in mobile traffic. With more and more people using wireless networks, the demand for the ultra-fast wireless communications systems is increasing. To date, this demand has been accommodated with advanced modulation schemes and signal-processing technologies at microwave frequencies. However, without increasing the carrier frequencies for more spectral resources, it may be quite difficult to keep up with the needs of users. Although there are several alternative bands, recent advances in terahertz-wave (THz-wave) technologies have attracted attention due to the huge bandwidth of THz waves and its potential for use in wireless communications. The frequency band of 275 ~ 3000 GHz , which has not been allocated for specific uses yet, is especially of interest for future wireless systems with data rates of 10 Gb/s or higher. Although THz communications is still in a very early stage of development, there have been lots of reports that show its potential. In this review, we will examine the current progress of THz-wave technologies related to communications applications and discuss some issues that need to be considered for the future of THz communications.

Present and Future of Terahertz Communications

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

https://iopscience.iop.org/article/10.1088/1361-6463/50/4/043001/pdf

The 2017 terahertz science and technology roadmap

A focal-plane array (FPA) for room-temperature detection of 0.65-THz radiation has been fully integrated in a low-cost 0.25 mum CMOS process technology. The circuit architecture is based on the principle of distributed resistive self-mixing and facilitates broadband direct detection well beyond the cutoff frequency of the technology. The 3 timesZ 5 pixel array consists of differential on-chip patch antennas, NMOS direct detectors, and integrated 43-dB voltage amplifiers. At 0.65 THz the FPA achieves a responsivity (Rv) of 80 kV/W and a noise equivalent power (NEP) of 300 pW/ radic{Hz}. Active multi-pixel imaging of postal envelopes demonstrates the FPAs potential for future cost-effective terahertz imaging solutions.

A 0.65 THz Focal-Plane Array in a Quarter-Micron CMOS Process Technology

In search of novel detectors of electromagnetic radiation at terahertz frequencies, field-effect transistors (FETs) have recently gained much attention. The current literature studies them with respect to the excitation of plasma waves in the two-dimensional channel. Circuit aspects have been taken into account only to a limited degree. In this paper, we focus on embedding silicon FETs in a proper circuitry to optimize their responsivity to terahertz radiation. This includes impedance-matched antenna coupling and amplification of the rectified signal. Special attention is given to the investigation of high-frequency short-circuiting of the gate and drain contacts by a capacitive shunt, a common approach of high-frequency electronics to induce resistive mixing in transistors. We theoretically study the effect of shunting in the framework of the Dyakonov–Shur plasma-wave theory, with the following key results. In the quasistatic limit, the capacitive shunt induces the longitudinal high-frequency field neede...

Rational design of high-responsivity detectors of terahertz radiation based on distributed self-mixing in silicon field-effect transistors

A 325-GHz ×18 frequency multiplier chain implemented in a fτ/fmax = 250 GHz/380 GHz evaluation SiGe heterojunction bipolar transistor technology is presented. The chain achieves a peak output power of -3 dBm and consists of a balanced doubler driven by two cascaded tripler stages. It operates from 317 to 328 GHz with a 0-dBm 18-GHz input signal and a 1.5-W power consumption. Additionally, 220- and 325-GHz doubler breakout circuits with integrated driver amplifiers are presented. The doublers reach an output power of -1 dBm at 220 GHz and -3 dBm at 325 GHz with a power dissipation of 630 and 420 mW, respectively.

Active 220- and 325-GHz Frequency Multiplier Chains in an SiGe HBT Technology

Monolithically integrated 220- and 320-GHz receiver front-ends manufactured in an engineering version of anfT/fmax=280/435-GHz SiGe technology are presented. Subharmonic mixing is provided by a Gilbert cell with stacked switching quads fed by quadrature 110/160-GHz local oscillator (LO) signals. The 220-GHz version of the front-end is equipped with an integrated LNA with a measured 15-dB gain and 28-GHz bandwidth. This front-end yields a conversion gain of 16 dB, an 18-dB single-sideband (SSB) noise figure (NF), and a 30-GHz bandwidth when pumped with a 0-dBm 110-GHz LO signal. The 320-GHz version of the front-end omits the low-noise amplifier and features an integrated × 9 LO multiplier chain to facilitate operation and characterization. A conversion gain of -14 dB and a 36-dB SSB NF is obtained over the 313-to-328-GHz frequency range. The presented circuits demonstrate that a fully integrated receiver front-end can be implemented up to submillimeter-wave frequencies in an SiGe HBT technology.

Subharmonic 220- and 320-GHz SiGe HBT Receiver Front-Ends

The spatial resolution of microwave and mmWave imaging systems can be improved by an increase of their operating frequencies into the submillimeter-wave range (300GHz to 3THz). Electronic terahertz sources and receivers are presently dominated by III/V semiconductor and waveguide packaging technologies. Multipliers and mixers capable of an output power of 1.4mW at 875GHz [1], as well as a conversion loss of 9.25dB at 850GHz [2], have been demonstrated in remote sensing and radio astronomy applications. However, short-range active terahertz imaging systems exhibit less stringent link-budgets, thus opening up new opportunities for highly integrated low-cost silicon TX and RX front-ends. Previous circuit design examples include a 410GHz CMOS VCO in a 45nm technology capable of an output power of −47dBm [3], as well as a 650GHz subharmonic receiver with a 44dB noise figure [4]. In this paper, recent advances in SiGe HBT device technology [5] are used to demonstrate a 820GHz TX/RX chipset for active terahertz imaging applications.

Erik Öjefors

Papers

A 0.65 THz Focal-Plane Array in a Quarter-Micron CMOS Process Technology

Rational design of high-responsivity detectors of terahertz radiation based on distributed self-mixing in silicon field-effect transistors

Active 220- and 325-GHz Frequency Multiplier Chains in an SiGe HBT Technology

Subharmonic 220- and 320-GHz SiGe HBT Receiver Front-Ends

A 820GHz SiGe chipset for terahertz active imaging applications