Planarization of the YBa2Cu3O7-x Base Electrodes in Trilayer Josephson Junctions

We have applied the chemical-mechanical polishing (CMP) planarization technique to YBa2Cu3O7-x (YBCO) films for the base electrodes in trilayer Josephson junctions. In our planarization process, YBCO films were directly polished using a diamond-based slurry and cleaned by low-angle ion etching. The planarized films showed extremely flat surfaces with the average roughness (R a) less than 0.5 nm. Moreover, the c-axis-oriented YBCO/PrBa2Cu3O7-y (PBCO)/YBCO trilayer junctions fabricated using the planarized films as the base electrodes showed resistively shunted junction-like characteristics even when the PBCO barriers were as thin as 10 nm. The I c R n products of the junctions were more than 1 mV at 4.2 K. Our results indicate that CMP is an effective method for obtaining flat YBCO films and for improving the properties of trilayer Josephson junctions.