Low-resistivity epitaxial YBa2Cu3O7 thin films with improved microstructure and reduced microwave losses

Abstract

Epitaxial thin films of YBa2C!u307 have been prepared on SrTiOs and LaAlOs substrates by a high-pressure planar dc-sputtering technique. By covering the substrate heater with a frame of polycrystalline YBazCu30~ -substantial improvements of the YBa2Cu307 film properties were achieved. These are characterized by dc-resistivity values p(T) of less than 50 @I cm at 100 K and ~(300 K)/p( 100 K) values of up to 3.9. Significant deviations from the usual linear p(T) behavior were found. Critical temperatures above 90 K, resistive transition widths down to 0.3 K, and critical current densities of about 5 x lo6 A/cm2 at 77 K confirm the high quality of the films. As indicated by Rutherford backscattering and high-resolution transmission electron microscopy the films exhibit a microstructure characterized by a reduced density of lattice defects. However, lattice-coherent precipitates with a diameter of about 5-10 nm were observed. As an outstanding feature the films exhibit, besides the initial steep falloff at T, a further gradual decrease of the microwave surface resistance at 87 GHz below 50 K by at least one order of magnitude. These results are very promising for millimeter-wave applications of epitaxial YBaz.Cu307 thin films.

Epitaxial Oxide Heterostructures for Ultimate High-Tc Quantum Interferometers

“…The typical superconducting transition temperature T c of YBCO films obtained by PLD is ≈ 89 K, which is significantly lower than T c ≈ 93 K obtained for bulk ceramic samples of YBCO. The technique of sputtering at high oxygen pressures allows a smart and homogeneous onaxis in-situ deposition of high-quality metal-oxide thin films from stoichiometric targets (Poppe et al, 1990(Poppe et al, , 1992. Conventional sputtering is used extensively in the semiconductor industry to deposit thin films of various materials in integrated circuit processing.…”

Electromagnetic properties andHe+irradiation effects onYBa2Mulas1, Quesada2, Navacerrada3 2000Phys. Rev. B180140View full textAdd to dashboardCite

“…YBCO films having 500 Å thickness and c-axis orientation were epitaxially grown in a high pressure ͑3.4 mbar͒ pure oxygen dc sputtering system. 22 In the deposition process the substrate temperature is 900°C. Electrodes had transition temperatures (T C ) in the range 89.5-91 K, transition widths smaller than 0.2 K and critical currents densities higher than 10 6 A/cm 2 at 77 K. Films were patterned by wet etching in H 3 PO 4 , obtaining junctions widths ranging between 2 and 50 m. Patterned microbridges ͑barriers and electrodes͒ were irradiated at room temperature with 80 keV He ϩ ions incident 7°from the surface normal to avoid channelling effect.…”

Operation of high-temperature superconductor magnetometer with submicrometer bicrystal junctions

“…A subsequent encapsulation then ensures the long-term stability of the sensor. The average size of the growth spirals of the YBa 2 Cu 3 O 7Ϫx films, deposited by the high-oxygen-pressure dc-sputtering technique, 6 is about 1 m compared to the about 0.3 m grains of conventional laser-ablated films. 9 This makes it possible for the sputtered films to produce junctions between the individual growth spirals, thus contributing to the homogeneity and increasing the tunneling part of the critical current density of the junction.…”

“…It was observed 4,5 that the I c R n product of bicrystal junctions increases with critical current density J c as I c R n ϰ(J c ) 0. 6 . In order to keep I c fixed at an optimal level for SQUID operation, to provide narrow junction conditions, and simultaneously to increase J c and R n it is necessary to reduce the junction width to a submicrometer scale.…”

“…The high-oxygen-pressure dc-sputtering technique 6 The flip-chip magnetometers were sealed vacuum tight in fiberglass epoxy encapsulations. 3 A Pt heater integrated into the encapsulation allowed trapped flux to be removed.…”