REPRODUCIBLE STEP-EDGE JUNCTION SQUIDS

High-T-c super-conducting YBCO SQUIDs have been developed based on ste p-edge junctions. The step-edges were fabricated by using electron-bea m lithography and Ar-ion milling on SrTiO3 substrates. The V(Phi) peak -to-peak voltage is around 10 mu V, and the I(c)R(n) product is 150 mu V at 77 K. The SQUIDs prepared on the same substrate show reproducibl e parameters within 30%. At 77 K the noise properties of the SQUIDs ha ve been studied. At tower frequencies (1 Hz - 100 Hz), we observe a na t noise level just below 10(-4) Phi(0)/Hz(1/2), probably limited by sw itching effects. Above 100 Hz the noise is gradually reduced to 10(-5) Phi(0)/Hz(1/2) at 1 kHz. The geometry of the stepedges has also been investigated by scanning electron microscopy, and the relation between the properties of the SQUID and the step height is reported.