Effect of planarization of the bottom superconducting yttrium-barium-copper-oxide layer in the multilayer structure

YBCO/YSZ/SiO2/YSZ/YBCO multi-layer structures have been successfully grown on single crystal YSZ substrates. The YBCO superconducting layers (300 nm t hick) were deposited using pulsed laser deposition (PLD). The YSZ layers (3 00 nm thick) which are biaxially aligned were deposited using PLD and the i on beam assisted deposition (IBAD). ri thick silicon dioxide layer (2-4 mic rons) was sandwiched between the YSZ layers to meet the low dielectric cons tant requirement for multi-chip module applications. However, if the bottom superconducting layer was patterned into interconnecting lines as required in device applications, the surface of the YSZ/SiO2/YSZ on top of the patt erned bottom superconducting layer had a roughness of about 500 nm. As a re sult, the top YBCO was no longer superconducting. Thus, planarization of th e patterned bottom superconducting layer becomes a keg issue. We have devel oped a "fill-in and lift-off" process to fill the gap between the patterned bottom superconducting lines with YSZ. As a result, we were able to reduce the surface roughness of the bottom YBCO layer to about 10 nm so the top l ayer was superconducting with a critical temperature of 87 K.