Homoepitaxial MgO Buffer Layers for YBCO Thin Films Prepared by Pulsed Laser Deposition

摘要

The high-temperature superconductor Yba_2Cu_3O_(7-δ)(YBCO) is widely regarded as the material-of-choice for thin film superconducting device fabrication. Since its discovery, it has been successfully grown on a number of single-crystal substrates; all with their respective advantages and disadvantages. In particular, magnesium oxide (MgO) has been widely utilised for both low-frequency applications, such as superconducting quantum interference devices (SQUIDS) and high-frequency microwave devices. Although the dielectric properties of MgO make it ideal for microwave applications, its hygroscopic property is a major disadvantage. This makes storage difficult and reduces the quality of subsequently deposited films. To improve the quality and reproducibility of YBCO films deposited on MgO substrates that are not freshly polished, we have investigated the deposition of homoepitaxial (100) MgO buffer layers by pulsed laser deposition (PLD). Although the MgO films are smooth, they are covered with sub-micron sized particles which reduce in number as the deposition temperature increases. YBCO films grown on 30nm and 60nm (100) MgO buffer layers (deposited at 770°C) show no degradation when compared to YBCO films grown on unbuffered substrates. However, YBCO grown on 15nm MgO buffer layers shows an inferior electron channeling pattern (ECP) indicating reduced crystallinity.