JPH06150407A - Memory medium - Google Patents

Abstract

PURPOSE:To provide the reloadable memory medium which does not change with lapse of time and has stable and high reliability by controlling the quantity of the oxygen included in an oxide and recording information by in such a manner that large and small state changes of the oxygen content in the oxide correspond to signals; CONSTITUTION:An Ag electrode 2 is deposited by evaporation on an MgO single crystal substrate 1 and a recording medium 3 consisting of the YSr2Cu2.8 W0.2O6.8 oxide is deposited by evaporation thereon. Ruggedness is formed at 0.5mum intervals on the medium 3 and the size of the ruggedness is specified to about >=3nm. An acicular electrode 4 is moved to the projecting parts of the medium 3 obtd. in such a manner and a voltage is applied between terminals 5 and 6. The medium remains in a high-resistance state up to 4V but current begins to flow out and the medium attains the low-resistance state when the voltage rises higher than this value. The cause thereof lies in that the oxygen is absorbed from the inside of the atmosphere and the electric resistance of the medium decreases as the temp. of the medium is partially increased by applying the voltage. Namely, voltage-current characteristics are obtd. with good reproducibility and the stable storage of input information is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium for a file storage device such as a computer, and more particularly to a rewritable storage medium suitable for high density and large storage capacity.

[0002]

2. Description of the Related Art A magnetic material is often used as a storage medium for a conventional mass storage device. For example, "magnetic material ceramics" (Ohma Sakurai, Kanamaru knitting, p14)
3 (1986)). Further, as an example of using an oxide as the medium, use at a temperature lower than the superconducting critical temperature is disclosed in JP-A-63-268087. A recording medium using an oxide as a recording medium and utilizing a change in oxygen content is disclosed in JP-A-2-253.
There is a publication of 668.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the above prior art, when a magnetic material is used, the magnetization state of the magnetic material is used. Therefore, for example, in the case of high density, due to the relationship between the miniaturization of magnetic domains and the detected signal intensity, 1 μm
It was considered that a certain bit period was the limit. On the other hand, in a storage medium using a superconducting oxide, the medium is cooled to a temperature at which it exhibits a superconducting state, and in this state, oxygen ions and hydrogen ions are irradiated from a needle-shaped irradiation source to produce a superconducting state and a normal conducting state. The two states correspond to binary signals in binary. With this method, the storage capacity can be increased, but the critical temperatures of currently known superconductors are only lower than about 160K. Therefore, the storage medium must be cooled to a low temperature of -100 ° C or higher. Therefore, there is a big problem that a cooling medium such as liquid nitrogen or liquid helium is required, or a special cooling device such as a cryopump must be used.

The recording medium disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 2-253668, which uses an oxide as a recording medium and utilizes a change in the amount of oxygen, is represented by Y ₁ Ba ₂ Cu ₃ O _7-x. Although this material system satisfies the basic performance as a memory material, it has high reactivity with water vapor and carbon dioxide gas, and the amount of oxygen near the surface easily changes. However, there is a problem that it is necessary to seal the oxide material in order to store information because of poor chemical safety. The object of the present invention is to solve the above-mentioned problems of the prior art, to increase the storage capacity more than when using a magnetic material,
Another object of the present invention is to provide a highly reliable, rewritable storage medium that does not use a special cooling medium or a cooling device and is chemically stable and does not change with time in normal air.

[0005]

The above objects have been achieved by the present invention described below. That is, the present invention is a storage medium characterized in that the amount of oxygen contained in an oxide is controlled and information is recorded by utilizing the state of the amount of oxygen.

[0006]

As a result of intensive studies to solve the above problems, the present inventors have controlled the amount of oxygen contained in an oxide and made the state change of the oxygen content in the oxide correspond to a signal. By recording the information by, it is possible to increase the storage capacity than when using a magnetic material, and without using a special cooling medium or a cooling device, further, there is no change with time in normal atmosphere, The present invention has been accomplished by finding that a rewritable storage medium that is chemically stable and has high reliability is provided. That is, the amount of oxygen contained in the oxide is controlled by utilizing the fact that the amount of oxygen in the oxide changes due to voltage, light, heat, etc., and the physical properties of the oxide are changed by changing the amount of oxygen in the oxide. Information is stored by utilizing the fact that (for example, electrical resistance, reflectance, etc.) changes greatly.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the present invention will be described in detail with reference to preferred embodiments. The storage medium of the present invention, the amount of oxygen in the oxide is changed by voltage, discharge, light or heat,
It is characterized in that a signal is stored by utilizing changes in physical properties such as electric resistance and reflectance of the oxide caused by this.
A series of substances represented by conventional Y ₁ Ba ₂ Cu ₃ O _7-x satisfy the basic performance as a target storage medium, but cause other than the input signal (especially water vapor, carbon dioxide gas, etc.). However, there is a problem that it cannot be used unless it is placed in a closed container. It is considered that the main cause of this alteration is the Ba element contained in the material. Therefore, by completely replacing the Ba element with another element, that is, Sr, a storage medium having a higher surface stability than the conventional material and a high reliability as a storage medium has been developed.

With respect to a specific method of using the storage medium, the principle of applying a voltage will be described with reference to the drawings. FIG. 1 is a block diagram showing the principle of recording / reproduction. 1 is a substrate, 2 is an electrode, 4 is a needle electrode, 5 and 6 are storage media 3
It is a power supply terminal for applying a voltage to. In such a configuration, a voltage is applied to the storage medium using the electrodes 2 and 4, and the voltage-current characteristic between the terminals 5 and 6 is measured at that time.

[0009] Although the results are shown in Figure 2, there voltages V ₁
Is in a high resistance state, that is, in a high resistance state,
_It can be seen that applying a voltage higher than ₁ results in a low resistance state. By utilizing such voltage-current characteristics, it is possible to record a binary signal in a high resistance state and a low resistance state on a storage medium depending on whether or not a voltage exceeding V ₁ is applied during recording. Furthermore, when reading a signal, the resistance value of the storage medium may be detected. In addition, when erasing recorded information, partial erasing is possible by applying a voltage whose sign is opposite to that at the time of recording, and when erasing the whole, heating the entire medium by a device (not shown). Good. It has been confirmed that the oxide used in the storage medium of the present invention changes its electrical resistance and maintains this state even if the amount of oxygen in the crystal changes, as shown in FIG. .

The storage medium of the present invention has a high electric resistance when the amount of oxygen in the crystal is reduced. When the amount of oxygen decreases extremely, the storage medium decomposes and changes into another substance. It is possible to use such a phenomenon,
In this case, it becomes difficult to erase the stored information. Further, the amount of oxygen can be increased or decreased by heating in an atmosphere containing oxygen. That is, when the state before heating is in a state where the amount of oxygen is small, the amount of oxygen increases by heating, but in the opposite case, the amount of oxygen decreases by heating. It goes without saying that either phenomenon can be used as a storage medium. Which phenomenon is to be used may be freely determined according to the method of creating the storage medium, the signal control method, and the like. Further, the storage medium of the present invention is chemically extremely stable, so that it is not usually necessary to protect the surface with a protective layer or the like, but a protective layer is formed directly on the surface or sealed in a specific atmosphere. However, it goes without saying that its function has not changed.

[0011]

EXAMPLES The present invention will be described in more detail with reference to specific examples. [Embodiment 1] FIG. 1 is a diagram schematically illustrating a storage medium of the present embodiment. Reference numeral 1 is a substrate, and here, a MgO single crystal was used. 2 and 4 are electrodes, 2 is an Ag electrode, 4
Is a needle electrode made of W. 3 is YSr ₂ Cu _2.8 W _0.2
A storage medium made of O _6.8 oxide. The manufacturing method is as shown below. First, an Ag electrode is vapor-deposited to a thickness of about 500 nm on a substrate MgO single crystal by vacuum vapor deposition. Then Y
Sr ₂ Cu _2.8 W _0.2 O _6.8 oxide is deposited by RF magnetron sputtering at a substrate temperature of 600 ° C. to a thickness of about 1 μm. As shown in FIG. 1, this is subjected to a normal patterning technique (for example, etching by an ion beam).
Unevenness is added at intervals of 5 μm. The size of the unevenness may be about 3 nm or more, but in this embodiment, it is 100 nm. For this reason, one memory element has a size of 0.5 × 0.5 μm ² , but five memory elements are arranged one-dimensionally in order to investigate the performance as a memory medium. Regarding the amount of oxygen in the oxide,
It was measured by EPMA.

The needle electrode 4 is moved to the convex portion of the storage medium 3 obtained as described above, and a voltage is applied between the terminals 5 and 6. Up to 4 V, it was in a high resistance state, but when the voltage became higher than that, a current flowed out and it was in a low resistance state.
This is because when the voltage is applied, the temperature of the medium partially rises, and oxygen is absorbed from the atmosphere to reduce the electric resistance of the medium. That is, it can be seen that the voltage-current characteristics as shown in FIG. 2 were obtained with good reproducibility and the input information was stored.

The storage medium of the present invention is chemically very stable and can be stored in the air without any problem. To check that the storage medium of the present invention is chemically stable, 40
A water resistance test was carried out under a saturated steam pressure of ℃. Also, Y
A comparison with Ba ₂ Cu ₃ O _7-x was also made. This material is
At least 6 when left in the atmosphere under normal conditions
It is extremely stable for more than a month, but under the conditions of the above water resistance test, it completely decomposes in about 3 days in a powder state with an average particle size of about 100 μm. FIG. 4 shows the water test before and after the X-ray diffraction pattern, YBa ₂ Cu ₃
With the O _7-x material, white extrudates were seen after 3 hours,
After 3 days, it was completely decomposed into Y ₂ O ₃ , BaCO ₃ and C.
Change to uO. On the other hand, in spite of such a harsh endurance test, the storage medium of the present invention shows no change in the X-ray diffraction pattern even after 3 months, as shown in FIG. Since it is not seen at all, it is extremely chemically stable.

[Second Embodiment] FIG. 6 is a diagram schematically illustrating a storage medium according to the present embodiment. The production method is the same as that of the first embodiment except that the storage medium 3 is not provided with irregularities. However, in the storage medium 3, YSr ₂ Cu _2.8 W _0.2 O _7.1
An oxide material was used. As in Example 1, terminals 5 and 6
When a voltage was applied between them, the electric resistance increased from 4.2 V, which enabled the information to be stored. In this embodiment, the storage medium has no irregularities. In such a case, a marker for positioning is often inserted at the end of the storage medium, but the value of the applied voltage may be changed to distinguish the marker from the information. For example, if 6 V is applied to the marker and 4.5 V is applied to the information input, the marker portion has a higher resistance than the information portion, so that it can be distinguished from the information. Further, it goes without saying that the marker may use the same voltage as in the case of information input and determine the input pattern thereof. The material of the storage medium 3 of the present embodiment has a different oxygen content from the material used in the first embodiment, but the chemical stability is extremely stable like the material used in the first embodiment. In this embodiment, the storage capacity is determined by the shape of the tip of the needle electrode 4 and the positioning accuracy of the needle electrode 4. Usually, the radius of curvature of the tip of the needle electrode 4 is about 1 nm, and the size of the memory cell is also about the same. Furthermore, the positioning accuracy is 0.02
It is possible to have a resolution of about nm.

[Embodiment 3] FIG. 7 is a diagram schematically illustrating the present embodiment. The material forming the storage medium 3 is YS.
r ₂ Cu _2.85 Re _0.15 O _7.1 , which was deposited using the cluster ion beam deposition method. The evaporation materials used at this time were Y, SrCO ₃ , CuO, and ReO ₃ , and the Y component had an acceleration voltage of 0 KV, an ionization current of 0 mA, and
The Sr, Cu, and Re components were vapor-deposited at an acceleration voltage of 2 KV and an ionization current of 100 mA, the substrate temperature was 500 ° C., and heat treatment was performed at 350 ° C. for 60 minutes in the apparatus even after the vapor deposition was completed. The film thickness after heat treatment is 400 nm. The substrate 1 was made of Si, and Y ₂ O ₃ was deposited as a diffusion prevention layer 7 with a thickness of 10 nm by a cluster ion beam deposition method so that the storage medium 3 would not diffuse into Si during vapor deposition.

Reference numeral 8 denotes light (semiconductor laser; wavelength 780 nm, output 10 m) condensed by an optical system 9 such as a lens.
W). The light 8 is moved to a position where information is recorded by a driving device (not shown), and the storage medium 3 is irradiated with the light. The temperature of the portion irradiated with light partially rises and the amount of oxygen decreases. As a result, the reflectance is different between the portion irradiated with light and the portion not irradiated with light, and this phenomenon can be used to record information. In this example, the reflectance of the irradiated portion was increased by about 5% at a wavelength of 780 nm, and the presence or absence of information could be easily detected by a normal detection method (for example, a photodiode). A water resistance test similar to that of Example 1 was performed using the storage medium of the present example. However, similar to Example 1, the storage medium of the present invention was produced in spite of the presence of carbon dioxide gas. Chemically very stable, 3
No changes were observed even after months.

[Embodiment 4] The constituent material of the storage medium 3 is Y
_0.8 Ca _0.2 Sr ₂ Cu _2.8 Ge _0.2 O _7.0 , Example 1
It was vapor-deposited on the substrate 1 by the same method. Other than that, the configuration was the same as that of the third embodiment. Semiconductor laser (wavelength 7
Information is written by irradiating 80 nm, output 20 mW). In the irradiated part, the amount of oxygen decreases and the reflectance becomes about 10% higher than the peripheral part. Information can be read out by utilizing this fact. However, the wavelength of the reading light is the same as that of the writing light, but the output is generally made smaller than that at the time of input in order to prevent erroneous input by the reading light. Therefore, in this embodiment, it is set to 3 mW. Further, the same water resistance test as in Example 1 was conducted on the storage medium of this example.
Similar good results were obtained.

[0018]

As described above, the recording medium of the present invention stores information by utilizing a change in the amount of oxygen in an oxide, particularly an oxide exhibiting superconducting properties. −
Although the storage capacity is similar to that of the storage medium utilizing the normal transition, it can be used as a storage medium even at room temperature because it does not need to be cooled to a low temperature. The storage medium of the present invention is used in the atmosphere, an inert atmosphere such as nitrogen, or 10
^Since it is stable up to about 200 ° C in a vacuum of about ^-3 Toor, information can be stored even in a high temperature environment to some extent. Needless to say, the memory characteristics do not change even when cooled and used at a low temperature. Furthermore, YBaCuO
Since it has a smaller specific gravity than the system materials, it becomes a light storage medium.
Further, the storage medium of the present invention has extremely high chemical stability against moisture and the like, can be used without sealing the storage medium, and is harder than a metal such as aluminum and is not scratched. is there. In the examples given in the present specification, MgO or Si was used as the substrate, Ag and W electrodes were used as the electrodes, and Y ₂ O ₃ was used as the diffusion prevention layer, but the present invention is not limited to these. is not. That is, since the mechanical strength of the substrate material is guaranteed substantially in this portion as the storage medium, a plastic material such as plastic may be used as long as it has the required mechanical strength. Any material may be used as the electrode as long as it is a conductive material, and if the needle-shaped electrode can be processed into a needle shape, it may be ceramics without any problem. There are no restrictions on the method for producing the metal oxide as the memory material, and any method can be used without any problem.

[Brief description of drawings]

FIG. 1 is a schematic diagram schematically illustrating a first embodiment of the present invention.

FIG. 2 is a voltage-current characteristic diagram.

FIG. 3 is a diagram showing a relationship between oxygen amount and electric resistance.

FIG. 4 is an X-ray diffraction pattern of a Y ₁ Ba ₂ Cu ₃ O _7-x material for comparison.

FIG. 5: X of the storage medium material of the present invention used in Example 1
It is a line diffraction pattern.

FIG. 6 is a schematic diagram schematically illustrating a second embodiment of the present invention.

FIG. 7 is a schematic diagram schematically illustrating Example 3 of the present invention.

[Explanation of symbols]

 1: substrate 2, 4: electrode 3: storage medium 5, 6: terminal 7: diffusion prevention layer 8: light 9: optical system 10: part where oxygen amount changes

Claims (4)

[Claims] 1. A storage medium, wherein the amount of oxygen contained in an oxide is controlled, and information is recorded by utilizing the state of the amount of oxygen. 2. The oxide contains Sr and Cu as essential constituent metal elements, and other than that, at least one of atomic groups consisting of lanthanoid elements, Ca and Y, and Ti, V, and G.
An oxide containing at least one selected from atomic groups of a, Co, Fe, Ge, Mo, W and Re.
The storage medium described in. 3. The oxide is represented by the general formula of ASr ₂ Cu _1-X M _X O _y , A is at least one element selected from lanthanoid elements, Ca and Y, and M is Ti, V , G
at least one selected from atomic groups of a, Co, Fe, Ge, Mo, Al, W and Re, and 0.05 <
The storage medium according to claim 2, wherein x <0.7 and 6 <y <9. 4. The storage medium according to claim 1, wherein the amount of oxygen is controlled by controlling light irradiation, voltage application, electric heating or discharge.