| 1. |
- Chukharkin Leonidovich, Maxim, 1980
(författare)
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Fabrication and noise properties of high-Tc SQUIDs with multilayer superconducting flux transformers
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis describes the development of highTc superconducting quantum interference devices (SQUIDs) with multilayer thin film flux transformers. High-Tc SQUID magnetometers are promising in various biomedical applications, including magnetoencephalography (MEG) and ultra-low field magnetic resonance imaging (ulf-MRI). Both MEG and ulf-MRI demand magnetic field sensitivity of less than 10 fT/Hz1/2 at frequencies as low as 10 Hz. The magnetic field sensitivity of single-layer high-Tc SQUID magnetometers is typically about 50 fT/Hz1/2. To improve the magnetic field sensitivity, superconducting flux transformer with a multiturn input coil should be used. The flux transformer requires multilayer superconducting structures, which is a significant challenge for high-Tc superconducting materials due to the anisotropy of the material and high temperatures required for a deposition of thin films.Chemical-mechanical polishing (CMP) of high-Tc superconducting films has been developed in this work to fabricate multilayer structures. CMP improves surface smoothness of films, thereby reducing galvanic shorts between top and bottom superconducting electrodes. It has been shown that edge slope angles of about 2 degree can be fabricated using CMP, meaning that crossovers with very high critical current densities 2*10$6 A/cm2 can be obtained. These results were important for successful fabrication of high-quality multilayer structures with high yield.The CMP technique was used to fabricate multiturn magnetic flux transformers on 10*10 mm2 STO substrates. A flip-chip magnetometer based on the developed multilayer flux transformer and a bicrystal SQUID was designed, fabricated and characterized. Magnetic field sensitivity of 8 fT/Hz1/2 at 2 kHz and 80 fT/Hz1/2 at 10 Hz has been demonstrated. Low-frequency magnetic flux noise was investigated and related with the microstructure of the flux transformer.The developed multilayer flip-chip flux transformer was used in ulf-NMR experiments and demonstrated the improvement in the signal-to-noise ratio (SNR) when compared to a planar SQUID magnetometer. The demonstrated gain in SNR indicates the new multilayer structures are a promising technology for high-Tc SQUID-based ulf-MRI systems. Lastly, high-Tc superconducting quantum interference filters (SQIFs) were designed and fabricated. The SQIF consisted of array of 50 SQUID loops connected in series along the bicrystal grain boundary. Electrical characterizations revealed a large spread of individual SQUID parameters that lead to the situation when only few SQUIDs from the whole array are operational at a certain bias current and voltage-to-field response demonstrates an absence of voltage dip at the zero external field. At the same time, it has been demonstrated that an array of identical SQUIDs benefit from higher voltage-to-flux transfer function as compared with a single SQUID.
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| 2. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Improvement of Ultra-Low Field Magnetic Resonance Recordings With a Multilayer Flux-Transformer-Based High-T-C SQUID Magnetometer
- 2013
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Ingår i: Ieee Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1051-8223 .- 1558-2515. ; 23:3
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a multilayer flux-transformer-based high-T-C SQUID (flip-chip) magnetometer that improves signal-to-noise-ratios (SNR) in ultra-low field magnetic resonance (ulf-MR) recordings of protons in water. Direct ulf-MR-based benchmarking of the flip-chip versus a standard planar high-T-C SQUID magnetometer resulted in improvement of the SNR by a factor of 2. This gain is attributable to the improved transformation coefficient (1.9 vs 5.3 nT/Phi(0)) that increased the signal available to the flip-chip sensor and to the lower noise at the measurement frequency (15 vs 25 fT/Hz(1/2) at 4 kHz). The improved SNR can lead to better spectroscopic resolution, lower imaging times, and higher resolution in ulf-MR imaging systems based on high-T-C SQUID technology. The experimental details of the sensors, calibration, and ulf-MR benchmarking are presented in this report.
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| 3. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Noise properties of high-T-c superconducting flux transformers fabricated using chemical-mechanical polishing
- 2012
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 101:4, s. Article Number: 042602 -
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Tidskriftsartikel (refereegranskat)abstract
- Reproducible high-temperature superconducting multilayer flux transformers were fabricated using chemical mechanical polishing. The measured magnetic field noise of the flip-chip magnetometer based on one such flux transformer with a 9 x 9 mm(2) pickup loop coupled to a bicrystal dc SQUID was 15 fT/Hz(1/2) above 2 kHz. We present an investigation of excess 1/f noise observed at low frequencies and its relationship with the microstructure of the interlayer connections within the flux transformer. The developed high-T-c SQUID magnetometers may be advantageous in ultra-low field magnetic resonance imaging and, with improved low frequency noise, magnetoencephalography applications.
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| 4. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Noise properties of HTS flux transformers fabricated by chemical-mechanical polishing
- 2011
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Ingår i: European conference on applied superconductivity.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We present on fabrication and noise properties of high-temperature superconducting (HTS) thin-film integrated multilayer flux transformers fabricated using planarization of YBCO films by chemical-mechanical polishing (CMP). The polishing allows fabrication of very shallow slope edges (less than 5°) in the YBa2Cu3O7, that makes it possible to avoid formation of grain boundary junctions in crossovers and obtain very high critical current densities in the top electrode of about 2•106 A/cm2. The same planarization process is used to create interconnections between top and bottom superconducting electrodes through the SrTiO3/PrBa2Cu3O7/SrTiO3 insulating layer. HTS multilayer flip-chip flux transformer with 8x8 mm2 pickup loop and 20-turn input coil was fabricated and coupled to a bicrystal dc SQUID in a flip-chip configuration. We measured magnetic field gain of 1.2 nT/Ф0 and magnetic flux noise of the magnetometer 10 µФ0/√Hz at 1 kHz, which corresponds to magnetic field noise of 12 ft/√Hz. FLUX NOISE AT LOW FREQUENCIES! The work is supported by European FP7 project "MEGMRI" under contract number 200859.
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| 5. |
- Chukharkin Leonidovich, Maxim, 1980, et al.
(författare)
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Novel HTS DC squid solutions for NMR applications
- 2014
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Ingår i: NATO Science for Peace and Security Series B: Physics and Biophysics. - Dordrecht : Springer Netherlands. - 1874-6500. - 9789400772649 ; 2014, s. 151-159
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a multilayer flux-transformer-based high-TC SQUID (flip-chip) magnetometer that improves signal-to-noise-ratios (SNR) in ultra-low field magnetic resonance (ulf-MR) recordings of protons in water. Direct ulf-MR-based benchmarking of the flip-chip versus a standard planar high-T C SQUID magnetometer resulted in improvement of the SNR by a factor of 2. This gain is attributable to the improved transformation coefficient (1.9 vs 5.3 nT/Φ0) that increased the signal available to the flip-chip sensor and to the lower noise at the measurement frequency (15 vs 25 fT/Hz1/2 at 4 kHz). The improved SNR can lead to better spectroscopic resolution, lower imaging times, and higher resolution in ulf-MR imaging systems based on high-T C SQUID technology. The experimental details of the sensors, calibration, and ulf-MR benchmarking are presented in this report.
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| 6. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
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Operation of a high-T-C SQUID gradiometer with a two-stage MEMS-based Joule-Thomson micro-cooler
- 2016
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Ingår i: Superconductor Science and Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 29:9
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Tidskriftsartikel (refereegranskat)abstract
- Practical applications of high-T-C superconducting quantum interference devices (SQUIDs) require cheap, simple in operation, and cryogen-free cooling. Mechanical cryo-coolers are generally not suitable for operation with SQUIDs due to their inherent magnetic and vibrational noise. In this work, we utilized a commercial Joule-Thomson microfluidic two-stage cooling system with base temperature of 75 K. We achieved successful operation of a bicrystal high-T-C SQUID gradiometer in shielded magnetic environment. The micro-cooler head contains neither moving nor magnetic parts, and thus does not affect magnetic flux noise of the SQUID even at low frequencies. Our results demonstrate that such a microfluidic cooling system is a promising technology for cooling of high-T-C SQUIDs in practical applications such as magnetic bioassays.
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| 7. |
- Porokhov, N.V., et al.
(författare)
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Superconducting properties of YBCO thin films grown on [001] quartz substrates by pulsed laser deposition
- 2019
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Ingår i: Physica C: Superconductivity and its Applications. - : Elsevier BV. - 0921-4534. ; 562, s. 20-24
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Tidskriftsartikel (refereegranskat)abstract
- We present an investigation of the superconducting properties of thin YBa 2 Cu 3 O 7-x (YBCO) films grown on [001] single-crystalline quartz substrates by pulsed laser deposition (PLD) technique. The growth of YBCO on quartz is challenging due to large crystal lattice mismatch between YBCO and quartz. We obtained highly c-oriented textured films with superconducting transition at about 85 K, transition width of 1 K, and critical current density j c ≈ 10 4 A cm −2 at 77 K. Analysis of the temperature dependences of the resistivity and current-voltage characteristics has shown the presence of the thermally-assisted flux flow at temperatures above 70 K. From the temperature and magnetic field dependences of critical current, vortex activation energy, U 0 (H), was estimated for both parallel and perpendicular orientation of magnetic field. Second critical field, H c2 (0), was estimated from extrapolation of the H c2 (T) dependences. The obtained results are an important step towards realization of YBCO thin films on amorphous silica fibers for the third generation (3 G) of the HTS long wire with low losses in alternative current applications.
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| 8. |
- Porokhov, N.V., et al.
(författare)
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The physical basis of the fabrication of the third generation of high-temperature superconducting wires on quartz substrates
- 2015
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Ingår i: Moscow University Physics Bulletin (English Translation of Vestnik Moskovskogo Universiteta, Fizika). - 0027-1349 .- 1934-8460. ; 70:2, s. 134-139
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Tidskriftsartikel (refereegranskat)abstract
- The problem of the fabrication of third-generation high-temperature superconductors (HTSCs) that are designed for the transmission of electric energy and the creation of nanoelectronic devices is studied in this work. The issues of the fabrication of dielectric substrates for the third generation wires are considered. The technology of HTSC film deposition on the quartz substrates is presented. Complex studies of sputtering of the buffer and superconducting YBa2Cu3O7 − δ (YBCO) layers were performed. The results of studies of electrophysical properties of the HTSC films on the quartz substrates are discussed.
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| 9. |
- Ruffieux, Silvia, 1990, et al.
(författare)
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Feedback solutions for low crosstalk in dense arrays of high-T-c SQUIDs for on-scalp MEG
- 2017
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Ingår i: Superconductor Science & Technology. - : IOP Publishing. - 0953-2048 .- 1361-6668. ; 30:5
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Tidskriftsartikel (refereegranskat)abstract
- Magnetoencephalography (MEG) systems based on a dense array of high critical temperature (high-T-c) superconducting quantum interference devices (SQUIDs) can theoretically outperform a state-of-the-art MEG system. On the way towards building such a multichannel system, we evaluate feedback methods suitable for use in dense high-T-c SQUID arrays where the sensors are in very close proximity to the head (on-scalp MEG). We test on-chip superconducting coils and direct injection of the feedback current into the SQUID loop as alternatives to the wire-wound copper coils commonly used in single-channel high-T-c SQUID-based MEG systems. For the evaluation, we have performed coupling, noise, and crosstalk measurements. We conclude that direct injection is the optimal solution for dense on-scalp MEG as it gives crosstalk below 0.5% even between SQUIDs whose pickup loops are within 0.8 mm of one another. Further, this solution provides sufficient flux coupling without adding additional noise. Finally, it does not compromise the standoff distance, which is important for on-scalp MEG.
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| 10. |
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