FABRICATION OF A QUASI-3-DIMENSIONAL JOSEPHSON-JUNCTION ARRAY

In a first step towards fabricating a truly 3-dimensional (3-d) Josephson-junction array, we have fabricated a quasi-3-d one, i.e. an array consisting of two 2-d arrays stacked on top of and capacitively- and inductively-coupled to one another. We discuss in detail the fabrication techniques we have employed to create this novel type of an array. Such techniques include alignment using topological markers, electron-beam lithography, shadow evaporation, and planarization. We have fabricated different samples whose 2-d arrays consist of underdamped Al-Al2O3-Al junctions in which either the Josephson-coupling energy E(J)=HBARi(c)/2e, where i(C) is the junction critical current, dominates the single-junction charging energy E(C)=e2/2C, where C is the junction capacitance, or vice versa. With these arrays, we plan to study the interaction between vortices and/or charges.