We have fabricated step edged dc SQUID and measured its property. Step on $SrTiO_3$ substrte was fabricated using ECR(Electron Cyclotron Resonance) ion milling system. Since photoresists was removed during $O_2^+$ ion milling, we deposited am orphous MgO/CaO and liftoffed it. Steps of 1000-8000 Å were obtained and the step angle was about 62.5°. $YB_2Cu_3O_{7-\delta}$ was deposited on the step edged $SrTiO_3$ substrate by dc magnetron sputtering method and by $Ar^+$ ion milling, step edged dc SQUID was finally obtained.
We couldn't see any sign of step edged Josephson junction characteristic when we changed the ratio of the step height to the $YB_2Cu_3O_{7-\delta}$ thickness from 1 to 1/6. Due to not well defined step boundary or its poor morphology, Josephson junction was not formed inspite of sharp step angle of ~ 62.5°. To suppress c-axis normal growth of $YB_2Cu_3O_{7-\delta}$ on the step, we deposited MgO about 30Å before $YB-2Cu_3O_{7-\delta}$ deposition. Clear Josephson junction I-V charateristic was observed. Critical current was ~ 80mA and $I_cR_n$ product was about 80 μV at liquid nitrogen temperature(~ 77K). By the change of flux through the SQUID, the critical current changed from 0.2mA to 0.8mA. But it seems to be due to the non-superconducting phase inside the step edged Josephson junction.
For future developement, the fabrication of well defined step on $SrTiO_3$ substrate seems to be needed.
