New conductive IBAD buffer for HTS applications

Abstract

Biaxially aligned Indium Tin Oxide (ITO) thin films to be used as electrically conductive buffer layers were prepared by an Ion-Beam Assisted Deposition (IBAD) process on various substrates. Two Kaufman ion sources with 2.5 cm diameter were employed for the assisting and the sputtering beam, respectively. All deposited films revealed (001) oriented film growth with a strong in-plane alignment. The degree of the in-plane orientation was studied depending on the ion-beam parameters and the incident angle. Investigations (TEM and X-ray) of the texture evolution of these IBAD films during film growth were carried out. An in-plane texture of 12.6°FWHM for a 1 μm thick film has been achieved so far. The quality of the buffer has been demonstrated by the subsequent deposition of high-current carrying YBCO-films deposited by thermal coevaporation using a 3-5 nm thick Y₂O₃ interlayer. A j_c of 0.76 MA/cm² (77K, 0T) has been obtained for a 1 cm × 1 cm sample with ITO of 20° FWHM.

The in-plane texture of ITO improves with increasing film thickness similar to the well established texture development in YSZ (Yttria-Stabilized Zirconia). However, the dependence on the etching rate and the angle of incidence is different in both materials, which indicates different mechanisms that might be responsible for the texturing.