| 1. |
- Chakalov, R, et al.
(författare)
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Fabrication and investigation of YBa2Cu3O7-delta/Ba0.05Sr0.95TiO3 thin film structures for voltage tunable devices
- 1998
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Ingår i: Physica C: Superconductivity and its Applications. - 0921-4534. ; 308:3-4, s. 279-288
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Tidskriftsartikel (refereegranskat)abstract
- High-temperature superconducting/ferroelectric thin film structures were deposited by laser ablation. Three types of voltage tunable devices were fabricated and investigated-trilayer capacitor, planar interdigital capacitor and coplanar waveguide. As ferroelectric the solid solution BaxSr1-xTiO3 was chosen with barium content x = 0.05 because its Curie temperature is close to the liquid nitrogen boiling point (77 K). Temperature and voltage dependences of the Ba0.05Sr0.95TiO3 dielectric constant epsilon(r,BSTO) were studied. High epsilon(r,BSTO) values were determined-up to 3000 at 75 K, 20 GHz and zero de bias. Efficient voltage tunability was demonstrated (up to 40%) at loss level tan delta=0.01-0.1. Compact YBa2Cu3O7-delta/Ba0.05Sr0.95TiO3 coplanar waveguide with as narrow gap as 18 mu m was tested as electrically tunable phase-shifter and field-induced phase shifts of more than 180 degrees were obtained by 35 V de bias at 20 GHz. This improvement was attained by proper choice of the ferroelectric material, accomplished epitaxial growth of the films and decrease of the specific dimensions. (C) 1998 Published by Elsevier Science B.V. All rights reserved.
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| 2. |
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| 3. |
- Chen, HonQui, et al.
(författare)
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Determining the crystal symmetry of epitaxial Tl-2201 thin films by X-ray diffraction
- 2002
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Ingår i: Physica. C, Superconductivity. - 0921-4534. ; 371:2, s. 83-89
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Tidskriftsartikel (refereegranskat)abstract
- The crystal symmetry of epitaxial Tl-2201 films on LaAlO3 and SrTiO3 substrates is investigated by X-ray diffraction. In the case of Tl1.85Ba2CuO6 film, a φ-scan of the (1 1 10) reflection showed four diffraction peaks separated by 90.00±0.02°. A 2θ-scan of the same reflection exhibited a single peak. 2Θ−ω- and φ-scans of the corresponding reflection in Tl2.04Ba2CuO6 show splitting and broadening of the diffraction peaks indicating an orthorhombic distortion. The effect of errors in film alignment on the φ-scan and 2Θ−ω-scans is discussed. A periodic function, δ=a+bsin(ω−φ), was used to correct the φ-scan measurements. The influence of lattice mismatch between film and substrate on the structural symmetry of the films is discussed.
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| 4. |
- Chen, H.Q., et al.
(författare)
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Critical behavior of vortices in epitaxial Tl-2201 films at zero external field
- 2004
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Ingår i: PHYSICA STATUS SOLIDI B-BASIC RESEARCH. - : Wiley. - 0370-1972 .- 1521-3951. ; 241:15, s. 3556-3562
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Tidskriftsartikel (refereegranskat)abstract
- The resistive transition and current–voltage characteristics of a Tl-2201 superconducting microbridge are measured close to the critical temperature in zero external magnetic field. The dissipation mechanism is studied by analyzing dV/dI and power dissipation P(= IV) as functions of transport current. The Jc–T curves exhibit three distinct types of behavior depending on temperature. In the low temperature regime, the critical current density is proportional to (1 – T/Tc). At intermediate temperatures, thermally activated flux creep dominates and Jc is proportional to 1 – n(T/Tc) – m(T/Tc)2. In the high temperature regime, Jc is equal to the G–L depairing current. The depinning current, Jc1, is determined, taking into account thermally activated flux motion and flux motion induced by the transport current. Jc1 depends linearly on temperature and vanishes at 82 K, Jc1 = Jc1(0) (1 – T/Tc1).
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| 5. |
- Claeson, Tord, 1938, et al.
(författare)
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High speed components based on high-Tc superconducting grain boundary junctions
- 1996
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Ingår i: 1996 International Workshop on Superconductivity. `High Temperature Superconducting Electronics: Fundamentals and Applications. Program and Extended Abstracts. ; , s. 3-6
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Artificial grain boundary junctions of both bi-crystal and step edge configurations have been characterized at high frequency using Fiske type resonances as well as flux flow induced steps in the current-voltage curve. A dielectric behavior of the barrier with sufficiently low microwave losses to allow resonances is indicated. Deduced values of the barrier thickness, the penetration depth, and surface microwave losses agree with those from other measurements. Long grain boundary junctions, as well as parallel arrays of shorter junctions, have been used in Josephson Flux Flow Transistors (J-FFT). Asymmetrically coupled devices give considerable current gain at low temperature. Grain boundary junctions have also been employed in simple Rapid Single Flux Quantum (RSFQ) circuits to demonstrate functions like flip flop, voltage divider and voltage doubler. A single superconducting layer technology implies small inductances formed as narrow slits in the deposited film. A tri-layer technology is superior but puts demands on insulation and strip cross-overs. Presently available high-Tc junctions are not sufficiently reproducible to allow large scale integrated circuits. Another limitation is the limited performance (for example given by the junction IcRn product) of present junctions at 77 K
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| 6. |
- Gevorgian, Spartak, 1948, et al.
(författare)
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Strain induced ferroelectrosity in epitaxial SrTiO3 films
- 2001
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 33:1-4, s. 311-321
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Tidskriftsartikel (refereegranskat)abstract
- Microwave performances of planar capacitors formed on epitaxial SrTiO 3 (STO) films reveal that two-dimensional, in-plane strain in the film lead to a formation of a stable non-cubic, low symmetry ferroelectric phase. The residual polarization vector has two stable states, normal to the film surface, and may be switched under applied DC bias. Due to the charges in surface/interface levels, the films may contain either a single or opposing domains
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| 7. |
- Gevorgian, Spartak, 1948, et al.
(författare)
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Tailoring the temperature coefficient of capacitance in ferroelectric varactors
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:12, s. 1861 - 1863
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Tidskriftsartikel (refereegranskat)abstract
- Two BaxSr1-xO3, films with different contents of Ba (Ba0.25Sr0.75O3 and Ba0.75Sr0.5O3), separated by a MgO film, are used to fabricate planar varactors with low temperature coefficient of capacitance (TCC), high tunability and low losses. The TCC of the varactors are small in the temperature interval between the dielectric permittivity peaks of the Ba0.25Sr0.75O3 and Ba0.75Sr0.5O3 films
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| 8. |
- Gunnarsson, Robert, 1972, et al.
(författare)
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Fabrication and characterisation of La0.67Sr0.33MnO3 submicron grain boundary junctions
- 2004
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Ingår i: Annalen der Physik (Leipzig). ; 13:1-2, s. 101-102
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Konferensbidrag (refereegranskat)abstract
- We have successfully fabricated LSMO grain boundary bicrystaljunctions with widths down to 200 nm. The grain boundaries aresymmetric with misorientation angles of 24degrees or 36.8degrees, and the microbridges are positioned across thosewith a precision better than 0.5 micro-meter. Grain boundary magnetoresistance is observed in the wider junctions but not in the most narrow junction.
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| 9. |
- Gunnarsson, Robert, 1972, et al.
(författare)
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Low-field magnetoresistance in perovskite manganites: Magnetic field, temperature, and current dependence
- 2004
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Ingår i: Physical Review B. ; 69:5, s. 054413-
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Tidskriftsartikel (refereegranskat)abstract
- The low-field response from single bicrystal grain boundary junction of La0.7Sr0.3MnO3 has been investigated. We provide experimental data for the temperature, magnetic field and bias current dependence of its low-field magnetoresistance. We are then able to separate the contribution from anisotropic magnetoresistance, and the magnetization processes in the vicinity of the grain boundary. Our data indicate that with the magnetic field applied parallel to the grain boundary the magnetization process is dominated by domain wall motion, whereas with the field in the perpendicular direction the magnetoresistance is determinedby coherent rotation of magnetization directions.
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| 10. |
- Huang, MQ, et al.
(författare)
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Small Scale Integrated Technology for HTS RSFQ Circuits
- 2001
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Ingår i: IEEE Transactions on Applied Superconductivity. - : Institute of Electrical and Electronics Engineers (IEEE). - 1051-8223. ; 11:1, s. 558-
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Tidskriftsartikel (refereegranskat)
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