Ion beam assisted deposition of textured templates
Ion beam assisted deposition (IBAD) is widely used on developing textured templates on amorphous substrates in last few years. It should be realized that majority of thin films used for electronical and electrical devices need to be grown epitaxially, which normally requires a single crystal substrate with perfect lattice match and chemical compatibility. This has been a great limitation in practical applications. The IBAD texturing technique provides a novel approach for epitaxy of thin films on nontextured substrates. IBAD-MgO has been successfully used to build texture on long metallic tapes for large scale application of HTS YBCO coated conductors. High quality texture can be built within few minutes on about 10 nm IBAD-MgO deposition. Homo-epitaxial MgO layer and other buffer layers can be used to further improve the epitaxy and surface compatibility with YBCO.
IBAD-MgO on non-metallic flexible Ceraflex. AC loss has been a serious concern of YBCO coated conductor applications since most of HTS electrical devices need to work in a strong AC field. Non-metallic flexible Ceraflex is a possible candidate as substrate to reduce AC loss of YBCO coated conductors. It has very high resistivity so the eddy current loss will be totally removed; it also has excellent compatibility with YBCO since its composition is YSZ. It is flexible but the surface is very rough with Ra~100nm, which is not suitable for IBAD-MgO texturing. We used multi-layer Spin-on-Glass (SOG) coat the original surface and reduce the Ra to about 1nm. Textured IBAD-MgO template has been developed on the SOG smoothened Ceraflex; then highly textured SrTiO3 film has been grown on top. Preliminary YBCO growth experiment on IBAD-MgO textured Ceraflex shows the phase is pure and the Tc is about 88K, optimization is still in progress.
IBAD-MgO on glass. Amorphous buffer layers are normally necessary for IBAD-MgO texturing process. These buffer layers will induce additional loss and decrease the efficiency. We tried to use Ar+ pre-bombarding to activate the substrate surface and obtained highly textured IBAD-MgO template on unbuffered glass. By optimizing the pre-bombarding time, the best texture quality, in-plane ??~6.5o and out-of-plane FWHM~2o, has been obtained.