| 1. |
- Cibiraite, D., et al.
(author)
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Thermal noise-limited sensitivity of FET-based terahertz detectors
- 2017
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In: 2017 International Conference on Noise and Fluctuations, ICNF 2017, Vilnius, Lithuania, 20-23 June 2017.
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Conference paper (peer-reviewed)abstract
- Here we present a detailed study on estimation of noise-dependent parameters, such as signal-to-noise ratio (SNR) or noise equivalent power (NEP), of field-effect-transistor based terahertz detectors (TeraFETs). Commonly, these parameters are estimated from a well-known assumption, that detector's performance is limited by the thermal noise of transistor's channel. However, practice shows that the influence of other noise sources or transient effects is considerable. We summarize TeraFET noise measurements performed on different material systems based transistors, such as AlGaN/GaN, AlGaAs/GaAs, silicon CMOS, and monolayer graphene. We have achieved a good agreement between thermal noise and measured data. However, attention has to be paid to gate leakage currents and slow defect charging and discharging effects, which can strongly influence TeraFET's performance estimation.
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| 2. |
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| 3. |
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| 4. |
- Jensen, Maja, 1978, et al.
(author)
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High-resolution macromolecular crystallography at the FemtoMAX beamline with time-over-threshold photon detection
- 2021
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In: Journal of Synchrotron Radiation. - 1600-5775 .- 0909-0495. ; 28, s. 64-70
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Journal article (peer-reviewed)abstract
- Protein dynamics contribute to protein function on different time scales. Ultrafast X-ray diffraction snapshots can visualize the location and amplitude of atom displacements after perturbation. Since amplitudes of ultrafast motions are small, high-quality X-ray diffraction data is necessary for detection. Diffraction from bovine trypsin crystals using single femtosecond X-ray pulses was recorded at FemtoMAX, which is a versatile beamline of the MAX IV synchrotron. The time-over-threshold detection made it possible that single photons are distinguishable even under short-pulse low-repetition-rate conditions. The diffraction data quality from FemtoMAX beamline enables atomic resolution investigation of protein structures. This evaluation is based on the shape of the Wilson plot, cumulative intensity distribution compared with theoretical distribution, I/σ, Rmerge /Rmeas and CC1/2 statistics versus resolution. The FemtoMAX beamline provides an interesting alternative to X-ray free-electron lasers when studying reversible processes in protein crystals.
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| 5. |
- Olsen, A Ø, et al.
(author)
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HBV frequency quintuplers
- 2005
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In: Book of abstracts: Intl Symp on Space Terahertz Technol, Göteborg, Sweden (2005).
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Conference paper (peer-reviewed)
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| 6. |
- Stake, Jan, 1971, et al.
(author)
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Effects of Self-Heating on Planar Heterostructure Barrier Varactor Diodes
- 1998
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In: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383. ; 45:11, s. 2298-2303
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Journal article (peer-reviewed)abstract
- The conversion efficiency for planar Al0.7GaAs-GaAs heterostructure barrier varactor triplers is shown to be reduced from a theoretical efficiency of 10% to 3% due to self-heating. The reduction is in accordance with measurements on planar Al0.7GaAs-GaAs heterostructure barrier varactor (HBV) triplers to 261 GHz at room temperature and with low temperature tripler measurements to 255 GHz. The delivered maximum output power at 261 GHz is 2.0 mW. Future HBV designs should carefully consider and reduce the device thermal resistance and parasitic series resistance. Optimization of the RF circuit for a 10 ?m diameter device yielded a delivered output power of 3.6 mW (2.5% conversion efficiency) at 234 GHz
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| 7. |
- Alderman, Byron, et al.
(author)
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A New Pillar Geometry for Heterostructure Barrier Varactor Diodes
- 2001
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In: 12th International Symposium on Space Terahertz Technology. ; , s. 330-339
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Conference paper (peer-reviewed)abstract
- We report on a novel diode geometry, with reduced thermal resistance, for Heterostructure Barrier Varactor, HBV, diodes. The pillar geometry presented here involves the complete removal of the substrate, electrical contacted is made by the forward and reverse side processing of metallic pillars. We propose that there is a limit to the maximum number of barriers that can be used to increase the power capability of a HBV. An analytical model has been developed to study these effects. In considering the case of a perfect thermal heat sink the limit is found to be fourteen, in applying this model to the new pillar structure this is reduced to six.
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| 8. |
- Asad, M., et al.
(author)
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Graphene FET on Diamond for High-Frequency Electronics
- 2022
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In: IEEE Electron Device Letters. - : Institute of Electrical and Electronics Engineers (IEEE). - 0741-3106 .- 1558-0563. ; 43:2, s. 300-303
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Journal article (peer-reviewed)abstract
- Transistors operating at high frequencies are the basic building blocks of millimeter-wave communication and sensor systems. The high charge-carrier mobility and saturation velocity in graphene can open way for ultra-fast field-effect transistors with a performance even better than what can be achieved with III-V-based semiconductors. However, the progress of high-speed graphene transistors has been hampered by fabrication issues, influence of adjacent materials, and self-heating effects. Here, we report on the improved performance of graphene field-effect transistors (GFETs) obtained by using a diamond substrate. An extrinsic maximum frequency of oscillation fmax of up to 54 GHz was obtained for a gate length of 500 nm. Furthermore, the high thermal conductivity of diamond provides an efficient heat-sink, and the relatively high optical phonon energy of diamond contributes to an increased charge-carrier saturation velocity in the graphene channel. Moreover, we show that GFETs on diamond exhibit excellent scaling behavior for different gate lengths. These results promise that the GFET-on-diamond technology has the potential of reaching sub-terahertz frequency performance.
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| 9. |
- Barrientos Z, C. M., et al.
(author)
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Vertically illuminated TW-UTC photodiodes for terahertz generation
- 2012
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In: Proceedings of SPIE - The International Society for Optical Engineering. - : SPIE. - 0277-786X .- 1996-756X. - 9780819491534 ; 8452
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Conference paper (peer-reviewed)abstract
- More efficient and powerful continuous-wave photonic mixers as terahertz sources are motivated by the need of more versatile local oscillators for submillimeter/terahertz receiver systems. Uni-Travelling Carrier (UTC) photodiodes are very prospective candidates for reaching this objective, but so far only have been reported as lumped-elements or as edge-illuminated optical-waveguide travelling-wave (TW) devices. To overcome the associated power limitations of those implementations, we are developing a novel implementation of the UTC photodiodes which combines a traveling-wave photomixer with vertical velocity-matched illumination in a distributed structure. In this implementation called velocity-matched travelling-wave uni-travelling carrier photodiode, it is possible to obtain in-situ velocity matching of the beat-fringes of the two angled laser beams with the submm/THz-wave on the stripline. In this way, minimum frequency roll-off is achieved by tuning the angle between the two laser beams. A first design of these TW-UTC PDs from our Terahertz Photonics Laboratory at University of Chile has been micro-fabricated at the MC2 cleanroom facility at Chalmers Technical University.
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| 10. |
- Bulcha, Berhanu, et al.
(author)
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Phase Locking of a 2.5 THz Quantum Cascade Laser to a Microwave Reference using THz Schottky Mixer
- 2015
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In: 40th International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz 2015, Hong Kong, China, 23-28 August. - 2162-2027. - 9781479982721
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Conference paper (peer-reviewed)abstract
- The frequency of a 2.5 THz QCL are stabilized to sub-hertz accuracy by phase-locking to a stable 100 MHz microwave reference, using a 2.3–3.2 THz room temperature Schottky diode based harmonic mixer. The down-converted phase locked beat note is stable over a long term test.
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