JPH0650600B2 - Superconducting memory - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a superconducting memory device for storing information in the superconductor in the form of Abrikosov magnetic flux quanta.

[Conventional technology]

A device that uses Abrikosov flux quanta as memory information is
Applied Physics Let
ters, Vol. 39 No. 12 December 1981, pp. 992 to 998).

FIG. 9 is a schematic perspective view showing one of conventional examples of the Abrikosov magnetic flux quantum memory device. A thin superconductor layer 51 for holding the Abrikosov magnetic flux quantum, and a Josephson junction 53 for magnetic flux quantum detection in which a part of the superconductor film 51 is a lower electrode and the superconductor film 52 is an upper electrode. , A magnetic flux quantum write line 54 provided near the end 55 of the superconductor film 51,
Superconductor film 5 surrounding the periphery of the superconductor film 51 excluding the end 55.
1 and a superconductor film 51 'having a thickness greater than 1. Note that B conceptually represents the Abrikosov magnetic flux quantum retained in the superconductor film 51.

This Abrikosov magnetic flux quantum memory device has a superconductor film 51.
The presence / absence of the Abrikosov magnetic flux quanta held therein is associated with "1" and "0" in the memory state. That is, when the Abrikosov magnetic flux quantum is retained in the superconductor film 51,
The fact that the magnetic flux quantum affects the Josephson junction 53 to lower the threshold current Ij in the Josephson junction 53 is utilized, and the change in the threshold current Ij is made to correspond to “1” and “0” of the memory state. Is there.

Information is read by applying a bias current Ib having an appropriate value to the Josephson junction 53. That is,
A bias current Ib having a value between the threshold current Ij when the Abrikosov magnetic flux quantum is held in the superconductor film 51 and the threshold current Ij when the superconducting film is not held in the Josephson junction 53.
, The voltage is generated in the Josephson junction 53 (voltage state) if the Abrikosov magnetic flux quantum is held,
If it is not held, the voltage becomes zero (zero voltage state).

[Problems to be solved by the invention]

However, this conventional Abrikosov magnetic flux quantum storage device has a very serious problem in writing.

To write the memory state “1”, a current is applied to the write line 54 in a predetermined direction to generate a magnetic field, and the superconductor film 51 has an end 5 at the end 5.
This is achieved by internally generating Abrikosov flux quanta from 5 in a predetermined direction (for example, upward). on the other hand,
Writing of the storage state “0” must be performed using a different procedure depending on the storage state at that time. That is, if the storage state before writing is “1”, a reverse current is applied to the write line 54 to cause downward flux quanta to be generated in the superconductor film 5.
Abrikosov magnetic flux quantum number is made zero by internally generating 1 and annihilating the upward magnetic flux quantum. Also,
If the memory state is "0", no current is passed through the write line 54 to maintain the state as it is, and "0" is written.

As described above, in the conventional Abrikosov magnetic flux quantum storage device, it is necessary to read the storage state each time before writing, and if the access time for writing is unnecessarily lengthened and a computer is configured using this storage cell, the machine cycle time There was a problem that it becomes longer.

In addition, when writing "0" from the memory state "1", it is very difficult to exactly eliminate the pair of magnetic flux quanta. If the pair annihilation is insufficient, a part of the upward Abrikosov magnetic flux quantum remains, and if the pair annihilation is excessively performed, the downward Abrikosov magnetic flux quantum is retained. Therefore, the write operation margin is extremely narrowed due to the necessity of annihilating the Abrikosov magnetic flux quanta without excess or deficiency, and stable operation is difficult. In addition, there is a problem in that residual Abrikosov magnetic flux quanta, which have not been completely pair-annihilated, gradually accumulate during repeated write operations, resulting in malfunction.

[Means for solving problems]

The superconducting memory device of the present invention has been made in view of the above problems, and a magnetic field is generated by supplying a current corresponding to information, and this magnetic field internally generates the Abrikosov magnetic flux quanta. Is sensitive to a magnetic field created by an information writing and storing means having a superconductor layer that retains itself even when the magnetic field is removed, and an Abrikosov magnetic flux quantum self-held in the superconductor layer of the information writing and storing means. It is provided with at least one or more Josephson junction elements and an information reading means for providing a control line for generating a magnetic field having a component parallel to the magnetic field due to the Abrikosov magnetic flux quanta in the Josephson junction elements.

[Action]

Depending on the direction of the current applied to the superconductor layer forming the information writing / storing means, an upward or downward Abrikosov flux quantum corresponding to "0" or "1" of stored information in the superconductor layer of the information writing / storing means. Are selectively retained. Then, when the control current Ics is applied to the control line and the bias current Is is applied to the Josephson junction element, the Josephson junction element becomes either in the voltage state or the zero voltage state depending on the direction of the Abrikosov magnetic flux quantum.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to Examples.

FIG. 1 is a plan layout view showing an embodiment of the present invention, and FIG. 2 is a II-II sectional view thereof. Information writing storage means 1
Generates a magnetic field by being supplied with a predetermined current, internally generates the Abrikosov magnetic flux quantum α by the magnetic field, and the superconducting layer 2 that self-holds the Abrikosov magnetic flux quantum even after the magnetic field is removed. It has an information writing element and an information storage element. The superconductor layer 2 is formed in, for example, a rectangular shape or a rectangular shape. When the pair of opposing sides are 3a and 3bb, respectively, and the other pair of opposing sides are 3c and 3d, respectively, the sides 3a and 3b. Stripe-shaped superconductor layers 4a and 4b are extended outward from the side 3c side integrally with the side 3c as current supply terminals. The superconductor layer 2 is made of a second type superconductor together with the superconductor layers 4a and 4b.

The information reading means 21 includes a Josephson junction element 22 which is sensitive to the Abrikosov magnetic flux quantum self-held by the superconductor layer 2 of the information writing and storing means 1 and a control line which gives a predetermined magnetic field to the Josephson junction element 22. 34 is provided as an information reading element. The Josephson junction element 22 is configured by interposing a tunnel barrier layer 25 between a superconductor layer 32 as a lower electrode and a superconductor layer 26 as the electrode. That is, the superconductor layer 3 is formed on the superconductor layer 2 of the information writing / storage means 1 through the insulating layer 31.
2 is formed as a lower electrode, and the window 2 is formed on the superconductor layer 32.
3 is formed, the insulating layer 24 is formed, and the superconductor layer 32 is formed.
, A tunnel barrier layer 25 made of, for example, an oxide of the material of the superconductor layer 32 is formed in a region facing the window 23, and the superconductor layer 26 serves as an upper electrode on the insulating layer 24 so as to cover the window 23. Has been formed. The control line 34 is composed of a stripe-shaped superconductor layer, and is formed on the superconductor layer 26 via the insulating layer 33 so as to cross over the tunnel barrier layer 25.

Next, the operation of this embodiment will be described.

When a current corresponding to the information "1" is flown from the write current terminals 4a to 4b of the information writing / storage means 1, the magnetic field corresponding to the information "1", that is, the paper surface in FIG. A clockwise magnetic field as viewed from above is generated around the superconductor layer 2 of the information writing / storage means 1 according to Ampere's law. The magnetic field generated at this time is also applied to the superconductor layer 2 itself of the information writing / storage means 1. At this time, the Abrikosov magnetic flux quantum α cannot be generated alone in the superconductor layer 2, and in order for the Abrikosov magnetic flux quantum α to enter the superconductor layer 2, the magnetic field of the superconductor layer 2 must be set. There is no choice but to enter from the peripheral area. Now, due to the current flowing in the IA direction, an upward magnetic field is generated on the left side of FIG. 2, that is, on the side 3c side of the superconductor layer 2, while a downward magnetic field is generated on the right side, that is, the side 3d side. . Therefore, due to the pressure of this magnetic field, an upward magnetic field enters the superconductor layer 2 from the side 3c portion, and a downward magnetic field enters from the side 3d portion. Therefore, the Abrikosov magnetic flux quantum α corresponding to the information “1” is internally generated in the first direction (upward “↑”) on the side 3c of the superconductor layer 2 of the information writing / storage means 1. Then, when the application of the magnetic field is continued, the Abrikosov magnetic flux quanta are generated one after another at the side 3c, and the Abrikosov magnetic flux quanta internally generated earlier are pushed into the information reading means 21 side by the repulsive force acting on each other.

At this time, the write current flowing through the superconductor layer 2 of the information writing / storage means 1 in the IA direction is internally generated at the side 3c and gives a force to the Abrikosov magnetic flux quantum by Lorentz interaction, Since this Abrikosov magnetic flux quantum is quickly moved to the information reading means 21 side, the writing time is very short.

The presence of the relatively thick superconductor layer 32, which is the lower electrode of the Josephson junction element 22, prevents further movement of the Abrikosov magnetic flux quantum that has moved to the information reading means 21 side. In this way, if the Abrikosov magnetic flux quanta intrude into the information writing / storage means 1 and a certain amount or more of the Abrikosov magnetic flux quanta invade, the repulsive force of the Abrikosov magnetic flux quanta makes it difficult to invade them, and the saturated state occurs. Becomes That is, Abrikosov magnetic flux quantum is edge 3
In the region surrounded by a, 3b, 3c and the side 3d 'of the lower electrode 32 of the Josephson junction element 22 on the side of the information writing / storage means 1, a saturation state occurs. The Abrikosov magnetic flux quantum is self-held by the pinning force of the superconductor layer 2 (the force that captures the Abrikosov magnetic flux quantum) when the write current is removed.

Next, when a current corresponding to information "0" is passed in the IB direction from the write current terminals 4b to 4a of the information writing / storage means 1, the above-mentioned information "1" is obtained in the superconductor layer 2. A magnetic field in the direction opposite to the corresponding magnetic field, that is, a counterclockwise magnetic field when viewed from above in the paper of FIG. 2 is generated. Due to this magnetic field, in the superconductor layer 2 itself of the information writing / storage means 1, the Abrikosov magnetic flux quantum corresponding to the information "0" is opposite to the second direction (downward) from the Abrikosov magnetic flux quantum corresponding to the information "1". It occurs internally in "↓"). The Abrikosov magnetic flux quantum corresponding to the internally generated information "0" invades similarly to the above-mentioned upward Abrikosov magnetic flux quantum, and is coupled with the upward Abrikosov magnetic flux quantum corresponding to the information "1" that is already self-held. Then disappears. Furthermore, the Abrikosov magnetic flux quanta corresponding to the information "0" intrudes so that finally only the Abrikosov magnetic flux quanta corresponding to the "0" is stored in the superconductor layer 2 of the information writing and storing means 1.
Remain and are retained. This is the holding state of the information “0”. Even when this information "0" is written, the write current flowing through the superconductor layer 2 of the information writing / storage means 1 in the IB direction is due to Lorentz interaction with the internally generated Abrikosov magnetic flux quantum at the side 3c. A force is applied and the Abrikosov magnetic flux quantum and the information reading means 21 are moved quickly.

Next, reading of information will be described. To detect the storage state, a control current Ics is passed through the superconductor layer 34 of the information reading means 21, and a predetermined bias current Is is applied to the Josephson junction element 22 of the information reading means 21.
6 through the tunnel barrier layer 25 and the superconductor layer 32. FIG. 3 is a diagram showing the threshold characteristics of the Josephson junction element 22, in which the horizontal axis represents the control current value flowing in the control line 34 and the vertical axis represents the bias current value flowing in the Josephson junction element 22. In the figure, a broken line 7 is a threshold characteristic curve when the Abrikosov magnetic flux quantum is not held in the information writing storage means 1, and a solid line 8 is a threshold characteristic when the Abrikosov magnetic flux quantum corresponding to the “0” state is held. curve,
A solid line 9 is a threshold characteristic curve when the Abrikosov magnetic flux quantum corresponding to the “1” state is held. As described above, the threshold characteristic transits along the horizontal axis depending on the storage state because of the influence of the magnetic field created by the Abrikosov magnetic flux quantum held in the superconductor layer 2 of the information writing storage unit 1.

Now, the bias current Is is passed through the Josephson junction element 22, and the control current Ics is applied to the control line 34 in the first direction.
Can be moved to the position of the operating point A. From the figure, in the “0” state, the operating point A is inside the threshold characteristic curve 8, so the Josephson junction device 22
Is maintained at zero voltage, and if it is "1", operating point A
Is output to the outside of the threshold characteristic curve 9, so it can be seen that the voltage shifts to the voltage state. This phenomenon occurs when the magnetic field created by the downward Abrikosov flux quanta and the magnetic field created by the control current Ics cancel each other in the tunnel barrier layer 25 in the "0" state, and when in the "1" state, It is caused by mutual application of the magnetic field and the magnetic field of the control current Ics. By such an action, the predetermined bias current Is and control current Ics
It is possible to read out whether the storage state is "1" or "0" according to the voltage state of the Josephson junction element 22 when and are simultaneously passed.

FIG. 4 is a plan view showing another embodiment of the present invention.
FIG. 5 is a VV sectional view thereof. In FIGS. 4 and 5, the same or corresponding parts as those in FIGS. 1 and 2 are designated by the same reference numerals. In this embodiment, the information writing / storing means 1 has two regions 2a and 2 in the superconductor layer 2.
b, these areas are symmetrically arranged about the control line 34 of the information reading means 21 (mirror-symmetrical with respect to the one-dot chain line CL in FIG. 4). That is, in the structure of the first embodiment, a new information writing area 2b is provided by extending the end surface 3d of the superconductor layer 2 in the direction opposite to 3c. In addition, the write current terminals 4a and 4b are connected to the superconductor layer 2 of the information writing / storing means 1.
It has the same width as. Note that 3c 'indicates the side of the lower electrode 32 of the Josephson junction element 22 on the information write storage area 2b side.

The writing of the information "1" in the device of the present embodiment is performed by uniformly supplying the write current IA from the write current terminals 4a to 4b. This write current IA generates a clockwise magnetic field when viewed from above the paper surface of FIG. That is,
In the information writing storage area 2a, an upward magnetic field is applied to internally generate and hold an upward Abrikosov magnetic flux quantum,
In the information writing storage area 2b, a downward magnetic field is applied and downward Abrikosov magnetic flux quanta are internally generated and held.
The magnetic fluxes due to the Abrikosov magnetic flux quanta accumulated in these two information writing areas in different directions are additively linked to the Josephson junction element 22. When writing the information "0", the write current IB is set to the write current terminal 4b.
To 4a may be uniformly energized. By this energization, a magnetic field in the opposite direction to that at the time of writing the information "1" is generated, and downward Abrikosov magnetic flux quanta are accumulated in the information writing area 2a and upward Abrikosov magnetic flux quanta are accumulated in the information writing storage area 2b. To be done. It is similar to the case of writing the information "1" that the magnetic flux by these Abrikosov magnetic flux quanta interlinks with the Josephson junction element 22. However, the direction of the magnetic flux in this case is opposite.

As described above, according to the apparatus of this embodiment, since the information writing / storing means 1 spreads into two regions, the magnetic field by the Abrikosov magnetic flux quantum in the stored state becomes large in both cases of “1” and “0”. The detection sensitivity can be further improved. The information reading operation is the same as that in the first embodiment, and therefore its explanation is omitted.

FIG. 6 is a plan layout view showing still another embodiment, and FIG. 7 is a VII-VII sectional view thereof. In FIGS. 6 and 7, the same or corresponding parts as those in FIGS. 4 and 5 are designated by the same reference numerals. In this embodiment, the width of the information writing storage areas 2a and 2b of the information writing storage means 1 in the second embodiment shown in FIGS. 4 and 5 is narrowed in the vicinity of the tunnel barrier layer 25 of the Josephson junction element 22. Further, the vicinity of the tunnel barrier layer 25 of the portion of the superconductor layer 32, which is the lower electrode of the Josephson junction element 22, facing the information write storage areas 2a and 2b is narrowed.

The basic operations of writing and reading information in this device are the same as in the second embodiment. However, as described above, the invasion of the Abrikosov magnetic flux quantum in the writing operation is restricted by the superconductor layer 32. Therefore, in the present embodiment in which the superconductor layer 32 is constricted in the vicinity of the tunnel barrier layer 25, Abrikosov magnetic flux quanta are concentrated and accumulated in the information writing storage areas 2a and 2b surrounded by the constricted portion. Therefore, the Abrikosov magnetic flux quantum can be saturated with a small write current, and low power consumption and high speed can be achieved. Further, since the widths of the information writing storage areas 2a and 2b of the information writing storage means 1 are narrowed in the vicinity of the tunnel barrier layer 25 of the Josephson junction element 22, the current density in this portion increases. Therefore, the magnetic field generated in the information writing storage areas 2a and 2b becomes strong, and the Abrikosov magnetic flux quantum can be internally generated with a low current.

Although the Josephson junction element having the single tunnel barrier layer 25 as shown in the conceptual diagram of FIG. 8A is used in the above-mentioned three embodiments, as shown in FIG. A so-called SQUID (SQU) with two tunnel barrier layers
ID) type may be used. In the figure, 26, 2
6'is an upper electrode, 25 and 25 'are tunnel barrier layers, 3
Numerals 2 and 32 'are lower electrodes, and in the case of using the SQUID type, the threshold characteristic can be changed by configuring the magnetic flux (broken line arrow) by the Abrikosov magnetic flux quantum so as to cross the central space.

Also, in the third embodiment, the Josephson junction device 2
Although the information writing storage areas 2a and 2b are regulated by providing the recessed portion in the second lower electrode 32, the superconductor layer 2 is partially thickened so as to have the same shape as the lower electrode 32 of the embodiment. If it is provided, the same effect can be obtained without the lower electrode 32 having such a special shape.

In addition, in the second and third embodiments, the information writing storage areas 2a and 2b are arranged on the same plane at positions equidistant from the Josephson junction element 22, but they are accumulated in both areas. The magnetic fields created by the Abrikosov magnetic flux quanta need not be equidistant, and may be provided three-dimensionally, as long as the magnetic fields created by the Abrikosov magnetic flux quanta are such that the magnetic fields are additively linked to the Josephson junction element 22.

〔The invention's effect〕

As described above, according to the superconducting memory device of the present invention,
An upward or downward Abrikosov flux quantum corresponding to "1" or "0" of stored information in the superconductor layer itself of the information writing / storing means depending on the direction of the current applied to the superconductor layer constituting the information writing / storing means. Is selectively retained.Even if the upward Abrikosov magnetic flux quanta are retained or the downward Abrikosov magnetic flux quanta are retained, the Abrikosov magnetic flux quanta in the memory state before writing are pair-disappeared. Since the data is written until the saturation state is reached, the contents of the magnetic flux are confirmed in each case at the time of writing like a conventional Abrikosov magnetic flux quantum storage device that uses the presence or absence of the Abrikosov magnetic flux quantum as an information element. Exact pair annihilation is not necessary. Therefore, not only the writing operation becomes simple, but also the writing operation margin can be widened. Moreover, there is no malfunction due to accumulation of residual Abrikosov flux quanta.

Furthermore, since a signal line dedicated to information writing is not required, high integration is easy, and the write current moves the Abrikosov magnetic flux quantum already internally generated by the Lorentz force to the information reading means side at high speed. Writing speed is extremely fast.

[Brief description of drawings]

FIG. 1 is a plan layout view showing an embodiment of the present invention, FIG. 2 is a sectional view taken along line II-II thereof, and FIG. 3 is a Josephson junction element 22.
Showing the threshold characteristic of the present invention, FIG. 4 is a plan view showing another embodiment of the present invention, FIG. 5 is a VV sectional view thereof, and FIG. 6 is a plane showing another embodiment of the present invention. FIG. 7 is a layout view, FIG. 7 is a sectional view taken along line VII-VII, FIG. 8 is a perspective view showing the concept of a Josephson junction element, and FIG. 9 is a perspective view showing a conventional Abrikosov magnetic flux quantum memory device. 1 ... Information writing / storing means, 2 ... Superconductor layer, 2a, 2
b ... Information writing storage area, 21 ... Information reading means, 22
...... Josephson junction element, 34 ...... Control line.

Claims (3)

[Claims] 1. A superconductor which generates a magnetic field by supplying a current corresponding to information, internally generates an Abrikosov magnetic flux quantum by the magnetic field, and self-holds the Abrikosov magnetic flux quantum even when the magnetic field is removed. Information writing and storing means having a layer, at least one Josephson junction element and the Josephson junction element sensitive to a magnetic field created by Abrikosov flux quanta self-held in a superconductor layer of the information writing and storing means Information read means having a control line for generating a magnetic field having a component parallel to the magnetic field due to the Abrikosov flux quantum in 2. The superconducting memory device according to claim 1, wherein the superconductor layer of the information writing and storing means is narrowed near the Josephson junction element of the information reading and storing means. 3. At least one electrode of the Josephson junction element of the information reading means is formed so as to be laminated on the superconductor layer of the information writing and storing means, and the electrode is partially constricted. A superconducting memory device according to claim 1.