NOISE PROPERTIES OF SINGLE-LAYER YBACUO STEP-EDGE DC SQUIDS ON MGO SUBSTRATES

DC-SQUID's prepared on MgO substrates with deep steps have been invest igated. The I-V characteristics at 77 K of devices with 6 mu m wide ju nctions can be described by the resistively shunted junction model for steep step edges and by the flux-flow model for low-angle step edges. Steep substrate steps result in a higher yield of working devices. Pe ak-to-peak flux modulated voltages up to 60 mu V could be measured, co rresponding to transfer functions between 20 and 200 mu V/phi(0) at 77 K. Energy sensitivities between 1X10(-30) and 8X10(-30) J/HZ in the w hite-noise region and between 2.5X10(-29) and 8X10(-28) J/Hz at 1 Hz f or SQUID inductances up to 100 pH could be obtained. There was no obvi ous dependence of the energy sensitivity on the step angle of the Jose phson junctions for devices with 20 pH inductance. These results are c omparable to our best results obtained with step-edge DC SQUID's on Sr TiO3 substrates.