JPH0754625B2 - Magnetic memory element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a nonvolatile high density solid-state magnetic memory element.

(Prior Art) A solid-state magnetic memory has a high reliability because it has no mechanical drive and is a non-volatile memory. Random access type memory,
It becomes a serial access type memory. The core memory is typical of the former, and the bubble memory is typical of the latter. When aiming for a high-density storage element, the random access type needs to have a detector for each bit, and thus there is a limit to reducing the cell size.
On the other hand, the serial access type is relatively easy to increase the density, but the increase in access time accompanying the increase in density is a serious problem. Further, an element such as a bubble memory that requires movement of a bubble, which is an information carrier, has a drawback that stability of information holding deteriorates with movement. Considering such a situation, it is desirable to realize high density with a random access memory as a solid magnetic memory. First, the basic operation of a random access memory using a magnetic material will be described using a core memory as an example. For the core, a magnetic material whose magnetization curve has a square hysteresis as shown in FIG. 6 is used. Then the material is biased
When H _Y = 0, the remanent magnetization in the + direction shown at the point A or in the − direction shown at the point B can be stabilized, and the device has bistability.
The respective directions can be used in the storage element by associating them with binary numbers "1" and "0".

In a real device, make a ring core with this magnetic material,
Three conductor wires are passed through the core, two of them are stretched vertically and horizontally (referred to as Y-axis and X-axis, respectively), and the core is placed at the intersection of the vertical and horizontal lines. The cores are arranged in a matrix as shown in FIG. 7 and assembled into a memory element. The principle of information storage is shown in FIG. Ring-shaped core 9
The magnetization direction 8 is set to the right along the circumference of the ring-shaped core 9 as shown in FIG. 8A or to the left as shown in FIG. 8B. For example, it is assumed that the magnetizations of all the ring cores are clockwise (-) in the initial state.
Invert the direction of magnetization of the core at the specified address to make it counterclockwise (+). For that purpose, a pulse current is sent to the Y-line and the X-line passing through the core to give a magnetic field to the core. Now, when this magnetic field is given by a pulse current of either X-ray or Y-line, it is insufficient to reverse the magnetization from the-state to the + state.
For example, when the pulse magnetic fields of the Y ₀ − line and the X ₀ − line are applied simultaneously, the reversal of the magnetization of the core at the intersection of both lines occurs, but the pulse magnetic field is applied only to the Y ₀ − line or the X ₀ − line. No magnetization reversal occurs in the core. This is the method of writing the signal "1" at any coordinate of the matrix. In order to read the written information, a pulse for reversing the magnetization from + to − is applied to the X ₀ − line and the Y ₀ − line at the same time, and it is checked whether or not a signal can be generated on the read line 10. If you get a signal, you know that the coordinate that sent the pulse was "1". However, in this method, once read, all become "0", which is so-called destructive read. If you are having trouble with this, you need to rewrite the read results as they were. Thus, the core memory has a problem that the bit cell size is large and it is difficult to increase the density.

Therefore, there is a magnetic memory element in which this principle is applied to a magnetic thin film in order to realize high density memory. The magnetic film is, for example, 19% Fe-81 which is a soft magnetic material having a magnetostriction constant λ = 0.
Using a Ni alloy, a vapor deposition film 11 is formed in a disk shape on the substrate as shown in FIG. The film thickness is about 1000Å. A uniaxial magnetic anisotropy is provided in the film surface by applying a magnetic field during vapor deposition. In the present case, the axis of easy magnetization is set so as to be in the Y-axis direction.

At the time of reversing the magnetization, a magnetic field H _Y X ₀ − line parallel to the easy axis and in the direction opposite to the direction of the magnetization is applied, and at the same time, a magnetic field H _{X is applied} by the Y ₀ − line in a direction perpendicular to the direction, thereby reversing the magnetization by the domain wall motion And the simultaneous rotation mode of the magnetic moment that can reverse the magnetization in a short time of the order of 10 ns is used. On the other hand, in the pattern of the magnetic film to which only H _Y is added, the magnetization reversal tends to occur due to the domain wall movement, but since the reversing time is long, the H width of the short width actually used for writing is high. Inversion does not occur in _Y. That is, the magnetic field that causes the magnetization reversal of the magnetic film pattern only when the magnetic field is applied simultaneously by the X-direction conductor line and the Y-direction conductor line.
H _X and H _Y are created by applying a current to the horizontal and vertical copper ribbons that are in close contact with the vapor deposition film 11.

(Problems to be solved by the invention) However, in this element, the reversed magnetization gradually returns to the original direction and the storage stability of information is not good, and when the magnetic film pattern is miniaturized. However, there is a problem that the detection output becomes small and it becomes difficult to read information.

(Means for Solving Problems) In the present invention, in order to solve these problems, a pattern formed of a superconducting material is introduced, and a diamagnetic current generated in a superconductor ring is utilized to store stored information. Provided is a high-density solid-state magnetic memory device which has improved stability and facilitates reading of stored information by utilizing the superconducting-normal electric transition of a superconductor ring.

That is, according to the present invention, the direction of magnetization in a pattern formed of a ferromagnetic film having a uniaxial easy magnetization direction in the film plane is used as an information unit. In a magnetic memory element in which two conductor lines intersect without contacting each other and are arranged parallel to the surface of the pattern at least in the vicinity of the pattern, the conductor line and the pattern are arranged in the direction of one conductor line. Two superconductor films having different critical currents are arranged above and below the conductor wire so as to surround them, and the superconductor film is surrounded by the superconductor film at a position where the conductor wires intersect. The magnetic storage element is characterized in that the magnetic storage element is formed as a ring of the superconductor so as to wind around the other conductor wire on the other side.

(Embodiment) FIGS. 1 and 3A to 3C show an example of the structure of a unit cell used for this memory element.

FIG. 3 (a) is a view of the basic cell of the element of the present invention seen from above, and FIG. 3 (b) is a cross-sectional view of the basic cell of FIG. FIG. 3 (c) is a sectional view of the basic cell of FIG. 3 (a) cut in the left-right direction.

First, a superconducting layer is formed on a substrate, and this superconducting layer is X-
The linear superconductor wire 3 extending in the axial direction is patterned.
After forming an insulating layer thereon, the conductor wire 1 is patterned and arranged on the superconducting wire 3 extending in the X-direction via the insulating layer so as to ride on the insulating layer. The width of the conductor wire 1 is smaller than that of the superconductor wire 3. After forming an insulating layer again thereon, a soft ferromagnetic film pattern is formed in a predetermined shape through this insulating layer as shown in 7 of FIG. Conductor wire 2Y over it again through the insulating layer
-Axial. A second superconductor layer is formed thereon with an insulating layer interposed. Before forming the second superconductor layer, the laminated insulating layers in the regions indicated by 5 and 5'in FIG. 3 are removed in advance. By doing so,
As shown by 5, 5 ', in the region of the second superconductor layer, which is above the superconductor line 3 and has no conductor lines 1 and 2, there is a direct contact with the superconductor line 3. Processed as if they were in contact. The second superconductor layer is patterned to form the superconductor wire 4. By doing this, the magnetic material is surrounded and Y-
A ring-shaped superconductor whose axial normal is the surface normal of the ring is formed. Since the unit cells shown in FIG. 1 are used as storage elements, they are arranged in a matrix form in FIG. The portion surrounded by the dotted line indicated by A in FIG. 2 is the unit cell of FIG. What is important as the size of the basic cell is that the film thickness of the superconducting film forming the ring is larger than the magnetic flux penetration depth. Considering existing magnetic materials, it is orthogonal to the normal to the superconducting ring surface. It is necessary that the area around the intersection of the inner surface of the ring and the inner wall of the ring be about 0.25 μm ² . If this area becomes smaller, the magnitude of the magnetic field for confining one quantum magnetic flux will be on the order of 10 ⁵ Gauss, and it will be difficult to realize with the magnetic materials that are normally used, so new magnetic materials will be developed. Since there is no direct limitation on the width of the superconductor wire, if the width of the conductor wire can be reduced to 0.3 μm, the size of the basic cell can be reduced to about 0.5 μm × 0.5 μm. The material used for the element of the present invention is a conductor such as gold or aluminum, and a superconductor is Pb-based or Nb-based.
System or the like Ba-Y-Cu-O system ceramics, and SiO ₂ can be used as the insulator. A wide range of materials can be used for the magnetic film as long as it is a soft material. Known techniques can be used for the thin film forming technique. Sputtering or laser vapor deposition can be used for the ceramics, and dry etching using chlorine gas, for example, can be considered for etching.

Writing information will be described. As an initial state, the magnetization direction of the magnetic body is saturated in a predetermined direction. Now, let us say that the direction is a positive direction along the Y-axis direction shown by 8 in FIG. The conductor wire is omitted in FIGS. 4 and 5 below.

The write operation is as follows. A pulse current is simultaneously applied to the conductor wire in the X-axis direction and the conductor wire in the Y-axis direction,
In the magnetic material pattern, the magnetization direction of the magnetic film pattern existing at the position where the X conductor line 1 and the Y conductor line 2 intersect is changed from the Y-axis direction shown in FIG. (B) The Y-axis direction and the negative direction are reversed. When the magnetic flux changes due to this magnetization reversal, the diamagnetic current i flowing through the superconductor ring (maximum value is n × 2B; B is the magnetic flux density that penetrates the ring, and n is the unit vector in the direction normal to the side surface of the ring). Because of the existence of
It is necessary that the current in the superconductor ring partially exceeds the critical current so that the superconductor ring once becomes normal and the diamagnetic current becomes zero. To satisfy this condition, the critical current value of the superconducting material and the magnitude of the magnetization of the magnetic film pattern should be selected appropriately, and the diamagnetic current associated with the magnetization reversal should be sufficient. There is a method in which, when a current exceeding the critical current of the superconductor line is obtained by applying magnetization to the body line and causing magnetization reversal, only a part of the current is responsible for the diamagnetic current accompanying the magnetization reversal. If even a part of the superconductor ring does not exceed the critical current at the time of magnetization reversal, there is a risk that the magnetization once reversed will return to its original direction due to the magnetic field of the diamagnetic current. However, during the magnetization reversal, once the normal conduction state is passed, the diamagnetic current that tries to maintain the original magnetization direction disappears. Furthermore, conveniently, once the reversed magnetization attempts to return to its original orientation, a diamagnetic current in the superconductor ring will now flow to prevent this magnetization reversal. That is, the stability of the written information becomes very good. Note that 1-bit data write time is 10ns when using this method.
Is the order.

The read operation will be described. At the time of reading, as shown in FIG. 5, a DC bias current I is applied to the superconducting ring in the X-axis direction and in the positive direction. Then, a pulse current is applied to the conductor line in the Y-axis direction to add H _X in the in-plane difficult magnetization direction of the magnetic film pattern to temporarily direct the magnetization in the X-axis direction. Then, the stabilized direction of the magnetization is along the Y-axis direction,
A diamagnetic current indicated by i _B in FIG. 5A or 5B flows in the superconductor ring depending on whether the direction is positive or negative. This blocking superconductor ring is formed using two long conductor layers. Then, in order to discriminate between the rightward diamagnetic current and the leftward diamagnetic current, two superconductor layers are formed of materials having different critical currents. In the example of FIG. 5, the superconductor layer 3 is formed of a material having a smaller critical current than the superconductor layer 4. Let the critical currents of the superconductor layers 3 and 4 be I _3C and I _4C , respectively. The operation will be described. The direction of the diamagnetic current and the direction of the bias current when the magnetization of the bit with the magnetization reversed is directed in the X-axis direction by applying a pulse current to the conductor line in the Y-axis direction are the superconductor ring. Among them, the regions in which the critical current is small (the superconducting layer 3 in FIG. 5B) have the same direction. In this state, the bias current value I is set to a value within a predetermined range, and when the magnetization direction of the magnetic material is negative, 1/2 · I + i _B exceeds the critical current I _3C of the superconducting layer 3. , The superconducting layer 3 is changed to normal conduction. Then, the bias current flowing through 3 comes to flow through the superconducting layer 4, and I flows through the superconducting layer 4. If this I is set to be larger than the critical current value I _4C of the superconducting layer 4, the ring becomes normal and a voltage appears across the superconductor ring. On the other hand, if the magnetization is not reversed, only a current of (1/2 · I−i _B ) flows in the superconducting layer 3 at this bias current value, so that the superconducting-normal transition does not occur.
Therefore, no voltage appears across the superconductor ring.
That is, it is possible to discriminate the direction of magnetization in the magnetic film pattern. Summarizing the above, between the critical currents of superconducting layer 3 and 4 is 1/2 · I _4C <I _3C <1/2 · I _4C.
The relationship + i _B must be established. The bias current I is set so as to satisfy I _4C <2I <2I _3C .

(Effects of the Invention) According to the present invention, high-performance high-density storage in which the instability of the magnetization state after the magnetization reaction and the instability of information reading accompanying the improvement of the storage density have both been remarkably improved by the present invention. The prevention can be realized.

[Brief description of drawings]

FIG. 1 is an external view of the basic cell structure of the present invention, FIG. 2 is a view showing an example in which basic cells are arranged in a matrix to form a memory element, and FIGS. 3 (a), (b), ( c) is a detailed structural diagram of the basic cell, FIGS. 4 (a) and 4 (b) are diagrams showing information writing, FIGS. 5 (a) and 5 (b) are diagrams showing information reading, and FIG. 6 is a uniaxial magnet. A magnetization curve diagram of a magnetic material having anisotropy when a magnetic field is applied in the easy magnetization direction, FIG. 7 is a configuration diagram of a core memory, FIG. 8 is a magnetization state diagram of the core, and FIG. 9 is a magnetic film pattern. Basic configuration diagram of the memory used. 1, 2 ... Conductor line, 3, 4 ... Superconductor line, 5, 5 '... Direct junction of superconductor line, 7 ... Magnetic film pattern, 8 ... Magnetization in magnetic film pattern Orientation.

Claims (1)

[Claims] 1. A direction of magnetization in a pattern formed of a ferromagnetic film having a uniaxial easy magnetization direction in the film plane is used as an information unit, and two lines are provided close to the pattern and on both sides or one side thereof. In a magnetic memory element in which the conductor lines intersect without contacting each other and are arranged parallel to the surface of the pattern at least in the vicinity of the pattern, the conductor line and the pattern are surrounded in the direction of one conductor line. Thus, two superconductor films having different critical currents are arranged above and below the conductor wire, and the superconductor film is not surrounded by the superconductor film at the position where the conductor wires intersect. A magnetic memory element, which is formed as a ring of the superconductor so as to wind around the other conductor wire on the other side.