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High Speed Cryogenic Logic Element Based on the Josephson Tunneling Effect

IP.com Disclosure Number: IPCOM000095887D
Original Publication Date: 1964-Aug-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 2 page(s) / 23K

Publishing Venue

IBM

Related People

Merriam, MF: AUTHOR

Abstract

The cryogenic logic element is based on the Josephson* effect to attain faster switching than is normally obtainable in conventional cryotrons.

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High Speed Cryogenic Logic Element Based on the Josephson Tunneling Effect

The cryogenic logic element is based on the Josephson* effect to attain faster switching than is normally obtainable in conventional cryotrons.

Two superconductive metals 2 and 4 are separated by a very thin oxide insulating layer 6. The entire junction is kept at depressed temperatures so that metals 2 and 4 are superconductive. The Josephson effect is essentially the tunneling of Cooper pairs of electrons through the oxide insulation even though there is no applied voltage between metals 2 and 4. Such tunneling can be deemed supercurrent. Current in a control winding 8 creates a critical magnetic field in layer 6 that interrupts the supercurrent tunneling and causes ordinary single particle tunneling, resulting in a potential drop across the junction. The device 18 is a switch operable near absolute zero. Such potential drop is sensed without having to drive metals 2 and 4 to their respective resistive states, yet such voltage drop is considerably greater than would appear across a similar cryotron gate when the latter is driven resistive.

In B, the Josephson type switch is employed as a bistable device. Current to be controlled enters input line 10 and is made to flow in path 12 or path 14 to exit at terminal 16 depending upon which control winding 8' or 8'' carries current. A current in 8', sufficient to create a critical magnetic field for junction 18', destroys supercurrent tunneling...