JPH03150737A - Optical recording method and optical recording medium - Google Patents

Abstract

PURPOSE:To allow the easy execution of not only the writing and reading out of information but the erasing and rewriting thereof as well as utilizing martensite transformation. CONSTITUTION:The point to be recorded with information of the thin film which is formed as a base phase over the entire part is irradiated with a laser beam so that the cooling after heating is rapidly executed to transform only this point from the base phase to the martensite phase in the case of recording of the information. A change in light reflectively arises in a pat of the thin film in this way and, therefore, the recording of the information is executed. On the other hand, the point to be erased of the thin film is irradiated with the laser beam to locally heat the thin film to the As point or above in order to execute partial erasing. The martensite phase is converted to the base phase in this way. On the other hand, the entire part of the thin film is heated together with the substrate to the As point or above in the case of simultaneous erasure. All the regions which are locally converted to the martensite phase are transformed to the base phase and the entire part of the record is simultaneously erased.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application J This invention relates to an optical recording method for writing and erasing information using a +12J laser beam and an optical recording medium used therefor.

"Prior Art" Optical recording has features such as high recording density, high speed access, and non-contact recording and reproduction, and is rapidly being put into practical use.

However, with current optical recording media such as video discs and audio discs, although it is possible to write and read information, they cannot be erased or rewritten, and are limited to so-called ROM (read-only memory). The issue of erasing and rewriting information remains unresolved.

By the way, along with the transformation of metal crystal structures,
It is known that the light reflection properties of the surface change.

The present inventors conducted research to apply this phenomenon to optical recording methods, and as a result, they came to obtain the following extraordinary knowledge.

■ Among metals that undergo phase transformation6, alloys that undergo martensitic transformation have a large change in light reflectance due to phase transformation.
The rate of change is maximum at a specific wavelength depending on the type of alloy.

■ When a thin film of the above alloy is formed on a substrate by sputtering or vapor deposition, it is possible to locally phase transform the thin film by irradiating it with a laser beam, and by changing the irradiation conditions, the cooling rate after heating can be adjusted. Then, the following a,
Two types of phase transformations (b) can be selected.

a. When the thin film is in a martensitic phase, the thin film is irradiated with a laser beam at a relatively low output and locally heated to a temperature higher than the reverse transformation σn onset temperature.7. The cooling rate after heating is small,
The martensitic phase is converted to the matrix phase.

b. When the thin film is the parent phase, when the thin film is irradiated with a laser beam at a higher power and shorter time than in a, and locally heated,
The cooling rate of the thin film after heating becomes higher than a, and the parent phase is converted to a martensitic phase.

This invention has been made based on the above findings, and an object of the present invention is to provide an optical recording method that allows not only writing and reading information but also erasing and rewriting information with ease.

"Means to solve problems" The present invention will be described in detail below.

The optical recording method according to the present invention involves forming a thin film of an alloy exhibiting martensitic transformation on a substrate, using an optical recording medium in which the thin film is unified as a matrix phase, and applying a laser beam to a location on the thin film where information is to be written. The main feature is that the parent phase is converted to the martensite phase by irradiating the area, heating the area, and then rapidly cooling it at a rate that allows the conversion from the parent phase to the martensite phase, thereby changing the light reflectance and writing information. It is said that

A wide variety of alloys are known that exhibit martensitic transformation, but the martensitic transformation alloy that can be used in this invention has a martensitic transformation starting temperature (Ms point), a reverse transformation starting temperature CAs point) It is necessary that the difference in ℃ or higher is preferable.

The drawing shows Cu-^(
This figure shows a hysteresis curve of a 1-Ni alloy, using light reflectance as an index of phase transformation.

As an alloy that satisfies the above conditions, (a) Ni-T
i system and Ni-Ti-X system (X; Co, Cu, Fe, U,
Cr, Th1n) (b) N1-A(! system and N1-A(1-X system (X; Co, Ga, Zn, Ti)
(8) Cu-2n system and Cu-Zn-X system (X; Ga, Ge, ^4. In,
Sb, Si, Sn, N1) (d) Cu-Arl system and Cu-^Q-X system (X; Fe, Ni, Co, Mn) (
N) ^u-Cd system and ^u-Cd-X system (X; Cu, In, fig, Mn
, 2n) (to) Au-2n system and Au-2n-X system (X; Ga, In, Cu, Mg,
Cd, Ag) ()) Ag-Cd system and Ag-Zn-Cd system (H) In-T& system and In-Cd system (S) Mn-Cu system (J) Fe-Mn system, Fe-Ni system, It is selected from alloys such as Fe-Pt and Fe-Ni-Cr.

Such an alloy is formed as a thin film with a thickness of about 0.03 to 2 μm on a substrate made of glass, metal, ceramics, or the like.

If it is less than 0.03μ degree, it is difficult to obtain a uniform thin film, and
Due to the influence of the board, phase change deafness becomes less likely.

In addition, if the thickness is more than 2 μm, the amount of heat required to raise the film temperature to the reverse transformation starting temperature will be large, and the cooling rate after laser beam irradiation will be slow, making it difficult to transform the parent phase into the martensitic phase. .

Note that a sputtering method or a vapor deposition method is suitable as a means for thinning the film. Even when formed into a thin film, this type of alloy maintains the above-mentioned martensitic transformation characteristics.

Note that a light-transmissive protective layer may be provided on the alloy thin film on the substrate, and a heat reflective color may be provided between the substrate and the thin film.

A thin film of an alloy formed on a substrate is generally initially in a martensitic phase because it is ultra-rapidly cooled on the substrate during sputtering or vapor deposition.

Therefore, a process to convert the thin film into a matrix is usually required. For this purpose, the entire thin film together with the substrate is heated above the Ms+ point to convert the thin film from a martensitic phase to a parent phase. As shown in the graph of the drawing, this matrix phase has a lower light reflectance than the martensitic phase.

Next, a method for performing optical recording using such an optical recording medium will be explained.

As a heating means for transforming the alloy thin film into martensitic transformation and reverse transformation, a laser beam having particularly high heating efficiency is used. Further, as a means for reading out changes in light reflectance of a thin film, light of a specific wavelength, particularly a laser beam, is suitable.

When writing information, a laser beam is irradiated onto the area where the information is to be written on the thin film, which is made entirely of the matrix as described above, and the irradiation conditions are controlled so that the cooling after heating is done in an ultra-rapid manner. so that only this portion is transformed from the matrix phase to the martensitic phase.

To ultra-quickly cool a thin film after heating, the output per unit area of the laser beam is adjusted to heat the irradiated surface of the thin film in a short time. This increases the thermal gradient near the irradiated area, and after irradiation, heat rapidly diffuses from the irradiated area to the surrounding area.
As a result, the irradiated area is ultra-quickly cooled to room temperature.

Note that the actual irradiation conditions cannot be specified because they vary depending on the thickness of the thin film, differences in thermal conductivity and reverse transformation start temperature depending on the type of alloy, and the type of substrate. This should be determined through experimentation.

The martensitic phase portion thus generated in the thin film stably exists as a martensitic phase at room temperature because the As point of the alloy is at a high temperature higher than room temperature. For example, Cu-^Q-N
As is clear from the graph, the light reflectance of the martensitic phase of the i-alloy is higher than that of the parent phase, and changes in light reflectance occur in some parts of the thin film, making it difficult to record (write) information.
can be done.

Then, by detecting this change in light reflectance using a light detection means such as a laser beam, the recording can be reproduced (read).
is possible.

On the other hand, in order to partially erase written information, a laser beam is irradiated to the part of the thin film where the information to be erased is written at a relatively lower output than in the writing operation, and the thin film is locally irradiated with As.
Heat above point. Then, the irradiation time will inevitably be relatively long, and the heat will diffuse to the surrounding area during irradiation, so the thermal gradient in the vicinity of the irradiation area will be small, which will reduce the cooling rate after irradiation and reduce martensite. The phase is converted into the parent phase.

In addition, the irradiation conditions in this case are the same as above, depending on the thickness of the thin film, the thermal conductivity depending on the alloy type, and the appropriateness! It is difficult to generalize because the difference in IJlffn starting temperature varies depending on the type of substrate. This should be determined through experimentation.

On the other hand, when erasing information written on the thin film all at once,
The entire thin film together with the substrate is heated above the As point. As a result, all the information-recorded portions that are locally in the martensitic phase are transformed into the matrix phase, and the entire record is erased at once.

As described above, in the present invention, information writing,
Can be read, erased, and rewritten. By selecting the wavelength, the light reflectance accompanying the transformation can be reduced to 2
The above can be achieved, and optical recording with a high SZN ratio can be performed. In addition, martensitic transformation can occur any number of times as long as the temperature conditions are met, so this optical recording medium can be repeatedly recorded and erased semi-permanently.
It has a long lifespan.

"Example" Hereinafter, the present invention will be specifically explained with reference to Examples.

Cu14vt%, A123.4w on a glass substrate
An alloy thin film having a thickness of 800% and consisting of NlrIjc portions was formed. This alloy thin film was in a martensitic phase at room temperature. The entire thin film together with the substrate was heated at 250° C. for 10 minutes to reversely transform into the parent phase. In this state, the wavelength is 830
The light reflectance at rv was 29%. A semiconductor laser beam with a wavelength of 633 nm is applied to the thin film in this state at a focus of 0.8 nm.
When focused to μm and irradiated, it was heated and ultra-quenched, transformed into a martensitic phase, and the light reflectance at 830 nm was 61%.
It increased to

As a result, it was found that writing and reading information was possible.

Furthermore, when the martensitic phase was irradiated with the semiconductor laser beam with a focus of 1.2 μm, it was reversely transformed into the matrix phase, and the light reflectance returned to its original value of 29%, making it possible to erase information. This was recognized.

Furthermore, when the entire thin film was heated at 250° C., all of the thin film was reversely transformed into the parent phase, and information could be erased all at once.

Furthermore, the above information is recorded and partially erased once every minute.
Although the test was repeated 1,000 times, no fluctuation was observed in the change in light reflectance due to phase transition, indicating that it can be used repeatedly many times.

In addition, Cu1.99wt%, Zn5.9wt%, AI2
The balance consists of an alloy, Ni21. Similar results were obtained for thin films of alloys consisting of Ivt%, A (balance) and alloys consisting of 45.9wt% Ni, balance Ti.

"Effects of the Invention" As explained above, in the optical recording method and optical recording medium according to the present invention, a laser beam is irradiated to the location where information of the /V film, which is the matrix phase, is to be written, and this location is heated. By rapidly cooling, the matrix phase is converted to a martensitic phase, and the light reflectance is changed so that information can be written. Therefore, simply by using a laser irradiation device, information can be written easily and at high speed, and the applications of optical recording can be expanded.

In addition, the light reflectance of the thin film changes in binary values as the phase changes, and by using light with a specific wavelength depending on the alloy type for reflectance measurement, the degree of change in the light reflectance can be increased. , a high SlN ratio is achievable.

On the other hand, in the second optical recording method of the present invention, the second! In addition to the above method, by irradiating the upward direction of the laser beam on the area where unnecessary information has been written, the irradiated area is returned to the parent phase. Therefore, partial erasure of information, which was difficult with conventional optical recording methods, can be easily performed.

Furthermore, in the third optical recording method of the present invention, when the information is no longer needed, the entire thin film is heated to a temperature above the starting temperature to remove all the information-recorded portions that are in the martensitic phase from the matrix phase. I will return to .

Therefore, all information can be erased at once by simply heating the thin film.

[Brief explanation of the drawing]

The figure is a graph showing the temperature hysteresis of martensitic transformation/moderate transformation. −◆Temperature

Claims (4)

[Claims] (1) After forming a thin film of an alloy with a martensitic transformation starting temperature of 0°C or lower and a reverse transformation starting temperature of 40°C or higher on a substrate by sputtering or evaporation, a light beam is formed using the thin film as the matrix. Using a recording medium, a laser beam is irradiated to a location on the thin film where information is to be written, and the location is heated and then rapidly cooled at a rate capable of converting the parent phase to the martensite phase, thereby converting the parent phase to the martensite phase. An optical recording method characterized by recording information by changing the light reflectance. (2) After forming a thin film of an alloy with a martensitic transformation starting temperature of 0°C or lower and a reverse transformation starting temperature of 40°C or higher on a substrate by sputtering or vapor deposition, light is produced using the thin film as the matrix. Using a recording medium, a laser beam is irradiated to a location on the thin film where information is to be written, and the location is heated and then rapidly cooled at a rate capable of converting the parent phase to the martensite phase, thereby converting the parent phase to the martensite phase. Then, while writing information by changing the light reflectance, it is possible to heat the part of the thin film where unnecessary information is written to a temperature higher than the reverse transformation start temperature, and after heating, the martensitic phase changes. The laser beam is irradiated with an intensity that allows the cooling rate to convert to the parent phase, and the irradiated area is returned to the parent phase.
An optical recording method characterized by partially erasing information. (3) After forming a thin film of an alloy with a martensitic transformation start temperature of 0°C or lower and a reverse transformation start temperature of 40°C or higher on a substrate by sputtering or vapor deposition, light is produced using the thin film as the matrix. Using a recording medium, a laser beam is irradiated to a location on the thin film where information is to be written, and the location is heated and then rapidly cooled at a rate capable of converting the parent phase to the martensite phase, thereby converting the parent phase to the martensite phase. Then, while changing the light reflectance to write information, if the information is no longer needed, the entire thin film is heated to a temperature higher than the reverse transformation start temperature, and all the parts that are in the martensitic phase are heated. An optical recording method characterized by returning to the matrix and erasing information all at once. (4) A thin film of an alloy having a martensitic transformation starting temperature of 0°C or lower and a reverse transformation starting temperature of 40°C or higher is deposited on a substrate with a thickness of 0.03 to 2 μm by sputtering or vapor deposition.
An optical recording medium characterized in that the thin film is formed to a thickness of m and the entire area of the thin film is converted into a matrix phase.