JPH067438B2 - Superconducting memory - Google Patents

Description

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

[Conventional technology]

A superconducting information storage device configured by using a superconductor layer as an information storage element that internally generates Abrikosov magnetic flux quanta when a magnetic field is applied and self-holds the Abrikosov magnetic flux quanta even when the magnetic field is removed. As a conventional device, a device as shown in FIGS. 6 and 7 has been proposed (Japanese Utility Model Application No. 60-16159).

In this conventional example, the information storage means 1 internally generates the Abrikosov magnetic flux quanta by applying a magnetic field, and the information storage means 1 stores information in the superconductor layer 2 which self-holds the Abrikosov magnetic flux quanta even after the magnetic field is removed. It has as a memory element.

The Abrikosov magnetic flux quantum is a magnetic flux quantum generated in the second type superconductor, and its explanatory view is shown in FIG.
1 is a superconductor layer of the second kind, 92 is a magnetic flux, 93 is a shield current, and the amount of magnetic flux of Abrikosov magnetic flux quantum is ₀ =
It is 2.07 × 10 ⁻¹⁵ Wb (weber).

Therefore, in FIGS. 6 and 7, the internally generated Abrikosov magnetic flux quantum is schematically represented as ₀ . The superconductor layer 2 has, for example, a rectangular shape or a rectangular shape, and when the pair of opposite sides is 3a and 3b and the opposite 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 them. In practice, this superconductor layer 2 consists of a second type superconductor together with the superconductor layers 4a and 4b.

The information writing unit 11 has, as an information writing element, a stripe-shaped superconductor layer 12 that generates a magnetic field applied to the superconductor layer 2 of the information storage unit 1 described above when a current is applied.

In this case, since the superconductor layer 12 is juxtaposed with the superconductor layer 2 of the information storage means 1, it extends along the side 3c of the superconductor layer 2.

The information reading means 21 is provided as a Josephson junction element 22 which is sensitive to the Abrikosov magnetic flux quantum which the superconductor layer 2 of the above-mentioned information storage means 1 self-holds. In FIGS. 6 and 7, the Josephson junction element uses a single junction gate. In this Josephson junction element 22, a superconductor layer 32 is formed as a lower electrode on the superconductor layer 2 of the information storage means 1 via an insulating layer 31, and a window 23 is formed on the superconductor layer 32. Insulating layer 2
4 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 superconductor layer 32 facing the window 23, and further, on the insulating layer 24,
Through the window 23 and through the tunnel barrier layer 25,
A stripe-shaped superconductor layer 26 facing the superconductor layer 32 is provided as an upper electrode. Further, a stripe-shaped superconductor layer 34 is formed as a control line on the superconductor layer 26 with an insulating layer 33 interposed therebetween. The above is the configuration of the conventionally proposed superconducting memory device.

The conventional superconducting memory device having such a configuration operates as described below.

That is, when the current IA corresponding to the information "1" is passed through the superconductor layer 12 of the information writing means 11 in the first direction, the superconductor layer 12 changes the information "1" accordingly. A corresponding magnetic field is generated. Then, the magnetic field is applied to the superconductor layer 2 of the information storage means 1. Therefore, the Abrikosov magnetic flux quantum ₀ corresponding to the information "1" is internally generated in the first direction (for example, upward) in the superconductor layer 2 of the information storage unit 1.

In this case, the current IC is added to the superconductor layer 2 of the information storage means 1.
From the superconductor layer 4a side to the superconductor layer 4b side,
Flow in the first direction. In this way, the information storage means 1
The magnetic flux quantum ₀ held in the superconductor layer 2 of is subjected to a force by Lorentz interaction with the current IC, and from the side of the superconductor layer 12 of the information writing means 11 to the opposite side (information reading). Promptly move in the direction of the means).

When a current IB corresponding to information "0" is passed through the superconductor layer 12 of the information writing means 11 in the second direction opposite to the above-mentioned current IA, the above-mentioned information is transmitted from the superconductor layer 12. A magnetic field in the opposite direction to the magnetic field corresponding to "1" is generated, and the Abrikosov magnetic flux quantum corresponding to "0" of information is generated in the superconductor layer 2 of the information storage means 1 by this magnetic field. The second opposite to the Abrikosov flux quantum corresponding to "1"
It occurs internally in the direction of (for example, downward). Some of the Abrikosov magnetic flux quanta corresponding to the internally generated information "0" are coupled with the magnetic flux quanta corresponding to the above information "1" and annihilate, and finally correspond to the information "0". Only the magnetic flux quantum remains and is retained in the superconductor layer 2 of the information storage means 1. This is the holding state of the information “0”. In writing this information “0”, a current ID is applied to the superconductor layer 2 of the information storage means 1, and the superconductor layer 4b is supplied from the superconductor layer 4b side.
By flowing in the second direction toward the a side, the magnetic flux quantum can be rapidly moved from the superconductor layer 12 side to the detection junction side by Lorentz interaction as in the case of writing information “1”. it can.

Further, the detection of the memory state is performed by applying a predetermined bias current Is to
The superconducting layer 26, the tunnel barrier layer 25, and the superconductor 32 are caused to flow through the Josephson junction element 22 of the information reading means 21, and the control current Ics is further passed.
It is carried out by flowing it into the superconductor layer 34 of. At this time, among the magnetic fluxes generated by the magnetic flux quanta held in the superconductor layer 2 of the information storage means 1, the magnetic flux interlinking with the Josephson junction element 22 of the information reading means 21 is the magnetic flux generated by the control current Ics. When the Josephson junction element 22 of the information reading means 21 is transferred to the voltage-applied state in the case of addition with the above, it is read that the cell is in the "1" state, while when it is subtracted from the magnetic flux generated by Ics. The Josephson junction element 22 of the information reading means 21 stays in the zero voltage state to read that the cell is in the "0" state.

As the Josephson junction element of the information reading means 21, a superconducting quantum interferometer gate (SQUID) can be used in addition to the above single junction gate.

FIG. 8 shows a configuration example in that case. In FIG. 8, the reference numerals of the respective parts are designated by the same reference numerals in order to correspond to the reference numerals of the superconducting memory device shown in FIGS. 6 and 7. In the case of FIG. 8, the location where the magnetic flux based on the Abrikosov magnetic flux quantum intersects is the insulating layer 81 that constitutes the inductance bridge of the superconducting quantum interferometer gate.

[Problems to be solved by the invention]

However, in the case of the conventional superconducting memory device described with reference to FIGS. 6, 7 and 8, among the Abrikosov magnetic flux quanta written in the superconductor layer 2 of the information storing means 1 at the time of writing information. The number of magnetic flux quanta retained in the superconductor layer 2 of the information storage means 1 is extremely small even if the write magnetic field is removed, and most of them are again emitted from the superconductor layer 2 of the information storage means 1. Will be done. This is because the magnetic flux quanta of the same polarity exert repulsive force on each other, and this repulsive force drives the magnetic flux quanta to the outside of the superconductor layer 2 of the information storage means 1.

The magnetic flux quantum stays in the superconductor layer 2 of the information storage means 1 because the superconductor layer 2 has a force for trapping the magnetic flux quantum, that is, a pinning force. The magnetic flux quantum is emitted to the outside until the pinning force becomes less than the pinning force.
If the pinning force of the superconductor layer 2 is strong, the movement of the magnetic flux quantum is hindered, and the superconductor layer 1 of the information writing means 11 is correspondingly disturbed.
Since the current to be written in the data 2 must be increased, the pinning force of the superconductor layer 2 is made as small as possible. Therefore, the number of magnetic flux quanta held in the superconductor layer 2 at the time of storing information is very small as compared with the written magnetic flux quantum number.

When the number of magnetic flux quanta retained in the superconductor layer 2 during information storage is small, among the magnetic fluxes based on the magnetic flux quanta, the magnetic flux interlinking with the Josephson junction element 22 of the information read-out means 21 is also small, so the magnetic flux. Is difficult to detect, and the operation margin at the time of reading information is reduced.

As described above, in the conventional example, since the number of magnetic flux quanta held in the superconductor layer 2 of the information storage means 1 in the information storage state is small, there is a serious drawback that the operation margin at the time of reading information is small. Was there. In order to secure this operation margin sufficiently wide, the superconductor layer 2 of the information storage means 1 is widened, and the write current supplied to the superconductor layer 12 of the information writing means 11 is increased to increase the information. The number of magnetic flux quanta retained in the superconductor layer 2 of the memory means 1 must be increased, which leads to an increase in power consumption,
The increase in the area occupied by the device causes serious drawbacks such as slow operation speed.

Therefore, the present invention reduces the number of magnetic flux quanta emitted from the superconductor layer of the information storage means and increases the number of retained magnetic flux quanta when the information writing magnetic field is removed after information writing in the above-mentioned conventional example. The present invention is intended to provide a novel superconducting memory device having the above structure.

[Means for solving problems]

The present invention is similar to the superconducting memory device described in FIG. 6 and FIG. 7 or FIG. 8, and when the magnetic field is applied, the Abrikosov magnetic flux quantum invades, and even if the magnetic field is not applied, Information storage means having a superconductor layer that self-holds the magnetic flux quantum of a part, information writing means having a superconductor layer that generates a magnetic field applied to the information storage means, and a superconductor layer of the information storage means. It is provided with a structure having information reading means having a Josephson junction element sensitive to self-held Abrikosov magnetic flux quanta.

However, according to the present invention, in the superconducting memory device having such a structure, further, in the vicinity of the intrusion end of the magnetic flux on the side of the superconductor layer of the information writing means covering the superconductor layer forming the information storing means. Provided is a structure characterized in that a portion of the portion excluding the portion where the magnetic flux penetrates is provided with a superconductor which is less likely to penetrate the magnetic flux than the superconductor layer of the information storage means.

[Action]

In the above-mentioned structure of the present invention, the information storage means is provided on the superconductor layer of the information storage means except the portion where the magnetic flux penetrates in the vicinity of the magnetic flux penetration end of the information writing means on the superconductor layer side. It has the same structure as the conventional example described in FIG. 6 and FIG. 7 or FIG. 8 except that a superconductor layer in which magnetic flux is less likely to enter is provided as compared with the superconductor layer in FIG. Because
Similar to that described above with reference to FIGS. 6 and 7 or 8, it has a function as an information storage device.

However, according to the superconducting memory device of the present invention, when the information writing magnetic field is removed after the information is written, the number of magnetic flux quanta emitted from the superconductor layer of the information storing means can be reduced, and therefore the information is retained. The number of magnetic flux quanta increases, the operation margin of the Josephson junction element of the information reading means at the time of reading information increases, and stable operation becomes possible.
In addition, since the superconductor layer of the information storage means can be narrowed and the current flowing through the superconductor layer of the information writing means can be reduced by the amount of margin in the operation margin, low power consumption can be realized.

〔Example〕

Example 1 Next, a first example of the present invention will be described with reference to FIGS. 1 and 2.

The structure of this embodiment is different from the structure of the conventional superconducting memory device previously described in FIGS. 6 and 7 in the following points,
Everything else is exactly the same. Therefore, in FIGS. 1 and 2, parts corresponding to those in FIGS. 6 and 7 are designated by the same reference numerals.

This embodiment is different from the conventional example in that the magnetic flux in the vicinity of the magnetic flux penetration end on the superconductor layer 12 side of the information writing means 11 penetrates on the superconductor layer 2 of the information storage means 1. The superconductor layer 2 of the information storage means 1 is provided on the other part except for a part.
The superconductor layer 41 is thicker than the
(Represented by a dotted line). The superconductor layer 41 and the superconductor layer 32 forming the lower electrode of the Josephson junction element may be electrically connected,
Alternatively, they may be separated by a thin slit or the like.

According to the first embodiment of the present invention having such a configuration, exactly the same function as the conventional example described above can be obtained except for the operation described in detail below.

That is, in the first embodiment, the action different from that of the conventional example is obtained because most of the vicinity of the magnetic flux penetration end on the superconductor layer 2 of the information storage means 1 is a film so that the magnetic flux is hard to penetrate. Since it is covered with the thick superconductor layer 41, the current flowing in the superconductor layer 12 of the information writing means 11 after writing the information is made zero and applied to the superconductor layer 2 of the information storing means 1. When the magnetic field is removed and the state transits to the information holding state, the superconducting layer 41 blocks the written flux quantum from being emitted outside the superconducting layer 2 of the information storage means 1 again. Most of the magnetic flux quantized is the superconductor layer 2 of the information storage means 1.
Held in.

As described above, in the first embodiment of the present invention, the number of holding magnetic flux quanta significantly increases, so that the influence of the holding magnetic flux quanta on the characteristics of the Josephson junction element 22 of the information reading means 21 at the time of reading information. Appears significantly, so that the operation margin at the time of reading information is greatly expanded. Further, if the configuration of the first embodiment is used, it becomes possible to use a superconductor layer having a smaller pinning force for the superconductor layer 2 of the information storage means 1, so that the magnetic flux quantum by reducing the pinning force is reduced. It is possible to move at high speed, and the time required for writing information can be shortened. As a result, the operation cycle time of the superconducting memory device can be shortened and high speed operation can be realized.

In addition, the information storage means 1 is provided only for the operation margin.
Since the superconductor layer 2 can be formed narrow and the current flowing through the superconductor layer 12 of the information writing means 11 can be reduced, low power consumption can be realized.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. The configuration of the second embodiment is exactly the same as the configuration of the first embodiment shown in FIGS. 1 and 2 except for the following points. Therefore, the reference numerals of the respective portions in FIGS. 3 and 4 are designated by the same reference numerals in the portions corresponding to those in FIGS. 1 and 2 and FIGS. 6 and 7 described above.

That is, the second embodiment is different from the first embodiment in that the film is formed on the superconductor layer 41 that functions to prevent the emission of the magnetic flux quantum from the superconductor layer 2 of the information storage means 1. Instead of using a thick superconducting layer, a superconducting material with a superconducting material having a large lower critical magnetic field Hc ₁ (that is, the value of the minimum applied magnetic field required for the magnetic field to penetrate into the superconductor) is used. Four
1 is configured.

According to the second embodiment of the present invention having such a configuration, the same function as that of the conventional example described above can be obtained, and
By using a superconductor material having a large lower critical magnetic field Hc _{1 for} the superconductor layer 41, which is a structure peculiar to the second embodiment, as in the case of the first embodiment, the magnetic flux quantum has the Since it is prevented from being emitted out of the superconductor layer 2 of the memory means 1, a large number of magnetic flux quanta are retained. Therefore, the operation margin at the time of reading information is greatly expanded.
Further, for exactly the same reason as described in the first embodiment, it is possible to reduce the operation cycle time and reduce the power consumption.

In the first and second embodiments of the present invention, a Josephson junction device having a single junction gate is used as the information reading means, but a superconducting quantum interferometer gate may be used instead of this. The effects of the present invention are exactly the same.
FIG. 5 shows a configuration example thereof, and likewise, the reference numerals of the respective parts are unified with those of FIG. 8 and the like, and the corresponding parts are given the same reference numerals, and the superconductor layer 2 of the information storage means 1 is shown. It has a superconductor layer 41 which functions to prevent the emission of magnetic flux quanta from the.

In addition, in the first and second embodiments of the present invention, the insulating layer 31
However, the case where the insulating layer 31 is not provided and the superconductor layer 32 constituting the lower electrode of the Josephson junction element 22 is formed thick enough to prevent the flux quantum from penetrating is described. Also, the effect of the present invention is exactly the same. Further, in the first and second embodiments, the Lorentz current is caused to flow by the current IC and ID at the time of operation, but this is not essential to the present invention.
Even if the Lorentz current is not passed (the Abrikosov magnetic flux quantum is pushed by the write current), the effect of the present invention exists in the same manner.

〔The invention's effect〕

As described above, according to the present invention, since the number of magnetic flux quanta held in the superconductor layer of the information storage means is significantly increased, the operation margin at the time of reading information is expanded and stable operation is possible. Become.

Further, since the superconductor layer of the information storage means can be narrowed and the current flowing through the superconductor layer of the information writing means can be reduced by an amount corresponding to the margin of operation, the power consumption can be reduced.

Furthermore, since a material having a small pinning force can be used for the superconductor layer of the information holding means, the mobility of the magnetic flux quantum can be increased and the operation cycle time can be shortened, which is a great advantage.

[Brief description of drawings]

1 and 2 show a first embodiment of a superconducting memory device according to the present invention.
FIG. 3 is a plan view showing a second embodiment of the superconducting memory device according to the present invention and FIG. 4 is a sectional view showing a second embodiment of the superconducting memory device according to the present invention. 5 is a perspective view showing a case where a superconducting quantum interferometer gate is used as a Josephson junction element of the information reading means in the first and second embodiments, FIGS. 6 and 7 are A plan view and A- of a conventional example of a superconducting memory device, respectively.
FIG. 8 is a cross-sectional view taken along the line A ′, and FIG. 8 is a perspective view of an example in which a superconducting quantum interferometer gate is used as information reading means of a superconducting memory device,
FIG. 9 is an explanatory diagram of the Abrikosov magnetic flux quantum. 1 ... Information storage means 2 ... Superconductor layer of information storage means 3a, 3b, 3c, 3d ... Sides of superconductor layer 4a, 4b ... Stripe-shaped superconductor layer 11 ... Information writing means 12 ... Superconductor layer of information writing means 21 ... Information reading means 22 ... Josephson junction element 23 ... Insulating layer window 24 ... Insulating layer 25 ... Tunnel barrier layer 26 ... Josephson junction element Superconductor layer (upper electrode) 31, 33 ... Insulating layer 32 ... Superconductor layer of Josephson junction element (lower electrode) 34 ... Superconductor layer of control electrode 41 ... Super information storage unit 1 Superconductor layer 51 that acts to prevent the emission of magnetic flux quanta from the conductor layer 51 .... Insulation layer for the inductance bridge of the quantum interferometer gate

Claims (5)

[Claims] 1. An information storage means having a superconductor layer in which Abrikosov magnetic flux quanta penetrate by application of a magnetic field, and which self-holds the Abrikosov magnetic flux quanta even when the magnetic field is removed, and a current corresponding to information. Information writing means having a superconductor layer that generates a magnetic field to be applied to the superconductor layer of the information storage means when energized, and Abrikosov magnetic flux quantum self-held in the superconductor layer of the information storage means. In a superconducting memory device including an information reading unit having a Josephson junction element sensitive to the, in the vicinity of a magnetic flux penetration end of the superconductor layer of the information storing unit on the superconductor layer side of the information writing unit. A superconducting layer characterized by comprising a superconducting layer in which a magnetic flux is less likely to enter than a superconducting layer of the information storage means except for a part where a magnetic flux penetrates.憶 apparatus. 2. The superconducting memory device according to claim 1, wherein the superconductor layer in which magnetic flux is less likely to enter as compared with the superconductor layer of the information storing means is a superconductor layer of the information storing means. A superconducting memory device, characterized in that the superconducting layer is thicker than the conductor layer. 3. The superconducting memory device according to claim 1, wherein the superconductor layer in which magnetic flux is less likely to enter as compared with the superconductor layer of the information storing means is a superconductor layer of the information storing means. A superconducting memory device comprising a superconductor material having a lower critical magnetic field larger than that of the material of the conductor layer. 4. The superconducting memory device according to claim 1, wherein the Abrikosov magnetic flux quantum interlinks with a tunnel barrier layer of a Josephson junction element of the information reading means. A superconducting memory device characterized in that the magnetic flux of is detected. 5. The superconducting memory device according to claim 1, wherein the Josephson junction element of the information reading means is a superconducting quantum interferometer gate, A superconducting memory device characterized in that a magnetic flux of the Abrikosov magnetic flux quantum interlinking with an insulating layer forming an inductance bridge is detected.