JPS61153829A - Optical information storage device - Google Patents

Abstract

PURPOSE:To improve the S/N ratio of reproduction, to speed up recording and erasure, and to prolong the life of a device with simple constitution by using a single-layer crystalline film which has martensite transformation at specific temperature and with specific stress as a recording medium. CONSTITUTION:A preferable recording medium has the reverse transformation of martensite transformation at 150-500 deg.C and has the martensite transformation at -50-120 deg.C. For example, a Cu-Al alloy thin film is used. Then, a light beam is stopped down to about 1mumphi and focused on the recording medium 11 accurately through an objective 15 to heat the medium locally. In this case, a plastic deforming part 3 due to the martensite transformation which is caused locally is used as a recording part and the difference in reflection factor of a light beam between the deforming part 3 and a flat part 4 is detected by a photodetector 17 to reproduce information. When information is erased, the light beam is irradiated so that the temperature of the recording medium 11 is higher than temperature at which the reverse transformation of the martensite transformation occurs, erasing the deformation of the recording part 4. Thus, the performance of the optical information recording device is improved with the simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a storage device that optically records and reproduces binary 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 high-speed random access.

As such storage devices, recording media that utilize the magneto-optical effect of amorphous alloy decoys made of rare earth elements and transitional total bending elements, recording media that utilize phase transition between amorphous and crystalline materials, etc. are used. What was there is known.

However, in a magneto-optical storage device, (a) the reproduction principle is based on detecting rotation of the polarization plane of light by at most a few orders of magnitude, and the optical system does not include a polarizer, analyzer, etc. (b) Amorphous alloy thin films made of rare earth and transition metal elements are easily oxidized in the atmosphere and have a short lifetime; (C) Rare earth elements There are problems such as high raw material cost due to the use of (d) a means for applying an l field.

In addition, in a 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 is The time required for recording or erasing is long (1), and there is a limit to increasing the data transfer rate (b) reversibility is gradually lost due to thermal repetition, resulting in unerased data. has.

Besides this, at least two other layers are provided on the substrate, the first layer deforms and records the second layer, and the second layer is a reversible martensite layer at room temperature. A memory structure has been proposed (¥# Kaisho 56-124136
Publication No.). This method (a) requires at least two separate layers in the recording medium and also requires strict adhesion between the substrate and the first layer, and between the first layer and the second layer. The manufacturing process is complex due to the need to control
(b) When a metal with a low coefficient of thermal expansion is used as the first layer, the layer of the cylinder 1 returns to a flat surface after recording, and a light beam is input from the substrate surface side to generate information. is difficult,
(c) When a thermally decomposed polymer is used as the first layer, there is a problem that the number of times recording and erasing can be repeated is limited.

[Purpose of the invention]

The present invention has been made to overcome the problems of the conventional device described above, and uses a storage method that is fundamentally different from the conventional one to improve the SIN ratio for reproduction and speed up recording and erasing. The simple structure of the recording medium has a long life and cheaper raw materials! It uses 5 components and the optical system is simple! ! An object of the present invention is to provide an optical information storage device with a simple configuration that does not use means for applying a field.

[Ill essentials of invention]

In order to achieve the above-mentioned objects, the present invention uses, as a recording medium, a single-layer crystalline film that undergoes martensitic transformation at a specific temperature and stress. Martensitic transformation and its reverse transformation change the crystal structure through coordinated movement of atoms without diffusion movement, and are highly reversible, and the phase transition occurs at high speed. These transformations are observed with a certain hysteresis as the temperature rises and falls,
Since it is a lattice deformation, it can also be induced by applying stress. For example, below a predetermined characteristic temperature, when stress is applied to a crystal that is in a high temperature phase, it becomes a martensitic phase. This is called stress-induced transformation. Assuming that the temperature at which reverse transformation begins when the temperature is raised without applying stress is As, and the temperature at which reverse transformation ends and all the components become high-temperature phase is A, then below A8, martensite is formed due to the above stress-induced transformation. The phase exists stably.Also, many of the substances that undergo martensitic transformation are A
If a stress is applied under rJ: J% and a strain, that is, deformation that remains even after the stress is removed, is applied, the strain recovers to zero due to reverse transformation when the temperature exceeds At 11. happens. This is called the shape memory effect.

The present invention realizes the above-described effects of stress and temperature increase in martensitic transformation as a storage IA device by means of using a light beam. In other words, a short poem is created by focusing a light beam close to the diffraction limit! The recording medium is irradiated with a pulse width of This storage device uses a light beam to raise the temperature in a state where local stress is small, erases deformation due to the shape memory effect, and detects and reproduces the difference in light reflectance between the deformed portion and the flat surface. Furthermore, in the present invention, in order to enable recording by localized heating, the recording medium is made of a Wi film with a single layer structure so as to suppress in-plane thermal diffusion.

Furthermore, in a practical storage device that records and erases information using a light beam while being kept at room temperature, it is necessary to use a recording medium with a martensitic transformation temperature and an inverse/transformation temperature suitable for that purpose.
A well-known bulk shape chart! ! Most of the effective alloys had a reverse transformation temperature of 130°C, making it difficult to use many of them at temperatures below room temperature. This requirement has been overcome in the present invention by using a recording medium that has a thin film and has optimized pattern forming conditions. That is, as a preferred recording medium in the present invention, one that undergoes a reverse transformation of martensitic transformation at 150 to 500°C and undergoes martensitic transformation at -50 to 120°C is used.

〔Effect of the invention〕

According to the present invention, (a) fast recording and erasing is possible by utilizing martensitic transformation without diffusion movement of atoms, and reversibility is high; (b) polarizer and There is no need to use an analyzer, the optical system is simple, and the S/N is high. (C) Cu, Affi, N can be used as the recording medium.
It is possible to use elements such as i, and the raw materials are cheap, (
d) Since the recording medium is mainly composed of the above-mentioned elements, it has better oxidation resistance and weather resistance than when rare earth elements are used. (e) Recording medium! Ill has sufficient performance and the manufacturing process is simple. (f) Effects such as no need for means for applying a magnetic field and a simple configuration of the storage device can be obtained.

[Example 7II of Application] FIG. 1 is a sectional view of an embodiment of a recording medium and a substrate according to the present invention. 1 is the substrate, which is glass.

Made of organic resin, etc. 2 is a recording medium, and in the case of the present invention, a single layer serves a sufficient function. For example, 1 of the binary information is recorded by the recording procedure described below according to the present invention.
4 is the recorded part where ゛′ is recorded, and 4 is the white information of recording medium 2 “
This is an unrecorded portion (or an erased portion) of 0P. For the recording medium 2, a material is selected so that martensitic reverse transformation occurs in As-Ar at a temperature higher than room temperature Ta, and its composition is am. Furthermore, the recording medium 2 is in the first state as an initial state.
It is a flat surface as shown in the unrecorded area 4 in the figure, and even if the temperature is raised to A1 or higher with no stress applied to the entire recording medium, the temperature phase is a flat surface, and the substrate 1 of the recording medium 2 has weak adhesion.

FIG. 2 is a configuration 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 tungsten! It is a heating heater. 9 is glass, quartz.

It is a substrate made of organic resin, Si, etc., and is rotated while the film is attached. “The vacuum container 5 is evacuated to 1×10−·% Torr or less by the exhaust system 6, and the evaporation source filled in the crucible 7 is evaporated from the crucible 7 heated by the heater 8, and the recording medium 11 is filmed on the substrate 9. The first embodiment of the present invention is a case where a Cu-A polyalloy wl film is used as a recording medium.The heater 8 and crucible 7 are combined as shown in FIG. Prepare 2 pieces, put Cu on one side,
The other side was filled with AQ, and by controlling the power supplied to the heater 8, the individual evaporation amounts were precisely and stably controlled, and a Cu-A4 alloy film was attached to the substrate 9. 1. When we measured the temperature change in electrical resistance of Cu-AR alloy films created by changing the composition, we found that the Aρ gold content was 9 to 15.
The recording medium that undergoes martensitic transformation is blue in the case of heavy @ 9 (,. Measuring the temperature change of electrical resistance is a suitable means to know the transformation temperature of martensitic transformation. Measurement is performed using an AC four-terminal According to the method, the rate of heating and cooling was set at 20 degrees per minute.

FIG. 3 shows an example of the temperature change in electrical resistance of a Cu-Afi alloy film deposited to a thickness of 5000 on a 3i wafer with a thermally oxidized film. As described in Journal of the Japan Institute of Metals 25 G39 (1961), in the case of a bulk Cu-AQ gold alloy, the temperature hysteresis of martensitic transformation is about 80 degrees. In contrast, the recording medium of the present invention shown in FIG. 3 has a temperature hysteresis of about 250 degrees. By optimizing the film creation conditions, the martensitic transformation begins during cooling, and the moisture content M
stsu, 70℃, temperature to complete reverse transformation 11Af-300℃
As described later, a recording medium was obtained which caused martensitic transformation suitable for the present invention and did not have strong adhesion to the substrate.

Furthermore, an accelerated deterioration test was conducted on a CLJ-A2 alloy film deposited on a glass substrate at a high temperature of 70° C. and a relative humidity of 85%. As a measure of deterioration, the optical reflectance was measured at regular intervals of 1I5. FIG. 4 is an example of the result. The horizontal axis is the time under high temperature and humidified 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(o) ), 'R(o) is the change in optical reflectance defined. Figure 4 shows a typical T-b as a magneto-optical recording medium that was tested at the same time for comparison.
Examples of results for Fe amorphous films and GbCO amorphous films are also described. As is clear from Fig. 4, the Cu-An alloy thin film has a smaller decrease in reflectance under high temperature and humid conditions than a light distribution medium using rare earth elements, and has much higher oxidation resistance. Excellent weather resistance.

FIG. 5 is a block diagram of an embodiment of a storage device that uses a recording medium that undergoes the above-described martensitic transformation and performs recording, reproduction, and erasing using a light beam.

10 is a substrate made of glass or organic resin.

Reference numeral 11 denotes the single-layer thin film recording medium described above, which is rotated about a shaft 12. Reference numeral 13 denotes a light beam generator, which also includes a tiIl 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 . 16
The half mirror 917 is a photodetector, and the recording medium 11
A part of the reflected light from the photodetector 17 enters the photodetector 17 via the half mirror 16.

Information is recorded by locally heating the recording medium. That is, the objective lens 151. : Therefore, the light beam is focused accurately on the recording medium 11 and narrowed down to about 1 μmΦ with a pulse width such that thermal diffusion within the plane of the recording medium 11 does not become a problem, and a temperature of the light beam irradiated part is Ar.
Recording was possible by irradiating with a power that did not exceed the maximum power.

When the recorded area was observed using a microscope MII, it was confirmed that it had deformed into the shape shown in Figure 1.

Information is erased by heating the recording medium to Ar or higher. In other words, a light beam is irradiated onto the area to be erased with energy such that the temperature of the recording medium 11 becomes A' or higher. By irradiating a light beam with a pulse width and a beam diameter larger than that during recording, it was confirmed that the recorded portion 3 in FIG. 1 lost its deformation and returned to a flat surface.

The above-mentioned recording and erasing procedures are based on the following principles. When local heating is performed using a light beam for recording, the portion of the recording medium 2 shown in FIG. An internal stress σ occurs.

σ-=E'(Δa/2) Here, E is Young's modulus, Δ°C, /Q is the elongation rate due to thermal expansion when not restrained, and is expressed as Δ2/Q=β(T-Ta). β is the coefficient of thermal expansion, and Ta is room temperature.

King is the temperature of the part irradiated with the light beam. In normal alloys, such as Cl-AM alloys, 'β~2xl'-0-5 (
Considering that IKl,E~1o11 (Pa), an internal stress of σ-31)0 (MP a ) is generated when the temperature of the light beam irradiated portion 114 rises by 150 degrees from room temperature. When the adhesion of the recording medium 2 to the Hayasu 1 is weak, this internal stress σ is the yield stress σ of the M'R body 2.
If cr is exceeded, the light beam irradiated part will undergo plastic buckling,
It is transformed into the shape shown in FIG. If the temperature of the recording medium 2 does not exceed AS during recording, in the case of the recording medium according to the present invention, this deformation may be due to stress-induced stress in the martensitic phase or, in addition to this, due to the twin interface within the martensitic phase. It is carried out by movement and conversion between martensite brother products.

Here, the recording medium 2 according to the present invention may be in a high-temperature phase as an initial state at room temperature, or may be in a mixed state of a high-temperature phase and a martensitic phase (depending on which state it is in, the above-mentioned variations may occur). However, in the material that undergoes martensitic transformation used in the present invention, the yield stress σC' is the minimum value (,100 M
(below pa). Further, during recording, it is necessary that the thermal stress caused by local heating to a temperature not exceeding Af exceeds the yield stress σcr. Therefore, Af of recording medium 2 is 15
Is it above 0℃ and MS is near room temperature? , -50-・120℃
It is desirable that the In response to this requirement, the embodiment described above and shown in FIG. 3 is a recording medium having a transformation temperature R suitable for the present invention.

The recording portion 3 that has been deformed by plastic buckling as shown in FIG. 1 by the procedure on the LS exists stably as long as the temperature is below AS, and this results in a recording state of, for example, 1°. Erasing is due to the shape memory effect already mentioned. When the temperature of the recording medium increases, martensitic reverse transformation occurs at a temperature of As to Δ. During recording, the deformation caused by the stress-induced movement of the martensite phase and the twin boundaries within the martensite phase and the transformation of the martensite brother products into each other was
All become zero when reverse transformation occurs and it 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 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 was overcome by making the erasing light beam pulse have a longer pulse width and pulse rise time than those used during recording, and a beam diameter larger than those used during recording. Making the beam 1\ thicker is achieved by adjusting the objective lens 15 for flight B and slightly shifting the focus compared to when recording. Further, an optical path for an erasing light beam may be provided separately from that for recording. Erasing is completed by the above principle.

Here, in the recording process, if the thermal stress is too large and the deformation is caused by stress-induced martensite phase, movement of the twin interface within the martensite phase, and transformation between martensite older products, etc., the deformation is caused by slipping, etc. It is impossible to erase. Therefore, information that may be erased later needs to be recorded with a thermal stress below the critical stress for slip σSH (>σcr). On the other hand, information that is not desired to be permanently erased can be recorded and stored with a thermal stress of σ8H or more.

To reproduce the recorded fRN, a light beam is irradiated onto the recording medium, and the difference in the amount of reflected light between the recorded part and the unrecorded part (or erased part) is detected by the photodetector 17 shown in FIG. Do it by doing this. The light beam used for black is set to have a power so large that the amount of reflected light is 1 as detected by the photodetector 17c, and a power smaller than that 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 the illuminating light beam may be from the recording medium surface side or from the substrate surface side. The same applies to the direction of the erasing/recording light beam.

In addition to the above-mentioned points, the optical information storage device according to the present invention has the following features:
There is no need for means for applying a magnetic field or a polarizer in the optical path, resulting in a simple configuration as shown in FIG. Of course, in order to make a more practical high-density storage device, in addition to the ones shown in Figure 5, there are also guide grooves on the substrate that are commonly used, means for making the optical system follow the guide grooves, steps, and automation of the optical system. Needless to say, a means for focusing etc. is required.

As already described as the principle of the present invention, the recording medium using the CU-AE alloy described in the example above can be replaced with other similar martensitic transformation enhancing materials. be. For example, CLI-A2 (9 to 15 wt%)-Ni, an alloy known to have a shape memory effect in bulk.
(0-5wt%) alloy.

Ti-Ni' (15-56W [%) alloy, and this N
Alloy, N1-AQ (
19~23wt%) alloy, Mn-Cu (5~36w
t%) alloy, C, u-Z n (38-42wt%)
Si in the alloy.

An iJ film made of an alloy containing O to 5 atomic % of 3n, An, Ga, etc. can be used as the recording medium of the present invention.

In the above embodiment, the state where local thermal stress is generated and deformed is the recorded state, that is, the binary information "i" is expressed, but conversely, the state after the deformation is erased after being exposed to a distance of 51 m is recorded. It is also possible to set the state to ゛′1°°. In this case, the initial state becomes the deformed portion shown in FIG. 1, and the recorded state becomes the Heisei 11 state. Therefore, by forming a deformed portion 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 can be used as a guide groove for guiding the above-mentioned optical head.

In such a case, there is no need to form a guide groove on the substrate, and even a glass substrate or the like on which it is difficult to form a guide groove can be used as a high-density storage device with a flat surface.

Although the recording medium of the present invention can function satisfactorily with a single layer,
For example, if you want to adjust the adhesion of the recording medium to the substrate, you can provide a thermally stable layer between the recording medium and the substrate, or you can add a thin F-layer on both sides of the recording medium to further increase weather resistance. Multi-layering is possible, such as by providing layers.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a recording medium and a substrate in a practical example 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 recording medium according to the present invention. Figure 4 shows the temperature change in electrical resistance of one example of the medium, showing the state of martensitic transformation.
FIG. 5 is an overall configuration diagram of an embodiment of an optical information storage device according to the present invention. 'l... Substrate, 2... Recording medium, 5... Vacuum container, 6... Exhaust system, 7... Crucible, 8... Heater,
9... Substrate, 1O... Substrate, 11... Recording medium,
12...Rotation axis, 15...Objective lens, 16...
Half mirror 117...photodetector. Applicant's agent Patent attorney Takehiko Suzue 1111! II Figure 2 3ti! It AM (C')

Claims (4)

[Claims] (1) A recording medium consisting of a single-layer material film that undergoes martensitic transformation at a specific temperature and stress, a substrate that supports this recording medium, and a light beam that irradiates the recording medium to a temperature below a characteristic temperature. a means for applying heat to deform the recording medium through martensitic transformation; and a means for irradiating the recording medium with a light beam to raise the temperature of the recording medium to the characteristic temperature or higher to cause a reverse transformation of the martensitic transformation to recover the shape. ,
An optical information storage device comprising: means for detecting the presence or absence of deformation of the recording medium 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 a temperature of 150 to 500°C. (3) Claim 1, wherein the recording medium undergoes martensitic transformation at -50 to 120°C.
Optical information storage device as described in . (4) The optical information storage device 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.