JPH0334153B2 - - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a superconducting memory circuit that stores at least one piece of information in the form of Abrikosov flux quanta (hereinafter abbreviated as flux quanta) in a superconductor. More specifically, the present invention relates to a superconducting memory circuit in which information is written by causing magnetic flux quanta to enter (or emit) into a superconductor.

[Technical background of the invention and its problems]

The Abrikosov flux quantum memory circuit has been published, for example, in Applied Physics Letters.
Letters) Vol・39No.12December1981.pp.992〜
993, it is known.

FIG. 3 shows one of the conventional examples of the Abrikosov magnetic flux quantum memory circuit. In this example, a superconductor 1 with a thin film thickness for holding magnetic flux quanta, a part of the superconductor 1 as a lower electrode, and a Josephson junction for magnetic flux quantum detection (hereinafter referred to as a detection (abbreviated as junction) 3 and a magnetic flux quantum writing control line 4 provided near the end 5 of the superconductor 1. A is a magnetic flux quantum. In the Abrikosov magnetic flux quantum memory circuit described above, a magnetic field is generated by passing a current through the control line 4, magnetic flux quanta enter the superconductor 1 to write "1", and the control line 4
A current in the opposite direction is applied to the superconductor 1 to cause magnetic flux quanta in the opposite direction to enter the superconductor 1 and annihilate them with the forward direction magnetic flux quanta, thereby writing "0". In addition, the storage state is detected by applying a bias current to the detection junction 3, making use of the fact that the Josephson current value of the detection junction 3 decreases when magnetic flux quanta exist near the detection junction 3, so that the junction reaches a finite voltage. Depends on whether it metastasizes or not.

However, in the Abrikosov magnetic flux quantum memory circuit described above, the weak superconductivity localized in superconductor 1,
That is, when a pin center exists, magnetic flux quanta are captured there. Therefore, when writing "1", the magnetic flux quantum that enters from the end 5 of the superconductor 1 is captured by the pin center and does not reach the vicinity of the detection junction 3. In order to move this magnetic flux quantum to the vicinity of the detection junction 3, a larger current is applied to the "1" write control line 4, and a large amount of magnetic flux quantum enters the superconductor 1.
It must be moved using the repulsive force between magnetic flux quanta of the same polarity. For this reason, the Abrikosov magnetic flux quantum memory circuit has an important drawback in that when writing "1", a writing current that is two orders of magnitude larger than that for other signal levels is required.

Furthermore, when magnetic flux quanta move within the superconductor 1, viscous resistance acts, which limits the moving speed. Therefore, in the method of driving the magnetic flux quanta by the repulsion between the magnetic flux quanta, the driving force is small, so the moving speed is low, and therefore the time required to write "1" becomes long. This has the disadvantage of increasing the "1" write access time.

Furthermore, in the above-mentioned driving method using the repulsive force between the magnetic flux quanta, the force for driving the magnetic flux quanta toward the vicinity of the detection junction is weak, so the magnetic flux quanta and the detection junction do not come sufficiently close to each other. Therefore, the interaction between the magnetic flux quantum and the detection junction is weak, and the detection sensitivity of the magnetic flux quantum of the detection junction during readout is low. As a result, a major drawback was that a large amount of magnetic flux quanta had to be used as information carriers.

[Purpose of the invention]

In order to eliminate these drawbacks, the present invention applies a driving force due to Lorentz interaction to magnetic flux quanta,
This is intended to reduce the write current, shorten the write time, and increase the sensitivity of the detection junction, and will be explained in detail below with reference to the drawings.

[Embodiments of the invention]

FIG. 1 shows a first embodiment of the present invention, in which an information storage area is constructed of a second type superconductor 1 with a thin film thickness into which Abrikosov magnetic flux quanta can penetrate and which can retain the magnetic flux quanta. , a Josephson junction (detection junction) 3 for memory state detection that uses a part of the superconductor 1 as a lower electrode and a part of the superconductor 2 as an upper electrode to detect the magnetic field accompanying the penetrating magnetic flux quantum.
A magnetic flux quantum writing control line 4 made of at least one superconductor is arranged near the end 5 of the superconductor 1, and a magnetic flux quantum drive current is applied to one end of the superconductor 1. superconductor 1
It has a current terminal 6 made of a superconductor for supplying current to the superconductor 1, and the other end of the superconductor 1 except for the end 5 has a thick superconductor film that is difficult for magnetic flux quantum to penetrate compared to the superconductor 1. The structure is such that the body 7 is arranged to prevent magnetic flux quantum emission. A is the magnetic flux quantum, I is the driving current, P
is the driving force.

In this embodiment, writing "1" in the memory circuit operation involves passing a current through the magnetic flux quantum writing control line 4, causing magnetic flux quanta to enter the superconductor 1, and then passing the magnetic flux quantum driving current from the current terminal 6. conductor 1
This is done by causing the magnetic flux quanta to exert a driving force in the direction of the detection junction 3 by Lorentz interaction with the current, and to move the magnetic flux quanta to the vicinity of the detection junction 3. To write "0", a current is passed through the magnetic flux quantum writing control line 4 in the opposite direction to that when writing "1", and magnetic flux quantum in the opposite direction to that when writing "1" enters into the superconductor 1. Furthermore, by flowing a magnetic flux quantum driving current in the opposite direction to that when writing "1" from the current terminal 6, the magnetic flux quantum in the opposite direction is moved to the vicinity of the detection junction 3 by the Lorentz force, and becomes a magnetic flux quantum in the forward direction. This can be done by a method of reducing or eliminating the magnetic flux, or by passing a magnetic flux quantum driving current in the opposite direction to that when writing "1" from the current terminal 6.
"0" by driving forward magnetic flux quanta held in the superconductor 1 from the detection junction 3 toward the end 5 of the superconductor 1 and then expelling them out of the superconductor 1. Write. To read the memory state, a predetermined bias current is applied to the detection junction 3 by utilizing the fact that the Josephson current value of the detection junction 3 decreases when magnetic flux quanta exist near the detection junction 3, and the bias value is set at that bias value. This is determined by whether the junction transitions to a finite voltage. In this example,
The control current value required for writing "1" is the current value that generates the magnetic field necessary to cause the magnetic flux quantum to enter near the edge 5 of the superconductor 1, and this value is different from the "1" write control current in the conventional example. It is less than 1/10 of the value.
After the magnetic flux quantum enters, it is driven to the detection junction 3 by the driving force caused by the current flowing from the current terminal 6. This effect causes oppositely directed magnetic flux quanta to flow through the superconductor 1
The same holds true for the "0" write method in which data is written within the memory and the number is reduced.

In addition, in this embodiment, since the Lorentz driving force acts on the magnetic flux quantum during writing, the moving speed of the magnetic flux quantum is fast, and it takes a long time for the magnetic flux quantum to enter the edge 5 of the superconductor 1 and reach the detection junction 3. The write access time can be significantly reduced.

In addition, in this embodiment, even at the time of reading, by flowing a current from the magnetic flux quantum drive current terminal 6 to the superconductor 1, the retained magnetic flux quantum is detected by the junction 3.
can be gathered near. As a result, the magnetic field of the magnetic flux quantum is effectively applied to the detection junction 3, so that
The detection sensitivity of the detection junction is greatly improved. this is,
This makes it possible to reduce the number of magnetic flux quanta to be held as an information carrier, and is very effective in reducing the size and power consumption of memory cells.

In addition, in FIG. 1, all the current flowing in from the current terminal 6 flows out to the lower left direction of the superconductor 1,
Therefore, it is necessary that the current flows in the opposite direction through the detection junction 3 and does not act as a reverse bias on the maximum Josephson current value. For this purpose, it is necessary to provide a resistance (bias) upstream of the superconductor 2.

FIG. 2 shows a second embodiment of the present invention, in which an information storage area is constructed of a thin second type superconductor 1 that allows Abrikosov magnetic flux quanta to penetrate and retain the magnetic flux quanta, A part of the superconductor 1 is used as a lower electrode, a part of the superconductor 2 is used as an upper electrode,
At least one Josephson junction (detection junction) 3 for memory state detection is configured to detect the magnetic field associated with the intruding magnetic flux quantum, and at least one control line 4 for magnetic flux quantum writing is provided near the end 5 of the superconductor 1. At the other end of the superconductor 1 except for the end 5, a thicker superconductor 7, which is more difficult for magnetic flux quantum to penetrate than the superconductor 1, is disposed for preventing magnetic flux quantum emission. A portion 8 of 7 is arranged such that when a driving force is applied to the flux quantum, a force component is generated such that the flux quantum is driven towards the sensing junction. That is, as shown in FIG. 2, the thin superconductor 1 and the part 8 of the thick superconductor 7 surrounding it are at a predetermined angle (preferably
45°). The memory circuit operation in this embodiment is similar to that in the first embodiment. However, in this embodiment, the magnetic flux quantum driving current is supplied from the superconductor 2 to the superconductor 1 through the detection junction 3. In this case, since the part 8 of the superconductor 7 is arranged so that a component force is applied such that the magnetic flux quantum moves towards the detection junction 3,
Although the current is supplied from the sensing junction 3, the magnetic flux quanta are driven towards the sensing junction 3. According to this embodiment, since the current line for applying Lorentz force is also used as the detection junction bias line, the current supply line is one
I need fewer books. Furthermore, it becomes possible to connect the memory cells in cascade, that is, to connect the detection junctions 3 in cascade, and it becomes possible to easily configure a memory cell matrix. Furthermore, in the first and second embodiments of the present invention, when writing "0", "1"
In the method of writing magnetic flux quanta in the opposite direction to the writing into the superconductor 1 and reducing the pairing, if the number of magnetic flux quanta in the forward direction and the reverse direction do not match, the pairing is not completely eliminated and one of the magnetic fluxes Quantum remains, which causes a decrease in operating margin, but compared to that, when writing "0",
If a method is used in which a magnetic flux quantum drive current is applied in the opposite direction to that when writing "1" and the magnetic flux quanta are ejected from the superconductor 1, the operating margin is reduced because the magnetic flux quanta do not remain inside the superconductor 1. It has the advantage of not having

〔Effect of the invention〕

As explained above, according to the present invention, by driving the magnetic flux quantum with the Lorentz force caused by the current, it is possible to reduce the write current value, shorten the write access time, and further improve the detection sensitivity to retain data in the memory cell. This has the great advantage of reducing the number of magnetic flux quanta that occur, resulting in smaller cells and lower power consumption. Furthermore, if a method of eliminating magnetic flux quanta from a superconductor by a magnetic flux quantum driving force caused by an electric current is used as a "0" writing method, it is possible to prevent a decrease in the operating margin due to incomplete magnetic flux quantum erasure.

[Brief explanation of the drawing]

FIG. 1 is a memory circuit structure diagram of a first embodiment according to the present invention, FIG. 2 is a memory circuit structure diagram of a second embodiment according to the present invention, and FIG. 3 is a memory circuit of a conventional Abrikosov magnetic flux quantum memory circuit. A structural diagram is shown. 1... Superconductor with a thin film that holds magnetic flux quanta, 2... Superconductor, 3... Detection junction, 4... Control line for writing, 5... End of superconductor 1 into which magnetic flux quanta enter , 6... Current terminal for supplying magnetic flux quantum drive current, 7... Thick superconductor for preventing magnetic flux quantum emission, 8... Part of superconductor 7.

Claims (1)

[Scope of Claims] 1. An information storage region is formed of a first superconductor into which Abrikosov magnetic flux quanta can penetrate and in which the magnetic flux quanta can be retained, and the information storage region has means for intruding Abrikosov magnetic flux quanta into the information storage region. , has a storage state detection Josephson junction that detects the magnetic field associated with the magnetic flux quantum, and indicates the state in which the Abrikosov magnetic flux quantum is held in the information storage area and the state in which it is not held as information "1" or "0". When writing and/or reading information, a current is caused to flow through the first superconductor, and the magnetic flux quanta existing within the first superconductor interact with the current. A superconducting memory circuit characterized by exerting a driving force by 2. An information storage region is constituted by a first superconductor into which Abrikosov magnetic flux quanta can enter and in which the magnetic flux quanta can be retained, a part of the first superconductor is used as a lower electrode, and a second superconductor As part of the upper electrode,
At least one Josephson junction for memory state detection is configured to detect the magnetic field associated with the intruding magnetic flux quantum, and at least one third superconductor has an Abrikosov magnetic flux quantum writing control line near the end of the first superconductor. The Abrikosov flux quantum driving current is placed at one end of the first superconductor as the first superconductor.
It has a current terminal configured of a fourth superconductor for supplying the current to the superconductor, and has a current terminal configured of a fourth superconductor to prevent magnetic flux quantum emission at one end of the first superconductor except for one end where magnetic flux quanta are written. The superconducting memory circuit according to claim 1, having a structure in which a fifth superconductor is arranged. 3. In the superconducting memory circuit according to claim 2, instead of supplying the magnetic flux quantum drive current from the current terminal made of the fourth superconductor, a Josephson junction for detection is provided from the second superconductor. 1st through
A flux quantum driving current is supplied to the superconductor, and Abrikosov flux quanta are placed around the thin first superconductor to generate a component force that drives the flux quanta toward the detection junction. The sixth superconductor, which has a thicker film than the first superconductor and which is more difficult to penetrate than a conductor, is arranged so as to form a predetermined angle that is neither parallel nor perpendicular to the Abrikosov magnetic flux quantum writing control line. A superconducting memory circuit featuring: 4. In the superconducting memory circuit according to any one of claims 1 to 3, as a method for erasing Abrikosov magnetic flux quanta held in the first superconductor, a third superconductor A current in the opposite direction to that during writing is passed through the control line for magnetic flux quantum writing, which is made up of A superconducting memory circuit characterized by erasing magnetic flux quanta. 5. In the superconducting memory circuit according to any one of claims 1 to 3, as a method for erasing Abrikosov magnetic flux quanta held in the first superconductor, magnetic flux quanta are removed from the first superconductor. A superconducting memory circuit characterized in that a magnetic flux quantum drive current is caused to flow through a first superconductor so as to exert a driving force in the direction of discharging the superconductor to the outside of the superconductor to perform magnetic flux quantum erasure.