JP2585392B2 - Superconducting storage device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting storage device suitable for a large-capacity, non-volatile storage device that stores information in a superconductor in the form of Abrikosov flux quanta.

[Conventional technology]

An apparatus using Abrikosov flux quantum as stored information is disclosed in, for example, Japanese Patent Publication No. 6-34194. FIG. 14 is a perspective view of a conventional example of an Abrikosov magnetic flux quantum storage device. A superconductor film 41 having a small thickness for holding Abrikosov magnetic flux quantum, a Josephson junction 43 for magnetic flux quantum detection using a part of the superconductor film 41 as a lower electrode and a superconductor film 42 as an upper electrode, A magnetic flux quantum write line 44 provided near the end 45 of the film 41 and an end of the superconductor film 41
The superconducting film 41 ′ is thicker than the superconducting film 41 surrounding the periphery except 45. Α in the figure is a superconductor film
This is a conceptual representation of the Abrikosov flux quantum held in 41.

In such a conventional storage device, the presence or absence of the Abrikosov flux quantum held in the superconductor film 41 is detected by the Josephson junction 43, and the storage state is made to correspond to “0” or “1”. In other words, when the Abrikosov flux quantum is held in the superconductor film 41, the flux quantum becomes
By utilizing the fact that lowering the threshold current I _j in 43, are made to correspond to changes in the threshold current I _j to "0" and "1" of the stored information.

[Problems to be solved by the invention]

The above prior art is based on the abrikosov flux quantum (α in FIG. 14).
Is represented by No consideration has been given to the movement and diffusion of the superconductor film 41 in FIG. 14, and the abrikosov flux quantum α generated at the end 45 of the superconductor film 41 tends to stagnate at the end 45, and the Josephson junction, which is the information reading means, It is difficult to move to 43. For this reason, there has been a problem that the Abrikosov flux quantum α cannot move sufficiently to the information reading means 43, and the presence or absence of the flux quantum cannot be accurately read. Also. At the installation position of the conventional information reading means, the magnetic flux emitted from the Abrikosov magnetic flux quantum cannot be effectively detected from the surface structure of the Josephson junction element. This is because the generation location of the Abrikosov flux quantum is far from the Josephson junction element, so that the magnetic flux density is weak.

Furthermore, the conventional technique cannot store a large amount of data, and it is impossible to increase the capacity of the device.

An object of the present invention is to provide a storage device that enables accurate detection of presence / absence of Abrikosov flux quanta with a Josephson junction element without moving Abrikovsov flux quanta, and eliminates information reading errors. is there.

It is another object of the present invention to provide a storage device which is small and capable of storing a large amount of data.

[Means for Solving the Problems] The above-mentioned object is to make the information writing means a grid-like conductive wire film so that the film thickness is larger than the thickness of the superconductor layer on the superconductor layer which is the information storage means. A lattice-shaped superconductor layer is formed, the information writing means is provided thereon, and an information reading means comprising a Josephson junction is connected to the lattice-shaped conductive layer on the surface opposite to the superconductor film on which the information writing means is provided. This is achieved by installing on the superconductor film corresponding to the center of the lattice of the line.

Further, the object is to form a hole which does not penetrate in the superconductor layer as the information storage means, to install an annular conductive line as the information writing means around the hole, and to set the information reading means to the information writing means. It can also be achieved by disposing the hole on the surface of the superconductor layer opposite to the surface where the hole is located so as to face the position of the hole.

[Action]

The information writing means formed of a grid-like conductive wire can generate an Abrikosov magnetic flux quantum by generating a magnetic field at an arbitrary location defined by a grid of a superconductor layer as an information storage means by energization. The Abrikosov flux quantum is
Since the thickness of the periphery of the superconductor layer is thickened like a lattice, the superconductor layer cannot move and is confined in the lattice wall of the superconductor layer. For this reason, there is no dissipation of the Abrikosov flux quantum due to diffusion. The presence or absence of the Abrikovsov magnetic flux quantum is read by a reading means comprising a Josephson junction attached to a point on the surface of the superconductor layer opposite to the information writing means and corresponding to the lattice center of the lattice-shaped conductive wire. For this reason, it is not necessary to move the Abrikosov flux quantum to the reading means, and the magnetic flux generated from the Abrikosov flux quantum can be effectively detected. By the above operation, it is possible to store a large amount of information in an arbitrary place defined by the lattice of the superconductor layer in accordance with the presence or absence of a large number of Abrikosov flux quanta, and to be able to read out without malfunction. Become. Abrikosov flux quantum can be the size of the minimum unit of magnetic flux, and can be considered to be approximately the same size as the perovskite structure which is considered to be a basic constituent unit of a superconductor. For this reason, it is theoretically possible to reduce one storage element to the size of a molecular level, and a small-sized superconductor storage device having a large storage capacity can be realized. Further, in the present invention, since the Abrikosov magnetic flux quantum is used for the storage means, it is possible to eliminate heat generation from the superconducting device. On the other hand, the Abrikosov flux quantum is not dissipated because it is semi-permanent self-preserved in the superconductor layer unless the superconducting state is destroyed by some external force. Therefore, the stored information does not evaporate with time.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1, 2, and 3. FIG. The information writing means 1 is a lattice-shaped conductive wire film and is composed of at least two or more parallel conductive lines 11 and at least two or more orthogonal conductive lines 12 orthogonal to the conductive lines. The information writing means 1 is provided on the superconductor layer 2 which is the information storage means 4 and on a lattice-shaped superconductor layer 20 which is thicker than the superconductor layer. The information storage means 4 uses, as an information storage element, the superconductor layer 2 which internally generates Abrikosov flux quanta α when a magnetic field is applied and self-preserves the Abrikosov flux quanta even after the magnetic field is eliminated. Have. In the present embodiment, the information reading means 3 is a Josephson junction element which is responsive to the Abrikosov flux quantum held by the superconductor layer 2 of the information storage means 4 by itself. As shown in FIG. 2, the Josephson junction forms a point on the opposite surface of the lattice-like superconducting hole 5 formed on the superconductor layer 2 by the parallel conductive line 11 and the orthogonal conductive line 12 of the information writing means 1. 50 are installed.
The Josephson junction element comprises a parallel conductive wire 11 and an orthogonal conductive wire 12.
At the point 50 on the opposite side of all the grid-like superconducting holes 5 made by In this embodiment, the information reading means 3 is a Josephson junction element having one tunnel barrier layer 62 as shown in the conceptual diagram of FIG. However, as shown in FIG.
It may be a so-called squid (SQUID) type that has one.
In FIGS. 4 and 5, reference numeral 61 denotes an upper electrode, and 63 denotes a lower electrode. When a squid type as shown in FIG. 5 is used, a magnetic flux (solid arrow) 64 by an abrikosov flux quantum crosses the central space. , The threshold characteristic can be changed.

Next, the operation of this embodiment will be described with reference to FIGS. 6, 7, and 8. FIG.

An Abrikosov flux quantum corresponding to information 1 is generated in A of the lattice-shaped superconducting hole 5 in FIG. 6, and the procedure of writing, storing, and reading information will be described. Information "1"
The currents I _W1 , I _W2 , I _W3 , and I _W4 corresponding to the following are written to the grid-shaped conductive wires T ₁ to T ₂ , H ₃ to H ₄ , T ₄ to T ₃ , H
When flow from the ₂ to H _1, the superconductor layer 2 is an information storage means 4
Has the same effect as flowing an annular current around the lattice-shaped superconducting hole A, a magnetic field is generated in A, and the magnetic field is applied to the superconductor layer 2. For this reason, the Abrikosov flux quantum α corresponding to the information “1” is internally generated downward in the lattice-shaped superconducting hole A of the superconductor layer 2. When the current is kept flowing, a large number of Abrikosov flux quanta are generated and accumulated in A. The Abrikosov flux quantum cannot move and diffuse around the A because the superconductor layer 2 ′ around the A is thicker than the superconductor layer 2 of the information storage means 4. Abrikosov flux quantum is superconductor layer 2
Is self-preserved by the pinning force (force for capturing the Abrikosov flux quantum). FIG. 8 is a write characteristic diagram showing a relationship between a threshold transition amount and a write current of the Josephson junction device shown in FIG. 4, in which the horizontal axis represents the write current value and the vertical axis represents the transition amount. As shown in the figure, the transition amount of the threshold is symmetric with respect to the write current at the origin, and shows a steep rising characteristic and a saturation characteristic. The steep rising characteristic is that when the write current is less than a certain value (4I _{W in} FIG. 8) or less, the Abrikosov flux quantum cannot be generated in the superconductor layer of the information storage means 4, but the current value is 4I _W Beyond
A large number of Abrikosov flux quanta are generated based on an internally generated phenomenon. The saturation characteristic is that when a certain amount of Abrikosov flux quanta is generated, the write current is reduced to a certain value (eighth
In the figure, even if it increases to 4I _W ) or more, it occurs because the abrikosov flux quantum is hard to generate due to mutual repulsion of the abrikosov flux quantum.

Here, for example, the threshold value of the writable current for the information “1” is 4I _W , and the non-writable current is 3I _W. Further, the magnitudes of the currents I _W1 , I _W2 , I _W3 and I _W4 in FIG.
Let I _W be all equal. Thus, the currents I _W1 , I _W2 , I _W3 ,
When I _W4 flows at the same time, the write current becomes 4I _W , which is larger than the writable current 3I _W , and the information “1” becomes the abrikosov flux quantum α, which is written only to the lattice superconducting hole A shown in FIG. However, the lattice-like superconducting Hall B, not flow 3I _W or more current is D, also in the magnetic field generated by the current I _W1, I _W3 flowing around the B is generated in the opposite directions, I _W1 , _IW3 write effect is halved. (Similarly, a magnetic field in the opposite direction is generated for D.) For this reason, the lattice superconducting holes B, C, D, and
The Abrikosov flux quantum α does not occur in E and F. Writing of the information “0” is also performed by the write currents I _W1 , I _W2 , I
_{The same} can be done by reversing the directions of _W3 and _IW4 . In the present embodiment, it is possible to generate an abrikosov flux quantum in an arbitrary grid-shaped superconducting wire hole by selectively giving a write current using a grid-shaped conductive wire, and 2 rows and 3 columns That is, it is a 6-bit storage device. For example, if you want to store information "1" in D,
_W2, a current I _W5 from T ₃ in addition to I _W4 to T _4, may be energized a current of I _W6 from T ₆ to T _5. However, the magnitudes of I _W6 and I _W4 are the same as I _W. Thus, a current of 4I _W is around the D flows into the annular, occurs Abrikosov flux quantum α is in the D, are retained. In this manner, selective writing of information becomes possible, and the storage device functions as a 6-bit storage device as described above.

Next, the selective read operation will be described. Reading of information is performed by applying an appropriate bias current _Ib to the Josephson junction element which is the information reading means 3. That is, when applying a bias current I _b having a value between that of the case where Abrikosov flux quantum is not held to a threshold current I _j when it is held in the superconducting-to-layer 2 on Jiyosefuson junction device, the Abrikosov flux quantum If it is held, a voltage is generated in the Josephson junction device (voltage state)
If the voltage is not held, the voltage becomes zero (zero voltage state). Therefore, it is sufficient to determine the stored information ▼ 0０ and １1 ▼ in accordance with the change in the voltage. In the present embodiment, a Josephson junction element, which is the reading means 3, is attached to all the lattice superconducting holes, so that information can be read at an arbitrary place. In the Josephson junction device of the present embodiment, as shown in FIG.
Although the structure is sandwiched by 63, the upper or lower electrode may be replaced by the superconductor layer 2 so as to sandwich the tunnel barrier layer 62.

9 and 10 show a second embodiment of the present invention. This embodiment is characterized in that the superconducting storage device of the first embodiment is laminated after being separated by an insulating layer 7 shown in FIG. In this embodiment, by stacking the storage devices, the storage capacity per unit installation area can be easily increased. Fabrication can be easily performed by inserting the insulating layer 7. This insulating layer 7
Functions to prevent a short-circuit accident due to contact between the conductive wires of the storage device above and below the insulating layer and to prevent mutual interference of magnetic fields generated from both devices.

FIGS. 11, 12, and 13 show a third embodiment of the present invention. As shown in FIG. 11, a hole 8 is provided in the superconductor layer 2 which is the information storage means 4, and the hole 8 does not penetrate the superconductor layer 2. Information writing means 1
An annular conductive line 13 is provided around the hole 8, and the information reading means 3 is provided on the superconductor layer surface opposite to the surface where the hole 8 exists.
As the information reading means 3, the Josephson junction element described in the first embodiment is used. Writing of information is performed by energizing the annular conductive line 13 as the information writing means 1 and using a magnetic field generated by the energization. The location (position) where information is written can be easily selected by selecting the ring-shaped conductive line 13 to be energized. In the present embodiment, the eleventh
As shown in the figure, a matrix of 2 rows and 3 columns is provided, and 6 bits (2
× 3) information can be stored. Specifically, by selecting the annular conductive wire 13 to be energized, the superconductor layer 2
It is possible to store information at an arbitrary hole 8, that is, at a position. The mechanism of writing, erasing and reading of information is the same as that of the first embodiment. 6 to determine the presence or absence of the Abrikosov flux quantum, and the information ▼ 0 ▼, ▼ 1 ▼
Read as In this embodiment, it is possible to secure a storage capacity corresponding to the number of holes provided in the superconductor layer. It is easy to form holes in the superconductor layer with the current technology, and in this embodiment, it is necessary to pass current through predetermined four orthogonal conductive wires at the same time as in the first embodiment when storing information. Since there is no control circuit, the control circuit for writing information can be simplified. For the above reasons, in this embodiment, a large-capacity superconducting storage device can be manufactured at low cost.

〔The invention's effect〕

According to the present invention, information can be stored in an arbitrary place of the superconductor layer as the information storage means by the information writing means with or without the Abrikosov flux quantum, and the Abrikosov flux quantum can be stored by the Josephson junction element as the reading means. Can be accurately read. For this reason, a large-capacity storage device becomes possible, and in order to use Abrikosov magnetic flux quantum as a storage means, not only it is possible to eliminate heat generation from the device, but also when the power supply is cut off as in a conventional RAM, There is no problem such as volatilization of information.

In addition, this storage device is small in size and large in capacity because it is possible to make the size of a 1-bit storage element in principle approximately the same as the perovskite structure which is the minimum structural unit of the superconductor layer. A storage device becomes possible.

[Brief description of the drawings]

FIG. 1 is a front view of a first embodiment of the present invention, and FIG.
FIG. 3 is a sectional view taken along line II-II of FIG. 3, FIG. 3 is a sectional view taken along line III-III of FIG.
4 and 5 are conceptual diagrams of a specific example of the information reading means in the present invention, FIGS. 6 to 8 are explanatory views of the operation of the first embodiment of the present invention, and FIG. FIG. 7 is a sectional view taken along the line VI-VI of FIG. 6, FIG. 8 is a view showing a change amount of a threshold characteristic of the information storage means in the first embodiment, and FIG. 9 is a view of a second embodiment of the present invention. FIG. 10 is a front view of the third embodiment of the present invention, FIG. 12 is a cross-sectional view taken along line XII-XII of FIG. 11, and FIG. Is XIII-XIII in FIG.
FIG. 14 is a cross-sectional view illustrating a conventional example. DESCRIPTION OF SYMBOLS 1 ... Information writing means, 2 ... Superconductor layer, 3 ... Information reading means, 4 ... Information storage means, 5 ... Lattice-shaped superconducting hole, 11 ... Parallel conductive line, 12 ... Orthogonal conductive line, 17
.... Insulating layer.

Continuing from the front page (72) Inventor Masamichi Ito 502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi, Ltd. Inventor Yuzo Yamaguchi 502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref., Hitachi, Ltd.Mechanical Research Laboratory Co., Ltd. (72) Inventor Kazuhiro Umekita 502-Kindachi-cho, Tsuchiura-City, Ibaraki Pref.

Claims (4)

(57) [Claims] 1. An information storage device having a superconductor layer, an information writing device, and an information reading device, wherein the information writing device includes two or more parallel conductive lines, and two or more parallel conductive lines orthogonal to the parallel conductive lines. It is composed of a lattice conductive film composed of at least two orthogonal conductive lines, and a lattice superconductor layer is formed on the superconductor layer of the information storage means so as to be thicker than the superconductor layer. Installing the information writing means thereon, and installing at least one or more information reading means on the superconductor layer of the information storage means on a surface opposite to the surface on which the information writing means is installed. A superconducting storage device, comprising: 2. An information storage device having a superconductor layer, an information writing device, and an information reading device, wherein a hole that does not penetrate through the superconductor layer of the information storage device is formed, and a ring is formed so as to surround the hole. Wherein the conductive wire is provided as information writing means, and the information reading means is provided on the surface of the superconductor layer opposite to the surface on which the information writing means is provided. apparatus 3. A superconductor which performs an information storage function is provided with a conductor which performs an information writing function capable of generating a magnetic field at an arbitrary position on one surface of a superconductor which performs an information storage function, and reads information on another surface of the superconductor. Superconducting storage device characterized by a storage element provided with a Josephson junction element that operates 4. A conductor for performing an information writing operation capable of generating a magnetic field at an arbitrary place is provided on one surface of a superconductor which performs an information storage operation, and information is read on another surface of the superconductor. A superconducting storage device, comprising: a storage element provided with a Josephson junction element performing an operation, wherein a plurality of the storage elements are stacked via an insulator.