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Browse Prior Art Database

High Density Josephson ROM

IP.com Disclosure Number: IPCOM000052820D
Original Publication Date: 1981-Jul-01
Included in the Prior Art Database: 2005-Feb-11
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Kilgannon, TJ: AUTHOR

Abstract

Read only memories (ROMs) are known using Josephson junctions. These generally employ so-called ""dummy'' junctions. However, there is no absolute need for ""dummy'' junctions in a ROM, and they can therefore be eliminated with a resulting density improvement. The ROM circuits of this invention have high density and can be fabricated by well-known processes in a straightforward manner.

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High Density Josephson ROM

Read only memories (ROMs) are known using Josephson junctions. These generally employ so-called ""dummy'' junctions. However, there is no absolute need for ""dummy'' junctions in a ROM, and they can therefore be eliminated with a resulting density improvement. The ROM circuits of this invention have high density and can be fabricated by well-known processes in a straightforward manner.

Fig. 1 shows a string of Josephson junctions J1, J2, ..., J6 which are connected in series. The current-carrying lines M2 and M3 are layers of metallization, as is apparent from Fig. 2, which is a layout of a column of Josephson junctions Jl, J2, and J3. The M2 layer is located below the M3 layer. These layers are close together in the region where the tunnel junctions J1-J6 are formed, and are separated by a thick insulation layer in other regions. Typically, the M2 layer is used to form the base electrodes of the tunnel junctions, while the M3 layer is used to form the counterelectrode of the junctions.

In Fig. 1, breaks in the M2 and M3 conductors are illustrated as B1, B2, ..., B5. B1 is a break in the M2 line, B2 is a break in the M3 line, etc. Thus, the breaks are in alternating lines along the string of junctions J1-J6.

Current can be made to flow in these Josephson junctions in either direction by introducing breaks at selected points in either the M2 or M3 metallization layer. Thus, current will flow in J1 by providing a break in the M2 layer at B1. If there is no break in M2, all current will remain in the M2 layer and, because there is no current flow in any junction, no junction will switch even though a control line associated with any junction is energized. Under such circumstances, the circuit of Fig. 1 will represent a string of binary ""0's'...