Witold Kula

High-T/sub c/ thin films on low microwave loss alkaline-rare-earth-aluminate crystals

It is demonstrated that the alkaline-rare-earth aluminates (K/sub 2/NiF/sub 4/-type perovskites) are an excellent choice as the substrate material for the growth of high-T/sub c/ thin films suitable for microwave and far-infrared applications. The CaNdAlO/sub 4/ and SrLaAlO/sub 4/ single crystals have been grown by Czochralski pulling and fabricated into the form of

Formation of the 110‐K superconducting phase in Pb‐doped Bi‐Sr‐Ca‐Cu‐O thin films

Investigation of the 110‐K Bi2Sr2Ca2Cu3Ox phase formation in superconducting thin films of Bi‐based cuprates is reported. The films were dc magnetron sputtered from single Bi(Pb)‐Sr‐Ca‐Cu‐O targets of various stoichiometries, and subsequently annealed in air at high temperatures. The influence of the initial Pb content, annealing conditions, as well as the substrate material on the growth of the 110‐K phase was investigated. We found that the films, fully superconducting above 100 K could be reproducibly fabricated on various dielectric substrates from Pb‐rich targets by optimizing annealing conditions for each initial Pb/Bi ratio. Heavy Pb doping considerably accelerated formation of the 110‐K phase, reducing the film annealing time to less than 1 h. Films containing, according to the x‐ray measurement, more than 90% of the 110‐K phase were obtained on MgO substrates, after sputtering from the Bi2Pb2.5Sr2Ca2.15Cu3.3Ox target and annealing in air for 1 h at 870u2009°C. The films were c‐axis oriented, with 4.5...

Fabrication and microwave properties of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films

Studies are reported of the interaction of Y-Ba-Cu-O and Bi-Ca-Sr-Cu-O thin films with microwaves. The films were prepared on cubic zirconia and magnesium oxide substrates using a modified spray deposition technique. The tested films were about 1-3 mu m thick and exhibited good superconducting properties. Several test structures have been designed by spraying a mixture of nitrate precursors on heated substrates through very thin stencil marks. The supercurrent dependence on millimeter wavelength microwave illumination was measured, and microwave detection and mixing experiments were performed. The films of both materials exhibited properties characteristic of granular superconductors, with Josephson-type coupling at the intergrain connections. The results also indicate that these materials can be successfully used as very sensitive millimeter radiation detectors operational at liquid-nitrogen temperatures. >

D.C. magnetron sputtering of YBa2 Cu3 O7-y thin films

We report our studies on fabrication and superconducting properties of YBa2 Cu3 O7-y thin films prepared by d.c. magnetron sputtering from a single 1-2-3 target and subsequent heat treatment. The films exhibited sharp resistive transitions and zero-resistance temperatures above 85 K. XPS results indicate that the stoichiometry of our films was close to the target composition.

Deposition and properties of high critical temperature superconducting ceramic thin films

We report our studies on the fabrication and superconducting properties of thin films in the Yue5f8Baue5f8Cuue5f8O and Biue5f8Srue5f8Caue5f8Cuue5f8O systems. The films were manufactured on ZrO2:Y, ZrO2:Gd, MgO, and LaAlO3 substrates, by chemical deposition of properly mixed nitrate precursors, as well as by d.c. magnetron sputtering from a single oxide target. In all cases, as-deposited films required a high temperature heat treatment to become superconducting. After annealing, our films were granular with the thickness ranging from 0.5 to 5 μm, and exhibited sharp superconducting transitions with the zero resistivity state reached at 89 K and 77 K for Yue5f8Baue5f8Cuue5f8O and Biue5f8Srue5f8Caue5f8Cuue5f8O films respectively. Patterning techniques, most suitable for our deposition methods, were also developed and tested.

Detection of Millimetre Wave Radiation by Y-Ba-Cu-O Thin Films at Liquid Nitrogen Temperatures

Detecting properties of Y-Ba-Cu-O granular thin film structures obtained by two differnt technological methods and using three different substrate materials have been studied at millimetre waves. The response to 25 and 100 GHz radiation is presented as the function of dc bias current for several temperatures around 77 K. For power levels below saturation the amplitudes of the recovered video signals were found to be proportional to the incident power. Sensitiviy obtained at 110 GHz is comparable to that of crystal point-contact detector. Preliminary results on mixing of two Ku-band sources for IF frequencies up to 5 GHz are presented, indicating that the response time of Y-Ba-Cu-O films is shorter than 40 ps. Due to pronounced quantum effects, which manifest themselves especially in narrow superconducting strips below 60 K, at present state of the technology the usefulness of investigated detectors is limited to liquid nitrogen temperatures.

Highly oriented Bi-based thin films with zero resistance at 106 K

The authors report on the fabrication and characterization of nearly single-phase superconducting Bi/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ thin films. The films are DC-magnetron-sputtered from heavily Pb-doped (Pb/Bi molar ratios up to 1.25), sintered targets on unheated MgO, SrTiO/sub 3/, CaNdAlO/sub 4/, and SrLaAlO/sub 4//sur single crystals. For the films grown on the

Optimum annealing temperature dependence on initial lead content in dc magnetron sputtered Bi(Pb)-Sr-Ca-Cu-O thin films

Influence of the initial lead content in Bi(Pb)-Sr-Ca-Cu-O thin films on the annealing conditions, which make the films fully superconducting above 100 K is reported. We have found that the optimum annealing temperature was very close to the temperature of the film partial melting and decreased with the increase of the lead content in the film. The increase of the lead content also dramatically accelerated formation of the 110-K phase, resulting in short (1 hour) annealing times.

Josephson effects and microwave response of HTS thin films

Abstract The response of thin films YBCO and BSCCO to microwave fields has been investigated. Some unexpected features have been observed and an explanation is given in terms of a robust fluxon lattice whose motion is correlated with the applied microwave field.

Voltage-controlled magnetization switching in MRAMs in conjunction with spin-transfer torque and applied magnetic field

Voltage-controlled magnetic anisotropy (VCMA) effect has attracted a significant amount of attention in recent years because of its low cell power consumption during the anisotropy modulation of a thin ferromagnetic film. However, the applied voltage or electric field alone is not enough to completely and reliably reverse the magnetization of the free layer of a magnetic random access memory (MRAM) cell from anti-parallel to parallel configuration or vice versa. An additional symmetry-breaking mechanism needs to be employed to ensure the deterministic writing process. Combinations of voltage-controlled magnetic anisotropy together with spin-transfer torque (STT) and with an applied magnetic field (Happ) were evaluated for switching reliability, time taken to switch with low error rate, and energy consumption during the switching process. In order to get a low write error rate in the MRAM cell with VCMA switching mechanism, a spin-transfer torque current or an applied magnetic field comparable to the criti...