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Monolithically integrated, antenna-coupled field-effect transistors (TeraFETs) are rapid and sensitive detectors for the terahertz range (0.3–10 THz) that can operate at room temperature. We conducted experimental characterizations of a singlepatch-antenna-coupled TeraFET optimized for 3.4 THz operation and its integration into an 8×8 multielement detector configuration. In this configuration, the entire TeraFET array operates as a unified detector element, combining the output signals of all detector elements. Both detectors were realized using a mature commercial Si-CMOS 65-nm process node. Our experimental characterization employed single-mode quantum-cascade lasers (QCLs) emitting at 2.85 and 3.4 THz. The 8×8 multielement detector yields two major improvements for sensitive power detection experiments. First, the larger detector area simplifies alignment and enhances signal stability. Second, the reduced detector impedance enabled the implementation of a TeraFET+QCL system capable of providing a -3 dB modulation bandwidth up to 21 MHz, which is currently limited primarily by the chosen readout circuitry. Finally, we validate the system's performance by providing high-resolution gas spectroscopy data for methanol vapor around 3.4 THz, where a detection limit of $1.6 \times 10^{-5}$ absorbance or $2.6\times 10^{11} \text{molecules}/\text{cm}^{3}$ was estimated.

This article presents a study on performance optimization and resonant frequency modification of terahertz (THz) detectors by the use of hyper-hemispherical silicon superstrate lenses. The detectors are patch-TeraFETs, i.e., field-effect transistors (FETs) with monolithically integrated patch antennas fabricated with a commercial 65-nm CMOS foundry process and designed for an operation frequency of 580 GHz. We demonstrate a strong improvement of the optical noise-equivalent power (optical NEP, referenced against the total radiation power) reaching a value of 16 pW/ $\sqrt {\text {Hz}}$ . We show furthermore that the resonance frequency can be efficiently fine-tuned by the choice of the material and the thickness of a dielectric layer placed between the transistor and the superstrate lens. The resonance frequency can be shifted by more than 15% of the center frequency (up to 100 GHz for the 580-GHz devices). The design of the on-chip optics can be employed for post-fabrication tailoring of the detector’s resonance frequency to target specific spectral positions.

Terahertz (THz) multifrequency digital holography within the range from 1.39–4.25 THz is demonstrated. Holograms are recorded using an optically pumped molecular THz laser operating at emission lines of 1.39-, 2.52-, 3.11-, and 4.25 THz frequencies, and nanometric field effect transistor with integrated patch antennae as a THz detector. It is revealed that phase-shifting methods allow for qualitative reconstruction of multifrequency THz holograms combined into one “colored” image. It provides more information about the low-absorbing objects with additionally improved quality achieved by removing unwanted information related to the so-called dc term and conjugated beam forming a virtual image. It is shown that the THz holography can be applied for the investigation of low-absorbing objects, and it is illustrated via inspection of stacked graphene layers placed on a high-resistivity silicon substrate.

We report on the modeling and experimental characterization of Si complementary metal-oxide-silicon (CMOS) detectors of terahertz radiation based on antenna-coupled field-effect transistors (TeraFETs). The detectors are manufactured using Taiwan semiconductor manufacturing company (TSMC's) 65-nm technology. We apply two models—the TSMC RF foundry model and our own advanced design system (ADS)-hydrodynamic transport model (HDM)—to simulate the Si CMOS TeraFET performance and compare their predictions with respective experimental data. Both models are implemented in the commercial circuit simulation software keysight ADS. We find that the compact model TSMC RF is capable to predict the detector responsivity and its dependence on frequency and gate voltage with good accuracy up to the highest frequency of 1.2 THz covered in this study. This frequency is well beyond the tool's intended operation range for 5G communications and 110-GHz millimeter wave applications. We demonstrate that our self-developed physics-based ADS-HDM tool, which relies on an extended 1-D HDM and can be adapted readily to other material technologies, has high predictive qualities comparable to those of the foundry model. We use the ADS-HDM to discuss the contribution of diffusive and plasmonic effects to the THz response of Si CMOS TeraFETs, finding that these effects, while becoming more significant with rising frequency, are never dominant. Finally, we estimate that the electrical noise-equivalent power (perfect power coupling conditions) is on the order of 5 pW/$\sqrt{\mathrm{Hz}}$ at room-temperature.

We report on the design and characterization of a novel backside-radiating antenna-coupled direct terahertz detector fabricated in 65 nm CMOS technology. The novelty of the design lies in the low-metal coverage of the biquad antenna geometry, which adapts well to the particular challenging conditions of on-chip antenna integration in silicon and allows optimization for a versatility of operation conditions. The biquad antenna was modified here to achieve wideband radiation and matching to a gate-coupled single-finger field-effect transistor with ac open condition at the drain terminal. The successful detector performance was the result of a careful treatment of transistor, antenna, and optics from a codesign perspective, since the beginning of the design. This included the frequency-dependent complex impedance for optimum matching, the technology restrictions to ensure proper chip fabrication, and the overall detection efficiency after backing the device with a silicon lens. Calibrated detector measurements for 7777 Hz modulation frequency yielded minimum optical noise-equivalent-power (NEP) of 25 pW/$\sqrt{\,}$Hz at 1 THz, with NEP values below 50 pW/$\sqrt{\,}$Hz in the 0.84–1.29 THz frequency range. These figures achieve state-of-the-art of wideband CMOS-based detectors and are only a factor of ${{\sim}2}$ inferior to the best reported narrowband devices close to 1 THz.

Many emerging applications in the terahertz (THz) frequency range demand highly sensitive, broadband detectors for room-temperature operation. Field-effect transistors with integrated antennas for THz detection (TeraFETs) have proven to meet these requirements, at the same time offering great potential for scalability, high-speed operation, and functional integrability.

We present experimental results of an investigation into the performance of a commercial, packaged GaAs high-electron-mobility transistor (HEMT) as a detector of terahertz (THz) radiation in the frequency ranges 0.22-0.32 and 0.520-0.650 THz. Enclosed in a standard ceramic housing and without a dedicated antenna for radiation coupling, the transistor is capable of sensitive direct detection (power detection) of THz radiation at room temperature. The device responsivity shows a strong variation with wavelength, indicating that various device features (transistor metallization, contact pads, wires) act as an effective THz antenna. With the THz radiation focused with a parabolic mirror (and without a substrate lens), the maximum responsivity reaches 2.5 and 0.72 V/W with values of the minimum optical noise-equivalent power (NEP) of 1.4 and 2.5 nW/√(Hz) at the sensitivity peaks at 0.271 and 0.632 THz, respectively. The performance of the HEMT, in comparison with antenna-coupled FET detectors optimized for THz detection (TeraFETs), can be assessed better if the responsivity and the NEP are referred to the effective antenna cross-section determined experimentally for the device. We arrive at a cross-sectional responsivity of 42 V/W (1.6 V/W) and a cross-sectional NEP of 135 pW/√(Hz) (1250 pW/√(Hz)) at 0.271 THz (0.632 THz), for measurements through the ceramic cap. The cross-sectional NEP values are about one order of magnitude at 0.271 THz and two orders of magnitude at 0.632 THz higher than those achieved with the best TeraFETs, yet in a range where they enable many practical applications at low cost for the detector.

We report on circuit simulation, modeling, and characterization of field-effect transistor based terahertz (THz) detectors (TeraFETs) with integrated patch antennas for discrete frequencies from 1.3 to 5.7 THz. The devices have been fabricated using a standard 90-nm CMOS technology. Here, we focus in particular on a device showing the highest sensitivity to 4.75-THz radiation and its prospect to be employed for power monitoring of a THz quantum cascade laser used in a heterodyne spectrometer GREAT (German REceiver for Astronomy at Terahertz frequencies). We show that a distributed transmission line based detector model can predict the detector's performance better than a device model provided by the manufacturer. The integrated patch antenna of the TeraFET designed for 4.75 THz has an area of 13 × 13 μm2 and a distance of 2.2 μm to the ground plane. The modeled radiation efficiency at the target frequency is 76% with a maximum directivity of 5.5, resulting in an effective area of 1750 μm2. The detector exhibits an area-normalized minimal noise-equivalent power of 404 pW/√Hz and a maximum responsivity of 75 V/W. These values represent the state of the art for electronic detectors operating at room-temperature and in this frequency range.

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This letter reports on the influence of illumination conditions on the detector response of three-terminal devices. Antenna-coupled field-effect transistors for the plasmonic detection of THz radiation (TeraFETs) were realized using a 0.25- $\mu\hbox{m}$ AlGaN/GaN process. Integrated bow-tie antennas are connected to the source, drain and gate terminals of electrically identical transistors in various ways. If radiation power is coupled symmetrically to the source and drain sides of the transistors' channels, TeraFETs become sensitive to gradient-intensity of the illumination power. It is found that fully asymmetric coupling, nontrivial to ensure at THz-frequencies, is required for a pure response to incident power.

We demonstrate the principle applicability of antenna-coupled complementary metal oxide semiconductor (CMOS) field-effect transistor arrays as cameras for real-time coherent imaging at 591.4 GHz. By scanning a few detectors across the image plane, we synthesize a focal-plane array of 100×100 pixels with an active area of 20×20??mm^2, which is applied to imaging in transmission and reflection geometries. Individual detector pixels exhibit a voltage conversion loss of 24 dB and a noise figure of 41 dB for 16 μW of the local oscillator (LO) drive. For object illumination, we use a radio-frequency (RF) source with 432 μW at 590 GHz. Coherent detection is realized by quasioptical superposition of the image and the LO beam with 247 μW. At an effective frame rate of 17 Hz, we achieve a maximum dynamic range of 30 dB in the center of the image and more than 20 dB within a disk of 18 mm diameter. The system has been used for surface reconstruction resolving a height difference in the μm range.

We explore terahertz imaging with CMOS field-effect transistors exploiting their plasmonic detection capability and the advantages of CMOS technology for the fabrication of THz cameras with respect to process stability, array uniformity, ease of integration of additional functionality, scalability and cost-effectiveness. A 100×100-pixel camera with an active area of 20×20 mm² is physically simulated by scanning single detectors and groups of a few detectors in the image plane. Using detectors with a noise-equivalent power of 43 pW/√Hz, a distributed illumination of 432 W at 591.4 GHz, and an integration time of 20 ms (for a possible frame rate of 17 fps), this virtual camera allows to obtain images with a dynamic range of at least 20 dB and a resolution approaching the diffraction limit. Imaging examples acquired in direct and heterodyne detection mode, and in transmission and reflection geometry, show the potential for real-time operation. It is demonstrated that heterodyning (i) improves the dynamic range substantially even if the radiation from the local oscillator is distributed over the camera area, and (ii) allows sensitive determination of object-induced phase changes, which promises the realization of coherent imaging systems.