P. Tiwari

High current YBa2Cu3O7−δ thick films on flexible nickel substrates with textured buffer layers

High current YBa2Cu3O7−δ (YBCO) thick films on flexible nickel substrates with textured buffer layers were fabricated. Highly textured yttria‐stabilized‐zirconia buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c‐axis oriented with respect to the film surface but also strongly in‐plane textured. The in‐plane mosaic spread of YBCO films was ∼10°. A critical current density of 8×105 A/cm2 was obtained at 75 K and zero field for thin YBCO films. It was also demonstrated that thick YBCO films with a high critical current and excellent magnetic field dependence at liquid nitrogen temperature can be obtained on flexible nickel substrates by using the textured buffer layers. The result indicates that thick film technology in combination with IBAD buffer layers could be a viable method for fabricating YBCO tapes in long lengths.

Pulsed laser deposition of thick YBa2Cu3O7−δ films with Jc≥1 MA/cm2

Using pulsed laser deposition, YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] (YBCO) films ranging in thickness from 0.065 to 6.4 [mu]m have been deposited on yttria-stabilized zirconia substrates with an intermediate layer of CeO[sub 2]. The thinnest films have critical current densities of over 5 MA/cm[sup 2] at 75 K with zero applied field; as film thickness is increased, [ital J][sub [ital c]] decreases asymptotically to 1 MA/cm[sup 2]. X-ray analysis of a 2.2-[mu]m-thick film shows that the YBCO is predominantly [ital c]-axis oriented and textured in-plane, while a Rutherford backscattering spectrometry minimum channeling yield of [approx]75% indicates that the film contains disordered material at this thickness.Using pulsed laser deposition, YBa2Cu3O7−δ (YBCO) films ranging in thickness from 0.065 to 6.4 μm have been deposited on yttria‐stabilized zirconia substrates with an intermediate layer of CeO2. The thinnest films have critical current densities of over 5 MA/cm2 at 75 K with zero applied field; as film thickness is increased, Jc decreases asymptotically to 1 MA/cm2. X‐ray analysis of a 2.2‐μm‐thick film shows that the YBCO is predominantly c‐axis oriented and textured in‐plane, while a Rutherford backscattering spectrometry minimum channeling yield of ≊75% indicates that the film contains disordered material at this thickness.

Structural and electrical properties of Ba0.5Sr0.5TiO3 thin films with conductive SrRuO3 bottom electrodes

Epitaxial Ba0.5Sr0.5TiO3 (BST) thin films were deposited on LaAlO3 substrates with the conductive metallic oxide SrRuO3 (SRO) as a bottom electrode by pulsed laser deposition. The BST and SRO films were (h00) and (00l) oriented normal to the substrate surface, respectively. The epitaxial nature of both BST and SRO layers was determined by the measurement of in‐plane orientation with respect to the major axes of the substrate. Ion beam channeling with a minimum yield of around 10% from Rutherford backscattering spectrometry demonstrated the films to be of high crystallinity. A dielectric constant around 500 and dielectric loss less than 0.01 at a frequency of 10 kHz were measured on the capacitors with a configuration of Ag/BST/SRO. Electrical measurements on such epitaxial BST films showed a breakdown voltage above 106 V/cm and a leakage current density of less than 5×10−8 A/cm at a field intensity of 2×105 V/cm. These results prove the BST/SRO heterostructure to be a good combination for microelectronic device applications.

SiOx luminescence from light‐emitting porous silicon: Support for the quantum confinement/luminescence center model

Measurements of hydrogen loss and luminescence as a function of annealing temperature in porous silicon suggest that luminescence is attributable to electron‐hole recombination in SiOx surface layers with an intensity that is dependent upon the surface hydrogen content. The luminescence is composed of three Gaussian bands similar to those found in amorphous SiO2. X‐ray photoelectron spectroscopy and scanning electron microscopy show porous silicon has SiOx on the surface, which is comprised of many particles of about 10 nm size. Collectively, the data strongly support the previously proposed quantum confinement/luminescence center model.

Heteroepitaxial growth of highly conductive metal oxide RuO2 thin films by pulsed laser deposition

Highly conductive ruthenium oxide (RuO2) has been epitaxially grown on LaAlO3 substrates by pulsed laser deposition. The RuO2 film is (h00) oriented normal to the substrate surface. The heteroepitaxial growth of RuO2 on LaAlO3 is demonstrated by the strong in‐plane orientation of thin films with respect to the major axes of the substrate. High crystallinity of RuO2 thin films is also determined from Rutherford backscattering channeling measurements. Electrical measurements on the RuO2 thin films demonstrate a quite low room‐temperature resistivity of 35±2 μΩ cm at deposition temperatures of above 500 °C.

Preparation of diamondlike carbon films by high‐intensity pulsed‐ion‐beam deposition

Diamondlike carbon (DLC) films were prepared by high‐intensity pulsed‐ion‐beam ablation of graphite targets. A 350 keV, 35 kA, 400 ns beam, consisting primarily of hydrogen, carbon, and oxygen ions was focused onto a graphite target at a fluence of 15–45 J/cm2. Amorphous carbon films were deposited at up to 30 nm per pulse, corresponding to an instantaneous deposition rate greater than 1 mm/s. Electrical resistivities were between 1 and 1000 Ω cm. Raman spectra indicate that diamondlike carbon is present in most of the films. Electron‐energy‐loss spectroscopy indicates significant amounts of sp3‐bonded carbon, consistent with the presence of DLC. Scanning electron microscopy showed most films contain 100 nm features, but micron size particles were deposited as well. Initial tests revealed favorable electron field‐emission behavior.

Fabrication of biaxially oriented YBCO on (00{ell}) biaxially oriented yttria-stabilized-zirconia on polycrystalline substrates

Ion-assisted, ion-beam sputter deposition is used to obtain (00l) biaxially oriented films of cubic yttria-stabilized-zirconia (YSZ) on polycrystalline metal substrates. Yttrium-barium-copper-oxide (YBCO) is then heteroepitaxially-pulse-laser deposited onto the YSZ. Phi scans of the films show the full-width-half maxima of the YSZ (202) and the YBCO(103) reflections to be 14{degree} and 10{degree} respectively. Our best dc transport critical current density measurement for the YBCO is 800,000 A/cm{sup 2} at 75K and 0T. At 75K, the total dc transport current in a 1 cm wide YBCO film is 23 A.

Deposition of epitaxial yttria-stabilized zirconia on single-crystal Si and subsequent growth of an amorphous SiO2 interlayer

Abstract A processing technique is developed to fabricate single-crystal yttria-stabilized zirconia (YSZ) on amorphous SiO2 on (100) single-crystal Si. The YSZ layer shows high crystallinity with an ion beam channelling minimum of 11 % from Rutherford backscattering. Even though there is a thick intervening amorphous SiO2 layer between the Si and the YSZ, the single-crystal YSZ layer is aligned with the crystal Si. The tilt and rotation variations are 0·64° and 1·11° respectively, based on X-ray diffraction Ω-rocking curves on [100] and π scans on [202] of YSZ films. The epitaxial nature of the YSZ on the thick SiO2 layer (from 10 to 100 nm) is further confirmed by high-resolution cross-sectional transmission electron microscopy analysis. This processing and the resulting multilayer structure might provide a new option for fabricating innovative microelectronic devices.

Epitaxial YBa2Cu3O7−δ thin films on SrRuO3/Pt/MgO

Epitaxial YBa2Cu3O7−δ (YBCO) thin films were deposited on (100) MgO using platinum and SrRuO3 (SRO) buffer layers by pulsed laser deposition. The films were (001) textured normal to substrate surface with a high degree of in‐plane orientation with respect to the substrate’s major axes. YBCO films showed superconducting transition temperature (Tco) at 91 K and critical current densities were found to be 2–3×106 A/cm2 at 77 K and zero field. An ion beam minimum channeling yield of 16% was obtained for YBCO films, indicating high crystallinity. The orientation relationship for this epitaxial multilayer structure was found to be (100) YBCO∥(100) SRO∥(100)Pt∥(100) MgO. This result showed that high‐quality superconducting thin films can be deposited on metal with an appropriate buffer layer.

Preparation of high quality YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thick films on flexible Ni-based alloy substrates with textured buffer layers

High current YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films on flexible nickel substrates with textured buffer layers were fabricated. Highly textured yttria-stabilized-zirconia (YSZ) buffer layers were deposited by using ion beam assisted deposition (IBAD). Pulsed laser deposited YBCO films were not only c-axis oriented with respect to the film surface but also strongly in-plane textured. The in-plane mosaic spread of YBCO films was/spl sim/10/spl deg/. A critical current density of 8/spl times/10/sup 5/ A/cm/sup 2/ was obtained at 75 K and zero field for thin YBCO films. It was also demonstrated that thick YBCO films with a high critical current and excellent magnetic field dependence at liquid nitrogen temperature can be obtained on flexible nickel substrates by using the textured buffer layers. Issues encountered in producing the films were discussed.<<ETX>>