A ROBUST FABRICATION PROCESS FOR A REFRACTORY INTEGRATED SQUID GRADIOMETER

We describe a process used successfully to fabricate large second-orde r planar gradiometers with integrated DC SQUIDs on two-inch silicon wa fers. All there fractory materials (Nb, Mo and SiO2) are deposited by magnetron sputtering. The Josephson junctions are based on the well-es tablished Nb/AlOx/Nb trilayer technology. All Nb layers are patterned by Reactive Ion Etching using a procedure optimized by experimental de sign. Since only one gradiometer can fit on a wafer, extra care had to be taken in both the design of the device and the fabrication process to ensure that the yield was high. Excellent process latitude is achi eved by sufficient built. in design margins to accommodate any toleran ce difficulties during fabrication.