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Double Flux Quantum Cell Without Bias Line

IP.com Disclosure Number: IPCOM000086357D
Original Publication Date: 1976-Aug-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Anacker, W: AUTHOR [+2]

Abstract

Josephson junction memory cells making use of a single flux quantum or a few flux quanta considered so far all have a bias line carrying a fixed control current I(co), so that the standby state of the cell is in the middle of the overlap region used for information storage. This bias allows the use of control currents which are equal in amplitude but opposite in polarity for writing.

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Double Flux Quantum Cell Without Bias Line

Josephson junction memory cells making use of a single flux quantum or a few flux quanta considered so far all have a bias line carrying a fixed control current I(co), so that the standby state of the cell is in the middle of the overlap region used for information storage. This bias allows the use of control currents which are equal in amplitude but opposite in polarity for writing.

The disadvantage of the bias line is that it needs space and, therefore, increases the cell size. To avoid this, a cell is used in which the overlap region used for information storage is symmetric with respect to the axis I(c) = 0 of the device characteristic. Fig. 1 shows such a characteristic for a two-junction interferometer with: Lambda absolutely = 2 pi LI(m)/ Phi(o) = 2 pi, according to Fig. 2.

The 1- and -1-vortex modes are seen to overlap in the cross-hatched region which is symmetric with respect to the axis I(c) = 0. If the -1 and 1-vortex modes are defined as the two possible states of the device, then the information can be held in the cell without a bias current I(co).

For the cell to operate as desired, it is necessary that it be sufficiently underdamped such that only double flux quantum transitions are possible. That is, if e.g., the cell is in the -1-mode and the vortex mode boundary is traversed to the right, the device switches into the 1-mode, and vice versa. For this type of symmetric operation, the lambda of the cell m...