Ramp-edge josephson junction devices and methods for fabricating the same

• US 20020074544A1
• Filed: 12/19/2000
• Published: 06/20/2002
• Est. Priority Date: 12/21/1999
• Status: Abandoned Application

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Sung, Gun Yong, Kang, Kwang Yong, Choi, Chi Hong
• Application Number:
  US09/741,955
• Publication Number:
  US 20020074544A1
• Time in Patent Office: Days
• US Class Current: 257/31
• CPC Class Codes: H10N 60/0941 comprising high-Tc ceramic materials
• CPC Class Codes: H10N 60/124 comprising high-Tc ceramic materials

Abstract

The invention relates generally to high-temperature superconducting Josephson junction devices necessary in implementing an advanced a single flux quantum circuit for a digital electronic device using superconductors. More particularly, the invention relates to ramp-edge Josephson junction devices and methods for fabricating the same, using copper-series oxide super-conducting thin films. According to the present invention, the ramp-edge Josephson junction device comprises a substrate, a first electrode layer having a ramp-edge and a first insulating layer formed on the substrate sequentially, a transformation layer formed at the ramp-edge of the first electrode layer by illumination of excimer laser and by annealing process, and a second electrode layer and a second electrode layer and a second insulating layer formed on the first electrode layer including the transformation layer and the first insulating layer sequentially.

Claims

1. A ramp-edge Josephson junction device, comprising:

a substrate;

a first electrode layer having a ramp-edge and a first insulating layer formed on said substrate sequentially;

a transformation layer formed at the ramp-edge of the first electrode layer by illumination of excimer laser and by annealing process; and

a second electrode layer and a second insulating layer formed on said first electrode layer including said transformation layer and said first insulating layer sequentially.

2. The ramp-edge Josephson junction device according to claim 1, wherein said first and second electrode layers are copper-series oxide superconductor.

3. The ramp-edge Josephson junction device according to claim 2, wherein said copper-series oxide superconductor is selected from a group consisting of Bi₂Sr₂Ca_nCu_n+1O_2n+6, Bi₂Ba₂Ca_nCu_n+1O_2n+6, Tl₂Sr₂Ca_nCu_n+1O_2n+6, Tl₂Ba₂Ca_nCu_n+1O_2n+6 ( is a fixed number from 0 to 4) or YBa₂Cu₃O₇₋

x, NtBa₂Cu₃O<sub>7−

x</sub>, SmBa₂Cu₃O<sub>7−

x</sub>, ErBa₂Cu₃O<sub>7−

x</sub>, GdBa₂Cu₃O<sub>7−

x</sub>, DyBa₂Cu₃O<sub>7−

x</sub>, HoBa₂Cu₃O<sub>7−

x</sub>, TmBa₂Cu₃O<sub>7−

x</sub>, LuBa₂Cu₃O<sub>7−

x</sub>, LnBa₂Cu₃O<sub>7−

x</sub> (x is 0 to 0.5).

4. The ramp-edge Josephson junction device according to claim 1, wherein said first insulating layer and said second insulating layer are perovskite-type oxide.

5. The ramp-edge Josephson junction device according to claim 4, wherein said perovskite-type oxide is selected from a group consisting of SrTiO₃, LaAlO₃, Sr₂AlTaO₆, Sr₂AlNbO₆ or BaTbO₃.

6. The ramp-edge Josephson junction device according to claim 1, wherein an inclination angle of said ramp-edge in said first electrode layer is formed to be below about 20°

.

7. The ramp-edge Josephson junction device according to claim 1, further comprising electrode pads each connected said first electrode layer and said second electrode layer.

8. A method of fabricating a ramp-edge Josephson junction device, comprising:

a first step of sequentially forming a first electrode layer having a ramp edge, and a first insulating layer on a substrate;

a second step of illuminating sad ramp-edge of the first electrode layer with an excimer laser and performing an annealing process to form a transformation layer; and

a third step of sequentially forming a second electrode layer and a second insulating layer on said first electrode layer including said transformation layer and said first insulating layer.

9. The method of fabricating a ramp-edge Josephson junction device according to claim 8, wherein in said second step, the energy density of the excimer laser illuminated is about 0.3˜

1.2 J/cm².

10. The method of fabricating a ramp-edge Josephson junction device according to claim 8, wherein in said second step, said excimer laser uses one of ArF, KrF and XeCl the wave lengths of which are 193 nm, 248 nm and 308 nm, respectively.

11. The method of fabricating a ramp-edge Josephson junction device according to claim 8, wherein in said second step, said annealing process is performed at a temperature of about 500˜

600°

C. under the pressure of oxygen for one hour.

12. The method of fabricating a ramp-edge Josephson junction device according to claim 8, wherein said first and second electrode layers are formed of copper-series oxide superconductor.

13. The method of fabricating a ramp-edge Josephson junction device according to claim 12, wherein said copper-series oxide superconductor is selected from a group consisting of Bi₂Sr₂Ca_nCu_n+1O_2n+6, Bi₂Ba₂Ca_nCu_n+1O_2n+6, Tl₂Sr₂Ca_nCu_n+1O_2n+6, Tl₂Ba₂Ca_nCu_n+1O_2n+6 (n is a fixed number from 0 to 4) or YBa₂Cu₃O₇₋

x, NdBa₂Cu₃O<sub>7−

x</sub>, SmBa₂Cu₃O<sub>7−

x</sub>, ErBa₂Cu₃O<sub>7−

x</sub>, GdBa₂Cu₃O<sub>7−

x</sub>, DyBa₂Cu₃O<sub>7−

x</sub>, HoBa₂Cu₃O<sub>7−

x</sub>, TmBa₂Cu₃O<sub>7−

x</sub>, LuBa₂Cu₃O<sub>7−

x</sub>, LnBa₂Cu₃O<sub>7−

x</sub> (x is 0 to 0.5).

14. The method of fabricating a ramp-edge Josephson junction device according to claim 8, wherein said first insulating layer and said second insulating layer are formed of perovskite-type oxide.

15. The method of fabricating a ramp-edge Josephson junction device according to claim 14, wherein said perovskite-type oxide is selected from a group consisting of SrTiO₃, LaAlO₃, Sr₂AITaO₆, Sr₂AlNbO₆ or BaTbO₃.

16. The method of fabricating a ramp-edge Josephson junction device according to claim 8, wherein said first and second electrode layers, and said first and second insulating layers are formed by pulsed laser deposition method using an excimer laser.

17. The method of fabricating a ramp-edge Josephson junction device according to claim 8, wherein in said first step, the step of forming the ramp-edge further comprises:

sequentially forming a first electrode an d a first insulating layer on a substrate;

forming a photoresist pattern on said first insulating layer by photolithography, and etching slantingly said first insulating layer by ion beam using said photoresist pattern as a mask; and

slantingly etching said first electrode layer by ion beams using said first insulating layer slantingly etched as a mask.

18. The method of fabricating a ramp-edge Josephson junction device according to claim 17, wherein said an inclination angle of said ramp-edge in said first electrode layer is formed to be below about 20°

.

19. The method of fabricating a ramp-edge Josephson junction device according to claim 8, further comprising a step of forming electrode pads each connected said first electrode layer and said second electrode layer.