Adjustment of Josephson junctions by ion implantation

• US 4,490,901 A
• Filed: 05/05/1983
• Issued: 01/01/1985
• Est. Priority Date: 05/05/1983
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Drake, Robert E., Clark, Gregory J., Raider, Stanley I.
• Primary Examiner(s): Roy, Upendra
• Application Number:
  US06/491,944
• Time in Patent Office: 607 Days
• Field of Search: 29/574, 29/576 B, 29/578, 148/1.5, 427/63, 357/5, 357/91
• US Class Current: 438/2
• CPC Class Codes: H10N 60/0912 of Josephson-effect devices
• CPC Class Codes: Y10S 505/922 Making josephson junction device

Abstract

A method for trimming the zero voltage Josephson current of a tunnel junction including the steps of measuring the I-V characteristics of the completed junctions to quantify the change in I_o necessary to meet the design requirements, placing the tested Josephson junctions on a metal block which is mounted in the sample chamber of an ion implanter structure which is pumped to 1.10^-6 Torr. The junctions, kept at room temperature and oriented at a direction nearly normal to the ion beam, are implanted with magnetically analyzed ions of energies 50 keV to 2300 keV. Spatial uniformity of the ion implant beam is ±2% over a sample. Uniform spatial implantation over a large area sample is obtained by either sweeping of the beam across the sample, or restoring the sample through a stationary beam, determining the required ion dose to effect trimming from calibration curves, remeasuring the I-V characteristics after implantation to confirm that the required I_o trim was effected, and then completing the fabrication of the Josephson device according to standard processing.

Claims

1. A method for adjusting the zero voltage Josephson current (I_o) of a tunnel junction by implanting ion including the steps of

providing first and second superconductive electrodes with a tunnel junction located between said first and second electrodes whereby tunneling current can flow therethrough between said superconductive electrodes,

measuring the voltage-current characteristics of said tunnel junction,

disposing said electrodes with said tunnel junction in an ion implantation structure, including an ion implantation beam, and implanting a boron ion species into said tunnel junction for trimming said zero voltage Josephson current I_o by decreasing the junction energy gap.

2. A method according to claim 1 wherein said ion species is magnetically analyzed ¹¹ B boron ions.

3. A method according to claim 1 wherein said junctions are implanted with a beam of magnetically analyzed ¹¹ B ions of energies in the range from 50 keV to 2300 keV at a direction substantially normal to said junctions.

4. A method according to claim 1 wherein said first superconductive electrode is composed of niobium, said second superconductive electrode is composed of lead, gold and indium, and said tunnel junction is composed of niobium oxide.

5. A method according to claim 4 wherein said ion species is magnetically ionized ¹¹ B species with energies in the range of 50 keV to 2300 keV which are implanted with doses in the range from 10¹³ /cm² to 10¹⁵ /cm².