ORIGIN OF 1 F NOISE IN Y1BA2CU3O7-X STEP-EDGE DC SQUIDS/

We have fabricated Y1Ba2Cu3O7-x step-edge junction de superconducting quantum interference devices (SQUIDs) and characterized their noise pe rformance. The current-voltage characteristics of our SQUIDs are of re sistively shunted junction type with critical current densities J(c) o f about 10(4) A/cm2 and maximum flux to voltage transfer functions del taV/deltaPHI of 20 muV/PHI0 at 77 K. We compare model predictions for 1/f noise in dc SQUIDs with experimental data and show that the freque ncy dependent noise in our devices results from critical current fluct uations of the Josephson junctions. A bias current reversing technique is effective in suppressing this noise contribution. A flux noise PHI (n) of 80 muPHI0/Hz1/2 at 1 Hz and 77 K was measured on a dc SQUID wit h an inductance L(s) of 60 pH.