Epitaxial growth of yBa2Cu3O7-x films on Si substrates with buffer layers

Several groups have prepared nearly-single-crystalline YBa2Cu3O7-X thin films on SrTiO3 substrates with critical temperatures of zero resistivity (Tα) exceeding 90 K and critical current densities at 77 K (Jc,77k) exceeding 106 A/cm2. However, films prepared on Si substrates, either directly or with buffer layers, are usually polycrystalline and with much lower Tα and Jc. Recently, much-improved YBa2Cu3O7-X thin films have been prepared on Si substrates with double buffer layers, BaTiO3 and MgAl2O4. Miura et al. prepared the films by rf magnetron sputtering at 640°C substrate holder temperature and their best as-deposited film exhibits Tα = 70 K and Jc,40k = 4 × 104 A/cm2. Wu et al. prepared the films by pulsed laser deposition at 650°C substrate holder temperature and their best film exhibits Tα = 87 K and Jc,77K = 6 × 104 A/cm2. X-ray diffraction studies indicated that the films are orientationally locked with the Si substrates. Here we present the transmission electron microscopy (TEM) analysis of the laser deposited films and show the epitaxial relations between the buffer layers and the Si substrates, as well as between the YBa2Cu3O7-X flims and the buffer layers. Defect generating mechanisms and possibilities for improving the crystalline properties of the YBa2Cu3O7-X films, and consequently the superconducting properties, will be discussed.