Effects of homoepitaxial surfaces and interface compounds on the in-plane epitaxy of YBCO films on yttria-stabilized zir
- PDF / 1,153,784 Bytes
- 11 Pages / 576 x 792 pts Page_size
- 9 Downloads / 154 Views
S. M. Garrison Conductus Inc., Sunnyvale, California 94086
Marilyn Hawley Los Alamos National Laboratory, Los Alamos, New Mexico 87545
T. H. Geballe Department of Applied Physics, Stanford University, Stanford, California 94305 (Received 22 November 1991; accepted 21 February 1992)
Control of the in-plane epitaxial alignment of c-axis YBa 2 Cu 3 0 7 _i (YBCO) films on yttria-stabilized zirconia (YSZ) substrates is necessary for achieving optimal transport properties. We have used pulsed laser deposition to grow homoepitaxial YSZ and heteroepitaxial CeO 2 on YSZ single crystal substrates. This procedure dramatically improves the epitaxy of YBCO and reduces the number of low and high angle grain boundaries. We have also studied the effects of preparing the YSZ growth surface with approximately monolayer amounts of CuO, Y 2 O 3 , BaO, and BaZrO 3 to determine the effects these compositional variations have on the subsequent YBCO epitaxy. CuO, Y 2 O 3 , and BaZrO 3 induce an in-plane crystallography of YBCO distinct from that initiated with BaO. Both homoepitaxy and monolayer depositions may be carried out in situ and are simple and effective for controlling the epitaxy and electrical properties of YBCO on YSZ. The effects of substrate temperature, oxygen pressure, and yttria content have also been studied.
I. INTRODUCTION Microelectronic applications require thin films of the high temperature oxide superconductor YBa 2 Cu 3 0 7 £ (YBCO) to be capable of carrying large critical current densities on readily available substrates. Excellent films with critical current densities (Jc) > 106 A/cm 2 at 77 K can be produced on lattice matched substrates such as SrTiO3, LaAlO 3 , and LaGaO 3 over a wide range of growth conditions. These substrates, however, are expensive and are frequently available in diameters no greater than 2 inches. Some are twinned, resulting in dielectric anisotropy, or have unacceptably large losses. Excellent YBCO films have been produced on MgO which is relatively inexpensive but mechanically fragile and difficult to polish. Buffer layers have made sapphire substrates viable for high quality thin film growth1"3; however, the small thermal expansion constant of sapphire appears to cause microcracking in multilayer structures,4 and sapphire has an inherent dielectric anisotropy due to its rhombohedral symmetry. Due to its mechanical strength, chemical stability, and low cost, yttria-stabilized zirconia (YSZ) has become a popular single crystal substrate for films of YBCO.5"10 YSZ has also been identified as an effective epitaxial buffer layer for producing YBCO films with high critical J. Mater. Res., Vol. 7, No. 7, Jul 1992 http://journals.cambridge.org
Downloaded: 13 Nov 2014
current densities on Si11'12 and on sapphire.3 Polycrystalline YSZ ceramics are being studied as potential substrates for YBCO tapes, i.e., for power leads.13 Polycrystalline YSZ thin films have been used as buffer layers for the deposition of YBCO on metallic substrates.14 YSZ substrates may provide a cost effective altern
Data Loading...
