High intensity study of THz detectors based on field effect transistors

Terahertz power dependence of the photoresponse of field effect transistors, operating at frequencies from 0.1 to 3 THz for incident radiation power density up to 100 kW/cm^2 was studied for Si metal-oxide-semiconductor field-effect transistors and InGaAs high electron mobility transistors. The photoresponse increased linearly with increasing radiation power up to kW/cm^2 range. The saturation of the photoresponse was observed for all investigated field effect transistors for intensities above several kW/cm^2. The observed signal saturation is explained by drain photocurrent saturation similar to saturation in direct currents output characteristics. The theoretical model of terahertz field effect transistor photoresponse at high intensity was developed. The model explains quantitatively experimental data both in linear and nonlinear (saturation) range. Our results show that dynamic range of field effect transistors is very high and can extend over more than six orderd of magnitudes of power densities (from 0.5 mW/cm^2 to 5 kW/cm^2)

Room Temperature Amplification of Terahertz Radiation by Grating-Gate Graphene Structures

We report on experimental studies of terahertz (THz) radiation transmission through grating-gate graphene-channel transistor nanostructures and demonstrate room temperature THz radiation amplification stimulated by current-driven plasmon excitations. Specifically, with increase of the direct current (dc) under periodic charge density modulation, we observe a strong red shift of the resonant THz plasmon absorption, its complete bleaching, followed by the amplification and blue shift of the resonant plasmon frequency. Our results are, to the best of our knowledge, the first experimental observation of energy transfer from dc current to plasmons leading to THz amplification. We present a simple model allowing for the phenomenological description of the observed amplification phenomena. This model shows that in the presence of dc current the radiation-induced correction to dissipation is sensitive to the phase shift between THz oscillations of carrier density and drift velocity, and with increase of the current becomes negative, leading to amplification. The experimental results of this work as all obtained at room temperature, pave the way towards the new 2D plasmons based, voltage tuneable THz radiation amplifiers.Comment: 17 pages with 15 figures, uses revtex4-2, additionally include 6 pages of supplementary materials with 6 figure

Homodyne Spectroscopy with Broadband Terahertz Power Detector Based on 90-nm Silicon CMOS Transistor

Over the last two decades, photomixer-based continuous wave systems developed into versatile and practical tools for terahertz (THz) spectroscopy. The high responsivity to the THz field amplitude of photomixer-based systems is predetermined by the homodyne detection principle that allows the system to have high sensitivity. Here, we show that the advantages of homodyne detection can be exploited with broadband power detectors combined with two photomixer sources. For this, we employ a THz detector based on a complementary metal-oxide-semiconductor field-effect transistor and a broadband bow-tie antenna (TeraFET). At 500 GHz and an effective noise bandwidth of 1 Hz, the response from one photomixer-based THz source resulted in an about 43 dB signal-to-noise ratio (SNR). We demonstrate that by employing a homodyne detection system by overlaying the radiation from two photomixers, the SNR can reach up to 70 dB at the same frequency with an integration time 100 ms. The improvement in SNR and the spectroscopic evidence for water vapor lines demonstrated up to 2.2 THz allow us to conclude that these detectors can be successfully used in practical continuous wave THz spectrometry systems

Antenna Characterization of Monolithically Integrated Detectors for 0.62 THz

Here we report on comprehensive investigations of receiving antenna characteristics of monolithically integrated field effecttransistor-based terahertz detectors with patch antennas which are often used for a variety of applications [1,2]. Devices are implemented using a standard 65-nm CMOS process technology. Furthermore, we investigate a set of devices coupled to the antenna with same geometrical parameters but connected to a device with a different channel length thus allowing to vary the impedance of antenna load not only through the bias voltage. The directivity values of antennas were determined by measuring the angle dependence of rectified voltage as a function of the tilt in E- and H-planes which are presented in Fig. 1 and through the thorough comparison with the results of electromagnetic simulations using CST software. Considering the amount of input radiation power impinging to the determined effective area of the detector, we report a room-temperature cross-sectional noise-equivalent power of 17.1 pW/√Hz at the resonant frequency of 0.62 THz. This value represents the state of the art for electronic detectors operating at room temperature in this frequency range

Sensitivity of Field-Effect Transistor-Based Terahertz Detectors

This paper presents an overview of the different methods used for sensitivity (i.e., responsivity and noise equivalent power) determination of state-of-the-art field-effect transistor-based THz detectors/sensors. We point out that the reported result may depend very much on the method used to determine the effective area of the sensor, often leading to discrepancies of up to orders of magnitude. The challenges that arise when selecting a proper method for characterisation are demonstrated using the example of a 2×7 detector array. This array utilises field-effect transistors and monolithically integrated patch antennas at 620 GHz. The directivities of the individual antennas were simulated and determined from the measured angle dependence of the rectified voltage, as a function of tilting in the E- and H-planes. Furthermore, this study shows that the experimentally determined directivity and simulations imply that the part of radiation might still propagate in the substrate, resulting in modification of the sensor effective area. Our work summarises the methods for determining sensitivity which are paving the way towards the unified scientific metrology of FET-based THz sensors, which is important for both researchers competing for records, potential users, and system designer

All-Electronic Emitter-Detector Pairs for 250 GHz in Silicon

The spread of practical terahertz (THz) systems dedicated to the telecommunication, pharmacy, civil security, or medical markets requires the use of mainstream semiconductor technologies, such as complementary metal-oxide-semiconductor (CMOS) lines. In this paper, we discuss the operation of a CMOS-based free space all-electronic system operating near 250 GHz, exhibiting signal-to-noise ratio (SNR) with 62 dB in the direct detection regime for one Hz equivalent noise bandwidth. It combines the state-of-the-art detector based on CMOS field-effect-transistors (FET) and a harmonic voltage-controlled oscillator (VCO). Three generations of the oscillator circuit are presented, and the performance characterization techniques and their improvement are explained in detail. The manuscript presents different emitter–detector pair operation modalities, including spectroscopy and imaging

Sub-terahertz feedback interferometry and imaging with emitters in 130 nm BiCMOS technology

Abstract In this work, we present the effect of self-mixing in compact terahertz emitters implemented in a 130 nm SiGe BiCMOS technology. The devices are based on a differential Colpitts oscillator topology with optimized emission frequency at the fundamental harmonic. The radiation is out-coupled through the substrate side using a hyper-hemispheric silicon lens. The first source is optimized for 200 GHz and radiates up to 0.525 mW of propagating power. The second source emits up to 0.325 mW at 260 GHz. We demonstrate that in these devices, feedback radiation produces the change in bias current, the magnitude of which can reach up to several percent compared to the bias current itself, enabling feedback interferometric measurements. We demonstrate the applicability of feedback interferometry to perform coherent reflection-type raster-scan imaging

Low Frequency Noise of Carbon Nanotubes THz detectors

We report studies of noise properties of carbon nanotube (CNT) networks-based devices used for the terahertz detectors. Low-frequency noise characteristics of CNTs as a function of temperature, UV illumination, and back-gate voltages were examined. Our results demonstrated the existence of at least two important resistance components of nanotubes rather than generally accepted dominant tube-to-tube junction resistance. We showed that noise spectroscopy can be employed to probe the structural quality of nanotube networks. Measurements as a function of back gate voltages revealed the existence of generation-recombination noise, related to deep tarps, which play a significant role in the performances of CNT networks-based terahertz detectors.QC 20211215</p

Compact terahertz devices based on silicon in CMOS and BiCMOS technologies

This paper reports on compact CMOS-based electronic sources and detectors developed for the terahertz frequency range. It was demonstrated that with the achievable noise-equivalent power levels in a few tens of pW/√Hz and the emitted power in the range of 100 μW, one can build effective quasi-optical emitter-detector pairs operating in the 200–266 GHz range with the input power-related signal-to-noise ratio reaching 70 dB for 1 Hz-equivalent noise bandwidth. The applicability of these compact devices for a variety of applications including imaging, spectroscopy or wireless communication links was also demonstrated