The compelling demand for higher performance and lower power consumption in electronic systems is the main driving force of the electronics industry's quest for devices and/or architectures based on new materials. Here, we provide a review of electronic devices based on two-dimensional materials, outlining their potential as a technological option beyond scaled complementary metal-oxide-semiconductor switches. We focus on the performance limits and advantages of these materials and associated technologies, when exploited for both digital and analog applications, focusing on the main figures of merit needed to meet industry requirements. We also discuss the use of two-dimensional materials as an enabling factor for flexible electronics and provide our perspectives on future developments.

Electronics based on two-dimensional materials

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

As silicon-based electronics approach the limit of improvements to performance and capacity through dimensional scaling, attention in the semiconductor field has turned to graphene, a single layer of carbon atoms arranged in a honeycomb lattice. Its high mobility of charge carriers (electrons and holes) could lead to its use in the next generation of high-performance devices. Graphene is unlikely to replace silicon completely, however, because of the poor on/off current ratio resulting from its zero bandgap. But it could be used to improve silicon-based devices, in particular in high-speed electronics and optical modulators.

A role for graphene in silicon-based semiconductor devices

A summary of the NASA Jet Propulsion Laboratory's 675 GHz imaging radar is presented, with an emphasis on several key design aspects that enable fast, reliable through-clothes imaging of person-borne concealed objects. Using the frequency-modulated continuous-wave (FMCW) radar technique with a nearly 30 GHz bandwidth, sub-centimeter range resolution is achieved. To optimize the radar's range resolution, a reliable software calibration procedure compensates for signal distortion from radar waveform nonlinearities. Low-noise, high dynamic range detection comes from the radar's heterodyne RF architecture, low-noise chirp source, and high-performance 675 GHz transceiver. The radar's optical design permits low-distortion fast beam scanning for single-pixel imaging, and a real-time radar image frame rate of 1 Hz is now possible. Still faster speeds are on the horizon as multi-beam THz transceivers are developed.

THz Imaging Radar for Standoff Personnel Screening

We report the first ever terahertz monolithic integrated circuit amplifier based on 25-nm InP high electron mobility transistor (HEMT) process demonstrating amplification at 1 THz (1000 GHz) with 9-dB measured gain at 1 THz. This milestone was achieved with a 25-nm InP HEMT transistor, which exhibits 3.5-dB maximum available gain at 1 and 1.5 THz projected $f_{\mathrm {\mathbf {MAX}}}$ .

First Demonstration of Amplification at 1 THz Using 25-nm InP High Electron Mobility Transistor Process

In this paper, we present the latest advancements of sub 50 nm InGaAs/lnAIAs/lnP high electron mobility transistor (InP HEMT) devices that have achieved extrapolated Fmax above 1 THz. This extrapolation is both based on unilateral gain (1.2 THz) and maximum stable gain/maximum available gain (1.1 THz) extrapolations, with an associated fT of 385 GHz. This extrapolation is validated by the demonstration of a 3-stage common source low noise MMIC amplifier which exhibits greater than 18 dB gain at 300 GHz and 15 dB gain at 340 GHz.

Sub 50 nm InP HEMT Device with Fmax Greater than 1 THz

In this paper, progress toward developing solid-state power-amplifier modules at 0.65 THz is reported. This work is enabled by a >;1 THz fMAX InP HEMT transistor with a 30-nm gate and an integrated circuit process specifically tailored for circuits operating at frequencies approaching 1 THz. The building block of the reported amplifier modules is an eight-stage terahertz monolithic integrated circuit (TMIC) amplifier. The first six stages of the TMIC use 20- transistors, while the final two output stages rely on two power-combined 20-μm transistors to increase the output power. For operation at 0.65 THz, the TMIC also relies on integrated electromagnetic transitions for direct coupling with the WR1.5 waveguide of the amplifier package. Two modules are reported, with the first module containing a single TMIC and demonstrating a peak saturated output power of 1.7 mW at 640 GHz with a measured small-signal gain ≥10 dB from 629 to 638 GHz. The second module features two power-combined TMICs to increase output power. This is done using a waveguide Y-junction as both the combiner and splitter. In test, this power-combined module reached a peak output power of 3 mW at 650 GHz and measured small-signal gain ≥10 dB from 625 to 640 GHz.

Power Amplification at 0.65 THz Using InP HEMTs

In this letter, low noise amplification at 0.67 THz is demonstrated for the first time. A packaged InP High Electron Mobility Transistor (HEMT) amplifier is reported to achieve a noise figure of 13 dB with an associated gain greater than 7 dB at 670 GHz using a high fMAX InP HEMT transistors in a 5 stage coplanar waveguide integrated circuit. A 10-stage version is also reported to reach a peak gain of 30 dB. These results indicate that InP HEMT integrated circuits can be useful at frequencies approaching a terahertz.

Low Noise Amplification at 0.67 THz Using 30 nm InP HEMTs

In this letter, we present an amplifier module operating at a frequency of 0.48 THz. This represents almost a 50% increase in solid-state amplifier operating frequency compared to prior state of the art, and is the highest reported amplifier to date. The amplifier demonstrates a peak gain of 11.7 dB measured in a waveguide split-block housing. Sub 50-nm InP HEMT transistors with an estimated f MAX > 1 THz are used to achieve this level of performance. The five stage amplifier is realized in coplanar waveguide, and uses monolithically integrated dipole probes to couple the chip from the WR 2.2 waveguide.

W. Yoshida

Papers

First Demonstration of Amplification at 1 THz Using 25-nm InP High Electron Mobility Transistor Process

Sub 50 nm InP HEMT Device with Fmax Greater than 1 THz

Power Amplification at 0.65 THz Using InP HEMTs

Low Noise Amplification at 0.67 THz Using 30 nm InP HEMTs

Demonstration of a 0.48 THz Amplifier Module Using InP HEMT Transistors