High-temperature superconductor devices and methods of forming the same

Abstract

An electronic device including a crystalline substrate, an electrode formed on and epitaxial to the substrate, the electrode including a first superconductive oxide, an insulator formed on and epitaxial to the electrode, a barrier that includes an ion-treated surface of the first superconductive oxide, and a counter-electrode formed on and epitaxial to the electrode and the barrier, the counter-electrode including a second superconductive oxide, whereby a Josephson junction is formed between the electrode and the counter-electrode. A superconductor device that includes an oxide superconductor having a surface exposed to ambient environment, and a passivation layer covering at least a portion of the surface of the oxide superconductor that is exposed to the ambient environment. Methods of forming the above devices are also included.

What is claimed is:  
     
         1 . An electronic device comprising: 
 (a) a crystalline substrate;    (b) an electrode formed on and epitaxial to the substrate, the electrode comprising a first superconductive oxide;    (c) an insulator formed on and epitaxial to the electrode;    (d) a barrier comprising an ion-treated surface of the first superconductive oxide; and    (e) a counter-electrode formed on and epitaxial to the electrode and the barrier, the counter-electrode comprising a second superconductive oxide, whereby a Josephson junction is formed between the electrode and the counter-electrode.    
     
     
         2 . The device of  claim 1 , wherein the barrier is a surface formed by treating the first superconductive oxide with a plasma comprising a gas selected from the group consisting of argon, xenon, oxygen, and halogen.  
     
     
         3 . The device of  claim 2 , wherein the gas is argon gas.  
     
     
         4 . The device of  claim 2 , wherein the gas is a 1:1 mixture of argon and oxygen.  
     
     
         5 . The device of  claim 1  wherein the first superconductive oxide has an a-b plane and a step-edge junction is formed in the a-b plane of the first superconductive oxide.  
     
     
         6 . The device of  claim 1  wherein the first superconductive oxide has an a-b plane, the a-b plane is epitaxial to the substrate, and the second superconductive oxide is on and epitaxial to the first superconductive element, whereby a junction is formed perpendicular to the a-b plane of the first superconductive oxide.  
     
     
         7 . The device of any one of claims  1 - 6 , wherein the first and second superconductive oxide is YBCO.  
     
     
         8 . The device of  claim 1 , the device having an I c R n  value of at least about 0.3 mV at a temperature of 4.2 K.  
     
     
         9 . The device of  claim 2 , the device having an I c R n  value of at least about 0.3 mV at a temperature of 4.2 K.  
     
     
         10 . The device of  claim 3 , the device having an I c R n  value of at least about 0.3 mV at a temperature of 4.2 K.  
     
     
         11 . The device of  claim 4 , the device having an I c R n  value of at least about 0.3 mV at a temperature of 4.2 K.  
     
     
         12 . The device of  claim 5 , the device having an I c R n  value of at least about 0.3 mV at a temperature of 4.2 K.  
     
     
         13 . The device of  claim 6 , the device having an I c R n  value of at least about 0.3 mV at a temperature of 4.2 K.  
     
     
         14 . The device of  claim 7 , the device having an I c R n  value of at least about 0.3 mV at a temperature of 4.2 K.  
     
     
         15 . The device of  claim 1 , the device having an I c R n  value of at least about 0.5 mV at a temperature of 40 K.  
     
     
         16 . The device of  claim 2 , the device having an I c R n  value of at least about 0.5 mV at a temperature of 40 K.  
     
     
         17 . The device of  claim 3 , the device having an I c R n  value of at least about 0.5 mV at a temperature of 40 K.  
     
     
         18 . The device of  claim 4 , the device having an I c R n  value of at least about 0.5 mV at a temperature of 40 K.  
     
     
         19 . The device of  claim 5 , the device having an I c R n  value of at least about 0.5 mV at a temperature of 40 K.  
     
     
         20 . The device of  claim 6 , the device having an I c R n  value of at least about 0.5 mV at a temperature of 40 K.  
     
     
         21 . The device of  claim 7 , the device having an I c R n  value of at least about 0.5 mV at a temperature of 40 K.  
     
     
         22 . A process for making a Josephson junction device comprising the steps of: 
 (a) preparing a substrate;    (b) depositing an electrode comprising a first layer of a superconductive oxide on the substrate;    (c) depositing an insulating layer on the first layer of superconductive oxide;    (d) patterning to form a pre-device having an exposed surface of the first superconductive oxide;    (e) placing the pre-device into a deposition chamber;    (f) forming a barrier on the exposed surface of the first layer of superconductive oxide by treating the exposed surface with ions; and    (g) depositing a second layer of a superconductive oxide on the pre-device, whereby a Josephson junction is formed between the first and the second superconductive oxides at the barrier.    
     
     
         23 . The process of  claim 22 , wherein the treating with ions is accomplished with a plasma of Ar gas at a pressure of between 10 and 100 mTorr.  
     
     
         24 . The process of  claim 22 , wherein the treating with ions is with a mixture of Ar and O 2  gas at a pressure of between 10 and 100 mTorr.  
     
     
         25 . The process of any one of claims  22 - 24 , further comprising the step of vacuum annealing the pre-device prior to depositing the second superconductive oxide.  
     
     
         26 . A superconductor device, comprising: 
 a) an oxide superconductor having a surface exposed to ambient environment; and    b) a passivation layer covering at least a portion of the surface of the oxide superconductor that is exposed to the ambient environment.    
     
     
         27 . The device  claim 26 , further comprising a buffer layer at least partially between the passivation layer and the oxide superconductor.  
     
     
         28 . The device of  claim 26 , wherein the passivation layer originates from the superconductor.  
     
     
         29 . The device of  claim 28 , wherein the passivation layer is an ion-modified layer of the superconductor.  
     
     
         30 . The device of  claim 26 , wherein the oxide superconductor comprises YBa 2 Cu 3 O 7-δ , wherein δ≧0.  
     
     
         31 . The device of  claim 26 , wherein the passivation layer is an electrical insulator.  
     
     
         32 . The device of  claim 26 , wherein the passivation layer is epitaxial and crystalline.  
     
     
         33 . The device of  claim 26 , wherein the passivation layer covers the entire surface of the oxide superconductor that is exposed to the ambient environment.  
     
     
         34 . The device of  claim 26 , further comprising a layer of a superconductive oxide on the passivation layer, whereby a Josephson junction is formed between the superconductive oxides.  
     
     
         35 . A method of providing a passivation layer on the surface of an oxide superconductor, the method comprising vacuum annealing and ion treating at least a portion of the surface of the oxide superconductor that is exposed to ambient environment.  
     
     
         36 . The method of  claim 35 , further comprising additional vacuum annealing after the ion treatment.  
     
     
         37 . The method of  claim 35 , further comprising heating in an oxygen-rich environment after the ion treatment.  
     
     
         38 . The method of  claim 35 , comprising vacuum annealing and ion treating the entire surface of the oxide superconductor that is exposed to ambient environment  
     
     
         39 . A method of making a superconductor device, the method comprising: 
 a) forming a layer of oxide superconductor on a substrate, the layer of oxide superconductor having a surface that is exposed to ambient environment; and    b) passivating at least a portion of the surface of the oxide superconductor that is exposed to ambient environment.    
     
     
         40 . The method of  claim 39 , comprising passivating the entire exposed surface of the oxide superconductor.  
     
     
         41 . The method of  claim 39 , wherein the passivating step comprises bombarding the exposed surface portion with ions.  
     
     
         42 . The method of  claim 41 , further comprising annealing the layer of oxide superconductor between steps (a) and (b).  
     
     
         43 . The method of  claim 42 , further comprising annealing the layer of oxide superconductor after step (b).  
     
     
         44 . The method of  claim 42 , wherein the bombarding step comprises treating the exposed surface portion with plasma.  
     
     
         45 . The method of  claim 39 , wherein step (a) comprises forming a layer of YBa 2 Cu 3 O 7-δ , wherein δ≧0.  
     
     
         46 . The method of  claim 42 , further comprising heating the oxide superconductor in oxygen after step (b).  
     
     
         47 . The method of  claim 46 , further comprising cooling the oxide superconductor to room temperature in oxygen after heating the oxide superconductor in oxygen.  
     
     
         48 . The method of  claim 41 , further comprising maintaining the layer of oxide superconductor at a temperature of between about 300° C. and about 650° C. while bombarding the exposed surface portion with ions.  
     
     
         49 . The method of  claim 46 , wherein the heating step comprises maintaining the layer of oxide superconductor at a temperature of between about 700° C. and about 800° C. after treating the exposed surface portion with plasma.  
     
     
         50 . The method of  claim 39 , wherein the passivation step comprises changing a surface layer of the oxide superconductor to a material different from the oxide superconductor.  
     
     
         51 . The method of  claim 50 , wherein the changing step comprises changing the surface layer of the oxide superconductor to a material having an oxygen mobility that is lower than the oxygen mobility in the oxide superconductor.  
     
     
         52 . The method of  claim 39 , further comprising forming a layer of oxide superconductor on at least a portion of the passivated surface portion, whereby a Josephson junction is formed between the oxide superconductors.  
     
     
         53 . A passivation layer comprising an ion-modified layer on an oxide superconductor, the ion-modified layer covering at least a portion of the surface of the oxide superconductor that would otherwise be exposed to ambient environment, and the ion-modified layer having an oxygen mobility that is lower than an oxygen mobility of the oxide superconductor.  
     
     
         54 . The passivation layer of  claim 53 , wherein the ion-modified layer is formed by material originating from the oxide superconductor.  
     
     
         55 . The passivation layer of  claim 53 , wherein the ion-modified layer is an externally applied layer that is bonded to the oxide superconductor.  
     
     
         56 . The passivation layer of  claim 55 , wherein the ion-modified layer is quasi-cubic and is not YBa 2 Cu 3 O 7-δ , wherein δ≧0.  
     
     
         57 . The passivation layer of  claim 53 , wherein the ion-modified layer is epitaxial and crystalline.  
     
     
         58 . The passivation layer of  claim 53 , the ion-modified layer covering the entire surface of the oxide superconductor that would otherwise be exposed to ambient environment