Epitaxial YBa₂Cu₃O_7-δ films on silicon using combined YSZ/Y₂O₃ buffer layers. A comprehensive study

Epitaxial YBa₂Cu₃O_7-δ films with excellent structural and electronic properties were grown on silicon by reactive thermal coevaporation employing a combination of yttria-stabilized zirconia (YSZ) and Y₂O₃ as a buffer layer. To provide optimum conditions, the YSZ growth was studied over a wide range of deposition parameter space. For the first time the effectiveness of the buffer has been derived quantitatively from SNMS profiles. Although the buffer layer can solve the problem of interdiffusion, the large differential thermal expansion between silicon and YBa₂Cu₃O_7-δ cannot be compensated in any way. In many cases this results in a fracture of films thicker than 70 nm and a fast degradation which imposes severe restrictions on the technical applications of silicon substrates. A thorough study of crack formation led to the conclusion that the theoretical limitation has not yet been reached and that there is still hope to overcome this problem.