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Random Access NDRO Memory Cell

IP.com Disclosure Number: IPCOM000050567D
Original Publication Date: 1982-Nov-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 3 page(s) / 54K

Publishing Venue

IBM

Related People

Rajeevakumar, TV: AUTHOR

Abstract

A ring-shaped junction is combined with an injection gate to provide a Josephson nondestructive readout (NDR0) memory cell. The ring-shaped junction stores the information, while the injection gate is used to sense the information nondestructively with good margins.

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Random Access NDRO Memory Cell

A ring-shaped junction is combined with an injection gate to provide a Josephson nondestructive readout (NDR0) memory cell. The ring-shaped junction stores the information, while the injection gate is used to sense the information nondestructively with good margins.

The ring-shaped junction and its equivalent circuit are shown in Figs. 1A and 1B, respectively. Physically, ring-shaped junction 10 is comprised of two ring- shaped electrodes 12A and 12B, separated by a tunnel barrier 14. An input gate current I(g) enters ring-shaped junction 10 via input 16, and an output is provided from the rectangular junction 18 which projects out from the ring 10, forming a "T" shape. The top electrode 12A of the ring-shaped junction itself contains a junction Q (Fig. 1B). Two control lines 20 and 22 carry control currents I(ci) and I(c2) which are coupled to top electrode 12A.

Fig. 2 shows the memory cell of Figs. 1A and 1B, together with an injection gate 24, that is coupled to the output 18 of ring junction 10, via the resistor R. Injection gate 24 is comprised of the Josephson devices J1 and J2, having critical currents I(o) and 4I(o), respectively. Josephson devices J1 and J2 are in a superconducting loop also including the inductors L(1) and L(2). Current I(s) is applied to the injection gate 24.

A ring-shaped junction can support stationary or moving flux-quanta if L divide Lambda(j) > 2 Pi, where L is the circumference of the ring and Lambda(j) is the Josephson penetration depth. Information can be stored in the ring in the form of one or more flux quanta. In the absence of a bias current, the flux quanta trapped in the ring remain stationary. Under the influence of a bias current, the flux quanta move around the ring with e frequency f = v/L, where v is the speed with which the flux quanta move.

By virtue of the continuity of phase, every time a flux quantum goes around the ring another flux-quantum reaches the output load R. R is made equal to the line impedence of the junction to avoid any reflection.

When the control current I(c1) and I(c2) exceeds I(0Q) the junction Q switches and one or more flux quanta get trapped in the ring junction. Here, I(00) is the maximum zero-voltage current of junction Q. When a gate current I(g) is applied, the trapped quanta move around the ring continuously. The upper limit of I(g) is I(OR), where I(OR) is the maximum zero-voltage current of the ring junction.

Assuming that n flux quanta are stored in the ring,...