JPH0642315B2 - 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 Desember 1981, pp.992-993).

FIG. 9 is a schematic perspective view showing one of conventional examples of the Abrikosov magnetic flux quantum memory device. A thin superconductor film 51 for holding Abrikosov magnetic flux quanta, and a superconductor film 5
1. A Josephson junction 53 for magnetic flux quantum detection in which a part of 1 is a lower electrode and a superconductor film 52 is an upper electrode; a magnetic flux quantum write line 54 provided near the end 5 of the superconductor layer 51; Superconductor film 51 surrounding the periphery of the conductor film 51 except for the end 55.
And a superconductor film 51 'having a larger film thickness. 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 influences the Josephson junction 53 to lower the threshold current Ij in the Josephson junction 53 is utilized, and the change of 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 ends 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 is made in view of the above problems, and internally generates Abrikosov magnetic flux quanta by applying a magnetic field, and self-holds the Abrikosov magnetic flux quanta even in a state where the magnetic field is removed. Information storage means having first and second superconductor layer areas, and generation of a magnetic field applied to the first and second superconductor layer areas of the information storage means by applying a current corresponding to information Information writing means having a superconducting layer, and at least one or more Josephsons sensitive to a magnetic field created by Abrikosov flux quanta self-held in the first and second superconducting layer regions of the information storing means. Information reading having a junction element and a control line for generating a magnetic field having a component parallel to the magnetic field by the Abrikosov flux quantum in the Josephson junction element In which and means.

[Action]

Depending on the direction of the electric current applied to the superconductor layer forming the information writing means, the first and second superconductor layer regions of the information storage means are directed upward or downward corresponding to the storage state "0" or "1", respectively. The Abrikosov magnetic flux quanta of 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 is in a voltage state or under the influence of the magnetic field created by the Abrikosov flux quantum corresponding to the direction of the Abrikosoff flux quantum. Either of the zero voltage states.

(Example) Hereinafter, the present invention will be described in detail together with 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. The information storage means 1 internally generates the Abrikosov magnetic flux quantum α by applying a magnetic field, and the superconductor storage areas 2a and 2a that self-hold the Abrikosov magnetic flux quantum even after the magnetic field is removed.
b is included as an information storage element. The superconductor layer 2 including the information storage areas 2a and 2b is formed in, for example, a rectangular shape or a rectangular shape, and has a pair of opposite sides each having 3 sides.
a and 3b, and when the other pair of opposing sides are 3c and 3d, the area along the side 3c is the information storage area 2a, and the area along the side 3d is the information storage area 2b. The superconductor layer 2 is made of a second type superconductor.

The information writing means 11 is supplied with a current,
Stripe-shaped superconductor layers 12 and 1 for generating a magnetic field applied to the information storage areas 2a and 2b of the information storage means 1.
3 is included as an information writing element. In this case, the superconductor layers 12 and 13 extend along the sides 3c and 3d of the superconductor layer 2 so as to be juxtaposed with the information storage areas 2a and 2b of the information storage means 1, respectively.

The information reading means 21 is the information storage area 2 of the information storage means 1.
a and 2b have a Josephson junction element 22 sensitive to the Abrikosov magnetic flux quantum self-held and a control line 34 for giving a predetermined magnetic field to the Josephson junction element 22 as information reading elements. Josephson junction element 2
2 is constituted by interposing a tunnel barrier layer 25 between a superconductor layer 32 as a lower electrode and a superconductor layer 26 as an upper electrode. That is, the superconductor layer 32 on the superconductor layer 2 of the information storage means 1 is formed as a lower electrode, the insulating layer 24 having the window 23 formed therein is formed on the superconductor layer 32, and the superconductor 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 of the layer 32 facing the window 23, and a superconductor layer 26 is formed on the insulating layer 24 so as to cover the window 23. It is formed as an electrode. The control line 34 for generating a magnetic field having a component parallel to the magnetic field due to the Abrikosov magnetic flux quantum in the Josephson junction element 22 is composed of a stripe-shaped superconductor layer, and the control line 34 crosses above the tunnel barrier layer 25 so as to cross the superconductor layer. The insulating layer 33 is formed on the insulating layer 26.

Next, the operation of this embodiment will be described.

When the currents IA and IA 'corresponding to the information "1" are passed through the superconductor layers 12 and 13 of the information writing means 11 in the direction indicated by the arrow (first direction), the superconductor layer is correspondingly generated. 1
A magnetic field corresponding to the information "1" is generated from 2 and 13, that is, a counterclockwise magnetic field centered on the superconductor layers 12 and 13 in FIG. 2, and the magnetic field is generated in the information storage area 2a of the information storage means 1 and 2b, respectively. 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 information storage area 2a, and the same information is generated on the side 3d of the information storage area 2b. The Abrikosov magnetic flux quantum α corresponding to “1” is internally generated in the second direction (downward “↓”). And
If you continue to apply the magnetic field, the Abrikosov magnetic flux quanta will become
The Abrikosov magnetic flux quanta that are generated one after the other in the section and the 3d section and are internally generated earlier are pushed toward the information reading means 21 side, that is, toward the central portion by the repulsive force that acts on each other.

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 storage areas 2a and 2b of the information storage means 1 and a certain amount or more of the Abrikosov magnetic flux quanta invade, the Abrikosov magnetic flux quanta will invade due to the repulsive force of each other. Becomes difficult and saturated. That is, the Abrikosov magnetic flux quantum is stored in the information storage area 2a (sides 3a, 3b,
3c and a region surrounded by one end 3d 'of the lower electrode 32 of the Josephson junction element 22) and the information storage area 2b (sides 3a, 3b, 3d and the other end of the lower electrode 32 of the Josephson junction element 22). Both of the regions surrounded by the portion 3c ') are saturated. This Abrikosov flux quantum is self-held by the pinning force of the superconductor layer 2 (the force that captures the Abrikosov flux quantum) when the currents IA and IA 'are removed.

Next, the currents IB and IB ′ corresponding to “0” of the information.
In the superconductor layers 12 and 13 of the information writing means 11,
When the currents IA and IA 'are applied in the second direction opposite to the above, the information "1" from the superconductor layers 12 and 13 is given.
A magnetic field in the direction opposite to the magnetic field corresponding to is generated, and by this magnetic field, the information storage areas 2a and 2b of the information storage means 1 are generated.
In addition, the Abrikosov magnetic flux quantum corresponding to the information “0” is in the opposite direction to the Abrikosov magnetic flux quantum corresponding to the information “1” (downward “↓” in the information storage area 2a and upward “↑” in the information storage area 2b). ) Occurs internally. The Abrikosov magnetic flux quantum corresponding to the internally generated information “0” invades in the same manner as the Abrikosov magnetic flux quantum corresponding to the information “1” described above, and the reverse direction corresponding to the information “1” which is already self-held. Paired with the Abrikosov magnetic flux quantum of. Furthermore, when the Abrikosov magnetic flux quantum corresponding to the information "0" invades, finally only the Abrikosov magnetic flux quantum corresponding to the information "0" remains and is retained in the information storage areas 2a and 2b of the information storage means 1, respectively. To be done. This is the holding state of the information “0”.

Next, reading of information will be described. To detect the memory state, the control current Ics is passed through the superconductor layer 34 of the information reading means 21, and the predetermined bias region 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, where the horizontal axis represents the control current value flowing in the control line 34 and the vertical and horizontal axes represent 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 storage means 1, and a solid line 8 is a threshold characteristic curve when the Abrikosov magnetic flux quantum corresponding to the "0" state is held. A solid line 9 is a threshold characteristic curve when the Abrikosov magnetic flux quantum corresponding to the “1” state is held. In this way, the threshold characteristic changes along the horizontal axis depending on the memory state.
This is due to the influence of the magnetic field created by the Abrikosov magnetic flux quantum held in the superconductor layer 2 of the information storage means 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.
The operating point can be moved to the position A by flowing. From the figure, in the “0” state, the operating point A is inside the threshold characteristic curve 8, so the Josephson junction device 2
It can be seen that the state 2 is maintained in the zero voltage state, and if the state is “1”, the operating point A goes out of the threshold characteristic curve 9, so that the state shifts to the voltage state. This phenomenon is caused by the magnetic field and control current Ic generated by the downward Abrikosov magnetic flux quanta in the information storage area 2a and the upward Abrikosov magnetic flux quanta in the information storage area 2b in the "0" state.
The magnetic field generated by s cancels each other out in the tunnel barrier layer 25, and when in the "1" state, the magnetic field generated by the upward Abrikosov magnetic flux quantum in the information storage area 2a and the downward magnetic field generated by the downward Abrikosov magnetic flux quantum in the information storage area 2b are controlled and controlled, respectively. It is caused by mutual application of the magnetic field of the current Ics. By such an action, it is possible to read out whether the storage state is "1" or "0" depending on the voltage state of the Josephson junction element 22 when a predetermined bias current Is and control current Ics are simultaneously passed. it can.

FIG. 4 is a plan view showing another embodiment of the present invention.
FIG. 5 is a VV sectional view thereof. This embodiment has the same basic structure as that of the first embodiment shown in FIGS. 1 and 2, but includes a lower electrode 32 of the Josephson junction element 22 and a superconductor including the information storage areas 2a and 2b. The insulating film layer 31 is interposed between the layer 2 and the information storage area 2a.
The current supply terminals 4a and 4b are extended along the superconductor layer 12 and the current supply terminals 4c and 4d are extended from the information storage area 2b along the superconductor layer 13. In FIGS. 4 and 5, the same or corresponding parts as those in FIGS. 1 and 2 are designated by the same reference numerals.

The writing of the information "1" in the present embodiment is performed by supplying the currents IA and IA 'and the Lorentz current Ix from the terminals 4b and 4d to the terminals 4a and 4c. As described above, when the current Ix is passed through the information storage areas 2a and 2b of the information storage means 1 in the second direction, the Abrikosov magnetic flux quantum held on the side 3c of the information storage area 2a of the information storage means 1 becomes a current. By the Lorentz interaction with Ix, the force is rapidly moved to the information reading means 21 side, and the Abrikosov magnetic flux quantum held on the side 3d of the information storage area 2b is also the current I.
Due to Lorentz interaction with x, the force is rapidly moved to the information reading means 21 side. Further, in the case of writing the information "0", if a Lorentz current in the direction opposite to the current Ix is passed, the Abrikosov magnetic flux quantum can be quickly moved to the information reading means 21 side by the same action. Therefore, the writing time can be further shortened.
Moreover, since the amount of Abrikosov magnetic flux quantum accumulated can be increased, the detection sensitivity can be increased.

FIG. 6 is a plan layout view showing still another embodiment of the present invention, and FIG. 7 is a VII-VII sectional view thereof.

In this embodiment, the information writing means 11 of the second embodiment shown in FIGS. 4 and 5 is unified as the superconductor layer 14, and the superconductor layer 2 constituting the information storage means 1 is formed. It is arranged on the back side of the via the insulating layer 15.

The writing of the information "1" in this embodiment is achieved by causing a current IC, which is opposite to the currents IA and IA 'of the second embodiment, to flow uniformly in the superconductor layer 14. Current IC
By supplying a magnetic field in the direction indicated by arrow H in FIG. 7, upward Abrikosov magnetic flux quanta are internally generated in the information storage area 2a, and downward Abrikosov magnetic flux quanta are internally generated in the information storage area 2b. To do. At this time, if the Lorentz current Ix is applied to the terminals 4b and 4d as in the second embodiment, the writing time can be shortened and the detection sensitivity can be increased. The writing of the information “0” gives a current ID in the opposite direction to the current IC to the superconductor layer 14, and the Lorentz current Ix.
A Lorentz current Ix 'in the opposite direction to the terminals 4a and 4
It should be given to c. According to this embodiment, the information writing means 1
Since 1 is stacked in the information storage means 1, the cell area can be reduced.

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.

Further, the information storage areas 2a and 2b are arranged at positions equidistant from the Josephson junction element 22, but the magnetic field created by the Abrikosov magnetic flux quanta accumulated in both areas is additive to the Josephson junction element 22. If they are arranged so as to interlink with each other, they need not be equidistant.

〔The invention's effect〕

As described above, according to the superconducting memory device of the present invention,
The stored information "1" is stored in the superconductor layer of the information storage means depending on the direction of the current applied to the superconductor layer forming the information writing means.
Alternatively, it is intended to selectively retain the upward or downward Abrikosov magnetic flux quanta corresponding to "0", and whether to hold the upward Abrikosov magnetic flux quanta or to hold the downward Abrikosov magnetic flux quanta. Since the Abrikosov magnetic flux quanta in the memory state before writing are pair annihilated and then written until the saturation state is reached, it is stored at the time of writing like a conventional Abrikosov magnetic flux quantum memory device that uses the presence or absence of the Abrikosov magnetic flux quanta as information elements. It is not necessary to confirm the contents each time and to make pair annihilation of the magnetic flux quanta accurately without excess or deficiency. 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 the information storage means 1 spreads into two regions, the magnetic field of the Abrikosov magnetic flux quantum in the stored state is large in both cases of "1" and "0", and the detection sensitivity can be further improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a sectional view taken along line II-II, and FIG. 3 is a Josephson junction element 22.
Showing the threshold value characteristic of FIG. 4, FIG. 4 is a plane layout view showing another embodiment of the present invention, its VV sectional view of FIG. 5, and FIG. 6 is a plane showing still 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 storage means, 2 ... Superconductor layer, 2a, 2b ...
... information storage area, 11 ... information writing means, 12, 13,
14 ... Superconductor layer, 21 ... Information reading means, 22 ...
Josephson junction element, 34 ... Control line.

Claims (1)

[Claims] 1. An information storage means having first and second superconductor layer regions which internally generate Abrikosov magnetic flux quanta when a magnetic field is applied and self-hold the Abrikosov magnetic flux quanta even when the magnetic field is removed. An information writing unit having a superconductor layer for generating a magnetic field applied to the first and second superconductor layer regions of the information storage unit when a current corresponding to information is applied. At least one Josephson junction element sensitive to the magnetic field produced by the Abrikosov flux quantum self-held in the first and second superconductor layer regions of the information storage means, and the magnetic field due to the Abrikosov flux quantum in the Josephson junction element And a data reading means having a control line for generating a magnetic field having a component parallel to the superconducting memory device.