International Journal of High Speed Electronics and Systems

TeraFET arrays operating in plasmonic regimes could support the transition from 5G to 6G communication if the constituent TeraFETs operate in synchrony. Such arrays are plasmonic crystals supporting Bloch-like waves of electron density oscillations. The key issues are breaking symmetry and maintaining appropriate boundary conditions between the unit cells. The symmetry must be broken to choose the response polarity to detect the direction of the plasmonic instability growth for generating THz oscillations. The coherence of plasma waves propagating in individual cells of the plasmonic crystal results in continuous waves in the entire structure. Using the narrow stripes at the unit cell edges (called plasmonic stubs) could maintain such coherence. Another advantage of TeraFET arrays is the reduced effects of parasitic contact resistance. This advantage is even more pronounced in ring plasmonic structures used for converting THz radiation into a magnetic field (giant inverse Faraday effect).

A terahertz (THz) wave generator for multiplying the output power from arrayed photomixers is developed. The generator is composed of two uni-traveling carrier photodiodes (UTC-PDs) as the photomixers, a $2\times 1$ T-junction power combiner and a microstrip rectangular patch antenna on a silicon carbide (SiC) substrate in which photocurrents of 300 GHz from the UTC-PDs are combined to be fed to the antenna. Experimental results show that the output power is multiplied by 5.8 dB (approximately fourfold) compared to that of a single UTC-PD. This advancement has the potential for further multiplication of THz power by cascaded combining of a larger number of UTC-PDs.

In this paper, we analyze the modulation characteristics and the ultimate modulation frequency of the terahertz (THz) hot-electron FET bolometers with the graphene channels (GCs), metal gate (MG), and gate barrier layers (BLs) in a wide temperature range. Our results predict that the responsivity of GC-FET bolometers decreases with decreasing operating temperature. This is attributed to a dramatic drop in the thermionic GC-MG current (characterized by the relatively large activation energy) and its modulated component when the temperature lowers. A further decrease in the temperature results in a fairly strong responsivity roll-off. In contrast, the responsivity of the GC-FET detectors with the temperature-adjusted load resistance rises with decreasing temperature because the temperature lowering leads to an increase in the electron energy relaxation time and promotes more effective heating by the impinging THz radiation. In this case, the weakening of the thermionic current is compensated by the commensurate increase in the load resistance.

Terahertz (THz) sensing technology enables 6G communication, detection of biological and chemical hazardous agents, cancer detection, monitoring of industrial processes and products, and detection of mines and explosives. THz sensors support security in buildings, airports, and other public spaces. They found important applications in radioastronomy and space research and, more recently, in Artificial Intelligence-driven THz sensing of MMICs and VLSI. Exploding demand for data transfers will require using the 300 GHz band after 2028 or even before and will make the deployment of THz sensing electronics inevitable. This paper discusses the new physics of THz sensing and THz sensing devices. It also reviews the THz sensing market, and key THz sensor companies.

In this paper, we propose and analyze the terahertz (THz) bolometric vector detectors based on the graphene-channel field-effect transistors (GC-FET) with the black-P gate barrier layer or with the composite b-BN/black-P/b-BN gate layer. The phase difference between the signal received by the FET source and drain substantially affects the plasmonic resonances. This results in a resonant variation of the detector response on the incoming THz signal phase shift and the THz radiation angle of incidence.

The grating-gate plasmonic crystal system represents a compelling arena for investigating strong light-matter interactions and diverse plasmon resonances. This study reviews the recent discovery of two distinctive terahertz phases of AlGaN/GaN plasmonic crystals that arise from varying the modulation of a two-dimensional electron density beneath the metallic gratings: the delocalized phase at weak modulation and the localized phase at strong modulation. Notably, we delve into an impact of the grating filling factor on the electrically driven transition between these phases. Our findings underscore the critical role of specific metal grating geometry parameters in facilitating this transition. Moreover, we explore the potential of utilizing graphene-based gratings as alternatives to metallic gratings. Through the integration of graphene, grown by Chemical Vapor Deposition method on copper foil and then transferred to the high electron mobility AlGaN/GaN heterostructures, we achieve an effective modulation of broadband absorption by free charge carriers within the 0.5–6 THz range via electrical biasing of the graphene electrode. However, while this approach successfully modulates absorption in a wide THz range, it does not elicit plasmon resonances within the graphene-based grating-gate plasmonic crystals. This intriguing observation poses a significant unresolved question warranting further theoretical and experimental exploration in subsequent studies.

Laser-induced Terahertz (THz) Emission Spectroscopy (TES) has demonstrated its potential utility in the realm of Metal-Oxide-Semiconductor (MOS) devices as an expedient and noncontact estimation methodology. Owing to its discerning response to the interface electric field, the amplitude of the THz emission peak in time-domain spectroscopy encapsulates rich information regarding MOS properties, notably the flat-band voltage. This paper concentrates on the precise quantitative estimation of the flat-band voltage within the Si MOS structure, elucidating the intricacies of the estimation process through the THz emission model.

We report on sub-terahertz plasmonic wave generation in the 2DEG channel of diamond TeraFET when biased by a DC current at the drain. Our numerical results demonstrated that p-diamond can support resonant oscillation of 300 GHz at room temperature, allowing it to function as a sub-THz emitter. We investigated the impact of different channel lengths, gate biases, drift velocities, and temperatures on the fundamental mode oscillation. The model incorporated the decay factors owing to electron scattering and electron fluid viscosity.

Field effect transistors (FETs) in plasmonic regimes of operation could detect terahertz (THz) radiation and operate as THz interferometers, spectrometers, frequency-to-digital converters and THz modulators and sources. We report on the development of compact models for Si MOS (Metal-Oxide-semiconductor) and heterostructure-based plasmonic FETs (or TeraFETs) suitable for circuit design in the THz range and based on the multi-segment unified charge control model. This model accounts for the electron inertia effect (by incorporating segmented Drude inductances), for the ballistic field effect mobility, which is proportional to the channel length, for parasitic resistances and capacitances and for the leakage current. It is validated by comparison with experimental data and TCAD simulation results. The model can be used for simulation and optimization of sub-THz and THz detectors. Our simulations use up to 200 segments in the device channel. The results are also in good qualitative agreement with the hydrodynamic simulations. Applications of our model could dramatically reduce astronomical design costs of nanoscale VLSI reaching US$1.5 billion for the 3 nm technological node.