JPS61177653A - Optical type information memory device - Google Patents

Abstract

PURPOSE:To improve the S/N of a reproducing signal by deforming recording media in a martensite phase at the room temperature by stress. CONSTITUTION:Recording media 2 and 11 are formed on substrates 1 and 10. The media 2 and 11 show the martensite phase at the room temperature, and are formed by the substance in which a martensite reverse transformation occurs at the special temperature higher than the room temperature and special stress. The information is recorded by heating locally the media 2 and 11. Name ly, the information is recorded so that in the optical beam irradiated from an optical beam generating device 13, the temperature of the optical beam irradiating part can drop below the above-mentioned specified temperature. The symbol 3 in the figure is the recording part. The information recorded in this way is deleted by irradiating the optical beam to the place hard to be deleted by the energy so that the temperature of the media 2 and 11 can be the above-mentioned special one. Thus, in a recording part 3, the deformation disappears and the flat surface is recovered. The information is reproduced by detecting the difference of the reflecting light quantity by a light detecting device 17.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a storage device that optically records and reproduces information, and more particularly to a storage device that allows repeated optical recording and erasing.

[Technical background of the invention and its problems]

Storage devices that optically record, reproduce, and erase information are
It is attracting attention because of its high recording density and its ability to be accessed quickly.

Such storage devices include recording media that utilize the magneto-optical effect of amorphous alloy thin films made of rare earth and transition metal elements, and recording media that utilize phase transition between amorphous and crystalline materials. something is known.

However, in the former magneto-optical storage device, (a)
The reproduction principle is based on detecting the rotation of the polarization plane of linearly polarized light by at most a few orders of magnitude, and the optical system is complicated, including polarizers, analyzers, etc., and the S/N is low. (b) Rare earth and Amorphous alloy thin films made of transition metal elements are easily oxidized in the atmosphere and have a short lifespan; (C) raw material costs are high due to the use of rare earth elements; and (d) a means for applying a magnetic field is required. It has a number of problems.

On the other hand, in the latter type of memory device that utilizes phase transition between amorphous and crystalline materials, recording and erasing basically involves diffusion and movement of atoms, so (a) 1-bit information The time required for recording or erasing is long, and there is a limit to increasing the data transfer speed. (b) Reversibility is gradually lost due to thermal repetition, resulting in unerasable residue. It has the following problems.

In addition, at least two other layers are provided on the substrate, the first layer deforms the second layer for recording, and the second layer is a reversible memory which is a martensitic layer at room temperature. A structure has been proposed (JP-A-56-124136). This method requires (a> at least two separate layers in the recording medium and further between the substrate and the first layer;
and the need to strictly control the adhesion between the first and second layers, complicating the manufacturing process. (
b) When a metal with a high coefficient of thermal expansion is used as the first layer, the first layer returns to a flat surface after recording, making it difficult to reproduce information by inputting a light beam from the substrate surface side. C
) When a thermally decomposable polymer is used as the first layer, there is a limit to the number of times recording and erasing can be repeated. It has the following problems.

[Purpose of the invention]

The present invention has been made in order to overcome the problems of the conventional device described above, and aims to improve the S/N ratio of the reproduced signal and speed up recording and erasing by using a storage method that is fundamentally different from the conventional one. In addition, we provide an optical information storage device with a simple structure, using a recording medium with a simple single-layer structure, long life, and cheaper raw materials, a simple optical system, and no means for applying a magnetic field. The purpose is to

[Summary of the invention]

In order to achieve the above-mentioned object, the present invention uses a single-layer material film that exhibits a martensitic phase at room temperature and undergoes martensitic transformation at a specific temperature and stress as a recording medium, and utilizes deformation within the martensitic phase. The main point is to do so.

Martensitic transformation and its reverse transformation are characterized by changes in crystal structure due to coordinated movement of atoms without diffusion and movement of atoms, and are highly reversible and phase transitions occur at high speed. These transformations are observed with a certain hysteresis as the temperature rises and falls. In the following, the temperature of reverse transformation when the temperature is increased is assumed to be AS, and the temperature at which the reverse transformation ends and all of the material becomes a high-temperature phase is assumed to be Af. In many materials that undergo martensitic transformation, if stress is applied to the martensitic phase and a strain that remains even after the stress is removed, that is, deformation is applied, when the temperature is raised to A1 or higher, the strain recovers to zero as a result of reverse transformation. A phenomenon occurs. This is called the shape memory effect.

The present invention is realized as a memory device with a configuration in which this shape memory effect is controlled by heating means using a light beam. In other words, a light beam narrowed to near the diffraction limit is irradiated with a short pulse width to the recording medium in the martensitic phase to locally heat it, causing plastic deformation due to the local stress generated at that time. For example, the state is set to a recording state, and the temperature of the recording medium is raised in a state with small local stress using a light beam adjusted differently from that during recording to erase the deformation due to the shape memory effect, and the deformation of the recording medium is further reduced. This is a storage device that reproduces recorded information by detecting the difference in light reflectance between a deformed portion and a flat surface. Another feature of the present invention is that the recording medium is made thin with a single layer structure so as to suppress in-plane thermal diffusion in order to enable recording by localized heating.

Note that in a practical storage device that records and erases information using a light beam while keeping the recording medium at room temperature, it is necessary to use a recording medium whose martensitic transformation temperature and reverse transformation temperature are suitable. From this point of view, in the present invention, it is desirable to use a material that undergoes a reverse transformation of martensitic transformation at 200 to 500°C.

〔Effect of the invention〕

According to the present invention, (a) high-speed recording and erasing is possible and highly reversible due to the use of martensitic transformation without diffusion movement of atoms; (b) polarizer and detector are used during reproduction; There is no need to use photons, the optical system is simple and the S/N is high; (C) recording media containing elements such as Cu, AQ, and Ni can be used as main components, and raw materials are inexpensive; be.

(d) Since the recording medium can be composed mainly of the above elements, it has better oxidation resistance and weather resistance than magneto-optical recording media that use rare earth elements. (e) Recording A single layer of media is sufficient and the manufacturing process is simple. (f) No means for applying a magnetic field is required, and the structure of the storage device is simple. This effect can be obtained.

[Embodiments of the invention]

FIG. 1 is a sectional view of an embodiment of a recording medium and a substrate in an embodiment of the present invention. The substrate 1 is made of glass, organic resin, or the like. A recording medium 2 is formed on this substrate 1. In the case of the present invention, this recording medium 2 can sufficiently function as a single layer. 3 is a recorded portion in which, for example, binary information 1'' is recorded by the recording procedure described later according to the present invention, and 4 is an unrecorded portion or an erased portion of information “0”.The recording medium 2 is A material is selected and its composition 9 structure is adjusted so that it exhibits a martensitic phase at ordinary mTa and reverse martensitic transformation occurs at a specific temperature AS to Af higher than ordinary ITa and at a specific stress. In this state, the surface is flat as shown in the unrecorded area 4 in FIG. Adherence is weak.

FIG. 2 is a block diagram of an example of an apparatus for producing a recording medium according to the present invention. 5 is a vacuum container, and 6 is an exhaust system.

7 is a ceramic crucible, and 8 is a heater for electrical heating made of tungsten. 9 is glass, quartz.

The substrate is made of organic resin, Si, or the like, and is rotated while the film that will become the recording medium is attached. The vacuum container 5 is heated to 1×10-' Torr by the exhaust system 6.
The evaporation source filled in the crucible 7 is evaporated from the crucible 7 heated by the heater 8, and a thin film as a recording medium is attached to the substrate 9.

A first embodiment of the present invention is a case where a Cu-A4 alloy thin film is used as a recording medium. Two combinations of heater 8 and crucible 7 are prepared as shown in Fig. 2, and one is CU,
The other side was filled with A.degree. C., and the amount of evaporation was precisely and stably controlled by controlling the power supplied to the heater 8, and a Cu-A4 alloy film was deposited on the substrate 9. When temperature changes in electrical resistance were measured for various Cu-Al2 alloy films prepared with varying compositions, recording media that underwent martensitic transformation were obtained when the Aj2 content was 9 to 15% by weight. Measuring the change in electrical resistance with temperature is a suitable means for determining the transformation temperature of martensitic transformation.

The measurement was carried out by the AC four-terminal method, and the rate of heating and cooling was 20° C. per minute.

Conventionally well-known bulk alloys with a shape memory effect often have a reverse transformation temperature of at most 100° C., which is below room temperature, and are not suitable as materials for recording media used at room temperatures. On the other hand, Cu-2 alloy, Ti-Ni-Cu
Thin films such as alloys and N1-Affi alloys can easily be made to recover their shape at high temperatures of about 150°C or higher, which is advantageous because they do not inadvertently return to their original shape at room temperature. . Alloy 1119 with these advantages
1, it is effective to deposit a film while heating the substrate with an infrared lamp, for example.

Figure 3 shows a 3i wafer with a thermal oxide film as a substrate.
Cu deposited to a thickness of 6000 mm while heating to 00℃
This figure shows the results of measuring temperature changes in electrical resistivity of An alloy Ill. As shown in the figure, it exhibits a martensitic phase at room temperature, and the temperature at which reverse transformation ends is Af-3.
A recording medium suitable for the present invention was obtained that had a temperature of 80° C. and did not have strong adhesion to the substrate.

On the other hand, regarding a Cu-Afi alloy thin film deposited to a thickness of 800 mm on a glass substrate by the same method as above, the temperature was 80° C.
An accelerated deterioration test was conducted under high temperature humidified conditions of 5% relative humidity. Optical reflectance was measured at regular intervals as a measure of deterioration. Figure 4 shows an example of the results. The horizontal axis is the time under high temperature and humid conditions, and the vertical axis is the reflectance of a commonly used semiconductor laser at a wavelength of 830 nm after X hours as R(X), (R(x) - R (0) )/R(0) is the change in optical reflectance. Figure 4 shows typical TbFe, GbC and magneto-optical recording media prepared for comparison.
An example of the results for each amorphous alloy thin film of o. As is clear from Figure 4, compared to magneto-optical recording media containing rare earth elements, the Cu-Affi alloy thin film exhibits less decline in reflectance under high temperature and humid conditions, and has much better oxidation resistance and weather resistance. Excellent.

FIG. 5 is a block diagram of an embodiment of a storage device according to the present invention that uses the above-mentioned recording medium and performs recording, reproduction, and erasing using a light beam. The above-described single-layer thin film recording medium 11 is formed on a glass substrate 10, and is rotated about an axis 12.

The light beam generator 13 is configured using, for example, a semiconductor laser, and also includes a mechanism for adjusting the pulse width and power of the irradiated light beam. 14 is a reflective mirror.

15 is an objective lens. A light beam focused by the objective lens 15 is irradiated onto the recording medium 11 . A half mirror 117 16 is a photodetector, and a part of the reflected light from the recording medium 11 enters the photodetector 17 via the half mirror 16 .

Information is recorded by locally heating the recording medium. That is, the objective lens 15 is used to accurately focus a light beam on the recording medium 11, and the light beam is narrowed down to about 1 μmφ with a pulse width that does not cause problems with thermal diffusion within the plane of the recording medium 11, and at a temperature of the light beam irradiated area. is A1
Recording was possible by irradiating with a power that did not exceed the maximum power. When the recorded areas were observed under a microscope,
It was confirmed that it had deformed into the shape shown in Figure 1.

To erase the information recorded in this way, the recording medium is heated to a temperature of Af.
This is done by raising the temperature above or above. That is,
A light beam was irradiated onto the portion to be erased with such energy that the temperature of the recording medium 11 became A1 or higher. However, during erasing, in order to avoid unnecessary concentration of thermal stress, a light beam was irradiated with a pulse width longer than that during recording and a beam diameter larger than that during recording. As a result, it was confirmed that the deformation of the recorded portion 3 in FIG. 1 disappeared and it returned to a flat surface.

The above recording and erasing is understood to be based on the following principle.

When localized heating is performed using a beam of light for recording,
Since the portion of the recording medium 2 shown in FIG. 1 that is irradiated with the light beam is restrained by the surrounding unrecorded portion 4, the following internal stress σ is generated.

σ-E (Δ(1/12> E is Young's modulus, Δβ/2 is the elongation rate due to thermal expansion when not restrained, and is expressed as Δ2/2-β(T-Ta). β is the thermal expansion coefficient , Ta is room temperature, and ■ is the temperature of the part irradiated with the light beam.Usual alloys, such as Cu-
In An-based alloys, β~2×10-' [1/K]
, E ~10" [Pa]r,
When the temperature of the light beam irradiated portion rises by 150° C. from room temperature, an internal stress of σ-300 [MPa] is generated.

When the adhesion of the recording medium 2 to the substrate 1 is weak, when this internal stress σ exceeds the yield stress σcr of the recording medium 2, the portion irradiated with the light beam undergoes plastic buckling and deforms into the shape shown in FIG.

Since the recording medium 2 according to the present invention is in the martensitic phase at room temperature, unless the temperature of the recording medium 2 exceeds As during recording, this deformation is caused by the movement of the twin interface within the martensite phase and the martensite older brother crystal. It is carried out by the conversion between them. The deformation caused by these mechanisms remains stable even after the local heating ends, that is, after the stress is removed.

As described above, the recording medium according to the present invention is in the martensite phase at room temperature, but the martensite phase is softer than the parent phase and easily deforms due to the above mechanism, and the yield stress σcr is about 150 [MPa] or less. . During recording, it is necessary that the thermal stress due to local heating to a temperature not exceeding Af exceeds σcr. Therefore, the Af of the recording medium is preferably 200° C. or higher to ensure reliable recording.

However, considering the output of compact semiconductor lasers etc. that can be used in optical information storage devices currently in practical use, the lower limit of Af is preferably 500'C or less. Note that the temperature Mf at which martensitic transformation ends during cooling may be any value as long as it is equal to or higher than room temperature.

Through the above procedure, the recorded portion 3 deformed by plastic buckling as shown in FIG. 1 exists stably as long as the temperature is below AS, and this becomes, for example, the recorded state of Pa 1n. Erasing is due to the shape memory effect already mentioned. That is, when the temperature of the recording medium increases, martensitic reverse transformation occurs at temperatures AS to Af.

The deformation carried out by the movement of the twin interface within the martensite phase and the transformation of the martensite elder crystals during recording becomes zero when the martensite undergoes reverse transformation and becomes a high-temperature phase. Therefore, the shape of the recording medium 2 becomes the original flat surface. This flat surface remains stable even when cooled to room temperature after irradiation with the erasing light beam, and remains stable as long as no stress is applied thereafter. In this erasing process, it is necessary that the thermal stress caused by the temperature increase be equal to or less than the above-mentioned yield stress σcr. This requirement can be overcome by making the erasing light beam have a longer pulse width and a longer pulse rise time than during recording, and a beam diameter larger than that during recording. Increasing the beam diameter is simply achieved by adjusting the objective lens 15 and shifting the focus a little compared to when recording. Furthermore, an optical path for an erasing light beam may be provided separately from that for recording. Erasing is completed by the above principle.

Here, if the thermal stress is too large during the recording process and the deformation is caused by factors other than the movement of the twin interface within the martensite phase and the transformation of the martensite elder crystals, such as slipping, erasure is impossible. It is. Therefore, information that may be erased later needs to be recorded with a thermal stress below the critical stress for slip σ88 (>σcr). On the other hand, for information that you do not want to permanently erase, use σ8H.
It is possible to record and preserve data under thermal stress above.

The recorded information is reproduced by irradiating the recording medium with a light beam and detecting the difference in the amount of reflected light between the recorded area and the unrecorded area (or erased area) using the photodetector 17 shown in FIG. Let's do it. The irradiated light beam has a power so large that the amount of reflected light can be detected by the photodetector 17, and a power smaller than that used during recording or erasing. In the recorded portion 3 deformed as shown in FIG. 1, the surrounding flat unrecorded portion 4
The presence or absence of recording can be determined by detecting the amount of light that is reflected back, since the optical conditions change due to the fact that the light is scattered compared to the previous one, and a cavity is created between the substrate and the recording medium. . In this case, the direction of incidence of the reproducing light beam may be from the recording medium surface side or from the substrate surface side. The same applies to the direction of incidence of the light beam for erasing and recording.

Note that the recording principle in the present invention is to deform the recording medium, which is in the martensitic phase at room temperature, by stress, so the difference in the amount of reflected light of the reproduced signal described above is due to the deformation of the flat surface shown in FIG. Only. Therefore, when designing a recording medium from the viewpoint of S/N of a reproduced signal, there is an advantage that only the shape and degree of deformation need to be considered.

As described above, the optical information storage device according to the present invention does not require a means for applying a magnetic field or a polarizer in the optical path, which is required in a magneto-optical storage device, and it is possible to use a simple optical information storage device as shown in FIG. The structure is as follows. However, in order to make the device of the present invention a more practical high-density information storage device, in addition to the components shown in FIG. Needless to say, a focusing servo means for focusing the optical system is required.

The present invention is not limited to the embodiments described above; for example, the recording medium using the CU-Aj2 alloy mentioned in the embodiments can be replaced with other similar substances that cause martensitic transformation. .

For example, alloys that are known to have a shape memory effect in bulk.

T i -N i (15 to 56 wt%) alloy in which Ni is replaced with O to 30 wt% il by Cu, N 1-An
(19-23 wt%) alloy, Mn-Cu (5-3
6wt%) alloy W+7)il film can be used as the recording medium of the present invention.

In addition, in the example, the state where local thermal stress is generated and the deformation is generated is the recorded state, that is, the binary information "1" is expressed, but conversely, the state after the deformation is erased by increasing the temperature is recorded. It is also possible to set the state to 1pa. In this case, the initial state becomes the deformed portion shown in FIG. 1, and the recorded state becomes a flat surface. Therefore, by forming deformed portions as shown in FIG. 1 in an initial state continuously over the entire surface of the recording medium in a concentric or spiral shape, it is possible to provide the function of a tracking guide groove for guiding the optical system. I can do it.

In this case, there is no need to physically form guide grooves on the substrate, and there is an advantage that glass substrates, etc., on which it is difficult to form guide grooves, can be used as high-density storage devices with their flat surfaces.

Further, although the recording medium of the present invention can function satisfactorily with a single layer, for example, when it is desired to adjust the adhesion of the recording medium to the substrate, a thermally stable layer may be provided between the recording medium and the substrate. Alternatively, in order to further increase the weather resistance, there is no problem in appropriately employing multilayering, such as providing a thin protective layer on both sides of the recording medium, and this does not impair the effects of the present invention.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a recording medium and a substrate according to an embodiment of the present invention, FIG. 2 is a schematic diagram of an example of an apparatus for producing a recording medium according to the present invention, and FIG. 3 is a schematic diagram of an example of a recording medium according to the present invention. FIG. 4 is a diagram showing temperature changes in electrical resistivity to explain the state of martensitic transformation; FIG. 4 is a diagram showing the weather resistance of a recording medium made of a Cu-Affi alloy thin film in comparison with other recording media; FIG. 5 is an overall configuration diagram of an embodiment of an optical information storage device according to the present invention. 1... Substrate, 2... Recording medium, 5... Vacuum container,
6... Exhaust system, 7... Crucible, 8... Heater, 9
... Substrate, 10... Substrate, 11... Recording medium, 1
2...Rotation axis, 15...Objective lens, 16...Half mirror 117...Photodetector. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 Temperature Pi C] Figure 4 Procedural Amendment 60.4.25 1920/1935 Commissioner of the Japan Patent Office Manabu Shiga 1, Patent Application for Indication of Case No. 60-16761 2, Name of the invention Optical information storage device 3, Relationship to the amended case Patent applicant (307) Toshiba Corporation 4, Agent 1-26-5 Toranomon, Minato-ku, Tokyo No. 17 Mori Building 〒1
05 Telephone 03 (502) 3181 (main representative)
6. Subject of amendment 7. Contents of amendment (1) The description of the claims shall be corrected as shown in the attached sheet. (2) "Temperature of reverse transformation" on page 5, line 11 of J specification
is corrected as "the starting temperature of reverse transformation". (a) "It is simple...It is a cross-sectional view." on page 7, line 14 to line 17 of the specification is corrected as follows. The following effect can be obtained. [Practice of the invention] Example] Figure 1 is a cross-sectional view of an embodiment of a recording medium and a substrate according to an embodiment of the present invention. 2. Claims (1) It exhibits a martensitic phase at room temperature and changes to martensite at a specific temperature and stress. A recording medium consisting of a single-layer material film that undergoes site transformation, a substrate that supports this recording medium, and a stress generated by locally heating this recording medium below a characteristic temperature by irradiation with a light beam. means for deforming the recording medium; means for raising the temperature of the recording medium to a temperature higher than the characteristic temperature by irradiating the recording medium with a light beam to cause a reverse transformation of the martensitic transformation to recover the shape; An optical information storage device characterized by comprising: means for detecting using a beam. (2) The recording medium undergoes a reverse transformation of martensitic transformation at 200 to 500°C. An optical information storage device according to claim 1. (Characterized in that the 3trJ recording medium is made of a copper-aluminum alloy film containing copper as a main component and 9 to 15% by weight of aluminum. Claim 1:
Optical information storage device as described in .

Claims (3)

[Claims] (1) A recording medium consisting of a single-layer material film that exhibits a martensitic phase at room temperature and undergoes martensitic transformation at a specific temperature and stress, a substrate that supports this recording medium, and a substrate that supports this recording medium by irradiating the recording medium with a light beam. A means for deforming a recording medium by stress generated by locally heating it below a characteristic temperature, and a means for heating the recording medium to a temperature above the characteristic temperature by irradiating the recording medium with a light beam to cause a reverse transformation of the martensitic transformation. An optical information storage device comprising: means for tightening the recording medium to restore its shape; and means for detecting whether or not the recording medium has been deformed using a light beam. (2) The optical information storage device according to claim 1, wherein the recording medium undergoes a reverse transformation of martensitic transformation at 200 to 500°C. (3) Optical information according to claim 1, wherein the recording medium is made of a copper-aluminum alloy film containing copper as a main component and 9 to 15% by weight of aluminum. Storage device.