JPS62124697A - Superconductive memory device - Google Patents

Abstract

PURPOSE:To simplify writing operation, and to facilitate high integration and to heighten writing speed by holding a specified Abrikosov vortex selectively to a superconductor layer and supplying specified current to a control line. CONSTITUTION:Depending on the direction of current given to a superconductor layer 2 that constitutes an information writing and storing means 1, upward or downward Abrikosov vortex alpha corresponding to '0' or '1' of memory information is held selectively in the superconductor layer 2 of the information writing means 1. When control current Ics is given to a control line 34, and at the same time, bias current Is is supplied to a Josephson junction element, the Josephson junction element 22 becomes either pressure state or zero voltage state corresponding to the direction of the Abrikosov vortex alpha. Thereby, the writing operation is made simple and the margin of writing operation can be widened. As the Abrikosov vortex is shifted to an information reading means side at high speed, writing speed is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a superconducting memory device that stores information in the form of Abrikosov flux quanta in a superconductor.

[Conventional technology]

A device that uses Abrikosov magnetic flux quanta as storage information is
Special Publication No. 6-34194 and Applied Physics Letter
rs, Vol, 39 No, 12 December
1981. pp. 992-993).

FIG. 9 is a schematic perspective view showing one of the conventional examples of the Abrikosov magnetic flux quantum memory device. A thin superconductor film 51 for holding Abrikosov magnetic flux quanta, and a Josephson junction 53 for detecting magnetic flux quantum in which a part of the superconductor film 51 is used as a lower electrode and the superconductor film 52 is used as an upper electrode. , a magnetic flux quantum writing line 54 provided near the end 5 of the superconductor film 51;
The superconductor film 5 surrounding the periphery of the superconductor film 51 except for the edge 55
The superconductor film 51' is thicker than the superconductor film 51'. Note that B conceptually represents the apricot tip magnetic flux quantum held within the superconductor film 51.

This Abrikosov magnetic flux quantum memory device consists of a superconductor film 51
The presence or absence of Abrikosov magnetic flux quanta held within is made to correspond to the memory state rlJ rOJ. That is,
When Abrikosov magnetic flux quanta are retained in the superconductor film 51, the magnetic flux quanta affects the Josephson junction 53 and lowers the dark value current rj in the Josephson junction 53. The change in current ■j is made to correspond to the memory state rlJ rOJ.

Information is read by applying a bias current Ib of an appropriate value to the Josephson junction 53.

That is, when a bias current 1b having a value between the dark value current Tj when the Abrikosov magnetic flux quantum is held in the superconductor film 51 and that when it is not held is applied to the Josephson junction 53, the Abrikosov magnetic flux If the quantum is held, a voltage is generated at the Josephson junction 53 (voltage state G), and if it is not held, the voltage is zero (zero voltage state).

[Problem that the invention seeks to solve]

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

To write the memory state "1", a current is passed in a predetermined direction through the write line 54 to generate a magnetic field, and the end 5 is applied to the superconductor film 51.
5 by internally generating Abrikosov flux quanta in a predetermined direction (for example, upward). on the other hand,
Writing of the memory state rOJ must be performed using different procedures depending on the current memory state. That is, if the memory state before writing is "1", a current in the opposite direction is passed through the write line 54 to transfer downward magnetic flux quanta to the superconductor film 5.
1 and annihilates it with an upward magnetic flux quantum, thereby reducing the Abrikosov magnetic flux quantum number to zero. Also,
If the memory state is "0", the current state is maintained by not passing any current through the write line 54, and substantially rO
Write J.

In this way, in conventional Abrikosov magnetic flux quantum memory devices, it is necessary to read the memory state each time before writing, which unnecessarily lengthens write access time, and when a computer is configured using this memory cell, the machine cycle time There was a problem that it became long.

Furthermore, when writing from a memory state of "1" to "0", it is very difficult to annihilate magnetic flux quanta accurately. If the pair annihilation is insufficient, some upward-oriented Abrikosov magnetic flux quanta will remain, and if the pair annihilation is performed excessively, the downward-oriented Abrikosov magnetic flux quanta will be retained. Therefore, since it is necessary to annihilate Abrikosov magnetic flux quanta in just the right amount, the write operation margin becomes extremely narrow, making stable operation difficult. Another problem is that as write operations are repeated, residual Abrikosov magnetic flux quanta that have failed to completely annihilate gradually accumulate, leading to malfunctions.

[Failure to solve the problem]

The superconducting memory device of the present invention has been made in view of the above problems, and generates a magnetic field by supplying a current corresponding to information, internally generates Abrikosov magnetic flux quanta by this magnetic field, and absorbs the Abrikosov magnetic flux. Information writing and storage means having a superconductor layer that self-retains quanta even when the magnetic field is removed, and sensing the magnetic field created by Abrikosov magnetic flux quanta that are self-retained in the superconductor layer of the information writing and storage means. and information reading means having a magnetic field generating a magnetic field having a component parallel to the magnetic field due to Abrikosov magnetic flux quanta in the Josephson junction element.

[Effect]

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

〔Example〕

Hereinafter, the present invention will be described in detail along with examples.

FIG. 1 is a plan layout showing an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line 1--2. The information writing storage means J generates a magnetic field by being supplied with a predetermined current,
The superconductor layer 2, which internally generates Abrikosov magnetic flux quanta α by this magnetic field and self-retains the Abrikosov magnetic flux quanta even after the magnetic field is removed, is provided as an information writing element and an information storage element. The superconductor layer 2 is formed into a square or rectangle, for example, and when a pair of opposing sides are 3a and 3b, and another pair of opposing sides are 3c and 3d, sides 3a and 3b
Striped superconductor layers 4a and 4b are integrally extended outward from side 3c as current supply terminals. Note that this superconductor layer 2, together with superconductor layers 4a and 4b, is made of a second type of superconductor.

The information reading means 21 includes a Josephson junction element 22 that is sensitive to the Abrikosov magnetic flux quantum self-held by the superconductor layer 2 of the information writing and storage means 1, and a control line that applies a predetermined magnetic field to the Josephson junction element 22. 34 as an information reading element.

The Josephson junction element 22 includes a superconductor layer 32 as a lower electrode and a superconductor layer 26 as an upper electrode.
- It is constructed by interposing a channel barrier layer 25. That is, the superconductor layer 2 of the information writing and storage means 1
A superconductor layer 32 is formed as a lower electrode with an insulating layer 31 interposed therebetween, and an insulating layer 24 with a window 23 formed therein is formed on the superconductor layer 32. A tunnel barrier layer 25 made of, for example, an oxide of the material of the superconductor layer 32 is formed in the facing region, and a window 2 is further formed on the insulating layer 24.
A superconductor layer 26 is formed as an upper electrode so as to cover 3. The control line 34 is made of a striped superconductor layer, and is formed on the superconductor layer 26 via the insulating layer 33 so as to cross above the tunnel barrier layer 25 .

Next, the operation of this embodiment will be explained.

When a current corresponding to the information "1" is caused to flow from the write current terminals 4a to 4b of the information writing/storage means l, the magnetic field corresponding to the information "1", that is, the area on the paper in FIG. A clockwise magnetic field when 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 of the information writing/storage means 1 itself. For this reason, the Abrikosov magnetic flux quantum α corresponding to the information "1" is placed on the side 30 of the superconductor layer 2 of the information writing/storage means 1 in the first direction (upward "↑").
) occurs internally. Then, when the magnetic field continues to be applied, Abrikosov magnetic flux quanta are generated one after another at the 30th side,
The internally generated Abrikosov magnetic flux quanta are pushed toward the information reading means 21 by the repulsive force acting on each other.

Also, at this time, the write current flowing through the superconductor layer 2 of the information writing/storage means 1 in the IA force direction applies a force due to Lorentz interaction to the Abrikosov magnetic flux quantum internally generated at the side 30, and this Since the Abrikosov magnetic flux quanta are quickly moved to the information reading means 21 side, the writing time is very short.

The Abrikosov magnetic flux quantum that has moved toward the information reading means 21 is prevented from moving any further due to the presence of the relatively thick superconductor layer 32 that is the lower electrode of the Josephson junction element 22. In this way, Abrikosov magnetic flux quanta invade the information writing/storage means 1, and once more Abrikosov magnetic flux quanta have invaded, the repulsion between the Abrikosov magnetic flux quanta makes it difficult for the Abrikosov magnetic flux quanta to penetrate, resulting in a state of saturation. becomes. That is, the Abrikosov magnetic flux quantum is on the side 3a
, 3b, 3c, and the region surrounded by the side 3d' of the lower electrode 32 of the Josephson junction element 22 on the side 3d' of the information writing/storage means l side becomes saturated.

When the write current is removed, this Abrikosov magnetic flux quantum is self-retained by the binding force of the superconductor layer 2 (the force that captures the Abrikosov magnetic flux quantum).

Next, when a current corresponding to the information "0" is caused to flow in the IB force direction from the write current terminal 4b to 4a of the information writing/storage means 1, in the superconductor layer 2, a current corresponding to the above-mentioned information rlJ is caused to flow. A magnetic field in the opposite direction to the magnetic field, that is, a counterclockwise magnetic field when viewed from the top of the page in FIG. 2, is generated. Due to this magnetic field, the information "
The Abrikosov magnetic flux quantum corresponding to the information "0" is internally generated in a second direction (downward "↓") opposite to the Abrikosov magnetic flux quantum corresponding to the information "1". This internally generated information rO
The Abrikosov magnetic flux quantum corresponding to J invades in the same way as the above-mentioned upward Abrikosov magnetic flux quantum, combines with the upward Abrikosov magnetic flux quantum corresponding to the already self-held information "1", and annihilates the pair. And furthermore,
As the Abrikosov magnetic flux quantum corresponding to the information "0" enters, only the Abrikosov magnetic flux quantum corresponding to the information "0" finally enters the superconductor layer 2 of the information writing/storage means 1.
remains and is retained. This is the state in which information "0" is held. Even in writing this information "0", the write current flowing in the superconductor layer 2 of the information writing storage means 1 in the IB force direction is due to Lorentz interaction with Abrikosov magnetic flux quanta generated internally at the side 30. A force is applied to quickly move this Abrikosov magnetic flux quantum toward the information reading means 21 side.

Next, information reading L7 will be explained. To detect the storage state, a control current Tcs 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 between the superconductor layer 26 and the tunnel barrier layer. 25 and superconductor layer 32. Figure 3 shows a Josephson junction element 22.
2 is a diagram showing the dark value characteristics of , where the horizontal axis is the control current value flowing through the control line 34, and the vertical axis is the bias current value flowing through the Josephson junction element 22. In the figure, the broken line 7 is the threshold characteristic curve when Abrikosov magnetic flux quanta are not held in the information writing storage means 1, and the solid line 8 is the threshold characteristic curve when Abrikosov magnetic flux quanta corresponding to the "0" state is held. The curve, solid line 9, is a threshold characteristic curve when the Abrikosov flux quantum corresponding to the "1" state is maintained. The reason why the dark value characteristic changes along the horizontal axis depending on the storage state is due to the influence of the magnetic field created by Abrikosov magnetic flux quanta held in the superconductor layer 2 of the information writing/storage means 1.

Now, a bias current Is is applied to the Josephson junction element 22, and a control current 1cs is applied to the control line 34 in the first direction.
By flowing , the operating point can be moved by the position of A. From the figure, if it is in the "0" state, the operating point A is inside the dark value characteristic curve 8, so the Josephson junction element 22 maintains a zero voltage state, and if it is in the "1" state, the operating point A is in the dark. It can be seen that the transition to the voltage-applied state occurs because the value goes outside the value characteristic curve 9. This phenomenon is caused by the fact that when in the "0" state, the magnetic field created by the downward-oriented Abrikosov flux quantum and the magnetic field created by the control current 1cs cancel each other out in the tunnel barrier layer 25, and when in the "1" state, the upward-oriented Abrikosov magnetic flux quantum Magnetic field and control current Ics
This is caused by the mutual application of magnetic fields. Due to this action, the predetermined bias current Is and control current Ic
It is possible to read out whether the memory state is "1" or rOJ by the voltage state of the Josephson junction element 22 when s and s are simultaneously applied.

FIG. 4 is a plan layout diagram showing another embodiment of the present invention,
FIG. 5 is a cross-sectional view taken along line 1--v. In FIGS. 4 and 5, the same or corresponding parts as in FIGS. 1 and 2 are given the same reference numerals.

In this embodiment, the information writing/storage means 1 consists of two regions 2a and 2b in the superconductor layer 2, and these regions are arranged symmetrically with the control line 34 of the information reading means 21 as the center. (It has mirror symmetry with respect to the dashed-dotted line CL in Figure 4).

That is, in the structure of the first embodiment, the superconductor layer 2
A new information writing area 2b is provided by extending the end surface 3d in the direction opposite to 3C. Further, the write current terminals 4a and 4b have the same width as the superconductor layer 2 of the information write/storage means 1. Note that 3cl is the information writing storage area 2 of the lower electrode 32 of the Josephson junction element 22.
The side on the b side is shown.

Writing of information "1" in the device of this embodiment is performed by uniformly passing a write current IA from write current terminals 4a to 4b. This write current IA generates a clockwise magnetic field when viewed from the top of the paper in FIG. That is,
In the information writing storage area 2a, an upward magnetic field is applied, and upward Abrikosov magnetic flux quanta are internally generated and retained.
In the information write storage area 2b, a downward magnetic field is applied, and downward Abrikosov magnetic flux quanta are internally generated and retained.

The magnetic fluxes generated by Abrikosov magnetic flux quanta accumulated in these two information writing areas in mutually different directions interlink with the Josephson junction element 22 in an additive manner. Also, information “
0" can be written by uniformly passing the write current IB from the write current terminals 4b to 4a. This energization generates a magnetic field in the opposite direction to that when writing information "1", 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. be done. The fact that the magnetic flux caused by these apricot magnetic flux quanta additively interlinks with the Josephson junction element 22 is the same as in the case of writing information "1". However, the direction of the magnetic flux in this case is opposite.

In this way, according to the device of this embodiment, since the information writing/storage means 1 is expanded into two regions, the magnetic field due to the apricot tip magnetic flux quantum in the storage state is rlJ rOJ
In either case, the size becomes larger and the detection sensitivity can be further improved. Note that the information reading operation is the same as in the first embodiment, so its explanation will be omitted.

FIG. 6 is a plan layout diagram showing still another embodiment, and FIG. 7 is a cross-sectional view taken along the line 1--2. In FIGS. 6 and 7, the same or equivalent parts as in FIGS. 4 and 5 are given the same reference numerals.

In this embodiment, the widths of the information write storage areas 2a and 2b of the information write storage means 1 in the second embodiment shown in FIGS. 4 and 5 are narrowed in the vicinity of the tunnel barrier layer 25 of the Josephson junction element 22. Furthermore, the tunnel barrier layer 2 is formed in the portion of the superconductor layer 32, which is the lower electrode of the Josephson junction element 22, facing the information writing storage areas 2a and 2b.
This is a narrower version of the 5 neighborhood.

The basic operations of writing and reading information in this device are the same as in the second embodiment. However, as mentioned above, since the penetration of Abrikosov magnetic flux quanta during the write operation is regulated by the superconductor layer 32, in this embodiment where the superconductor layer 32 is constricted near the tunnel barrier layer 25, , Abrikosov magnetic flux quanta are concentrated and stored in the information writing storage areas 2a and 2b surrounded by this constriction. Therefore, the Abrikosov magnetic flux quantum can be saturated with a small write current, making it possible to reduce power consumption and increase speed. Furthermore, since the widths of the information write storage areas 2a and 2b of the information write storage means 1 are narrowed in the vicinity of the tunnel barrier layer 25 of the Josephson junction element 22, the current density increases in this portion. Therefore, the magnetic field generated in the information write storage areas 2a and 2b becomes stronger, and Abrikosov magnetic flux quanta can be internally generated with a low current.

In the above three embodiments, a Josephson junction element having a single tunnel barrier layer 25 as shown in the conceptual diagram of FIG. 8(A) is used, but as shown in FIG. 8(B), The so-called SQUID (S) has two tunnel barrier layers in the
QUID) type may also be used. In the same figure, 26
．． 26' is the upper electrode, 25.25' is the tunnel barrier layer,
32 and 32' are lower electrodes, and when a SQUID type is used, the dark value characteristics can be changed by configuring them so that the magnetic flux (broken line arrow) due to Abrikosov flux quanta crosses the central space.

Furthermore, in the third embodiment, the Josephson junction element 2
Although the information writing storage areas 2a and 2b were regulated by providing a depression in the lower electrode 32 of Example 2, the thickness of the superconductor layer 2 was partially increased so that it had the same shape as the lower electrode 32 of this example. If the lower electrode 32 has such a special shape, the same effect can be obtained.

In addition, in the second and third embodiments, the information write storage areas 2a and 2b are arranged on the same plane at positions equidistant from the Josephson junction element 22, but the information stored in both areas is As long as the magnetic field created by the Abrikosov flux quanta interlinks with the Josephson junction element 22 in an additive manner, they do not need to be equidistant, and may be provided three-dimensionally.

〔Effect of the invention〕

As explained above, according to the superconducting storage device of the present invention,
Depending on the direction of the current applied to the superconductor layer constituting the information writing storage means, an upward or downward Abrikosov magnetic flux quantum is generated in the superconductor layer itself of the information writing storage means, which corresponds to "1" or "0" of the stored information. It selectively retains Abrikosov magnetic flux quanta in the memory state before writing, whether it is retaining an upward Abrikosov magnetic flux quantum or a downward Abrikosov magnetic flux quantum. Then, the data is written until the saturation state is reached, so unlike the conventional Abrikosov flux quantum memory device, which uses the presence or absence of Abrikosov flux quanta as an information element, the stored contents are checked each time when writing, and the magnetic flux quanta are not excessive or insufficient. Exact annihilation is not necessary. Therefore, not only the write operation becomes easy, but also the write operation margin can be widened. Furthermore, there is no malfunction due to the accumulation of residual Abrikosov flux quanta.

Furthermore, since there is no need for a signal line dedicated to information writing, it is easy to achieve high integration, and the writing current moves Abrikosov magnetic flux quanta already generated internally by the Lorentz force to the information reading means at high speed. Writing speed is extremely fast.

[Brief explanation of drawings]

FIG. 1 is a plan layout showing an embodiment of the present invention, FIG. 2 is a sectional view taken along ■--■, and FIG. 3 is a Josephson junction element 22.
FIG. 4 is a plan layout diagram showing another embodiment of the present invention, FIG. 5 is a V-V sectional view thereof, and FIG. 6 is a diagram showing still another embodiment of the present invention. FIG. 7 is a planar layout view, FIG. 7 is a sectional view taken along line 1--2, 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 storage means, 2... Superconductor layer, 2a
. 2b... Information writing storage area, 21... Information reading means, 22... Josephson junction element, 34... Control line.

Claims (3)

[Claims] (1) A superconductor layer that generates a magnetic field when a current corresponding to information is supplied, generates Abrikosov magnetic flux quanta internally by this magnetic field, and self-retains the Abrikosov magnetic flux quanta even when the magnetic field is removed. at least one Josephson junction element that is sensitive to a magnetic field created by Abrikosov magnetic flux quanta self-held in the superconductor layer of the information writing and storing means, and Abrikosov in the Josephson junction element. A superconducting storage device comprising an information reading means having a control line that generates a magnetic field having a component parallel to a magnetic field caused by magnetic flux quanta. (2) The superconducting memory device according to claim 1, wherein the superconductor layer of the information writing/storing means is narrow in the vicinity of the Josephson junction element of the information reading 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 storage means, and the electrode is partially constricted. The superconducting storage device according to item 1.