Terahertz (THz) radiation detection by junctionless metal-oxide-semiconductor field-effect transistors (JL MOSFETs) was studied and compared with THz detection using conventional MOSFETs. It has been shown that in contrast to the behavior of standard transistors, the junctionless devices have a significant responsivity also in the open channel (low resistance) state. The responsivity for a photolithographically defined JL FET was 70 V/W and the noise equivalent power 460 pW/√Hz. Working in the open channel state may be advantageous for THz wireless and imaging applications because of its low thermal noise and possible high operating speed or large bandwidth. It has been proven that the junctionless MOSFETs can also operate in a zero gate bias mode, which enables simplification of the THz array circuitry. Existing models of THz detection by MOSFETs were considered and it has been demonstrated that the process of detection by these junctionless devices cannot be explained within the framework of the commonly accepted models and therefore requires a new theoretical approach.

Recent advances in THz detection with the use of CMOS technology have shown that this option has the potential to be a leading method of producing low-cost THz sensors with integrated readout systems. This review paper, based on authors' years of experience, presents strengths and weaknesses of this solution. The article gives examples of some hints, regarding radiation coupling and readout systems. It shows that silicon CMOS technology is well adapted to the production of inexpensive imaging systems for sub-THz frequencies. As an example paper presents the demonstrator of a multipixel Si-CMOS THz spectroscopic system allowing for chemical identification of lactose. The THz detectors embedded in this system were manufactured using the CMOS process. (C) 2018 Association of Polish Electrical Engineers (SEP). Published by Elsevier B.V. All rights reserved.

The paper describes a convenient way to numerically model planar antennas dedicated to sub-terahertz (THz) radiation detectors while accounting for multiple oxide layers included in typical silicon-based substrates used in microelectronics. Several approaches are presented, including a solution based on calculations of effective permittivity of the layered substrate. The results suggest that this approach can work at lower frequencies, but will not be effective in the sub-THz range due to different mechanisms of dispersion occurring in transmission lines with either homogeneous or layered substrate. Therefore, an alternative approach based on anisotropic layers has been proposed, which proves to be efficient and easy to adopt in typical numerical models. It also explains well the results of experiments done using a set of patch antennas fabricated on thin membranes and operating at various frequencies from 240 GHz up to 370 GHz.

Silicon junctionless field-effect transistors (JLFETs) detect THz radiation even at frequencies above a few THz. This effect cannot be explained by classic laws of electron transport. The same behavior is observed for other types of FETs. However, the JLFET architecture makes this device an effective tool for testing the THz detection mechanism. In particular, a deeper insight into this effect is provided by a case study in which, the low concentration of electrons in the gate-controlled region contradicts potential plasmonic effects. Considering the experimental results, the authors critically discuss the plasmon-based theory of THz detection by JLFETs. Then, taking into account the revealed inconsistencies and based on numerical simulation results, they propose a simple, one-dimensional JLFET photoresponse model based on local electron heating at the channel-source contact which is located in the path of the THz signal between the gate and the source. The model is verified in a simulation-assisted experiment showing that the energy of hot electrons generates a sufficient photoelectric voltage, typical of silicon FETs integrated with antennas illuminated by THz radiation. The authors suggest that the model is universal and in the 3D version it can successfully explain the THz detection by various FETs, especially those operating in the subthreshold range in which the electron concentration under the gate is very low.

The paper presents a comprehensive look at the perspectives on the use of THz in digital communication systems. The publication aims to focus on arguments that justify a significant increase in the frequency of radio links and their integration with fibre-based networks. Comparison of THz links with their microwave and optical counterparts is discussed from basic physical limitations to technological constraints. Main attention is paid to the available channel capacity resulting from its bandwidth and signal-to-noise ratio. The short final discussion is about technology platforms that seem to be crucial to the availability of suitable THz sources. According to the author, the biggest advantage of using bands in the range of several hundred GHz for a digital data transmission is their use for mobile communication over short distances, as well as for broadband indoor links. However, these applications require a development of compact electronic THz sources with low noise and power reaching single watts. This is beyond the range of the most popular silicon-based technology platform, although a significant progress can be expected with the development of technologies based on wide bandgap semiconductors. Fibre optic connections remain the unquestioned leader in communication over long distances and permanent links.

We report on the absorption properties of polarization-insensitive transmissive and reflective metamaterial absorbers based on two planar aluminium periodic structures and SU-8 epoxy resist. These absorbers were investigated using numerical simulation and experimental methods in the terahertz range (below 2 THz). SU-8 is a very promising organic material for dielectric layers in planar metamaterials, because its application simplifies the process of fabricating these structures and significantly reduces the fabrication time. The experimental absorption of the metamaterial absorbers has narrowband characteristics that were consistent with the numerical simulations. Power flow analysis in the transmissive metamaterial unit cell shows that the absorption in the terahertz range occurs primarily in the SU-8 layer of the absorber.