Abstract-Plasmonic FET Terahertz Spectrometer

Xueqing Liu, Trond Ytterdal, Michael Shur

https://arxiv.org/abs/2001.06101

We show that Si MOSFETs, AlGaN/GaN HEMTs, AlGaAs/InGaAs HEMTs, and p-diamond FETs with feature sizes ranging from 20 nm to 130 nm could operate at room temperature as THz spectrometers in the frequency range from 120 GHz to 9.3 THz with different subranges corresponding to the transistors with different features sizes and tunable by the gate bias. The spectrometer uses a symmetrical FET with interchangeable source and drain with the rectified THz voltage between the source and drain being proportional to the sine of the phase shift between the voltages induced by the THz signal between gate-to-drain and gate-to-source. This phase difference could be created by using different antennas for the source-to-gate and drain-to gate contacts or by using a delay line introducing a phase shift or even by manipulating the impinging angle of the two antennas. The spectrometers are simulated using the multi-segment unified charge control model implemented in SPICE and ADS and accounting for the electron inertia effect and the distributed channel resistances, capacitances and Drude inductances.

Abstract-Terahertz plasmonic detector controlled by phase asymmetry

I. V. Gorbenko, V. Y. Kachorovskii, and Michael Shur

Fig. 1 TeraFET Spectrometer principle of operation: (a) phase shift induced by asymmetric antennas and circularly polarized radiation (b) nonzero incident angle of incoming radiation

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-4-4004

We demonstrate that a phase difference between terahertz signals coupled to the gate and source and gate and drain terminals of a field effect transistor (a TeraFET) induces a plasmon-assisted DC current, which is dramatically enhanced in the vicinity of plasmonic resonances. We describe a TeraFET operation with identical radiation amplitudes at the source and drain antennas but with a phase-shift-induced asymmetry. In this regime, the TeraFET operates as a tunable resonant polarization-sensitive plasmonic spectrometer, operating in the sub-terahertz and terahertz ranges of frequencies. We also propose an effective scheme of a phase-sensitive homodyne detector operating in this phase-asymmetry mode, which allows for a dramatic enhancement of the response. These regimes can be implemented in different materials systems, including silicon. The p-diamond TeraFETs could support operation in the 200 to 600 GHz atmospheric windows, which is especially important for beyond 5G communication systems.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz Plasmonic Detector Controlled by Phase Asymmetry

. V. Gorbenko, V. Yu. Kachorovskii, Michael Shur

https://arxiv.org/abs/1901.02036

We demonstrate that phase-difference between terahertz signals on the source and drain of a field effect transistor (a TeraFET) induces a plasmon-assisted dc current, which is dramatically enhanced in vicinity of plasmonic resonances. We describe a TeraFET operation with identical amplitudes of radiation on source and drain antennas but with a phase-shift-induced asymmetry. In this regime, the TeraFET operates as a tunable resonant polarization-sensitive plasmonic spectrometer operating in the sub-terahertz and terahertz range of frequencies. We also propose an effective scheme of a phase-sensitive homodyne detector operating in a phase-asymmetry mode, which allows for a dramatic enhancement of the response. These regimes can be implemented in different materials systems including silicon. The p-diamond TeraFETs could support operation in the 200 to 600 GHz atmospheric windows.

Abstract-Electrical modulation of terahertz radiation using graphene-phosphorene heterostructures

Victor Ryzhii, Taiichi Otsuji, Maxim Ryzhii, Dmitry Sergeevich Ponomarev, Valerij Karasik, Vladimir Leiman, Vladimir Mitin,  Michael Shur,

http://iopscience.iop.org/article/10.1088/1361-6641/aae9b2

We analyze the electrical modulation of the terahertz (THz) radiation associated with the carrier heating in the graphene-phosphorene (GP) heterostuctures. The heating of the carriers leads to the transfer of a significant fraction 
 of the light carriers in the G-layer to the P-layer with a relatively large carrier effective mass.
 This might result in a dramatic decrease in the conductivity of the GP-channel
 that could be used to modulate
 the incident THz radiation. We demonstrate that the depth of the THz radiation modulation can be large in relatively wide range of the modulation frequencies.

Abstract-Terahertz Beam Testing of Millimeter Wave Monolithic Integrated Circuits

Sergey L. Rumyantsev,  Andrey Muraviev, Sergey Rudin, Greg Rupper, Meredith Reed, John Suarez, Michael Shur

http://ieeexplore.ieee.org/document/7973166/


The measured response of a monolithic microwave integrated circuit (MMIC) to the sub-terahertz (300 GHz) radiation is in qualitative agreement with the analytical theory of the overdamped plasmonic detection and has been used to establish and identify the integrated circuit faults. The bias and polarization dependences of the response measured between the different pins provide information about the faults location. In contrast to a more conventional terahertz and radio frequency imaging and testing techniques, this method relies on the electronic response with the resolution determined by the transistor size. Another advantage of this non-destructive non-contact approach is that the MMICs or VLSIs can be tested either biased or unbiased. Multiple transistors within the circuit or the entire circuit can be tested fast.

Recent developments in terahertz sensing technology

Michael Shur

Rensselaer Polytechnic Institute (United States)

Proc. SPIE 9836, Micro- and Nanotechnology Sensors, Systems, and Applications VIII, 98362Q (May 25, 2016); doi:10.1117/12.2218682

http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=2526312

Terahertz technology has found numerous applications for the detection of biological and chemical hazardous agents, medical diagnostics, detection of explosives, providing security in buildings, airports, and other public spaces, shortrange covert communications (in the THz and sub-THz windows), and applications in radio astronomy and space research. The expansion of these applications will depend on the development of efficient electronic terahertz sources and sensitive low-noise terahertz detectors. Schottky diode frequency multipliers have emerged as a viable THz source technology reaching a few THz. High speed three terminal electronic devices (FETs and HBTs) have entered the THz range (with cutoff frequencies and maximum frequencies of operation above 1 THz). A new approach called plasma wave electronics recently demonstrated an efficient terahertz detection in GaAs-based and GaN-based HEMTs and in Si MOS, SOI, FINFETs and in FET arrays. This progress in THz electronic technology has promise for a significant expansion of THz applications.
 © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Abstract-Suppression of 1/f noise in near-ballistic h-BN-graphene-h-BN heterostructure field-effect transistors

Maxim A. Stolyarov¹, Guanxiong Liu¹, Sergey L. Rumyantsev^2,3, Michael Shur² and Alexander A. Balandin^1,a)
http://scitation.aip.org/content/aip/journal/apl/107/2/10.1063/1.4926872?TRACK=RSS
a) Author to whom correspondence should be addressed. Electronic mail: balandin@ee.ucr.edu
Appl. Phys. Lett. 107, 023106 (2015); http://dx.doi.org/10.1063/1.4926872

We have investigated low-frequency 1/f noise in the boron nitride–graphene–boron nitrideheterostructure field-effect transistors on Si/SiO2 substrates (f is a frequency). The device channel was implemented with a single layer graphene encased between two layers of hexagonal boron nitride. The transistors had the charge carrier mobility in the range from ∼30 000 to ∼36 000 cm²/Vs at room temperature. It was established that the noise spectral density normalized to the channel area in such devices can be suppressed to ∼5 × 10⁻⁹ μm²Hz⁻¹, which is a factor of ×5 – ×10 lower than that in non-encapsulated graphene devices on Si/SiO2. The physical mechanism of noise suppression was attributed to screening of the charge carriers in the channel from traps in SiO2 gate dielectric and surface defects. The obtained results are important for the electronic and optoelectronic applications of graphene.

Abstract-Double-graphene-layer terahertz laser: concept, characteristics, and comparison

My note: The entire article can be read for free online, at the posted link.

Victor Ryzhii, Alexander A. Dubinov, Taiichi Otsuji, Vladimir Ya. Aleshkin, Maxim Ryzhii, and Michael Shur  »View Author Affiliations
http://www.opticsinfobase.org/oe/fulltext.cfm?uri=oe-21-25-31567&id=276087

We propose and analyze the concept of injection terahertz (THz) lasers based on double-graphene-layer (double-GL) structures utilizing the resonant radiative transitions between GLs. We calculate main characteristics of such double-GL lasers and compare them with the characteristics of the GL lasers with intra-GL interband transitions. We demonstrate that the double-GL THz lasers under consideration can operate in a wide range of THz frequencies and might exhibit advantages associated with the reduced Drude absorption, weaker temperature dependence, voltage tuning of the spectrum, and favorable injection conditions.

IEMN , STMicroelectronics, and University of Wuppertal, develop video-rate CMOS camera sensitive to terahertz frequencies.

.

http://spectrum.ieee.org/semiconductors/optoelectronics/a-cheap-terahertz-camera/0

17 April 2012—In the entire electromagnetic spectrum, one of the most conspicuously inaccessible chunks sit smack dab between radio waves and infrared light. Researchers have been trying for decades to come up with better ways to exploit the little-used terahertz band, which could provide ways to find hidden objects and determine an object’s chemical makeup at a distance.

Now a team from IEMN and STMicroelectronics, in France, and the University of Wuppertal, in Germany, has come up with a practical first: a video-rate CMOS camera that’s sensitive to terahertz frequencies.

“I think it’s the hottest thing in terahertz technology at the moment,” says Peter Siegel, who works on terahertz imaging at Caltech and NASA’s Jet Propulsion Laboratory and is not affiliated with the team. “They’ve done a remarkable job of solving a bunch of very pesky problems in working with silicon at high frequencies.”

Up until now, terahertz detectors have tended to be pricey affairs, composed of devices like Schottky diodes or microbolometers. A Schottky diode–based detector  usually contains just one or a few pixels, which are raster-scanned across a scene to slowly form an image. Microbolometers can be arranged in arrays, but they must be cooled to boost their sensitivity.

With just 1024 pixels, this new transistor-based camera is unlikely to give a high-resolution window into the unseen terahertz realm. But the advance has researchers excited, because it suggests terahertz technologies may soon get a lot cheaper and more accessible. The single-pixel terahertz detectors in use now can easily cost as much as US $10 000, Siegel says, so developing a detector that could be mass-produced by chip manufacturers represents a significant advance. “I think you’re going to find a lot of applications opening up that didn’t exist before,” Siegel says.

Building terahertz detectors out of silicon is difficult, because even the best transistors don’t operate well at frequencies in excess of a few hundred gigahertz, the lower edge of the terahertz band. This limitation stems mainly from how fast electrons can shoot from one side of the transistor to the other, resulting in an intrinsic cutoff frequency above which a transistor can’t amplify signals sent into it. “Traditionally, people would say that beyond the cutoff frequency, the transistor wouldn’t work anymore,” says Hani Sherry, a doctoral candidate working at STMicroelectronics. But in 1996, device physicists Michel Dyakonov (now at the University of Montpellier, in France) and Michael Shur (of Rensselaer Polytechnic Institute, in Troy, N.Y.) argued in a paper that appeared in IEEE Transactions on Electron Devices that the cutoff frequency can be surpassed. Although they will not be able to amplify signals, some types of field-effect transistors can still respond to frequencies above the cutoff frequency due to electromagnetic oscillations within the transistor’s channel. (The channel is the main body of a transistor through which current flows when the transistor is on. It runs between two electrodes—the source and the drain—and is adjacent to a third, the transistor’s gate.)

The camera’s pixels, which were designed by Ullrich Pfeiffer and his colleagues at the University of Wuppertal, are made of transistors that surpass the cutoff frequency by using only a small patch of the channel. This patch of the channel is close to the transistor’s source electrode, which is connected to a copper ring antenna. The antenna is capable of picking up signals over a wide range of frequencies, from 0.6 to 1 terahertz. A turbulent process of “self-mixing” in the transistor channel turns wildly oscillating terahertz signals into a simple DC output, a voltage at the drain that’s proportional to the square of the amplitude of the incoming terahertz radiation.

The team constructed the camera chip, which was presented in San Francisco in February at the International Solid-State Circuits Conference, using a standard 65-nanometer CMOS chip-fabrication process. Both the transistors and antennas are part of the same chip, with the antennas embedded in wiring layers above the transistors. The ensemble is fixed to the back of a opaque-looking fish-eye lens made of silicon, which unlike glass is transparent to terahertz waves. The camera can capture frame rates of up to 25 frames per second and requires so little power it can be operated by USB.

Animation: Bergische Universität Wuppertal

SCANNER: The imager detects a terahertz radiation source in real time.

Despite its finely tuned antennas and optics, the camera’s sensitivity is fairly low. While the photodiodes in a typical optical CMOS sensor can convert nearly all incoming photons into charge, Sherry says, terahertz photons are so low in energy that his team’s camera needs roughly 100 000 of them to produce a single electron.

Sensitivity aside, the development of this video-rate chip, along with other efforts to produce CMOS-compatible detectors, suggests that terahertz detection will soon become more mainstream. “It represents a turning point in terahertz technology,” says Sigfrid Yngvesson, an expert in terahertz detection at the University of Massachusetts Amherst. “We can now look forward to terahertz technology that is less exclusive and less expensive than what we’ve had.”

The applications for this sort of technology are still unclear. A large number of molecules emit and absorb terahertz radiation. And the waves also occupy a Goldilocks-like spot on the electromagnetic spectrum that could be good for body scanning. Because they are lower in frequency than X-rays, terahertz waves don’t have enough energy to ionize human tissue. But the waves are also higher in frequency (shorter in wavelength) than microwave or millimeter radiation, which means they should be able to produce higher-resolution images. As a result, terahertz sensors could lead to new security scanners and medical imagers that can see through clothes, as well as spectrometers with new capabilities.

Terahertz cameras might also be used for a number of niche applications, from food quality control to industrial monitoring of drying processes. “The trouble is, there are a lot of [other] technologies to do this too,” Siegel says. “It will always be a trade-off between cost and efficacy.”

Adding to the cost is the need for an external source of terahertz radiation to go with the camera. The Wuppertal team’s camera isn’t sensitive enough to pick up on ambient terahertz signals; radiation needs to be created and reflected off of objects in order to form an image, like the flash on an optical camera.

Unfortunately, cheap compact terahertz sources that can operate at room temperature have yet to emerge from the lab. To get enough radiation, researchers often resort to tuning the output of expensive optical pump lasers or devices made out of compound semiconductors such as indium gallium arsenide. One common source uses Schottky diodes, but that technique tends to require a lot of energy to convert lower-frequency radiation into terahertz waves. Terahertz radiation can also be generated using fairly small III-V devices called quantum cascade lasers, but those still need to be cooled well below the freezing point of water.

“The primary objective of using CMOS for terahertz is to reduce the cost and lower the power consumption, but I think that objective is lost the moment you put the III-V source into the system,” says Adrian Tang, who works on CMOS-based terahertz imaging at the University of California, Los Angeles. “You [get] an expensive, high-power system immediately.” 

Even if terahertz detectors and sources can be made cheaply, there are still some basic physical limitations to contend with, Tang adds. Water vapor and oxygen in the atmosphere readily absorb terahertz photons, limiting an imager’s range. Researchers working on terahertz imaging also struggle with uniform reflectivity; objects over a wide range of depths reflect similar amounts of radiation, producing very cluttered images.

The lack of contrast has led some researchers, like Tang and Siegel, to focus on radar-like systems that measure the time of flight of terahertz waves in order to extract 3-D components from reflected signals. But progress is slow, Tang says: “Terahertz imaging still has a long way to go before significant impact or practical applications are possible.”

Siegel is more optimistic: “Terahertz imaging applications are on the verge of a significant leap forward, in both capability and cost-effectiveness.”

A Cheap Terahertz Camera

Photo: Bergische Universität Wuppertal

TERAHERTZ EYE: A new CMOS imaging chip behind a silicon lens could pave the way to cheap video rate terahertz detectors. 

CMOS detectors could drive down the cost of terahertz imaging, though difficulties remain

http://spectrum.ieee.org/semiconductors/optoelectronics/a-cheap-terahertz-camera

17 April 2012—In the entire electromagnetic spectrum, one of the most conspicuously inaccessible chunks sits smack dab between radio waves and infrared light. Researchers have been trying for decades to come up with better ways to exploit the little-used terahertz band, which could provide ways to find hidden objects and determine an object’s chemical makeup at a distance.

Now a team based mainly at the University of Wuppertal, in Germany, and at STMicroelectronics in Crolles, France, has come up with a practical first: a video-rate CMOS camera that’s sensitive to terahertz frequencies.

“I think it’s the hottest thing in terahertz technology at the moment,” says Peter Siegel, who works on terahertz imaging at Caltech and NASA’s Jet Propulsion Laboratory and is not affiliated with the team. “They’ve done a remarkable job of solving a bunch of very pesky problems in working with silicon at high frequencies.”

Up until now, terahertz detectors have tended to be pricey affairs, composed of devices like Schottky diodes or microbolometers. A Schottky diode–based detector  usually contains just one or a few pixels, which are raster-scanned across a scene to slowly form an image. Microbolometers can be arranged in arrays, but they must be cooled to boost their sensitivity.

With just 1024 pixels, this new transistor-based camera is unlikely to give a high-resolution window into the unseen terahertz realm. But the advance has researchers excited, because it suggests terahertz technologies may soon get a lot cheaper and more accessible. The single-pixel terahertz detectors in use now can easily cost as much as US $10 000, Siegel says, so developing a detector that could be mass-produced by chip manufacturers represents a significant advance. “I think you’re going to find a lot of applications opening up that didn’t exist before,” Siegel says.

Building terahertz detectors out of silicon is difficult, because even the best transistors don’t operate well at frequencies in excess of a few hundred gigahertz, the lower edge of the terahertz band. This limitation stems mainly from how fast electrons can shoot from one side of the transistor to the other, resulting in an intrinsic cutoff frequency above which a transistor can’t amplify signals sent into it. “Traditionally, people would say that beyond the cutoff frequency, the transistor wouldn’t work anymore,” says Hani Sherry, a graduate student working at STMicroelectronics. But in 1996, device physicists Michel Dyakonov (now at the University of Montpellier, in France) and Michael Shur (of Rensselaer Polytechnic Institute, in Troy, N.Y.) argued in a paper that appeared in IEEE Transactions on Electron Devices that the cutoff frequency can be surpassed. Although they will not be able to amplify signals, some types of field-effect transistors can still respond to frequencies above the cutoff frequency due to electromagnetic oscillations within the transistor’s channel. (The channel is the main body of a transistor through which current flows when the transistor is on. It runs between two electrodes—the source and the drain—and is adjacent to a third, the transistor’s gate.)

The camera’s pixels, which were designed by Ullrich Pfeiffer and his colleagues at the University of Wuppertal, are made of transistors that surpass the cutoff frequency by using only a small patch of the channel. This patch of the channel is close to the transistor’s source electrode, which is connected to a copper ring antenna. The antenna is capable of picking up signals over a wide range of frequencies, from 0.6 to 1 terahertz. A turbulent process of “self-mixing” in the transistor channel turns wildly oscillating terahertz signals into a simple DC output, a voltage at the drain that’s proportional to the square of the amplitude of the incoming terahertz radiation.

The team constructed the camera chip, which was presented in San Francisco in February at the International Solid-State Circuits Conference, using a standard 65-nanometer CMOS chip-fabrication process. Both the transistors and antennas are part of the same chip, with the antennas embedded in wiring layers above the transistors. The ensemble is fixed to the back of a opaque-looking fish-eye lens made of silicon, which unlike glass is transparent to terahertz waves. The camera can capture frame rates of up to 25 frames per second and requires so little power it can be operated by USB.