JPH01316978A - Ceramic superconductive memory element - Google Patents

Abstract

PURPOSE:To make a control energy small so as to enable the write-in and readout at a high speed by a method wherein a superconductive loop formed of a ceramic superconductor that has granules which are partially very susceptible to the effect of a magnetic field and a control conductor wire near to the loop are provided. CONSTITUTION:When a current of 4mA is made to flow through a superconductor wire section through the intermediary of electrode terminals a-b under a such a condition that it is cooled at a liquid nitrogen temperature, a current of 2mA half the current of 4mA flows through wires 1 and 2 respectively. Next, when a current of 10mA is made to flow through a conductor wire 3, a magnetic field of 0.4 gauss or so is applied onto the ceramic superconductor wire 1 separate from the wire 3 by a space of 50mum, which is brought into a normal conductive state and becomes electrically resistive, so that a current flows only through the superconductor wire 2. In this state, when a power source connected between the conductor wire 3 and the electrode terminals a-b of the superconductor wires is turned off, a permanent current of 4mA or so flows through a superconductive wire loop, so that a memory element retaining a magnetic flux inside the superconductive wire loop is brought into a write-in state.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a memory element for controlling the current of a superconducting loop having a conductor wire at least partially made of a ceramic superconductor.

<Prior Art> Conventionally, Josephson elements have been used in memory devices that utilize the characteristics of superconductivity. The presence or absence of magnetic flux quanta (fluxoid) passing through the loop connecting the Josephson elements was made to correspond to the memory states of "1" and "0".

However, the Joself non-element used in conventional superconducting memory devices has a structure in which a very thin insulating film is interposed between superconductors made of niobium, lead, or alloys thereof.

<Problems to be solved by the invention> In the above-mentioned Josephson element, there are several tens of intervening insulating films that allow superconducting electrons to pass through through the tunnel effect, and furthermore, the output level is low and it cannot be used unless it is at an extremely low temperature. This hindered its practical application.

It is an object of the present invention to solve the above-described problems of the Josephson element memory element, and to provide a superconducting memory element that has fewer problems in manufacturing, has excellent operating characteristics, and is easy to handle.

<Means for solving the problems> The superconducting memory element of the present invention which achieves the above object The superconducting state of a ceramic superconductor consisting of loops and grain boundaries is controlled by a magnetic field generated by a current flowing through a control conductor wire provided nearby.

In the superconducting memory element having the above configuration, a power source and a lead wire section for signal detection are provided at positions sandwiching the superconducting section having the grain boundaries, and a magnetic field due to the current of the conductor wire provided close to the ceramic superconducting section is provided. This constitutes a superconducting memory device that performs writing by accumulating magnetic flux in the superconducting loop, and reading and erasing by releasing the magnetic flux.

<Effect> Due to the state of its grain boundaries, the superconducting state of ceramic superconductors is broken by the application of a weak magnetic field.
It is stated that it was published in 1988. The present invention has the above characteristics,
It is applied to the switch section of a superconducting loop that operates as a memory element.

An example of the characteristics of a magnetoresistive element made of a ceramic superconductor having the above grain boundaries is shown in FIG.

This means that when no magnetic field is applied, the electrical resistance is completely zero, and when a magnetic field is applied and its strength is increased, a critical magnetic field is generated, and when the applied magnetic field is further increased, the electrical resistance rapidly increases. It shows.

Unlike conventional superconductors, the ceramic superconductor described above uses an extremely weak magnetic field (several Gauss), which allows superconducting storage devices to perform write, read, and erase operations at extremely high speeds unique to superconductors. .

<Example> Hereinafter, the present invention will be described in detail with reference to the drawings.

The ceramic superconductor produced in this example was produced using the spray pyrolysis film forming apparatus shown in FIG. Raw material y (NO3) s
@6H20, Ba (NO3)2 and Cu (NO3)
2@3H20 was weighed so as to have the elemental composition ratio of YIBa2Cua 07-X, made into an aqueous solution, and sprayed intermittently from the sprayer 6 to a film thickness of about 5 μm.
Annealing was performed in air at 50°C for 60 minutes and at 500°C for 10 hours. The resistance of the fabricated superconductor film began to decrease at 100K and reached completely zero resistance at 83K.

Next, the ceramic superconductor film was subjected to a conventional photolithography process and molded using a phosphoric acid-based etching solution in order to form the loop portion of the superconducting memory element shown in FIG. The molded superconductor loop is composed of a superconductor wire 1 that is subjected to the action of a magnetic field and a superconductor wire 2 that is not affected by the magnetic field.

Further, electrode terminals a and b, and a conductor wire 3 that generates a control magnetic field.
was produced by a lift-off method of a vacuum-deposited Ti film. The produced ceramic superconductor has weak junctions at the grain boundaries of its constituent particles, and isometrically it becomes an aggregation of a large number of Josephson junctions 121° 121, etc., as shown in Figure 8. It's considered fu. By applying a weak magnetic field, this ceramic superconductor has its Josephson junction 121, 121...
・The superconducting state is broken and the electrical resistance increases rapidly.

In the configuration shown in FIG. 1, the distance between the centers of the conductor wire 3 and the superconductor wire I was 50 μm, and the line widths of each were SO μm and 50 μm. The superconducting loop was approximately square with one side of about 00 μm. When a current of IOmA was passed through the conductor wire 3, a magnetic field of 04 Gauss was applied to the superconductor wire 1, and at this time, when a current of 2mA was passed through the superconductor wire I, a resistance of IOmΩ was generated. FIG. 2 shows the measured characteristics of wire 1 as a superconducting magnetoresistive element. From this figure, it can be seen that the characteristics of the superconducting wire 1 as a magnetoresistive element can be controlled by controlling the current flowing through the superconducting wire 1.

When the superconducting memory element having the configuration shown in Fig. 1 is cooled to a liquid nitrogen temperature of 77 K, and a current of 4 mA is passed through the superconducting wire portion through electrode terminals a and b, half of the current is applied to the 1st and 2nd wires. The current flows at 2 mA each, resulting in the state shown in Fig. 3(a). Next, when a current of IOmA is passed through the conductor wire 3, a magnetic field of about 0.4 Gauss is applied to the ceramic superconductor wire 1, which is 50 μm away, and it becomes a normal conductor and has electrical resistance, so the current When the power was turned off, a persistent current of approximately 4 mA flowed through the superconducting wire loop, maintaining magnetic flux within the loop, as shown in Figure 3(c), and the memory element became in a "writing" state.

The reason why this persistent current flowed is that the time for the superconducting wire to recover to the superconducting state is faster than the time for superconducting electrons to flow through the superconducting loop, and the impedance that determines the flow of superconducting electrons It is possible that the inside becomes smaller.

The memory of the superconducting loop that has been written to is retained by persistent current.

To read the memory element written in the above manner, a current is caused to flow in the direction of the electrode a in the opposite direction to the writing to the superconducting loop, and the current in the superconducting wire 1 portion is made to be equal to or higher than the critical current Ic, or the conductor wire 3 A destructive readout method was used in which a current was applied to the superconducting wire 1 to apply a magnetic field greater than the critical magnetic field HC, and a pulse voltage generated at the transition when the persistent current disappeared due to resistance was used.

Note that when changing from the written state to the erased state, the superconductor wire 1 may be made to have resistance by the method described above.

The present invention described above is not limited to the method of the above embodiments, and the superconductor wires 1 and 2 are sputtered.

It may be formed using a ceramic superconducting thin film using K such as MOCVD or electron beam evaporation, and in this case, Ic and Hc can be lowered by miniaturizing the processed shape. Further, the superconducting wires 1 and 2 may be manufactured in separate steps, and by adjusting the width of the wires, the superconductors 1 and 2 and the conductor wire 3 can also be formed from the same superconducting film.

As shown in Fig. 4, the superconductor wire 1 is made constricted in a part to increase the current density in that part, and the magnetic field conductor wire 3 is
As shown in the figure, the element area may be reduced through the inside of the loop, or as shown in (b) and (C), the generated magnetic field may be efficiently applied; The part where the superconducting wire 1 or 2 and the conductor wire 3 are layered is made of inorganic material such as 5i02, or
An organic insulating film such as polyimide resin was interposed. Also,
The superconducting conductor wire constituting the superconducting loop does not need to be a ceramic superconductor with grain boundaries and high magnetic sensitivity, except for the part controlled by the magnetic field of the conductor wire, and it is not necessary to use other superconductors or a ceramic superconductor with weak grain boundaries. It is possible to use a superconducting layer with a high Hc or a stack of such layers.Furthermore, by shortening the superconductor portion controlled by the magnetic field and shifting the power supply terminal to the superconducting loop closer to the superconductor 2. If the loop is made up of parts that are always in a superconducting state, the superconducting wire part generates magnetic flux that is stored in the loop when writing.
Writing can be made more reliable. For reading, there are two methods: instead of reading out the destruction described above, there is a method of optically reading out by providing a magneto-optical effect film, or a method of using a matrix of minute magnetic sensors.

As mentioned above, the present invention is not limited to the embodiments described above.

<Effects of the Invention> The present invention utilizes the characteristics of superconductivity, but does not use a Josephnon element that uses an ultra-thin insulating film, which is extremely difficult to manufacture in the past.
It is a memory element that uses the superconducting magnetoresistive effect due to weak bonds that can be easily formed at the grain boundaries of ceramic superconductors.It is easy to manufacture, has practical input and output power, has good noise resistance, and is easy to handle. It is not difficult, and furthermore, it can be provided with the feature that no electric power is required for record keeping.

The superconducting memory element of the present invention was previously disclosed in Japanese Patent Application No. 63-2952.
By using it in combination with a ceramic superconducting logic element proposed by Sharp Corporation, one of the applicants, in No. 6, etc., it is possible to construct a digital circuit that performs extremely high-speed superconducting operations.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a characteristic diagram showing an example of the ceramic superconducting magnetoresistive effect, Fig. 3 is an operation diagram of the embodiment of the present invention, and Fig. 4 is a diagram of the embodiment of the present invention. Fig. 5 is a block diagram of still another embodiment of the present invention, Fig. 6 is a diagram showing a method for manufacturing a ceramic superconductor film used in the present invention, and Fig. 7 is a diagram of the present invention. FIG. 8, which is a diagram showing the superconducting magnetoresistance characteristics of the invention, is an equivalent circuit diagram of the superconductor of the invention. 1... Superconductor wire subjected to the action of a magnetic field, 2... Superconductor wire, 3... Conductor wire, 4... Substrate, 5... Heater, 6... Injection device. Agent Patent attorney Takeshi Sugiyama (1 other person): $2 Figures (a) (b)
Figure 4 $5 f Figure 6 87 Figure 121 +21 121 Figure 8

Claims (1)

[Claims] 1. At least a part of the conductor wire of the superconductor loop is formed of a ceramic superconductor having grain boundaries, and a conductor wire is provided close to the conductor wire of the ceramic superconductor having grain boundaries, and a current is generated by flowing through the conductor wire. A ceramic superconducting memory element characterized in that a current flowing through the superconducting loop is controlled by the action of a magnetic field.