Microstructure characterization of MgO buffered YBa/sub 2/Cu/sub 3/O/sub 7/ on [100] Si during thermal cycling

Scanning electron microscopy (SEM) has been utilized to study the microstructure of YBa/sub 2/Cu3O/sub 7/ superconductor high-temperature thin films under thermal cycling loading. The thin films were deposited on MgO buffered [100] Si substrates by the laser ablation and sputtering methods. It is found that the characteristics of the MgO buffer layer have a significant influence on the thermal fatigue life of the superconductor films. The thickness of YBa/sub 2/Cu/sub 3/O/sub 7/ thin film plays a key role on the failure of the laser-ablated MgO buffer layer thin film assembly. The development of cracking and spalling, because of the coefficient of thermal expansion mismatch, is the leading mechanism that eventually causes the failure of the buffered MgO thin film system. Various microstructural factors and mechanisms responsible for the failure of the system are discussed in detail in this paper.