Measurements of a YBCO superconducting quantum interference filter with planar ion-damaged Josephson junctions*

We have fabricated a two dimensional series-parallel array of 565 $\times$28 \linebreak YBa$_2$Cu$_3$O$_{7-\delta}$ thin film ion damage Josephson junctions. The loop areas were varied incommensurately from 28.5 to 90~$\mu$m$^2$ so that the response of the current-biased array to an applied magnetic field is a prominent peak in voltage centered at zero field. We measured voltage versus applied magnetic field characteristics for several static bias currents at different temperatures. Additionally, we measured current-voltage ($I$-$V$) characteristics of the array with no applied magnetic field at several temperatures. To fit the $I$-$V$ characteristics, we assumed that each parallel section of the array could be modeled as a single resistively shunted junction with critical currents following a normal distribution. Fitting the summed voltage contributions of the parallel sections to measurements of the array, we computed the resistance and critical current mean and spread. The standard deviation of these critical currents was 15~percent at 74~K.