Abstract: Techniques and methods to form smooth metal layers deposited onto selected surfaces of Josephson junction devices are provided. For example, one or more embodiments described herein can comprise depositing a layer of a first material comprising metal atom species on a selected surface of a device layer; depositing a layer of a second material on a surface of the layer of first material; and performing plasma etching on the layer of second material and the layer of first material to form an etched surface of the layer of first material that is smoother than the surface of the layer of first material, as deposited.

Abstract: Techniques and methods to form smooth metal layers deposited onto selected surfaces of Josephson junction devices are provided. For example, one or more embodiments described herein can comprise depositing a layer of a first material comprising metal atom species on a selected surface of a device layer; depositing a layer of a second material on a surface of the layer of first material; and performing plasma etching on the layer of second material and the layer of first material to form an etched surface of the layer of first material that is smoother than the surface of the layer of first material, as deposited.

Abstract: A die stack that includes a first chip die, a second chip die connected to the first chip die by one or more controlled collapse chip connection (“C4”) solder bump bonds, and a spacer die interposed between the first and second chip dies. The spacer die includes through holes for the one or more C4 solder bumps, and has a thickness such that when the first and second chip dies are compressed into contact with the spacer die, the spacer die thickness is a minimum defined spacing between the first and second chip dies, and the spacer die operates as a hard stop against compression of the die stack after the first and second chip dies are compressed into contact with the spacer die.