Josephson junction with spacer
Various embodiments are directed toward a circuit configured to act as a Josephson junction. The circuit includes: a junction stack on a substrate, the junction stack including a portion of a first superconductor electrode, with an interface layer on a top side of the first superconductor electrode and configured to act as a tunneling barrier for the junction stack. The circuit may also comprise a first portion of a second superconductor electrode on top of the interface layer. A spacer may separate the portion of the first superconductor electrode in the junction stack from a second portion of the second superconductor electrode outside the junction stack where the second superconductor electrode overlays the first superconductor electrode.
1. A method for making a circuit configured to act as a Josephson junction, the method comprising:
creating a tri-layer stack on a substrate by:
depositing a first layer of superconductor material;
forming an interface layer on the first layer; and
depositing a second layer of superconductor material on the interface layer;
shaping a first superconductor electrode from the tri-layer stack by etching the tri-layer stack outside a first pattern to expose the substrate;
depositing a spacer on a perimeter of the first superconductor electrode;
depositing a third layer of superconductor material on the substrate, the spacer, and the first superconductor electrode; and
shaping a second superconductor electrode by:
creating a second pattern on the third layer of superconductor material that at least partially overlays a first portion of the first superconductor electrode; and
etching the third layer to expose the substrate and the interface layer such that a second portion of the second superconductor electrode overlays the first portion of the first superconductor electrode and such that the second portion of the second superconductor electrode contacts the substrate on at least one side of the spacer.
2. The method of claim 1 , wherein the interface layer is a non-superconductor metal.
3. The method of claim 2 , wherein the forming an interface layer further comprises oxidizing a top surface of the non-superconductor metal.
4. The method of claim 1 , wherein the depositing a spacer comprises:
depositing a conformal layer of a spacer material; and
etching the spacer material to expose the substrate and the second layer.
5. The method of claim 1 , wherein the shaping the first superconductor electrode from the tri-layer stack includes creating a first photolithographic pattern on top of the second layer.
6. The method of claim 1 , wherein the first pattern is a photolithographic pattern.
7. The method of claim 1 , wherein
the first superconductor electrode has a first pad area and a first extension;
the second superconductor electrode has a second pad area and a second extension;
the first portion of the first superconductor electrode is part of the first extension;
and the second portion of the second superconductor electrode is part of the second extension.
8. The method of claim 1 , wherein an extension area of the first superconductor electrode is overlaid by an extension area of the second superconductor electrode.