Browse Prior Art Database

Latent Image Josephson Memory

IP.com Disclosure Number: IPCOM000081063D
Original Publication Date: 1974-Mar-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Fang, FF: AUTHOR [+2]

Abstract

A memory array is shown in which a latent image (or information) can be pre-programmed and which retains the stored information permanently. The memory array is based on a superconducting loop in which two Josephson junctions (either tunnel junctions or weak links) are disposed and wherein the two junctions have significantly different critical currents (I(c)). The different critical currents are achieved with tunnel junctions by fabricating them with either different junction sizes or tunnel barrier thicknesses and materials, and with weak links, by adjusting the dimensions or the materials. An array of such loops can be used to store information that can be used as a read-only memory, a file or a look-up table. In addition, if control lines are added, full random access operation can be achieved.

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Latent Image Josephson Memory

A memory array is shown in which a latent image (or information) can be pre-programmed and which retains the stored information permanently. The memory array is based on a superconducting loop in which two Josephson junctions (either tunnel junctions or weak links) are disposed and wherein the two junctions have significantly different critical currents (I(c)). The different critical currents are achieved with tunnel junctions by fabricating them with either different junction sizes or tunnel barrier thicknesses and materials, and with weak links, by adjusting the dimensions or the materials. An array of such loops can be used to store information that can be used as a read-only memory, a file or a look-up table. In addition, if control lines are added, full random access operation can be achieved.

Fig. 1 shows a loop L containing Josephson junctions 1, 2. The relationship between the critical currents of junctions 1, 2 is as follows: I(c1) < I(c2).

When current I(w) is applied, the following relationship obtains:

I(c2) > I(w) > I(c1), and

I(w) over 2 < I(c1) < I(c2).

Under such circumstances, Josephson junction 1 assumes a resistive state resulting in a current in junction 2 only. When current I(w) is terminated, a circulating current of value I(w)/2 circulates in Loop L, as shown by arrow 3 in Fig. 2. This persistent current can always be regenerated due to the asymmetry of the loop. Thus, if all currents are lost as a result of th...