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

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

Graphene is a relatively new material with unique properties that holds promise for electronic applications. Since 2004, when the first graphene samples were intentionally fabricated, the worldwide research activities on graphene have literally exploded. Apart from physicists, also device engineers became interested in the new material and soon the prospects of graphene in electronics have been considered. For the most part, the early discussions on the potential of graphene had a prevailing positive mood, mainly based on the high carrier mobilities observed in this material. This has repeatedly led to very optimistic assessments of the potential of graphene transistors and to an underestimation of their problems. In this paper, we discuss the properties of graphene relevant for electronic applications, examine its advantages and problems, and summarize the state of the art of graphene transistors.

Graphene Transistors: Status, Prospects, and Problems

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

rdquoWe report the first submillimeter-wave monolithic microwave integrated circuit (MMIC) amplifier with 4.4-dB measured gain at 308-GHz frequency, making it the highest frequency MMIC amplifier reported to date. In this letter, a 35-nm InP high-electron mobility transistor process has been successfully developed with a projected maximum available gain of greater than 7 dB at 300 GHz. The excellent dc and RF performance makes it suitable for applications at frequencies well into the millimeter-wave band and, for the first time, in the submillimeter- wave band as well.

35-nm InP HEMT SMMIC Amplifier With 4.4-dB Gain at 308 GHz

In this paper, we present the latest advancements of short gate length InGaAs/InAlAs/InP high electron mobility transistor (InP HEMT) devices that have achieved extremely high extrapolated Fmax above 1 THz. The high Fmax is validated through the first demonstrations of sub-MMW MMICs (s-MMICs) based on these devices including the highest fundamental transistor oscillator MMIC at 347 GHz and the highest gain greater than 15 dB (greater than 5 dB per stage) at 340 GHz.

Fabrication of InP HEMT devices with extremely high Fmax

A new InP HEMT process has been developed with 35nm gate length and improved Ohmic contact. A gate-source capacitance of 0.4pF/mm is achieved with the reduced gate length, a 30% improvement over our baseline 70nm device. The contact resistance is successfully reduced to 0.07 with the newly designed contact layer combined with an alloyed Au/Ge/Ni/Au Ohmic metal. Good device characteristics has been demonstrated with a transconductance as high as 2 S/mm and a cutoff frequency fr of 420GHz. A single-stage common-source amplifier was fabricated with this new process. A peak gain of 5dB is measured at 265GHz. A MAG/MSG of 3dB at 300GHz was achieved, making the device suitable for applications at frequencies well into the millimeter-wave and even sub-millimeter-wave band.

35nm InP HEMT for Millimeter and Sub-Millimeter Wave Applications

We have recently developed a sub-50nm gate length InP HEMT (high electron mobility transistor) process with a peak transconductance of 2000 mS/mm at 1V. A 3-stage single-ended common source 150-220 GHz MMIC LNA demonstrates greater than 20 dB gain at 200 GHz (> 7 dB gain per stage) and is >5 dB higher LNA gain compared to the same MMIC design fabricated on our baselined 70 nm gate length InP HEMT MMIC process. To our knowledge, this is the highest amplifier gain per stage achieved at this frequency range.

Y.M. Kim

Papers

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

35-nm InP HEMT SMMIC Amplifier With 4.4-dB Gain at 308 GHz

Fabrication of InP HEMT devices with extremely high Fmax

35nm InP HEMT for Millimeter and Sub-Millimeter Wave Applications

High Gain G-Band MMIC Amplifiers Based on Sub-50 nm Gate Length InP HEMT