Critical parameters in the single-target sputtering of YBa2Cu3O7

Abstract

The critical parameters in the single-target magnetron sputtering of YBa2Cu3O7 have been identified and sufficiently optimized to allow the reproducible deposition of films with Tc’s of ≳90 K and Jc’s of ≫ 106 A/cm2 at 77 K. It was found that during film growth the bombardment of the YBa2Cu3O7 by energetic particles must be minimized and also a stronger oxidizing agent than molecular oxygen must be present to obtain films with these properties. Otherwise, films are deposited that, by x-ray diffraction and energy dispersive x-ray spectroscopy analyses, are indistinguishable from the highest-Tc 1:2:3 stoichiometric material but which have critical temperatures of ≪90 K. Films need not have 1:2:3 overall stoichiometry to have optimum superconducting properties. In such cases the excess elements are present as second-phase particles.

Paraconductivity in YBa2Cu3O7 and YBa2Cu3O7 thin film composites with cerium oxide and gold

“…The addition of hydrogen or water vapor to the Ar/O 2 gas mixture results in fully oxygenated films with high T c and low resistivity. 1,3 The YBCO was dc sputtered using facing targets at 450 mA to each gun and the CeO 2 at rf power levels up to 70 W depending on the desired film composition. The YBCO/ CeO 2 composite films were sputtered for 4 h resulting in film thickness of 2200 Å for 70 W rf power.…”

“…[3][4][5] These material issues can manifest themselves in the rounding of the resistivity within the transition region and in the paraconductivity at temperatures nearly twice T c MF . The mean field superconducting transition temperature (T c MF ) is defined as the inflection point or the maximum dR/dT of the resistance ͑R͒ versus temperature ͑T͒ characteristics of the thin film.…”

Characterization of thin films of YBa2Cu3O7−δ using an interdigital radio frequency proximity probe technique

“…This is indicative of a-axis growth, a problem often encountered in the formation of YBCO on LaAlO 3 . 9 It should be noted that resistance peaks are not uncommon in such films. 17 If the a-axis domains are not continuous, but rather separated from each other by an insulating matrix, then the two-channel conductivity model described above is reasonable.…”

A single flux quantum shift register operating at 65 K

“…The Nb mask was then removed, again by N E . A 200 nm film of YBCO was then deposited, using off-axis RF magnetron sputtering in a mixture of argon, oxygen, and water vapor [7]. A thin layer of gold, typically 30 nm, was then sputtered over the YBCO, in-situ.…”