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Superconducting RAM Using Coupled Squids

IP.com Disclosure Number: IPCOM000043129D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 3 page(s) / 36K

Publishing Venue

IBM

Related People

Chi, CC: AUTHOR [+3]

Abstract

This article relates generally to random-access memory (RAM) cells and more particularly to superconducting RAM cells using coupled SQUIDs (Superconducting Quantum Interference Devices). Fig. 1 shows a memory cell 1 which includes a storage loop 2. The latter includes a Josephson junction, J1, and an inductance, L1. A write/sense gate 3, including a pair of Josephson junctions, J2, J3, is inductively coupled to storage loop 2 via inductances L2, L2' and to y-line 4 via inductances L3, L3'. Gate 3 has current applied to it via x'-line 5, and x-line 6 is inductively coupled to storage loop 2 via inductance L1'. By definition, a binary "0" is stored in loop 2 when no flux quantum is stored therein and a binary "1" is stored in loop 2 when one flux quantum is stored therein.

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Superconducting RAM Using Coupled Squids

This article relates generally to random-access memory (RAM) cells and more particularly to superconducting RAM cells using coupled SQUIDs (Superconducting Quantum Interference Devices). Fig. 1 shows a memory cell 1 which includes a storage loop 2. The latter includes a Josephson junction, J1, and an inductance, L1. A write/sense gate 3, including a pair of Josephson junctions, J2, J3, is inductively coupled to storage loop 2 via inductances L2, L2' and to y-line 4 via inductances L3, L3'. Gate 3 has current applied to it via x'-line 5, and x-line 6 is inductively coupled to storage loop 2 via inductance L1'. By definition, a binary "0" is stored in loop 2 when no flux quantum is stored therein and a binary "1" is stored in loop 2 when one flux quantum is stored therein. In order to store exactly one flux quantum in storage loop 2, the requirement for the loop inductance L1 and junction J1 critical current io is 3 <2f io L1/do < 12 where do = 2x10-15 Weber is the flux quantum. Memory cell 1 has a threshold characteristic ig vs. im like that shown in Fig. 2. The stepfunction like drop-off in the threshold characteristic results from the way in which storage loop 2 is screened by gate 3 when current ix and modulation currents iy and ix are applied to memory cell 1. The operation of memory cell 1 when no flux quantum is present in storage loop 2 is as follows: 1. To write a binary "1" into memory cell 1, apply currents ix, ix' and iy to x-line 6, x'-line 5 and y-line 4 simultaneously. The application of currents ix' and iy to gate 3 causes devices J2, J3 to switch and admit a flux quantum into storage loop 2. Fig. 2 shows the manner in which the applied currents cause cell 1 to switch when the threshold curve is crossed. If storage loop 2 already stores one flux quantum, the threshold characteristic of device 1 is changed as shown in Fig. 3 and the application of only a single modulation current, rather than two such currents, is all that is required to cause device 1 to switch. The operation of memory cell 1 when a flux quantum is...