On ageing and critical thickness of YBa2Cu3O7 films on Si with CeO2/YSZ buffer layers

The ageing behaviour of epitaxial YBa2Cu3O7 (YBCO) films an Si (100) with C eO2/YSZ buffer layers is studied. For the YBCO/CeO2/YSZ/Si system, its agei ng is weaker than the YBCO/YSZ/Si system. The experimental critical thickne ss of YBCO films for YBCO/CeO2/YSZ/Si systems is only 40 nm, otherwise crac ks appear in the film. The formation of cracks is analyzed by means of frac ture mechanics theory. The estimated thermal stress and elastic strain in c rack-free YBCO layers reach 2.41 GPa and 1.5% at 77 K, respectively. Deposi ting another non-superconducting YBCO (YBCO*) film an top of YBCO as a pass ivation layer makes the critical thickness increase up to 70 nm. These film s cannot bear surface etching and tempering temperatures higher than 110 de grees C in lithography. (C) 1999 Elsevier Science S.A. All rights reserved.