| 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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| 11. |
- Ivanov, Zdravko G., 1949, et al.
(författare)
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Depairing critical currents and self-magnetic field effects in submicron YBa2Cu3O7-delta microbridges and bicrystal junctions
- 2004
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Ingår i: Low Temperature Physics. - : AIP Publishing. - 1063-777X .- 1090-6517. ; 30:3, s. 203-207
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Tidskriftsartikel (refereegranskat)abstract
- We report on depairing critical currents in submicron YBa 2 Cu 3 O 7-δ microbridges. A small-angle bicrystal grain boundary junction is used as a tool to study the entrance of vortices induced by a transport current and their influence on the I-V curves. The interplay between the depairing and the vortex motion determines a crossover in the temperature dependence of the critical current. The high entrance field of vortices in very narrow superconducting channels creates the possibility of carrying a critical current close to the depairing limit determined by the S-S ′ -S nature of the small-angle grain boundary junction. © 2004 American Institute of Physics.
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| 12. |
- Kadigrobov, Anatoli M., 1937, et al.
(författare)
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Giant lasing effect in magnetic nanoconductors
- 2004
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Ingår i: Europhysics Letters. - : IOP Publishing. - 1286-4854 .- 0295-5075. ; 67:6, s. 948-954
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Tidskriftsartikel (refereegranskat)abstract
- We propose a new principle for a compact solid-state laser in the 1–100 THz regime. This is a frequency range where attempts to fabricate small-size lasers up to now have met severe technical problems. The proposed laser is based on a new mechanism for creating spin-flip processes in ferromagnetic conductors. The mechanism is due to the interaction of light with conduction electrons; the interaction strength, being proportional to the large exchange energy, exceeds the Zeeman interaction by orders of magnitude. On the basis of this interaction, a giant lasing effect is predicted in a system where a population inversion has been created by tunneling injection of spin-polarized electrons from one ferromagnetic conductor to another—the magnetization of the two ferromagnets having different orientations. Using experimental data for ferromagnetic manganese perovskites with nearly 100% spin polarization, we show the laser frequency to be in the range 1–100 THz. The optical gain is estimated to be of order 107 cm−1, which exceeds the gain of conventional semiconductor lasers by 3 or 4 orders of magnitude. A relevant experimental study is proposed and discussed.
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| 13. |
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| 14. |
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| 15. |
- Larsson, Peter, 1966, et al.
(författare)
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Fabrication and transport measurements of YBa2Cu3O7−x nanostructures
- 2000
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Ingår i: Journal of Vacuum Science & Technology B: Microelectronics Processing and Phenomena. - : American Vacuum Society. - 0734-211X. ; 18:1, s. 1825-31
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Tidskriftsartikel (refereegranskat)abstract
- We have developed a process to fabricate nanostructures in oxide materials, especially YBa2Cu3O7−x (YBCO) thin films. The fabrication process is based on a multilayer mask with an amorphous carbon layer as a key component. Electron-beam lithography, reactive ion etching, and ion-beam etching have been the supporting techniques for the process. Nanobridges ranging in width from 50 to 170 nm have been fabricated and characterized. The initial YBCO film was 50 nm thick and had a Tc of 86 K. Tc of the fabricated bridges decreased about 3–5 K with respect to the initial film. The level of the critical current density was 4–9×105 A/cm2 at 77 K and 1.6–2×107 A/cm2 at 4.2 K. No increase of the critical current density was observed as the cross-section area became smaller. The process has also been applied to fabricate 30–50 nm wide trenches in a-axis-oriented YBCO on top of a similar-oriented PrBa2Cu3O7−x (PBCO) layer. No supercurrent was observed in such junctions. The current transport was governed by Mott variable range hopping.
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| 16. |
- Larsson, Peter, 1966, et al.
(författare)
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Manufacturing of nanometer structures in YBa2Cu3O7 thin films using a carbon based multilayer mask
- 1995
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Ingår i: Applied Superconductivity 1995. Proceedings of EUCAS 1995, the Second European Conference on Applied Superconductivity. - 0750303484 ; 2, s. 935-938
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Konferensbidrag (refereegranskat)abstract
- A process method that will produce ion milled bridges and trenches of ultra small dimensions in YBa2Cu3O7(YBCO) thin films is presented. The method is based on electron beam lithography, reactive ion etching (RIE), ion milling and a multilayer mask, which consists of an electron resist and an amorphous carbon layer with intermediate niobium. Carbon has two unique properties that are used in the process. First, carbon can easily be reactive ion etched in an oxygen atmosphere, since the oxides of carbon are gases. Furthermore, carbon has an extremely low ion milling etching rate. The electron resist pattern is transferred to the niobium and the carbon layers by a reactive ion etching process with CF4 and O2 In such a way a durable carbon mask for ion milling is formed. When the ion milling is completed, the result of the process is 50-60 nm wide bridges and 30-60 nm wide trenches in 100 nm thick YBCO films.
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| 17. |
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| 18. |
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| 19. |
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| 20. |
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| 21. |
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| 22. |
- Malisa, Anayesu, 1968, et al.
(författare)
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Colossal magneto-resistance effect in epitaxially grown La2/3Ca1/3Mno3 perovskite-like manganite thin films
- 2005
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 295:3, s. 277-283
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Tidskriftsartikel (refereegranskat)abstract
- We report in this work, study on colossal magnetoresistance (CMR) effect in epitaxial La2/3Ca1/3 MnO3 thin films grown on SrTiO3 (0 0 1) substrates by pulsed laser deposition (PLD) technique. The films were grown on as-received SrTiO3 substrates and on SrTiO3 substrates prepared by HF etching (Koster et al., Appl. Phys. Lett. 73 (1998) 2920; V. Leca et al., Wet etching methods for perovskite substrates, University of Twente, MESA+ Research Institute, Low Temperature Division). Two of the samples were annealed in different conditions to investigate the films heat treatment effect on electric and magnetic properties. Electrical resistance was done using the four-probe method at temperatures in the range of 2375 K without a magnetic field and in an external field of 5 T applied in the film plane. Resistance-magnetic field (R vs. H) at 77 K for the two annealed samples was done in a 5 T sweep magnetic field. The surface morphology and structural information of the films were obtained using atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. Secondary ion mass spectroscopy (SIMS) analysis was performed on the annealed samples to investigate any possible chemical reaction between La2/3Ca1/3MnO3 thin films and SrTiO3 substrate.
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| 23. |
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| 24. |
- Petrov, Peter, et al.
(författare)
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X-ray study of SrTiO3 thin films in multilayer structures
- 2000
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Ingår i: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - 0921-5093. ; 288:2, s. 231-234
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Tidskriftsartikel (refereegranskat)abstract
- A set of YBa2Cu3O7-x (YBCO)/SrTiO3 (STO) multilayer structures are investigated using conventional and grazing-incidence X-ray diffraction techniques. For all samples ω- and φ-scans are performed. From the peak position and broadening analysis of peak shape, the a, b, and c lattice parameters for STO films as well as the microstrain values along these directions are evaluated. It is observed that the crystal cell of the STO film becomes orthorhombic when a YBCO thin film is grown on top of STO. The differences between b and a parameters of STO crystal cell and the microstrain are reduced by using buffer layers.
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| 25. |
- Roy, Pierre, et al.
(författare)
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Interface magnetic properties of La0.7Sr0.3MnO3 thin films
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. ; 272-276:Part 2, s. 1207-1209
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Konferensbidrag (refereegranskat)abstract
- Magnetic properties of La0.7Sr0.3MnO3 thin films with various capping layers have been investigated by SQUID magnetometry and X-ray magnetic circular dichroism. Results on the temperature dependence of the magnetization, orbital to spin moment ratios and the magnetocrystalline anisotropy are presented. xxxx
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| 26. |
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| 27. |
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| 28. |
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| 29. |
- Wikborg, E., et al.
(författare)
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Electrically tunable device and a method relating thereto
- 2003
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Patent (övrigt vetenskapligt/konstnärligt)abstract
- A thin film ferroelectric varactor device comprising a substrate layer, a ferroelectric layer structure and an electrode structure is presented. The ferroelectric layer structure comprises a number of ferroelectric layers and a number of intermediate buffer layers arranged in an alternating manner. At least a first and a second layer of the ferroelectric layers have different Curie temperatures, i.e. the dielectric constant of the first ferroelectric layer has a maximum at a temperature which is different from the temperature at which the dielectric constant of the second ferroelectric layer has a maximum.
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| 30. |
- Wikborg, E., et al.
(författare)
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Electrically tunable device and a method relating thereto
- 2001
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The present invention relates to a thin film ferroelectric varactor device (10) comprising a substrate layer (1), a ferroelectric layer structure (12) and an electrode structure (91,92). The ferroelectric layer structure (12) comprises a number of ferroelectric layers (2,4) and a number of intermediate buffer layers (3) arranged in an alternating manner. At least a first (2) and a second (4) layer of said ferroelectric layers have different Curie temperatures, i.e. the dielectric constant of the first ferroelectric layer (12) has a maximum at a temperature which is different from the temperature at which the dielectric constant of the second ferroelectric layer (4) has a maximum.
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