JP2883166B2 - Storage media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a storage medium for a file storage device such as a computer and an electronic camera, and particularly to a rewritable storage suitable for high density and large storage capacity. Regarding the medium.

(Prior Art) Magnetic materials are often used as storage media for conventional mass storage devices. Such a storage medium is described in, for example, Ohmsha, "Magnetic Material Ceramics", edited by Sakurai and Kanamaru, p. 143 (1986).

Further, as an example of using the oxide as the storage medium,
JP-A-63-268087 discloses that recording and reproduction are performed at a temperature lower than the superconducting critical temperature using an oxide superconductor. However, this storage medium must be used at a low temperature below the superconducting critical temperature.

(Problems to be Solved by the Invention) In the above-described conventional technology, when a magnetic material is used, the magnetization state of the magnetic material is used. A bit period of about 1 μm is considered to be a limit, and there is a problem that high density cannot be achieved.

On the other hand, in a storage medium using an oxide superconductor, the medium is cooled to a temperature at which the superconducting state is exhibited, and in this state, oxygen ions and hydrogen ions are irradiated from a needle ion irradiation source to maintain the superconducting state. Since the two states of the conduction state correspond to the binary signals in the binary system, this method can increase the storage capacity, but has a practical problem.

That is, the currently known superconductor has a critical temperature of about 160K.
Only lower ones, and if you actually remember-
Since cooling must be performed at 100 ° C. or more, there is a major problem that a special cooling medium such as liquid nitrogen or liquid helium must be used, or a special cooling device such as a cryopump must be used.

Accordingly, an object of the present invention is to provide a rewritable storage medium in which the storage capacity is made larger than when a magnetic material is used, and in which information can be written and read without using a special cooling medium or a cooling device. That is.

(Means for Solving the Problems) The above object is achieved by the present invention described below.

That is, the present invention has, as a constituent element, an oxide conductor whose characteristics change according to the amount of oxygen contained, and the oxide conductor is planarly formed on a substrate or an electrode formed on the substrate. A storage medium, wherein the storage medium is provided in a shape in which a protective film is deposited and formed thereon, and the protective film is an oxygen-permeable film;
And an oxide conductor whose properties change according to the amount of oxygen contained therein, the oxide conductor being planarly deposited on a substrate or an electrode formed on the substrate, and A storage medium provided with a protective film formed thereon, wherein the protective film is an oxygen-absorbing film.

(Action) An oxide conductor whose characteristics change according to the amount of oxygen contained is a constituent requirement, and the amount of oxygen contained in the oxide conductor is controlled by means such as electric heating or light irradiation. Thus, a change in the characteristics of the oxide conductor caused by a change in the oxygen content in the oxide conductor is used, and writing and reading of information are performed in accordance with the change in the state of the oxide conductor.

For example, in a Y—Ba—Cu—O-based oxide that is an oxide conductor, a YBa ₂ Cu ₃ O _7-δ (0 <δ <1) material has a crystal structure when the δ value is larger than 0.5. Is a tetragonal structure and becomes a semiconductor, and if the δ value is less than 0.5,
It becomes a superconductor with a horhombic structure and a Tc of about 90K.
Therefore, various kinds of information can be recorded by using the change in the electrical resistivity caused by the change in the amount of oxygen in the oxide conductor.

However, when Y: Ba: Cu = 1: 2: 3, the Y—Ba—Cu—O-based oxide becomes a relatively stable substance, and it is difficult to cause a change in the amount of oxygen. Therefore, in the present invention, the energy required for writing is greatly reduced by setting the ratio of the Ln element such as Y in the metal component contained in the oxide conductor to be 7% to 16% in atomic ratio. To be reduced.

In addition, the Y-Ba-Cu-O-based oxide conductor changes its characteristics in accordance with the amount of oxygen contained in any crystalline material from an amorphous state to a completely crystalline state. Therefore, it is possible to arbitrarily select what kind of crystallinity is required, if necessary.

Further, in the present invention, the resolution of the storage medium can be increased to the atomic order by forming the oxide conductor in a shape that is planarly deposited on the substrate or an electrode formed on the substrate. . For example, even when a recording method using STM is used, high-density recording up to the limit of STM can be performed.

(Preferred Embodiment) Next, the present invention will be described in more detail with reference to preferred embodiments.

FIG. 1A is a schematic cross-sectional view showing an example of the configuration of a storage medium according to the present invention. An oxide conductor 3 is formed on an electrode 2 formed on a substrate 1. .

FIG. 1 (b) is a schematic view showing an example of a writing method for FIG. 1 (a). As shown in FIG. 1 (b), the needle electrode 4 is brought close to the surface of the oxide conductor layer 3 as shown in FIG. In this state, a voltage pulse is applied between terminals 8 and 9 to partially heat the terminal,
A portion 5 having a changed characteristic is formed in the oxide conductor layer, and a number of the portion 5 having a changed characteristic is formed by scanning the needle-shaped electrode 4 to perform writing.

FIG. 1 (d) shows an example of the number of application of the voltage pulses and the change of the electric resistivity of the portion 5 where the characteristic has changed in this case, but as shown in FIG. The electrical resistivity of the oxide conductor layer 3 changes continuously. Therefore, multi-level recording can be performed using this.

Further, in the storage medium of the present invention, a protective film 7 is provided on the oxide conductor layer 3 as shown in FIG.

That is, the oxide conductor layer 3 is formed on the electrode 2 formed on the substrate 1, and the protective film 7 is formed thereon. As a material of the protective film 7, a material that transmits oxygen, such as Ag or Si oil,
Alternatively, a substance that absorbs oxygen, such as Ti or Cr, can be used. By forming the protective film 7 using such a substance,
The oxide conductor layer 3 can be protected without impairing the function as a storage medium.

Further, by providing minute irregularities on the surface of the protective film 7, the deviation of the recording position is reduced, and the accuracy of writing and reading can be improved. Also, the positioning of the needle becomes easy.

The optimum shape of the concavo-convex shape can be determined depending on the type of the oxide conductor and the type of the protective film formed on the oxide conductor layer.

Note that writing to the storage medium of the present invention may be performed by any method as long as the amount of oxygen in the oxide conductor can be changed even in a very small portion. For example, the electric current shown in FIG. In addition to thermal heating, a method using light irradiation, a tunnel current, or the like can be used.

(Example) Next, the present invention will be described in more detail with reference to Reference Examples and Examples.

Reference Example 1 FIG. 1 (a) shows a schematic configuration diagram of a first reference example.

An electrode 2 was formed by using a glass (Corning 7059) as a substrate 1 and depositing Cr to a thickness of 30 ° and Cu to a thickness of 500 ° by a resistance heating method.

Next, Y is applied thereon by RF magnetron sputtering.
An oxide conductor layer 3 was formed by depositing a -Ba-Cu-O film at 3000 °. The film formation conditions at this time are such that the composition ratio of the three metals is
Y: Ba: Cu = 10.0: 30.0.0: 60.0) The Y—Bc—Cu—O sintered body adjusted to have the atomic ratio) was used as a sputtering target, and a sputtering gas having a pressure of 5 × 10 ⁻³ Torr was used. Sputtering power using Ar 50% + O ₂ 50% gas
150 W and the closing plate temperature were 300 ° C.

In the Y—Ba—Cu—O film formed by the above method, the composition ratio of three metals is Y: Ba: Cu = 10.0: 30.0.0: 60.0 (atomic ratio).
Then, it becomes almost amorphous state and the electric resistivity is 1Ω ·
cm.

Writing information to the storage medium of the reference example created in this way is performed, for example, by a method as shown in FIG. 1 (b).

In FIG. 1B, reference numeral 4 denotes a needle-like electrode, and tungsten was used as a material. The distance between the tip of the needle electrode 4 and the oxide conductor layer 3 is set to about 15 °, and the surroundings are filled with O ₂ gas. Next, when a voltage pulse of 5 V is applied between the needle electrode 4 and the oxide conductor layer 3, a part of the oxide conductor layer 3 is heated, oxygen is diffused, and the amount of oxygen is changed. There is a portion 5 where the resistivity has changed.

FIG. 1 (c) shows the relationship between the number of application of the voltage pulse and the change in the electrical resistivity.

Further, by scanning the needle-shaped electrode 4 in the XY direction, as shown in FIG. 1B, a large number of portions 5 having changed electric resistivity can be formed on the oxide conductor layer 3. As a result, a large amount of multi-valued information can be written.

In this embodiment, the storage capacity is determined by the shape of the tip of the needle electrode and the positioning accuracy of the needle electrode. Normally, the tip of the needle electrode has a radius of curvature of about 1 nm, so that the size of the memory cell is also about the same.

Further, the positioning accuracy can be set to a resolution of about 0.02 nm.

For information erasure, heat treatment at 250 ° C in vacuum is performed.
This was made possible by returning the oxide conductor layer to its original state.

Reference Example 2 FIG. 2 (a) shows a schematic configuration diagram of a second reference example.

In the present reference example, Si was used as the substrate 1 and a Y-Ba-Cu-O film was deposited thereon by the cluster ion beam method to form the oxide conductor layer 3. The film formation conditions at this time were as follows: Y, BaO, and Cu were used as the vapor deposition source. To
420 ° C. At the time of film formation, oxygen gas of 4 × 10 ^-4 Torr is blown around the substrate so that the composition ratio of the three metals on the substrate becomes Y: Ba: Cu = 8.0: 32.0: 62.0 (atomic ratio). Was formed. The film thickness was 1,000 mm.

The Y—Ba—Cu—O film prepared by the above method had an electrical resistivity of 1 × 10 ⁻² Ω · cm as it was.

Writing to the storage medium thus created could be performed in the same manner as in Reference Example 1.

However, the distance between the needle electrode 4 and the oxide conductor layer 3 is about
10 °, the applied voltage was 5V. FIG. 2 (b) shows the relationship between the number of pulse applications and the electrical resistivity in this case.

It should be noted that information could be erased in the same manner as in Reference Example 1.

Reference Example 3 FIG. 1A is also a schematic configuration diagram of Reference Example 3.

An electrode 2 was formed by using MgO single crystal as the substrate 1 and depositing Ag thereon by ion beam sputtering at 500 °. Further, a Y-Ba-Cu-O film was deposited thereon by a cluster ion beam evaporation method to form an oxide conductor layer 3.

The film forming conditions at this time were the same as in Reference Example 2 except that the substrate temperature was set at 500 ° C., and the film thickness and the composition ratio were also the same as in Reference Example 2.

The Y—Ba—Cu—O film prepared by the above method had an electric resistivity of 1 × 10 ⁻³ Ω · cm.

When information was written using the storage medium created in this way, the writing was almost the same as in Reference Example 2. However, the writing was performed in a vacuum, and the number of applied pulses and the electrical efficiency at that time were as shown in FIG. 1 (d).

 Note that information can be erased by heat treatment at 300 ° C. in oxygen.

First Embodiment FIG. 3 is a schematic diagram of a configuration of a first embodiment.

An electrode 2 and an oxide conductor layer 3 were formed on a substrate 1 in exactly the same manner as in Reference Example 2, and then Ag was deposited as a protective film 7. Ag was deposited 100Å by resistance heating.

Since Ag is used for the protective film 7 in the storage medium of this embodiment, oxygen passes through the protective film 7. Therefore, writing and erasing could be performed in exactly the same manner as in Reference Example 2. Furthermore,
The presence of the protective film 7 also improved the stability with respect to aging.

Embodiment 2 FIG. 3 is also a schematic diagram of Embodiment 2.

An electrode 2 and an oxide conductor layer 3 were formed on a substrate 1 in exactly the same manner as in Reference Example 3, and Ti was deposited as a protective film 7. Ti was deposited at 500 ° using the EB evaporation method.

Since Ti is used for the protective film 7 in the storage medium of this embodiment, oxygen diffuses into the protective film 7. Therefore, writing can be performed in substantially the same manner as in Reference Example 3, but oxygen released from the oxide conductor layer 3 diffuses into the protective film 7 and TiOx
Therefore, it is not necessary to write in a vacuum as in the case of Reference Example 3. Further, the stability with respect to aging is improved.

Third Embodiment FIG. 4 is a schematic diagram of a configuration of a third embodiment.

An electrode 2 and an oxide conductor layer 3 were formed on a substrate 1 in exactly the same manner as in Reference Example 3, and then Ag was deposited as a protective film 7. Ag was deposited at 50Å using a resistance heating method.

Next, after depositing Ag, only Ag was patterned by photolithography as shown in FIG.
Metal layers 6 having a size of m were formed at intervals of 0.3 μm.

The storage medium thus created could be written and erased in exactly the same manner as in Reference Example 3.

Since Ag has the property of transmitting oxygen, the oxide conductor layer 3
The entry and exit of oxygen to and from the sample can be performed in exactly the same manner as in Reference Example 3 having no Ag, and the metal layer 6 served as a marker at the time of reading, thereby improving the reading accuracy.

(Effect of the Invention) As described above, the storage medium of the present invention can increase the resolution of the storage medium to the atomic order,
High-density recording is possible, and the storage capacity can be greatly increased as compared with a conventional magnetic material. In addition, multi-value recording becomes possible as compared with a storage medium using a conventional superconducting oxide,
It can be used at room temperature.

[Brief description of the drawings]

FIGS. 1 (a), 2 (a), 3 and 4 are schematic sectional views showing an example of the storage medium of the present invention, and FIG. 1 (b) is a sectional view of the present invention. FIGS. 1 (c), 1 (d) and 2 (b) show an example of a method of writing to a storage medium, showing the relationship between the number of pulse applications and the electrical resistivity. 1: Substrate, 2: Electrode 3: Oxide conductor layer, 4: Needle electrode 5: Part with changed characteristics, 6, 7: Protective film 8, 9: Voltage terminal

──────────────────────────────────────────────────続 き Continued on the front page (72) Keisuke Yamamoto, Inventor 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Norio Kaneko 3-30-2, Shimomaruko, Ota-ku, Tokyo Canon (56) References JP-A-64-57438 (JP, A) JP-A-63-268087 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 9/04 G11B 9/00

Claims (4)

(57) [Claims] An oxide conductor whose characteristics change according to the amount of oxygen contained as a constituent element, wherein the oxide conductor is planarly deposited on a substrate or an electrode formed on the substrate. A storage medium provided with a protective film formed thereon, wherein the protective film is an oxygen-permeable film. 2. An oxide conductor whose characteristics change in accordance with the amount of oxygen contained as a constituent element, wherein the oxide conductor is planarly deposited on a substrate or an electrode formed on the substrate. A storage medium provided with a protective film formed thereon, wherein the protective film is an oxygen-absorbing film. 3. The oxide conductor of the formula Ln-Ba-Cu-O (Ln is
Represents an element belonging to Group IIIa subgroup of the Periodic Table such as Sc, Y, La, Ac, Yb, and Gd), and the proportion of the Ln element in the metal component contained in the oxide conductor is the number of atoms. 7% ~
3. The storage medium according to claim 1, which is 16%. 4. The storage medium according to claim 1, wherein irregularities are provided on the protective film.