CHARACTERIZATION OF MULTILAYER RAMP-TYPE REBA2CU3O7-DELTA STRUCTURES BY SCANNING PROBE MICROSCOPY AND HIGH-RESOLUTION ELECTRON-MICROSCOPY

We studied the morphology of ramps in REBa2CU3O7 (REBCO) epitaxial fil ms on SrTiO3 substrates, fabricated by RF magnetron sputter deposition and pulsed laser deposition (PLD), by scanning probe microscopy (SPM) and high resolution electron microscopy (HREM). The ramps were fabric ated by Ar ion beam etching using masks of standard photoresist and TI N. AFM-studies on ramps in sputter deposited films show a strong depen dence, i.e. formation of facets and ridges, on the angle of incidence of the ion beam with respect to the substrate surface as well as the r otation angle with respect to the crystal axes of the substrate. Ramps in pulsed laser deposited films did not show this dependence, Further more, we studied the effect of an anneal step prior to the deposition of barrier layers (i.e. PrBa2CU3O7, SrTiO3, CeO2) on the ramp. First r esults show a recrystallization of the ramp surface, resulting in terr aces and a non-homogeneous growth of the barrier material on top of it . The thickness variations, for thin layers of barrier material, con e ven become much larger than expected from the amount of deposited mate rial and are dependent on the deposition and anneal conditions. HREM s tudies show a well defined interface between barrier layer and electro des. The angle of the ramp depends on the etch rate of the mask and RE BCO, and on the angle of incidence of the ion beam. TiN has a much low er etch rate compared to photoresist, resulting in an angle of the ram p comparable to the angle of incidence, resulting in a low etching rat e on the ramp. These results will lead to improved electrical characte ristics of ramp-type junctions.