Uncooled Terahertz real-time imaging 2D arrays developed at LETI: present status and perspectives

Simoens, F.; Meilhan, Jean–Baptiste; Dussopt, Laurent; Nicolas, Jean-Alain; Monnier, Nicolas; Sicard, Gilles; Siligaris, Alexandre; Hiberty, Bruno

doi:10.1117/12.2263221

Cited by 10 publications

(6 citation statements)

References 9 publications

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“…Microbolometer arrays: The adaption of uncooled microbolometer arrays to THz frequency by the optimization of the cavity structures and antennas, respectively, metamaterial absorbers, as well as the read-out, continued to improve the sensitivity to a level that the cameras can be employed for passive imaging [420][421][422][423][424], albeit with a minimum detectable power of about 10 pW at 2.5 THz and a frame rate of 8 Hz [424] not for real-time passive imaging of the human body. Several companies are now on the market offering THz microbolometer cameras, for a list see Ref.…”

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Roadmap of Terahertz Imaging 2021

Valušis

Lisauskas

Yuan

et al. 2021

Sensors

178

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In this roadmap article, we have focused on the most recent advances in terahertz (THz) imaging with particular attention paid to the optimization and miniaturization of the THz imaging systems. Such systems entail enhanced functionality, reduced power consumption, and increased convenience, thus being geared toward the implementation of THz imaging systems in real operational conditions. The article will touch upon the advanced solid-state-based THz imaging systems, including room temperature THz sensors and arrays, as well as their on-chip integration with diffractive THz optical components. We will cover the current-state of compact room temperature THz emission sources, both optolectronic and electrically driven; particular emphasis is attributed to the beam-forming role in THz imaging, THz holography and spatial filtering, THz nano-imaging, and computational imaging. A number of advanced THz techniques, such as light-field THz imaging, homodyne spectroscopy, and phase sensitive spectrometry, THz modulated continuous wave imaging, room temperature THz frequency combs, and passive THz imaging, as well as the use of artificial intelligence in THz data processing and optics development, will be reviewed. This roadmap presents a structured snapshot of current advances in THz imaging as of 2021 and provides an opinion on contemporary scientific and technological challenges in this field, as well as extrapolations of possible further evolution in THz imaging.

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confidence: 99%

“…Several companies are now on the market offering THz microbolometer cameras, for a list see Ref. [423]. Current challenges and possible future trends: Today's imagers with superconducting detectors build on Nb or NbN technology.…”

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confidence: 99%

Roadmap of Terahertz Imaging 2021

Valušis

Lisauskas

Yuan

et al. 2021

Sensors

178

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“…At IR wavelengths, detectors can be operated at room temperature. Towards longer wavelengths, into the THz and sub-THz regime, the power of the Planck radiation drops strongly, with the consequence that unaided passive detection at room temperature, typically using bolometers and microbolometer-based cameras as sensors [ 1 , 2 , 3 ], is impractical. As an alternative, active illumination [ 4 , 5 , 6 , 7 , 8 , 9 ] has been explored in the literature.…”

Section: Introductionmentioning

confidence: 99%

Passive Detection and Imaging of Human Body Radiation Using an Uncooled Field-Effect Transistor-Based THz Detector

Čibiraitė-Lukenskienė

Ikamas

Lisauskas³

et al. 2020

Sensors

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This work presents, to our knowledge, the first completely passive imaging with human-body-emitted radiation in the lower THz frequency range using a broadband uncooled detector. The sensor consists of a Si CMOS field-effect transistor with an integrated log-spiral THz antenna. This THz sensor was measured to exhibit a rather flat responsivity over the 0.1–1.5-THz frequency range, with values of the optical responsivity and noise-equivalent power of around 40 mA/W and 42 pW/ Hz , respectively. These values are in good agreement with simulations which suggest an even broader flat responsivity range exceeding 2.0 THz. The successful imaging demonstrates the impressive thermal sensitivity which can be achieved with such a sensor. Recording of a 2.3 × 7.5-cm 2 -sized image of the fingers of a hand with a pixel size of 1 mm 2 at a scanning speed of 1 mm/s leads to a signal-to-noise ratio of 2 and a noise-equivalent temperature difference of 4.4 K. This approach shows a new sensing approach with field-effect transistors as THz detectors which are usually used for active THz detection.

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“…The bolometers are extremely sensitive detectors but they need a bulky cryogenic cooling system whereas microbolometers are less sensitive room-temperature detectors but extremely small and therefore are often used for IR cameras [9,20,68]. The main materials for microbolometers are amorphous Silicon and vanadium oxide.…”

Section: Bolometers and Microbolometersmentioning

confidence: 99%

Room-temperature passive terahertz imaging based on high sensitivity field-effect transistor detectors

Čibiraitė-Lukenskienė¹

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Terahertz (THz) technology is an emerging field that considers the radiation between microwave and far-infrared regions where the electronic and photonic technologies merge. THz generation and THz sensing technologies should fill the gap between photonics and electronics which is defined as a region where THz generation power and THz sensing capabilities are at a low technology readiness level (TRL). As one of the options for THz detection technology, field-effect transistors with integrated antennae were suggested to be used as THz detectors in the 1990s by M. Dyakonov and M. Shur from where the development of field-effect transistor-based detector began. In this work, various FET technologies are presented, such as CMOS, AlGaN/GaN, and graphene-based material systems and their further sensitivity enhancement in order to reach the performance of well-developed Schottky diode-based THz sensing technology. Here presented FET-based detectors were explored in a wide frequency range from 0.1 THz up to 5 THz in narrowband and broadband configurations. For proper implementation of THz detectors, the well-defined characterization is of high importance. Therefore, this work overviews the characterization methods, establishes various definitions of detector parameters, and summarizes the state-of-the-art THz detectors. The electrical, optical, and cryogenic characterization techniques are also presented here, as well as the best results obtained by the development of the characterization methods, namely graphene FET stabilization, low-power THz source characterization for detector calibration, and technology development for cryogenic detection. Following the discussion about the detector characterization, a wide range of THz applications, which were tested during the last four years of Ph.D. and conducted under the ITN CELTA project from HORIZON2020 program, are presented in this work. The studies began with spectroscopy applications and imaging and later developed towards hyperspectral imaging and even passive imaging of human body THz radiation. As various options for THz applications, single-pixel detectors as well as multi-pixel arrays are also covered in this work. The conducted research shows that FET-based detectors can be used for spectroscopy applications or be easily adapted for the relevant frequency range. State-of-the-art detectors considered in this work reach the resonant performance below 20 pW/√Hz at 0.3 THz and 0.5 THz, as well as 404 pW/√Hz cross-sectional NEP at 4.75 THz. The broadband detectors show NEP as low as 25 pW/√Hz at around 0.6 THz for the best AlGaN/GaN design and 25 pW/√Hz around 1 THz for the best CMOS design. As one of the most promising applications, metamaterial characterization was tested using the most sensitive devices. Furthermore, one of the single-pixel devices and a multi-pixel array were tested as an engineering solution for a radio astronomy system called GREAT in a stratosphere observatory named SOFIA. The exploration of the autocorrelation technique using FET-based devices shows the opportunity to employ such detectors for direct detection of THz pulses without an interferometric measurement setup. This work also considers imaging applications, which include near-field and far-field visualization solutions. A considerable milestone for the theory of FET technology was achieved when scanning near-field microscopy led to the visualization of plasma (or carrier density) waves in a graphene FET channel. Whereas another important milestone for the THz technology was achieved when a 3D scan of a mobile phone was performed under the far-field imaging mode. Even though the imaging was done through the phone’s plastic cover, the image displayed high accuracy and good feature recognition of the smartphone, inching the FET-based detector technology ever so close to practical security applications. In parallel, the multi-pixel array testing was carried out on 6x7 pixel arrays that have been implemented in configurable-size aperture and imaging configurations. The configurable aperture size allowed the easier detector focusing procedure and a better fit for the beam size of the incident radiation. The imaging has been tested on various THz sources and compared to the TeraSense 16x16 pixel array. The experimental results show the big advantage of the developed multi-pixel array against the used commercial technology. Furthermore, two ultra-low-power applications have been successfully tested. The application on hyper-frequency THz imaging tested in the specially developed dual frequency comb and our detector system for 300 GHz radiation with 9 spectral lines led to outstanding imaging results on various materials. The passive imaging of human body radiation was conducted using the most sensitive broadband CMOS detector with a log-spiral antenna working in the 0.1 – 1.5 THz range and reaching the optical NEP of 42 pW/√Hz. The NETD of this device reaches 2.1 K and overcomes the performance limit of passive room-temperature imaging of the human body radiation, which was less than 10 K above the room temperature. This experiment opened a completely new field that was explored before only by the multiplier chain-based or thermal detectors. ...

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Uncooled Terahertz real-time imaging 2D arrays developed at LETI: present status and perspectives

Cited by 10 publications

References 9 publications

Roadmap of Terahertz Imaging 2021

Roadmap of Terahertz Imaging 2021

Passive Detection and Imaging of Human Body Radiation Using an Uncooled Field-Effect Transistor-Based THz Detector

Room-temperature passive terahertz imaging based on high sensitivity field-effect transistor detectors

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