Josephson device, method of forming josephson device and superconductor circuit

Abstract

A Josephson device includes a first superconducting electrode layer, a barrier layer, and a second superconducting electrode layer that are successively stacked. The first and second superconducting electrode layers are made of an oxide superconductor material having (RE) 1 (AE) 2 Cu 3 O y as a main component, where an element RE is at least one element selected from a group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and an element AE is at least one element selected from a group consisting of Ba, Sr and Ca. The barrier layer is made of a material that includes the element RE, the element AE, Cu and oxygen, where the barrier layer has a composition different from compositions of the first and second superconducting electrode layers.

1 . A Josephson device comprising a first superconducting electrode layer, a barrier layer and a second superconducting electrode layer that are successively stacked, wherein:
 said first and second superconducting electrode layers are made of an oxide superconductor material having (RE) 1 (AE) 2 Cu 3 O y  as a main component, where an element RE is at least one element selected from a group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and an element AE is at least one element selected from a group consisting of Ba, Sr and Ca; and   said barrier layer is made of a material that includes the element RE, the element AE, Cu and oxygen, where in cations within the material forming the barrier layer, a Cu content is in a range of 35 At. % to 55 At. % and an RE content is in a range of 12 At. % to 30 At. %, and the barrier layer has a composition different from compositions of the first and second superconducting electrode layers.   
     
     
         2 . The Josephson device as claimed in  claim 1 , wherein the Cu content and the RE content in the composition of the barrier layer respectively differ from those of the compositions of the first and second superconducting electrode layers by 3 At. % or more. 
     
     
         3 . The Josephson device as claimed in  claim 1 , wherein the barrier layer has the element RE made of Y and the element AE made of Ba, and in the cations within the material forming the barrier layer the Cu content is in a range of 35 At. % to 55 At. % and a Y content is in a range of 12 At. % to 30 At. %. 
     
     
         4 . The Josephson device as claimed in  claim 1 , wherein:
 each of the first and second superconducting electrode layers and the barrier layer includes an element LRE, where the element LRE is at least one element selected from a group consisting of La, Ce, Pr, Nd, Sm and Eu; and   an LRE content of the barrier layer is larger than an LRE content of each of the first and second superconducting electrode layers.   
     
     
         5 . The Josephson device as claimed in  claim 4 , wherein the Cu content, the RE content or the LRE content of the barrier layer is analyzed by an Energy Distribution X-ray spectroscopy (EDX) by irradiating an electron beam having a beam diameter of 1 nm or less on the barrier layer. 
     
     
         6 . A Josephson device comprising:
 a substrate;   a first superconducting electrode layer formed on the substrate and having a first sloping surface portion on one end surface thereof;   an insulator layer formed on the first superconducting electron layer and having a second sloping surface portion on one end surface thereof, so that the first and second sloping surface portions form a continuous sloping surface;   a barrier layer deposited on the sloping surface; and   a second superconducting electrode layer covering the barrier layer,   wherein said first and second superconducting electrode layers are made of an oxide superconductor material having (RE) 1 (AE) 2 Cu 3 O y  as a main component, where an element RE is at least one element selected from a group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and an element AE is at least one element selected from a group consisting of Ba, Sr and Ca; and   said barrier layer is made of a material that includes the element RE, the element AE, Cu and oxygen, where in cations within the material forming the barrier layer, a Cu content is in a range of 35 At. % to 55 At. % and an RE content is in a range of 12 At. % to 30 At. %, and the barrier layer has a composition different from compositions of the first and second superconducting electrode layers.   
     
     
         7 . A Josephson device comprising:
 a substrate having a surface;   a first superconducting electrode layer formed on the surface of the substrate;   an insulator formed on the first superconducting electrode layer and having a penetration hole penetrating the insulator layer in a direction taken along a thickness of the insulator layer;   a barrier layer deposited on the first superconducting electrode layer and within the penetration hole; and   a second superconducting electrode layer filling the penetration hole and covering the barrier layer and the insulator layer,   wherein said first and second superconducting electrode layers are made of an oxide superconductor material having (RE) 1 (AE) 2 Cu 3 O y  as a main component, where an element RE is at least one element selected from a group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and an element AE is at least one element selected from a group consisting of Ba, Sr and Ca; and   said barrier layer is made of a material that includes the element RE, the element AE, Cu and oxygen, where in cations within the material forming the barrier layer, a Cu content is in a range of 35 At. % to 55 At. % and an RE content is in a range of 12 At. % to 30 At. %, and the barrier layer has a composition different from compositions of the first and second superconducting electrode layers.   
     
     
         8 . The Josephson device as claimed in  claim 7 , wherein each of the first and second superconducting electrode layers and the insulator have the Perovskite structure as its basic structure, and an atomic plane made up of Cu and oxygen in each of the first and second superconducting electrode layers is perpendicular to the surface of the substrate. 
     
     
         9 . The Josephson device as claimed in  claim 7 , wherein the Cu content and the RE content in the composition of the barrier layer respectively differ from those of the compositions of the first and second superconducting electrode layers by 3 At. % or more. 
     
     
         10 . The Josephson device as claimed in  claim 7 , wherein the barrier layer has the element RE made of Y and the element AE made of Ba, and in the cations within the material forming the barrier layer the Cu content is in a range of 35 At. % to 55 At. % and a Y content is in a range of 12 At. % to 30 At. %. 
     
     
         11 . The Josephson device as claimed in  claim 7 , wherein:
 each of the first and second superconducting electrode layers and the barrier layer includes an element LRE, where the element LRE is at least one element selected from a group consisting of La, Ce, Pr, Nd, Sm and Eu; and   an LRE content of the barrier layer is larger than an LRE content of each of the first and second superconducting electrode layers.   
     
     
         12 . The Josephson device as claimed in  claim 11 , wherein the Cu content, the RE content or the LRE content of the barrier layer is analyzed by an Energy Distribution X-ray spectroscopy (EDX) by irradiating an electron beam having a beam diameter of 1 nm or less on the barrier layer. 
     
     
         13 . A method of forming a Josephson device comprising the steps of:
 (a) forming on a substrate a first superconducting electrode layer made of an oxide superconductor material;   (b) forming an insulator layer covering the first superconducting electrode layer;   (c) removing a portion of the insulator layer to expose the first superconducting electrode layer;   (d) depositing a barrier layer made of an oxide material on an exposed surface of the first superconducting electrode layer; and   (e) forming a second superconducting electrode layer made of an oxide superconductor material to cover the barrier layer,   wherein the oxide material forming the barrier layer includes an element RE, an element AE, Cu and oxygen, where the element RE is at least one element selected from a group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and the element AE is at least one element selected from a group consisting of Ba, Sr and Ca.   
     
     
         14 . The method of forming the Josephson device as claimed in  claim 13 , wherein the oxide superconductor materials forming said first and second superconducting electrode layers have (RE) 1 (AE) 2 Cu 3 O y  as a main component, where an element RE is at least one element selected from a group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and an element AE is at least one element selected from a group consisting of Ba, Sr and Ca. 
     
     
         15 . The method of forming the Josephson device as claimed in  claim 13 , wherein the oxide material forming the barrier layer has a Cu content in a range of 35 At. % to 55 At. % and an RE content in a range of 12 At. % to 30 At. %, and a composition of the oxide material is different from compositions of the first and second superconducting electrode layers. 
     
     
         16 . The method of forming the Josephson device as claimed in  claim 13 , wherein said step (d) uses one of vacuum deposition, sputtering, Pulsed Laser Deposition (PLD) and Chemical Vapor Deposition (CVD). 
     
     
         17 . The method of forming the Josephson device as claimed in  claim 13 , wherein said step (d) uses one of vacuum deposition, sputtering and Pulsed Laser Deposition (PLD), and controls a composition of the barrier layer based on a distance between the substrate and a target and a pressure within an oxygen gas atmosphere. 
     
     
         18 . A superconductor circuit using magnetic flux quantum as signal carrier, comprising:
 at least one Josephson device comprising a first superconducting electrode layer, a barrier layer and a second superconducting electrode layer that are successively stacked,   wherein said first and second superconducting electrode layers are made of an oxide superconductor material having (RE) 1 (AE) 2 Cu 3 O y  as a main component, where an element RE is at least one element selected from a group consisting of Y, La, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu, and an element AE is at least one element selected from a group consisting of Ba, Sr and Ca; and   said barrier layer is made of a material that includes the element RE, the element AE, Cu and oxygen, where in cations within the material forming the barrier layer, a Cu content is in a range of 35 At. % to 55 At. % and an RE content is in a range of 12 At. % to 30 At. %, and the barrier layer has a composition different from compositions of the first and second superconducting electrode layers.