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 investigated. The I-V characteristics at 77 K of devices with 6 mu m wide junctions 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. Peak-to-peak flux modulated voltages up to 60 mu V could be measured, corresponding 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 white-noise region and between 2.5X10(-29) and 8X10(-28) J/Hz at 1 Hz for SQUID inductances up to 100 pH could be obtained. There was no obvious dependence of the energy sensitivity on the step angle of the Josephson junctions for devices with 20 pH inductance. These results are comparable to our best results obtained with step-edge DC SQUID's on SrTiO3 substrates.