| 1. |
- Afanas'ev, Victor P., et al.
(författare)
-
Study of NbN Ultra-thin Films for THz Hot-electron Bolometers
- 2014
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Ingår i: 25th International Sympsoium on Space Terahertz Technology, ISSTT 2014; Moscow; Russian Federation; 27 April 2014 through 30 April 2014. ; , s. 141-143
-
Konferensbidrag (refereegranskat)abstract
- Hot-electron bolometer (HEB) mixers based on superconducting ultra-thin NbN films are largely used for THz spectroscopy for space and ground-based observations. Performance of the HEB mixers directly depends on the details of the structure and composition of thin film surface, as well as the nitrogen composition and its depth distribution. In this work, we present the study of the composition and the surface oxidation state of NbN films grown at two different temperatures and of 5 and 10 nm thickness.
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| 2. |
- Antipov, Sergey, et al.
(författare)
-
Gain bandwidth of NbN HEB mixers on GaN buffer layer operating at 2 THz local oscillator frequency
- 2017
-
Ingår i: 28th International Symposium on Space Terahertz Technology, March 13-15, 2017. ; 2017-March
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we present IF bandwidth measurement results of NbN HEB mixers, which are employing NbN thin films grown on a GaN buffer-layer. The HEB mixers were operated in the heterodyne regime at a bath temperature of approximately 4.5 K and with a local oscillator operating at a frequency of 2 THz. A quantum cascade laser served as the local oscillator and a reference synthesizer based on a BWO generator (130-160 GHz) and a semiconductor superlattice (SSL) frequency multiplier was used as a signal source. By changing the LO frequency it was possible to record the IF response or gain bandwidth of the HEB with a spectrum analyzer at the operation point, which yielded lowest noise temperature. The gain bandwidth that was recorded in the heterodyne regime at 2 THz amounts to approximately 5 GHz and coincides well with a measurement that has been performed at elevated bath temperatures and lower LO frequency of 140 GHz. These findings strongly support that by using a GaN buffer-layer the phonon escape time of NbN HEBs can be significantly lower as compared to e.g. Si substrate, thus, providing higher gain bandwidth.
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| 3. |
- Antipov, S., et al.
(författare)
-
Improved bandwidth of a 2THz hot-electron bolometer heterodyne mixer fabricated on sapphire with a GaN buffer layer
- 2019
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 32:7
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the signal-to-noise and gain bandwidth of a niobium nitride (NbN) hot-electron bolometer (HEB) mixer at 2 THz fabricated on a sapphire substrate with a GaN buffer layer. Two mixers with different DC properties and geometrical dimensions were studied and they demonstrated very close bandwidth performance. The signal-to-noise bandwidth is increased to 8 GHz in comparison to the previous results, obtained without a buffer-layer. The data were taken in a quasi-optical system with the use of the signal-to-noise method, which is close to the signal levels used in actual astrophysical observations. We find an increase of the gain bandwidth to 5 GHz. The results indicate that prior results obtained on a substrate of crystalline GaN can also be obtained on a conventional sapphire substrate with a few micron MOCVD-deposited GaN buffer-layer.
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| 4. |
- Belitsky, Victor, 1955, et al.
(författare)
-
ALMA Band 5 receiver cartridge: Design, performance, and commissioning
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 611
-
Tidskriftsartikel (refereegranskat)abstract
- We describe the design, performance, and commissioning results for the new ALMA Band 5 receiver channel, 163-211 GHz, which is in the final stage of full deployment and expected to be available for observations in 2018. This manuscript provides the description of the new ALMA Band 5 receiver cartridge and serves as a reference for observers using the ALMA Band 5 receiver for observations. At the time of writing this paper, the ALMA Band 5 Production Consortium consisting of NOVA Instrumentation group, based in Groningen, NL, and GARD in Sweden have produced and delivered to ALMA Observatory over 60 receiver cartridges. All 60 cartridges fulfil the new more stringent specifications for Band 5 and demonstrate excellent noise temperatures, typically below 45 K single sideband (SSB) at 4 K detector physical temperature and below 35 K SSB at 3.5 K (typical for operation at the ALMA Frontend), providing the average sideband rejection better than 15 dB, and the integrated cross-polarization level better than -25 dB. The 70 warm cartridge assemblies, hosting Band 5 local oscillator and DC bias electronics, have been produced and delivered to ALMA by NRAO. The commissioning results confirm the excellent performance of the receivers.
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| 5. |
- Belitsky, Victor, 1955, et al.
(författare)
-
SEPIA - A new single pixel receiver at the APEX telescope
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 612
-
Tidskriftsartikel (refereegranskat)abstract
- Context. We describe the new Swedish-ESO PI Instrument for APEX (SEPIA) receiver, which was designed and built by the Group for Advanced Receiver Development (GARD), at Onsala Space Observatory (OSO) in collaboration with ESO. It was installed and commissioned at the APEX telescope during 2015 with an ALMA Band 5 receiver channel and updated with a new frequency channel (ALMA Band 9) in February 2016. Aim. This manuscript aims to provide, for observers who use the SEPIA receiver, a reference in terms of the hardware description, optics and performance as well as the commissioning results. Methods. Out of three available receiver cartridge positions in SEPIA, the two current frequency channels, corresponding to ALMA Band 5, the RF band 158-211 GHz, and Band 9, the RF band 600-722 GHz, provide state-of-the-art dual polarization receivers. The Band 5 frequency channel uses 2SB SIS mixers with an average SSB noise temperature around 45 K with IF (intermediate frequency) band 4-8 GHz for each sideband providing total 4 × 4 GHz IF band. The Band 9 frequency channel uses DSB SIS mixers with a noise temperature of 75-125 K with IF band 4-12 GHz for each polarization. Results. Both current SEPIA receiver channels are available to all APEX observers.
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| 6. |
- Ermakov, Andrey, 1960, et al.
(författare)
-
Broken-step Phenomenon in SIS Mixers
- 2016
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Ingår i: 27th International Symposium on Space Terahertz Technology, ISSTT 2016, Nanjing, China.
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we discuss a “broken step” phenomenonin an SIS mixer. This phenomena was observed in the production version of the SIS mixers, designed for the 159-211 GHz RF band,being used for the construction of the ALMA Band 5 receiver The broken step typically appears at LO frequencies above 180 GHz and manifests itself as a sharp onset in the DC current at the middle of the quasiparticle step. Correspondingly, this affects the mixer IF response in a way that is similar to the Josephson step but is however of a different nature. Such behaviour affects the SIS mixer dynamic range and complicates the tuning of the 2SB mixer to optimize its performance, for both the receiver noise as well as the sideband rejection. In this paper, we describe results of a few experiments which were performed to understand this undesirable phenomenon.
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| 7. |
- Krause, Sascha, 1989, et al.
(författare)
-
Ambient temperature growth of mono- and polycrystalline NbN nanofilms and their rigorous composition and surface analysis
- 2015
-
Ingår i: European Conference on Applied Superconductivity.
-
Konferensbidrag (refereegranskat)abstract
- This paper reflects on the rigorous investigation of high-quality 5nm thin NbN films which were deposited by means of reactive DC magnetron sputtering at ambient temperatures. Monocrystalline NbN films have been epitaxially grown onto hexagonal GaN buffer-layers (0002) and showing a distinct, low defect interface as confirmed from HRTEM. The critical temperature (Tc) of those films reached 10.4K. Furthermore, a poly-crystalline structure was observed on films grown onto Si (100) substrates, exhibiting a Tc of 8.1K albeit a narrow transition from the normal to the superconducting state. The deposition at ambient temperatures offers major advantages from a processing point of view and motivates the in-depth characterization and comparison of present films with high quality films grown at elevated temperatures. X-ray photoelectron spectroscopy and reflected electron energy loss spectroscopy verified that the composition of NbN did not differ irrespectively of applied substrate heating. Moreover, the native oxide layer at the surface of NbN has been identified as NbO2 and thus is in contrast to the Nb2O5, usually being formed at the surface of Nb when exposed to air. These findings are of great significance since it was proven the possibility of growing epitaxial NbN onto GaN buffer layer in the absence of high temperatures hence paving the way to employ NbN in more advanced fabrication processes involving a higher degree of complexity. Particularly low-noise THz receiver could benefit from the eased integration of e.g IF circuitry or general multi-layer structures which take advantage of lift-off techniques.
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| 8. |
- Krause, Sascha, 1989, et al.
(författare)
-
Ambient temperature growth of mono- and polycrystalline NbN nanofilms and their surface and composition analysis
- 2016
-
Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1558-2515 .- 1051-8223. ; 26:3
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the studies of high-quality 5 nmthin NbN films deposited by means of reactive DC magnetronsputtering at room temperature. The deposition withoutsubstrate heating offers major advantages from a processingpoint of view and motivates the extensive composition- andsurface characterization and comparison of the present filmswith high quality films grown at elevated temperatures.Monocrystalline NbN films have been epitaxially grown ontohexagonal GaN buffer-layers (0002) and show a distinct, lowdefect interface as confirmed by High-Resolution TEM. Thecritical temperature Tc of films on the GaN buffer-layer reached10.4 K. Furthermore, a poly-crystalline structure was observedon films grown onto Si (100) substrates, exhibiting a Tc of 8.1 Kalbeit a narrow transition from the normal to thesuperconducting state. X-ray photoelectron spectroscopy andreflected electron energy loss spectroscopy verified that thecomposition of NbN was identical irrespectively of appliedsubstrate heating. Moreover, the native oxide layer at the surfaceof NbN has been identified as NbO2 and thus, is in contrast to theNb2O5, usually claimed to be formed at the surface of Nb whenexposed to air. These findings are of significance since it wasproven the possibility of growing epitaxial NbN onto GaN bufferlayer in the absence of high temperatures hence paving the wayto employ NbN in more advanced fabrication processes involvinga higher degree of complexity. The eased integration andemployment of lift-off techniques could, in particular, lead toimproved performance of cryogenic ultra-sensitive terahertzelectronics.
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| 9. |
- Krause, Sascha, 1989, et al.
(författare)
-
Deposition of high-quality ultra-thin NbN films at ambient temperatures
- 2014
-
Ingår i: 25th International Sympsoium on Space Terahertz Technology, ISSTT 2014; Moscow; Russian Federation; 27 April 2014 through 30 April 2014. ; , s. 139-140
-
Konferensbidrag (refereegranskat)abstract
- This paper discusses the possibility of growing NbN ultra-thin films on Si-substrates and AlxGa1-xN buffer-layers by means of DC magnetron sputtering without intentional substrate heating. Resistance-temperature measurements were carried out and the superconducting properties such as Tc, ΔTc and R□ were deduced while HRTEM gave insight into the crystal structure and film thickness. The adjustment of the partial pressure of argon and nitrogen was found to be critical in establishing a reliable deposition process. The quality of the interface between the NbN film and the substrate was improved by optimizing the total pressure while sputtering, and is therefore particularly valuable for phonon-cooled HEB heterodyne receivers. NbN films of 5 nm thickness were obtained and exhibited a Tc from 8K on Si-substrates, and up to 10.5 K on the GaN buffer-layers. This result is significant since the absence of a high-temperature environment permits the establishment of more complex fabrication processes for intricate thin-film structures without compromising the overall integrity of e.g. dielectric layers, or hybrid circuitries with e.g. SIS junctions.
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| 10. |
- Krause, Sascha, 1989, et al.
(författare)
-
Design of a wideband balanced waveguide HEB mixer employing a GaN buffer-layer for the 1-1.5 THz band
- 2017
-
Ingår i: 28th International Symposium on Space Terahertz Technology. ; 2017-March
-
Konferensbidrag (refereegranskat)abstract
- We present the design and implementation of a wideband balanced waveguide NbN HEB mixer employing a GaN substrate in the frequency range of 1 - 1.5 THz.The balanced receiver scheme consisting of a 90˚ RF hybrid, a pair of NbN phonon-cooled HEB mixers and a 180˚ IF hybrid has major advantages over the single-ended configuration. The 3 dB RF hybrid is employed to couple the RF and LO signal into the HEBs, and allows for the efficient use of available LO power. Furthermore, the usually small IF bandwidth of phonon-cooled NbN HEB mixers has been addressed by employing a GaN substrate instead of a conventional substrate, e.g., Si or quartz. It has recently been shown that using GaN substrate reduces the escape time of phonons from NbN bridge to the substrate and thus, prospectively enhances the overall cooling rate of hot electrons and yielding higher IF bandwidth. The mixer housing is implemented in a back-end configuration and has been fabricated by means of a micro-machining method, providing excellent control of the dimensions and smoothness of the all-metal waveguide components. The expected RF performance of the proposed HEB design as well as its fabrication and DC characterization are presented
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| 11. |
- Krause, Sascha, 1989, et al.
(författare)
-
Epitaxial growth of ultra-thin NbN films on AlxGa1-xN buffer-layers
- 2014
-
Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 27:6
-
Tidskriftsartikel (refereegranskat)abstract
- The suitability of AlxGa1-xN epi-layer to deposit onto ultra-thin NbN films has been demonstrated for the first time. High quality single-crystal films with 5 nm thickness confirmed by high-resolution transmission electron microscopy (HRTEM) have been deposited in a reproducible manner by means of reactive DC magnetron sputtering at elevated temperatures and exhibit critical temperatures (Tc) as high as 13.2 K and residual resistivity ratio (RRR) ~ 1 on hexagonal GaN epi-layer. With increasing the Al-content x in the AlxGa1-xN epi-layer above 20% a gradual deterioration of Tc down to 10 K was observed. Deposition of NbN on bare silicon substrates served as reference and comparison. Excellent spatial homogeneity of the fabricated films was confirmed by R(T) measurements of patterned micro-bridges across the entire film area. The superconducting properties of those films were further characterized by critical magnetic field and critical current measurements. It is expected that the employment of GaN material as a buffer-layer for the deposition of ultra-thin NbN films prospectively benefit terahertz electronics, particularly hot electron bolometer (HEB) mixers.
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| 12. |
- Krause, Sascha, 1989, et al.
(författare)
-
Noise and IF Gain Bandwidth of a Balanced Waveguide NbN/GaN Hot Electron Bolometer Mixer Operating at 1.3 THz
- 2018
-
Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 8:3, s. 365-371
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the comprehensive characterization of a waveguide balanced phonon-cooled NbN hot electron bolometer (HEB) mixer on aGaNbuffer-layer operating at approximately 1.3 terahertz (THz). The measured uncorrected double sideband noise temperature was as low as 750 K at 1 GHz intermediate frequency (IF) and 900 K at 4 GHz IF, respectively, and suggests a noise bandwidth of 7 GHz. Moreover, the IF gain bandwidth of the HEB itself was deduced from a mixing experiment with a second monochromatic THz signal source and has shown a 3 dB roll-off at 5.5 GHz. The contribution of the HEB mixer on the overall receiver noise temperature was determined to be in the order of 300 K or 5 hf/k considering losses in the RF transmission path and the waveguide components as well as accounting for the receiver conversion loss, which was deduced from the U-factor method. The achieved performance sets a new benchmark for futureTHz instruments and emphasizes the technological readiness of waveguide-based NbN HEB mixers employing a GaN buffer-layer featuring significantly improved IF bandwidth without compromising on the receiver’s noise temperature.
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| 13. |
- Krause, Sascha, 1989, et al.
(författare)
-
Noise performance of a balanced waveguide NbN HEB mixer utilizing a GaN buffer-layer at 1.3 THz
- 2018
-
Ingår i: 2018 29th IEEE International Symposium on Space Terahertz Technology, ISSTT 2018. ; , s. 36-39
-
Konferensbidrag (refereegranskat)abstract
- We report on the initial measurement results of a balanced waveguide phonon cooled NbN mixer employing a 5.5 µm thin GaN membrane, which was operated at frequencies around 1.3 THz. The uncorrected DSB noise temperature amounts to approximately 750 K at 1 GHz IF and increases to only 900 K at 4 GHz IF, which was deduced from the standard Y-factor measurement technique. The recorded IF spectrum from 0.5 GHz to 8 GHz suggests a measured noise bandwidth of approximately 7 GHz owing to the employment of a GaN buffer-layer, which promotes the single crystal growth of NbN films and provides high phonon transparency, thus lowering the phonon escape time. We emphasize with the implementation of a waveguide balanced receiver scheme and using NbN/GaN mixers the possibility to extend the operational IF range of phonon cooled NbN HEBs, yet providing low noise performance.
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| 14. |
- Krause, Sascha, 1989, et al.
(författare)
-
Reduction of Phonon Escape Time for NbN Hot Electron Bolometers by Using GaN Buffer Layers
- 2017
-
Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 7:1, s. 53-59
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigated the influence of the GaN buffer-layer on the phonon escape time of phonon-cooled hot electron bolometers based on NbN material and compared our findings to conventionally employed Si substrate. The presented experimental setup and operation of the HEB close to the critical temperature of the NbN film allowed for the extraction of phonon escape time in a simplified manner. Two independent experiments were performed at GARD/Chalmers and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. By fitting the normalized IF measurement data to the heat balance equations, the escape time as fitting parameter has been deduced and amounts to 45 ps for the HEB based on Si substrate as in contrast to a significantly reduced escape time of 18 ps for the HEB utilizing the GaN buffer-layer under the assumption that no additional electron diffusion has taken place. This study indicates a high phonon transmissivity of the NbN-to-GaN interface and a prospective increase of IF bandwidth for HEB made of NbN on GaN buffer layers, which is desirable for future THz HEB heterodyne receivers.
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| 15. |
- Krause, Sascha, 1989, et al.
(författare)
-
Study of IF bandwidth of NbN hot electron bolometers on GaN buffer layer using a direct measurement method
- 2016
-
Ingår i: 27th International Symposium on Space Terahertz Technology, ISSTT 2016, Nanjing, China. ; , s. 3-
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we present a reliable measurement method to study the influence of the GaN buffer layer on phonon-escape time in comparison with commonly used Si substrates and, in consequence, on the IF bandwidth of HEBs. One of the key aspects is to operate the HEB mixer at elevated bath temperatures close to the critical temperature of the NbN ultra-thin film, where contributions from electron-phonon processes and self-heating effects are relatively small, therefore IF roll-off will be governed by the phonon-escape.Two independent experiments were performed at GARD and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. The entire IF chain was characterized by S-parameter measurements. We compared the measurement results of epitaxial NbN grown onto GaN buffer-layer with Tc of 12.5 K (4.5 nm) with high quality polycrystalline NbN films on Si substrate with Tc of 10.5 K (5 nm) and observed a strong indication of an enhancement of phonon escape to the substrate by a factor of two for the NbN/GaN material combination.
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| 16. |
- Krause, Sascha, 1989, et al.
(författare)
-
Suspended GaN beams and membranes on Si as a platform for waveguide-based THz applications
- 2018
-
Ingår i: Journal of Micromechanics and Microengineering. - : IOP Publishing. - 1361-6439 .- 0960-1317. ; 28:10
-
Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the suitability of employing suspended GaN beams on a Pi-shaped Si frame for waveguide-based cryogenic THz components and systems. This concept addresses major challenges and provides eased device handling, cryogenic operation, micron-alignment possibilities, high integratability and allows the electrical contacting by using bonding wires. In particular, a balanced hot electron bolometer (HEB) mixer was implemented for frequencies at 1.3 THz with state-of-the-art IF performance, which combines micro-machined all-metal waveguide components in conjunction with a suspended GaN beam. In addition, in order to accomplish a proper design of active or passive components, the accurate knowledge of the effective dielectric constant at THz frequencies is crucial when such membranes are employed. Thus, a direct measurement method based on a resonance structure and an S-parameter measurement between 1 THz and 1.5 THz is also presented.
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| 17. |
- Krause, Sascha, 1989, et al.
(författare)
-
Ultra-thin film NbN depositions for HEB heterodyne mixer on Si-substrates
- 2013
-
Ingår i: Proceedings of the 24th International Symposium on Space Terahertz Technology.
-
Konferensbidrag (refereegranskat)abstract
- The key of improving hot-electron bolometer (HEB) mixer performance lies inevitably in the quality of ultra-thin NbN films itself. This work presents a thorough investigation of crucial process parameters of NbN films deposited by means of reactive DC-sputtering on Si-substrates at elevated temperatures up to 750°C.The polycrystalline NbN films with thickness of 4 to 10nm were characterized by DC resistivity measurements, ellipsometry and high resolution transmission electron microscopy (HRTEM) in order to confirm thickness and film structure. Since the macroscopic properties such as critical temperature, thickness as well as the transition width to the superconducting state are directly linked to HEB mixer noise temperature and IF bandwidth, a set of experiments were conducted to enhance aforementioned properties. We considered deposition temperature, RF biasing, nitrogen and argon partial and total pressure during deposition as major process variable parameters. Careful optimization of the deposition conditions allowed setting up a process resulting in high-quality NbN ultra-thin films with thickness of 5.5nm exhibiting Tc of 10.5K. Moreover, the transition width could be kept as low as 1.4K. The produced films were stored at ambient conditions and re-characterized over a period of 4 month without measurable degradation.
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| 18. |
- Krause, Sascha, 1989
(författare)
-
Ultra-thin Niobium Nitride Films for Hot Electron Bolometer and THz Applications
- 2016
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The part of the electromagnetic spectrum between microwaves and infrared, also known as the terahertz band, is of particular interest for radio astronomy. The radiation intensity of the cold universe peaks at this frequency band, thus defining the demand on sensitive low-noise instruments in this particular frequency range. Phonon-cooled hot electron bolometers based on niobium nitride (NbN) thin films have been demonstrated for the first time in 1990 and evolved since then to the technology of choice for frequencies above 1.2 THz. At those wavelengths their noise temperature is typically between 5 to 10 times the quantum noise hence outperforming any other heterodyne receiver technology. However, the main concern of HEBs is there limited intermediate frequency (IF) of, in practice a few GHz, which is not sufficient for certain astronomical tasks requiring, e.g. 4-12 GHz of bandwidth. The cooling rate of “hot” electrons translates directly into the IF bandwidth of such devices and is intrinsically determined by the quality and thickness of the used NbN film and the substrate, which serves as a heat sink in these phonon-cooled devices [1]. This thesis deals with the development of NbN films particularly for the use in hot electron bolometers, and is addressing the optimization of superconducting properties of the NbN ultra-thin films. A particular emphasis was put on the influence of the underlying substrate. The suitability of hexagonal AlxGa1-xN as a buffer-layer for the NbN film growth was demonstrated for the first time and enabled the tuning of the superconducting properties by changing the Al content x. Single crystal NbN with 5 nm thickness has been grown onto GaN with Tc of 13.2 K, very narrow superconducting transition width and residual resistivity ratio (R20K/R300K) close to unity. The critical current density Jc was determined to be 3.8MA/cm2, compared to 1.2MA/cm2 of a high quality NbN film deposited onto a silicon substrate.The GaN buffer-layer is also believed to result in improved acoustic matching compared to commonly used substrates such as silicon or MgO, thus possibly enhancing the IF bandwidth. A first mixer experiment, where the HEB was operated in the bolometric mode at 180 GHz and at elevated bath temperatures, showed clearly that the measured IF roll-off, which is associated with the phonon escape time in this mode of operation was increased almost by 80% while the GaN buffer-layer was used as compared to a bare silicon substrate.
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| 19. |
- Lubenchenko, Alexander, 1966, et al.
(författare)
-
An XPS method for layer profiling of NbN thin films
- 2017
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2101-6275 .- 2100-014X. ; 132, s. Art no 03053-
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Konferensbidrag (refereegranskat)abstract
- Layer chemical and phase profiling of niobium nitride thin films on a silicon substrate oxidized on air was performed with the help of a method designed by us. The method includes: a new method of background subtraction of multiple inelastically scattered photoelectrons considering depth inhomogeneity of electron inelastic scattering; a new method of photoelectron line decomposition into component peaks considering physical nature of different decomposition parameters; joint solution of the background subtraction and photoelectron line decomposition problems; control of line decomposition accuracy with the help of a suggested performance criterion; calculation of layer thicknesses for a multilayer target using a simple formula.
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| 20. |
- Lubenchenko, Alexander, 1966, et al.
(författare)
-
X-RAY PHOTOELECTRON SPECTROSCOPY FOR LAYER-BY-LAYER PHASE ANALYSIS OF NbN THIN FILMS
- 2016
-
Ingår i: 25th Spectroscopy Meeting. - 9785426304420 ; , s. 415-
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Konferensbidrag (refereegranskat)abstract
- This paper studied the chemical and phase composition of NbN thin films by x-ray photoelectron spectroscopy (XPS).Determined the relative concentrations of (O, Nb, N, C, Si) and carried out layer-by-layer phase analysis of the filmsbefore sputtering and after each cycle of sputtering. Before spraying in the nitride film detected two different phasestates niobium nitride, NbN, and presumably this Nb5N6. Analysis of the Nb 3d and C 1s lines allowed to reveal inaddition to these phases of niobium nitride, various oxides of niobium (Nb2O5, NbO2, Nb2O3, NbO) and NbNOx
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| 21. |
- Lubenchenko, AV, 1966, et al.
(författare)
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XPS Depth Profiling of Air-Oxidized Nanofilms of NbN on GaN Buffer-Layers
- 2017
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 917:9
-
Konferensbidrag (refereegranskat)abstract
- XPS depth chemical and phase profiling of an air-oxidized niobium nitride thin film on a buffer-layer GaN is performed. It is found that an intermediate layer of Nb5N6 and NbON x under the layer of niobium oxide is generated.I
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| 22. |
- Lubenschenko, A., et al.
(författare)
-
Interface Layers of Niobium Nitride Thin Films
- 2019
-
Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 1410:1
-
Konferensbidrag (refereegranskat)abstract
- Intermediate layers formed by thin NbN films are studied. A surface phase of NbN different from the bulk one under the oxide layer and a layer consisting of NbNx-SiOy between the film and the substrate are found.
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| 23. |
- Lubenschenko, A., et al.
(författare)
-
Native oxide on ultra-thin NbN films
- 2019
-
Ingår i: ISSTT 2019 - 30th International Symposium on Space Terahertz Technology, Proceedings Book. ; , s. 95-98
-
Konferensbidrag (refereegranskat)abstract
- We report study of native oxide formation over NbN ultra-thin films. With a help of XPS, chemical and phase depth profiles of NbN film of 5 nm and 10 nm thickness exposed to room air for more than a month were recorded. The surface of those films were sputtered with Ar+ ions and consequently oxidized in room air for another few days. It was found that an intermediate layer of NbNx was formed between the niobium oxide layer and original NbN material.
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| 24. |
- Lubenschenko, A., et al.
(författare)
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XPS Study of Niobium and Niobium-Nitride Nanofilms
- 2018
-
Ingår i: Journal of Surface Investigation. - 1819-7094 .- 1027-4510. ; 12:4, s. 692-700
-
Tidskriftsartikel (refereegranskat)abstract
- A new, XPS-based approach to quantitative and nondestructive determination of the chemical and phase layer composition of multicomponent multilayer films is proposed. It includes a new method for subtracting the background of repeatedly inelastically scattered photoelectrons, taking into account the inhomogeneity of inelastic scattering over depth; a new way of decomposing a photoelectron line into component peaks, taking into account the physical nature of various decomposition parameters; solution of the problem of subtracting the background and decomposing the photoelectron line simultaneously; and determination of the thickness of the layers of a multilayer target using a simple equation. The phase-layer composition of nanoscale Nb and NbN films is determined, and the thicknesses of these layers are calculated.
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| 25. |
- Marouf Rashid, Hawal, 1982, et al.
(författare)
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Frequency Multiplier Based on Distributed Superconducting Tunnel Junctions: Theory, Design, and Characterization
- 2016
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 6:5, s. 724-736
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present the analysis, design, andcharacterization of the first frequency multiplier using distributed superconductor–insulator–superconductor (SIS) junctions. We derived analytical expressions describing the properties of the distributed SIS junction as a frequency multiplier. The modeling of the distributed SIS junctions shows that high conversion efficiency can be achieved when used as the multiplier. The measured outputpower generated by such multiplier employing the distributed SIS junction at the second harmonic of the input frequency is in good agreement with the model. Furthermore, the frequency multiplier based on the distributed SIS junction for the first time was able to pump an SIS mixer. The multiplication efficiency of thedistributed SIS junction is 15–30% for a fractional bandwidth of 10% with excellent spectral line purity. The –3 dB line width of the multiplied signal is 1 Hz, which was limited by the resolution bandwidth of the spectrum analyzer. The results attained in this paper show that the distributed SIS junction frequency multiplier has considerable future potential, and could possibly be used in LO source in single-end and multipixel SIS mixer receivers.
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