Josephson junction device and method of manufacturing the same
A Josephson junction device and a method of manufacturing the Josephson junction device are disclosed. The Josephson junction device includes a substrate having a top surface and a trench recessed below the first surface, wherein sidewalls of the substrate define sidewalls of the trench; a first superconducting electrode formed on the top surface of the substrate with sidewalls further defining the sidewalls of the trench; a tunneling thin film formed over the sidewalls of the substrate and over the sidewalls of the first superconducting electrode; and a second superconducting electrode formed in the trench in contact with the tunneling thin film and with top surface above the top surface of the substrate, wherein a superconducting tunnel junction is formed between the first superconducting electrode and the second superconducting electrode through the tunneling thin film.
1 . A Josephson junction device comprising:
a substrate having a first surface and a trench recessed below the first surface, wherein sidewalls of the substrate define sidewalls of the trench;
a first superconducting electrode formed on the first surface of the substrate to be adjacent to the trench;
a tunneling thin film formed over the sidewalls of the substrate and over a side surface of the first superconducting electrode adjacent to the trench; and
a second superconducting electrode formed in the trench in contact with the tunneling thin film and with a top surface above the first surface of the substrate,
wherein a superconducting tunnel junction is formed between the first superconducting electrode and the second superconducting electrode through the tunneling thin film,
wherein a top surface of the second superconducting electrode is above the substrate within a height range of the first superconducting electrode.
2 . The Josephson junction device of claim 1 , wherein a depth of the trench from the first surface of the substrate to a bottom surface of the second superconducting electrode is D 1 , a distance from the first surface to the top surface of the first superconducting electrode is D 2 , a vertical thickness of the second superconducting electrode is D 3 , and the second superconducting electrode satisfies D 1 <D 3 ≤D 1 +D 2 .
3 . The Josephson junction device of claim 1 , further comprising a protective layer of material protecting the tunneling thin film above the first superconducting electrode.
4 . The Josephson junction device of claim 3 , wherein the protective layer is formed together with the second superconducting electrode.
5 . The Josephson junction device of claim 1 ,
wherein the trench sidewalls include a first sidewall and a second sidewall facing each other,
a first junction formed by the tunneling thin film on the first sidewall, and
a second junction formed by the tunneling thin film on the second sidewall,
wherein the first junction and the second junction have junction areas of different sizes.
6 . The Josephson junction device of claim 5 , wherein a horizontal width of the second superconducting electrode contacting the tunneling thin film on the first sidewall is different from a width of the second superconducting electrode contacting the tunneling thin film on the second sidewall, so that the junction areas of the first junction and the second junction are different from each other.
7 . The Josephson junction device of claim 5 , wherein the first junction has a first area of contact between the second superconducting electrode and the tunneling thin film on the first sidewall, wherein the second junction has a second area of contact between the second superconducting electrode and the tunneling thin film on the second sidewall, and wherein the first area and the second area are different from each other by 5 times or greater.
8 . The Josephson junction device of claim 7 , wherein the first area and the second area are different from each other by 10 times or greater.
9 . The Josephson junction device of claim 5 , wherein the junction area of the first junction is less than the junction area of the second junction so that the first junction functions as a main junction and the second junction functions as a sub junction.
10 . The Josephson junction device of claim 9 , further comprising a conductive layer formed by doping a part of the substrate on the side of the second sidewall to reinforce concentration of a load on the main junction.
11 . The Josephson junction device of claim 1 , wherein the first superconducting electrode or the second superconducting electrode has a vertical thickness less than or equal to about 200 nm.
12 . The Josephson junction device of claim 1 , wherein the first superconducting electrode or the second superconducting electrode includes titanium nitride, niobium, niobium nitride, or titanium niobium nitride.
13 . The Josephson junction device of claim 12 , wherein the tunneling thin film includes a metal, a semiconductor, or an insulator.
14 . The Josephson junction device of claim 12 , wherein the tunneling thin film includes aluminum oxide (AlO), hafnium oxide (HfO), silicon nitride (SiN), or aluminum nitride (AlN).
15 . A Josephson junction comprising:
a planar substrate having a first superconducting electrode layered thereon and having a linear groove through the planar substrate and the first superconducting electrode, the linear groove having a left wall comprised of a left portion of the planar substrate and a left portion of the first superconducting electrode, the linear groove also having a right wall comprised of a right portion of the planar substrate and a right portion of the first superconducting electrode;
a tunneling film comprising a left portion lining the left wall of the linear groove and comprising a right portion lining the right wall of the linear groove;
a second superconducting electrode in the linear groove having a left end with a first contact area with the left portion of the tunneling film and having a right end with a second contact area with the right portion of the tunneling film, the second contact area larger than the first contact area.
16 . The Josephson junction of claim 15 , wherein the tunneling film further comprises a bottom portion lining a surface of the planar substrate that forms a bottom of the linear groove, and wherein a bottom of the second superconducting electrode contacts the bottom portion of the tunneling film.
17 . The Josephson junction of claim 15 , wherein the second superconducting electrode has an upper surface above the interface between the planar substrate and the first superconducting electrode.