Superconducting memory circuit and method of storing information in the same by generating and terminating a persistent current

• US 5,247,475 A
• Filed: 01/04/1993
• Issued: 09/21/1993
• Est. Priority Date: 03/25/1988
• Status: Expired due to Term

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Hasunuma, Masahiko, Takeoka, Akio
• Primary Examiner(s): LANE, JOHN A
• Application Number:
  US08/002,115
• Time in Patent Office: 260 Days
• Field of Search: 365/51, 365/63, 365/160, 365/162, 257/31, 257/34, 257/35, 307/277, 307/306, 307/307
• US Class Current: 365/162
• CPC Class Codes: G11C 11/44 using super-conductive elements, e.g. cryotron

Abstract

A superconducting memory circuit includes a superconducting loop composed of first and second superconducting lines, and bias lines are connected to connection points of the first and second lines. Inductance or critical current values of the first and second lines are different from each other. When a current is supplied to the bias lines, the current is divided and flows in the loop to maintain a magnetic flux thereof at zero. If the current is further increased, a current flowing in one superconducting line reaches the critical current value of itself prior to the other superconducting line, and a larger current flows in the other superconducting line such that a superconducting state is not destroyed. Therefore, a magnetic flux is generated in the loop. If the current of the bias lines is shut-off in this state, a persistent current flows in the loop to maintain the magnetic flux. Thus, "1" can be written. If a current in reverse direction is supplied to the bias lines so as to make the magnetic flux in the loop zero and the current is shut-off in that state, the persistent current does not flow in the loop. Therefore, the magnetic flux disappears, and thus, "0" can be written. The magnetic flux of the loop can be detected by a read line including a Josephson weak-link therein.

Claims

1. A superconducting memory circuit, comprising:

a superconducting loop having first and second superconductivity lines electrically connected to each other at connection points, said first superconductivity line having an electric characteristic value associated with a first critical current and said second superconductivity line having an electric characteristic value associated with a second critical current so that said first superconductivity line reaches the first critical current faster than said second superconductivity line reaches the second critical current;

a first signal line and a first bias line both connected to one of the connection points of said first superconductivity line and said second superconductivity line;

a second signal line and a second bias line both connected to the other one of the connection points of said first superconductivity line and said second superconductivity line;

means for changing a state of the superconducting loop to store information in the superconducting loop, said changing means including

first means for generating a magnetic flux by temporarily supplying a first current to said superconducting loop through each of said first signal line, said first bias line, said second signal line and said second bias line in a first direction so as to establish a persistent current in said superconducting loop, the persistent current generating the magnetic flux whereby the existence of the magnetic flux is indicative of a first state of the superconducting loop, and

second means for stopping generation of the magnetic flux by temporarily supplying a second current smaller than said first current to said superconducting loop through one of a pair of said first and second signal lines and a pair of said first and second bias lines, the second means temporarily supplying the second current in a second direction different from said first direction so as to terminate the persistent current in the superconducting loop and thereby cease generation of the magnetic flux, an absence of the magnetic flux being indicative of a second state of the superconducting loop which differs from that of the first state;

detection means spaced from said superconducting loop for detecting an existence of said magnetic flux in said superconducting loop and for detecting an absence of said magnetic flux in said superconducting loop, whereby detection of the existence of said magnetic flux signifies the first state of the superconducting loop and detection of the absence of said magnetic flux signifies the second state of the superconducting loop and,

a plurality of memory cells each having a respective superconducting loop with respective first signal and bias line and respective second signal and bias lines, a plurality of said respective first and second signal lines being connected such that said memory cells can be connected in series to each other in a row direction, and a plurality of said respective first and second bias lines being connected such that said memory cells can be connected in series to each other in a column direction.

2. A superconducting memory circuit in accordance with claim 1, wherein one of said first and second superconductivity lines having a smaller critical current includes a Josephson weak-link.

3. A superconducting memory circuit in accordance with claim 2, wherein elements in association with critical current of said first and second superconductivity lines are different from each other.

4. A superconducting memory circuit in accordance with claim 2, wherein length of said first and second superconducting lines are different from each other.

5. A method of storing information in a superconducting memory circuit, comprising the steps of:

changing a state of a superconducting loop to store information, the superconducting loop having first and second superconductivity lines electrically connected to each other at connection points, said first superconductivity line having an electric characteristic value associated with a first critical current and said second superconductivity line having an electric characteristic value associated with a second critical current so that said first superconductivity line reaches the first critical current faster than said second superconductivity line reaches the second critical current, the step of changing including the steps of

generating a magnetic flux by temporarily supplying a first current to said superconducting loop through each of a first signal line, a first bias line, a second signal line, and a second bias line in a first direction so as to establish a persistent current in said superconducting loop, the persistent current generating the magnetic flux whereby the existence of the magnetic flux is indicative of a first state of the superconducting loop, said first signal line and said first bias line both being connected to one of the connection points of said first superconductivity line and said second superconductivity line, said second signal line and said second bias line both being connected to the other one of the connection points of said first superconductivity line and second superconductivity line so that a plurality of memory cells each have a respective superconducting loop with respective first signal and bias lines and respective second signal and bias lines, a plurality of said respective first and second signal lines being connected such that said memory cells can be connected in series to each other in a row direction, and a plurality of said respective first and second bias lines being connected such that said memory cells can be connected in series to each other in a column direction, and

stopping generation of the magnetic flux by temporarily supplying a second current smaller that said first current to said superconducting loop through one of a pair of said first and second signal lines and a pair of said first and second bias lines, the second current being temporarily supplied in a second direction different from said first direction so as to terminate the persistent current in the superconducting loop and thereby cease generation of the magnetic flux, an absence of the magnetic flux being indicative of a second state of the superconducting loop which differs from that of the first state; and

detecting an existence of said magnetic flux in said superconducting loop and detecting an absence of said magnetic flux in said superconducting loop, whereby detection of the existence of said magnetic flux signifies the first state of the superconducting loop and detection of the absence of said magnetic flux signifies the second state of the superconducting loop.