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Sensing applications of THz technology include applications for space exploration, detection of concealed objects, explosive identification, and THz cancer detection. This paper will review these and other emerging applications and existing and potential THz sources and detectors, including photonic and electronic THz devices, such as plasmonic field effect transistors capable of detecting and emitting THz radiation. Plasma wave electronics devices demonstrated THz detection using GaAs-based and GaN-based HEMTs, Si MOS, SOI, and FINFETs and FET arrays. This technology has potential to become a dominant THz electronics technology.

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.

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).

The conversion mechanisms of microscopic low frequency noise sources (e.g. generation-recombination noise sources) located in the channel of a FET (Field Effect Transistor), in the presence of a large RF signal, are investigated. It is shown that the base-band (low frequency) input gate noise voltage spectral density is strongly dependent on the magnitude of the input RF power applied to the FET. Moreover, the microscopic generation-recombination noise sources distributed along the channel are also responsible of up-converted input gate noise voltage spectral density around the RF frequency.

Measurement results are presented from 0.1 Hz to 100 kHz of 1/f and thermal noise in different n-JFETs, and n- and p-MOSFETs. The comparison of the 1/f noise is based on Hooge's empirical relation with the 1/f noise parameter α as figure of merit, without suggesting a physical origin. We find that the empirical relation for 1/f noise in MOSFETs and JFETs can be used as a tool to pinpoint the dominant noise source (either ΔN number fluctuations or Δμ mobility fluctuations) and its location, either in the channel or in the parasitic series resistance. Similar relations hold in JFETs and MOSFETs for the 1/f noise corner frequency f_c, where thermal and 1/f noise are equal and the ratio f_c/f_T with f_T the unity current gain frequency. The geometry independent parameter α and ratio f_c/f_T are compared from MOSFETs and JFETs with different channel width (W) and length (L). The results show that very low-noise n-JFETs have a corner frequency f_c ≈ 40 Hz, and very low 1/f and thermal noise in agreement with the high W/L ratio and high area WL of the device. Specifically, the equivalent input noise voltage of the investigated JFET IF9030 was about 3.7 nV/√ Hz at 1 Hz, 1.3 nV/√Hz at 10 Hz, and about 0.6 nV/√ Hz (3.6 ×10^-19 V²/Hz or R_{eq th noise} = 23 Ω) for f ≥ 100 Hz. The 1/f noise parameter α for that JFET is as low as α = 2 × 10^-8. This α-value is among the lowest values ever observed. MOSFETs often have α, f_c and f_c/f_T values that are a few decades higher than for JFETs.

This paper presents a review on our recent work on carbon nanotube field effect transistors, including the development of ohmic contacts, high-κ gate dielectric integration, chemical functionalization for conformal dielectric deposition and pushing the performance limit of nanotube FETs by channel length scaling. Due to the importance of high current operations of electronic devices, we also review the high field electrical transport properties of nanotubes on substrates and in freely suspended forms. Owing to their unique properties originating from their crystalline 1D structure and the strong covalent carbon–carbon bonding configuration, carbon nanotubes are highly promising as building blocks for future electronics. They are found to perform favorably in terms of ON-state current density as compared to the existing silicon technology, owing to their superb electron transport properties and compatibility with high-κ gate dielectrics. Future directions and challenges for carbon nanotube-based electronics are also discussed.

The conversion mechanisms of microscopic low frequency noise sources (e.g. generation-recombination noise sources) located in the channel of a FET (Field Effect Transistor), in the presence of a large RF signal, are investigated. It is shown that the base-band (low frequency) input gate noise voltage spectral density is strongly dependent on the magnitude of the input RF power applied to the FET. Moreover, the microscopic generation-recombination noise sources distributed along the channel are also responsible of up-converted input gate noise voltage spectral density around the RF frequency.

Sensing applications of THz technology include applications for space exploration, detection of concealed objects, explosive identification, and THz cancer detection. This paper will review these and other emerging applications and existing and potential THz sources and detectors, including photonic and electronic THz devices, such as plasmonic field effect transistors capable of detecting and emitting THz radiation. Plasma wave electronics devices demonstrated THz detection using GaAs-based and GaN-based HEMTs, Si MOS, SOI, and FINFETs and FET arrays. This technology has potential to become a dominant THz electronics technology.