YBCO DC SQUID MADE ON STEP-EDGE SRTIO3 SUBSTRATES

We have fabricated dc superconducting quantum interference devices (dc SQUIDs) from thin films of YBCO deposited on step-edge SrTiO3 substra tes by the dc magnetron sputtering method. Steps on the SrTiO3 substra te were formed by low-energy Ar ion milling with photolithography usin g a photoresistor or Nb metal mask. The SQUID was formed by standard p hotolithography and showed a nice periodic voltage output up to 86 K. An atomic force microscope (AFM) study showed an angle-dependent morph ology on the step and the importance of the step angle to forming a we ak link. The flux noise measured in a flux-locked loop was 1.5 X 10(-8 ) PHI0(2)/Hz, with a corresponding noise energy of 2.2 x 10(-28) J/Hz at 77 K and 1 kHz.