Use of a focused ion beam for characterizing SIS circuits

We have found the use of a Ga+ based focused ion beam (FIB) system to be ve ry useful in characterizing our superconducting-insulating-superconducting (SIS) fabrication process. This tool enables us to physically carve cross s ections in any feature of interest on our wafer which we can then image wit h an SEM, This process is used to examine and monitor improvements in the c overage of metalization layers over different circuit topography and in the critical "sealing" capabilities of our SiO insulation layer around the per imeter of the Nb junction counter electrode. It has also been used to bette r establish a submerged trilayer deposition process where the base electrod e is imbedded in the quartz substrate. We have also improved our characteri zation of the tunnel barrier critical current density of our Nb/Al-oxide/Nb trilayer material by obtaining more accurate diameter measurements from FI B sectioned junctions.