D. Hutson et al., A ROBUST FABRICATION PROCESS FOR A REFRACTORY INTEGRATED SQUID GRADIOMETER, IEEE transactions on applied superconductivity, 5(2), 1995, pp. 2295-2298
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.