12-06-2012, 02:32 PM
JOSEPHSON JUNCTION MANUFACTURING
JOSEPHSON JUNCTION MANUFACTURING.doc (Size: 38 KB / Downloads: 31)
Today’s Josephson circuits are fabricated with a process technology that is reliable, reproducible and rugged. The superconductor is made of niobium (Nb) or sometimes niobium nitride. A tunnel barrier of aluminium oxide creates a sandwiched type barrier. Such junctions are very stable and can survive long.
The niobium electrodes are deposited either by vacuum evaporation or by sputtering. The critical step is the oxidation of the Nb electrode and the formation of a thin aluminium oxide tunnel barrier. However we can obtain very uniform insulating barriers using plasma oxidation.
The latest process for the development of Josephson junction is called the trilayer process. Instead of depositing and then patterning each layer of the Josephson junction separately the whole wafer is completely covered with three layers of films; first layer of Nb, then a barrier of aluminium oxide and then a final layer of Nb. Such junction shows no degradation with multiple cooling cycles to 5k and can be stored infinitely at the room temperature.
The resist and the metal on top of it are removed by chemical etching leaving the patterned top base electrode. In the next step one produces a resist pattern with openings for the top electrode and carries out plasma oxidation of the oxide barrier. Finally the top metal is deposited and by stripping of the resist one obtains the desired top electrode pattern of the completed junction.
For industrial production and patterning of the control lines over the junction, one requires several additional processing steps like the deposition and patterning of the control lines over the junctions. Present technology enables one to fabric several tens of thousands of working junctions of a chip.