JPS6029949A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To enable tens of thousand times of recording, erasing and rerecording as desired and to enable long-term preservation of record with the simple construction of a recording film which permits reproducing and erasing by constituting said recording film of an amorphous film contg. a metallic component to form a shape memory alloy when irradiated with a light beam as well as carbon and hydrogen. CONSTITUTION:An Ni-Ti-C film is formed to 500Angstrom thickness by reaction sputtering in gaseous CH4 on an acrylic resin disc base plate having, for example, 300mm. diameter and 1.5t with an alloy of Ni50Ti50 as a target. Such discoid optical information recording medium is rotated 600 times per minute and information is recorded thereon by irradiating a semiconductor laser beam having 50ns pulse width and 3mW power. When the information is reproduced by using the similar laser beam having the decreased power, the S/N obtd. with the reproduced output of the signal is >=40dB. If the laser beam having the power increased to 9mW is irradiated thereto, the recorded information is erased. Information is again recorded thereon when the laser beam of 3mW is thereafter irradiated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical information recording medium in which information is recorded, reproduced, and erased using a light beam such as a laser beam.

[Technical background of the invention and its problems] In recent years, so-called optical disk devices have been attracting attention as high-density, large-capacity information recording and reproducing devices.

This is achieved by focusing a light beam, such as a laser beam, to a diameter of about 1 μm and irradiating it onto the optical disk and the recording medium stored therein, thereby creating a width of 0.6 to 1 μm.

Information is recorded by forming pits with a length of about 0.6 to 2 μm on a recording medium, and the pits are read and reproduced using a similar laser beam.

As recordable optical information recording media used in such optical disk devices, there are known two types: an erasable type that allows information to be recorded multiple times, and a recordable type that cannot be erased or rerecorded. However, in practical terms, the former erasable type is naturally preferable.

The recording film of erasable information recording media can be divided into three types. The first is a magneto-optical film that records information in the direction of the perpendicular magnetization axis, the second is an optical density variable film that utilizes the phase change, density change, and refractive index change of the film, and the third is a film that records information in the direction of the perpendicular magnetization axis. It is a displacement type membrane that utilizes the positional displacement of the membrane. Each has advantages, but the common disadvantage of all three is that the recording film is complicated and a uniform film cannot be formed over a large area. For example, the first magneto-optical type is a combination of a rare earth metal and a transition metal, usually requires three components, and is a multilayer film. The second optical III variant requires three or four components of chalcogenide metals. The third displacement type also requires a material film that causes displacement and a material film that returns the displacement, and requires a multilayer film of three component films.

A known technique belonging to the third displacement type related to this invention is USP 4,371.954.

As shown in FIG. 1, a polymer or metal film 2 with a high heat absorption rate and a shape memory alloy film 3 having a martensitic structure are laminated on a substrate 1. : Based on the structure, the film 2 is locally fiwted by heating by laser beam irradiation, and the film 3 is also deformed, causing a displacement 4. This displacement 4
Therefore, when a weak laser beam is irradiated here, light scattering and interference occur, and as a result, a reproduced signal output can be obtained. When erasing, the films 2 and 3 are melted by irradiation with a laser beam having a stronger vibration, and the displacement 4 is made to disappear.

However, USP 2: Do not heat the film to the point where it evaporates.
According to the specification of 4.371.954, when recording information again, the films 2 and 3 are irradiated with a laser beam.
It is said that it is sufficient to displace it again. Further, as the film 2, Cd, Zn, TiMg, Aj! , Mn, AQ, etc. are exemplified, and as the film 3, Fe-N
i, Fe-pt, Ti-Ni, N1-AJl
, AU-Cd, Cu-Zn, Sy:z less, C
A metal film having a martensitic phase such as u-7n-Af (especially Cu7sZrlxsAJ17°Cu 79 Zrl 13 Afe) is exemplified.

The biggest drawback of this method is that the components of 1192.3 are complex, and since the recording film is formed by laminating these films 2.3, it cannot be recorded as displacement by irradiation with a recording laser beam. Also, the films 2 and 3 are erased with an erasing laser beam.
When melted, these films 2.3 mix with each other and change into a film with a new composition. Therefore, after erasing the recording, the film becomes a phase different from the martensite phase it had initially, and it has the disadvantage that it is extremely difficult to record information again in practice.

[Object of the invention] The object of the invention is to record information with a recording film having a simple structure.
An object of the present invention is to provide an optical information recording medium that can be reproduced and erased.

[Summary of the Invention] This invention provides an amorphous film containing a metal component, carbon, and hydrogen that becomes a shape memory alloy when irradiated with a light beam, as a recording film that can record, reproduce, and erase information by irradiation with a light beam. It is characterized by the use of

In the recording film according to the present invention, gas components containing carbon and hydrogen in the irradiated area are evaporated by the heat generated by the irradiation of the light beam, and the state of the film changes from an amorphous film to a shape memory alloy. At the same time, the crystalline film changes to a crystalline film with a martensitic phase consisting only of the components, and the crystalline film portion swells due to the evaporation pressure of the gas component, producing a convex portion, that is, a displacement.
Recording is done. Therefore, during reproduction, a reproduction light beam is irradiated as in the conventional case, and a reproduction signal output can be obtained by utilizing the fact that the amount of reflected light is reduced by being scattered and interfered with by the convex portion.

On the other hand, the recorded information is erased by the heat generated by the erasing light beam, which has a stronger power than the recording light beam, which melts the crystalline film in which the protrusions are formed and causes the protrusions to disappear. achieved.

Furthermore, when re-recording after erasing, the crystalline film part recalls the memorized shape of the convex part due to the heat generated by the irradiation of the re-recording light beam with the same power as the original recording light beam. Form. Of course, the portions that were not irradiated with the laser beam during the first recording and remained amorphous will form convex portions with the same effect as the first recording when the light beam is irradiated even during re-recording. A record will be made.

[Effect of the invention] The optical information recording medium according to the present invention is capable of recording, reproducing, and erasing information, and since the recording film has a single layer structure, it becomes a shape memory alloy during recording even after erasing. There is no change in the composition of the crystalline film portion, and therefore, it is possible to perform re-recording using the properties of the shape memory alloy without any problems. That is, recording, erasing, and re-recording can be freely performed tens of thousands of times, and since the recording film has a simple structure and uses shape memory, there is an advantage that recording can be stored for a long time.

[Embodiment of the Invention] An embodiment of the optical information recording medium according to the present invention will be described in detail with reference to FIG. FIG. 2(a) is a sectional view of an optical information recording medium according to the present invention, in which a recording film 12 is formed on a substrate 11. The material and shape of the substrate 11 are not particularly limited, but when considering application as a disk memory, a circular disk substrate made of a glass plate, an acrylic plate, an ester sheet, etc. is used.

As described above, the recording film 12 is made of a metal component that is to be a shape memory alloy, such as Ni-Ti or Fe-Pt.

In-TJl, N1-AJ! , Au-Cd, Cu
-AJl-Ni.

Preferably 5 carbon (C) and hydrogen (H) are added to at least one alloy film selected from Cu-7u-8i.
It consists of an amorphous film containing ~40 atomic percent. To explain an example of a method for forming the recording film 12 having such a configuration, first, a metal plate having a composition that is to be a shape memory alloy, that is, martensite is prepared. In this state, it is not necessary to be in the martensitic phase, for example, the atomic weight is 49 to 5.
A Ni-Ti alloy plate with 1% Ni may be used. 13. This alloy plate is used as a cathode and the substrate 11 is used as an anode between the two electrodes.
Connect a 56MHz RF power supply or DC power supply, and
A discharge is caused in -14 gas or a mixed gas of CH4 and Ar. As a result, a recording film 12 is formed on the substrate 11. This is a so-called film formation process using reactive sputtering in CH4 gas.

Next, before explaining the recording, reproducing, and erasing operations performed on this information recording medium, we will explain that although erasing is impossible, information can be written once, additionally written, and reproduced. A known example of a displacement type optical information recording medium that is optimal for long-term storage will be described. As such a recording medium, we have developed a recording film made of a sputtered film in CH4 gas using a Te (tellurium) target, as described in Japanese Patent Laid-Open No. 57-1652.
It has already been proposed as No. 92. The internal structure of the film formed by sputtering in CH4 gas (hereinafter referred to as 're-C film) is an aggregate of metal microcrystals with a diameter of approximately 30 mm, based on our analysis results. The middle part between the groups is filled with alkyl molecular groups, represented by methyl groups, which are connected together, and when viewed as a whole, it is a mixture-like amorphous 1.
It's now 19.

Because of this structure, it has the characteristics of high recording sensitivity as an optical information recording medium and an extremely long recording preservation state. On the other hand, a film with this structure also has the characteristic that when heated to around 140° C., the alkyl molecules evaporate, and the remaining metal film becomes crystalline.

The T(+-C film is an amorphous film at room temperature, but when it is heated to 140°C or higher by irradiation with the Sea 11 beam, it becomes Te
It changes into a crystalline film and melts at temperatures above 450°C, forming holes (bits). Instead of Te, Atl, which has a slightly higher melting point, for example, 956°C, was chosen and the film was created using the same method. When the laser beam is irradiated, the amorphous film changes to crystallized Ag at 140°C or higher. The membrane changes into a plasma membrane, and by the time it melts, the membrane is melted and a hole is formed. The expansion of the membrane before the hole is made, the so-called deformation or displacement of the membrane, can also be used to record information. However, TC! -C film or A
(For the 1-C film, it is possible to expand the film and make holes as described above), but it is possible to return the film to its original flat state.
In other words, records cannot be erased.

Therefore, in this invention, a metal that becomes a shape memory alloy, for example, Ni-Ti, is used instead of Te or Ag, and this is replaced with Te or Ag.
-C film and Ao-C film by the same method as N1-Ti
Recording by sputtering the target in CH4 gas 1
1JI (Ni-T i-C film) was formed, and as shown in FIG.
) Create the optical information recording medium shown in ().

In the state shown in FIG. 2(a), the recording film 12 is an amorphous film.

Now, when this recording film 12 is irradiated with a light beam 13, for example a laser beam, as shown in FIG. 2(b), A! J-C
The film expands under the evaporation pressure of the gas component of <C, l-1, which is the same as that of the film, and forms a convex part 14, and only the part of this convex part 14 changes into a crystalline film, following the pre-existing composition. phase, that is, the martensitic phase. Therefore, this convex portion 1
The shape of No. 4 is memorized only in this portion by the shape memory effect of the alloy film, which is a crystalline film. Next, when the convex portion 14 is irradiated with a laser beam with a stronger power as an erasing light beam and additionally heated near the melting point, the full tensile phase 1 to phase disappear and the recording film 12 becomes uniform as shown in FIG. 2(C). It changes to a flat shape. However, in this state, the recording film 12 is separated into an original amorphous film portion 15 and a crystalline film portion 16. This state is the recording erased state.

In the case of re-recording, it is sufficient to irradiate a laser beam as a re-recording light beam with a power comparable to that of the laser beam used as the recording light beam originally irradiated. The crystalline film portion 16 is heated by the beam irradiation, changes to a martensitic phase, and changes to the memorized shape. That is, as shown in FIG. 2(b), the convex portion 14 is formed again, and a recorded state is achieved.

This recording and erasing can be repeated over a million times because it is only a change in the phase of the alloy.

Furthermore, since the presence or absence of the convex portion 14, that is, the displacement of the recording film 12, can be detected and extracted as a reproduction signal output,
The S/N ratio can also be increased to 40 dB or more.

Although it differs depending on the magnitude of displacement, the S/N ratio is also higher for a film with a higher thermal expansion.

Next, a more specific example will be described.

Example 1 On a 300mΦ, 1.5t acrylic resin disk substrate, CH4 was applied using an alloy of N15oTfsn as a target.
Ni-Ti-C11 by reactive sputtering in gas
1 was formed to a thickness of 500 people. This disc-shaped optical information recording medium was rotated at 600 revolutions per minute and information was recorded by irradiation with a semiconductor laser beam (λ=0.8 μm) with a pulse width of 50 ns and a power of 3 mW. When this was reproduced using a similar laser beam with lower power, the signal reproduction output was S/
N was obtained at 40 dB or more. Next, when the same semiconductor laser was used to irradiate a laser beam with increased power to 911 W, the recorded information disappeared. Thereafter, information could be recorded again by irradiation with a 3IIIW laser beam. Even after repeating this recording, reproducing, and erasing process 100,000 times, no deterioration was found.

Example 2 ALI s o Cd known as shape memory alloy material
A recording film was similarly formed by sputtering 511 alloy as a target in CH4 gas to obtain an optical information recording medium. Recording using this recording medium in the same manner as in Example 1,
Similar results were obtained after repeated reproduction, erasing, and re-recording. However, the S/N of the reproduced signal output increased to 45 dB. It is presumed that the reason for this S/N improvement is due to the difference in the degree of expansion due to the difference in thermal expansion of the recording film, that is, the difference in the size of the convex portion.

In the above example, a recording film formed by sputtering in Cl-14 gas was described, but the same effect can be obtained using a gas containing C and H, such as ethane, propane, ethylene, acetylene, etc. other than CH4 gas. A recording film with a high quality can be obtained. This invention can be implemented with various other modifications.

[Brief explanation of drawings]

Figure 1 shows the structure of a known optical information recording medium.
Figures 1 and 2 are diagrams for explaining one embodiment of the present invention, in which (a) is a cross-sectional view of an information recording medium, and (b) is a cross-sectional view showing a state in which information is recorded by irradiation with a light beam. , (C) is a sectional view showing the state in which the recording has been erased. DESCRIPTION OF SYMBOLS 11... Closure plate, 12... Recording film, 13... Light beam, 14... Convex part, 15... Amorphous film part, 16...
・Crystalline membrane part. Applicant's agent Patent attorney Takehiko Suzue

Claims (5)

[Claims] (1) In an optical information recording medium provided with a recording film on a substrate that can record, reproduce, and erase information by irradiation with a light beam, the recording film is made of a metal component that becomes a shape memory alloy when irradiated with a light beam. An optical information recording medium comprising an amorphous film containing carbon and hydrogen. (2) The recording film is made of Ni-Ti, Fe-Pt, In-
TJl. N1-Af, Au-Cd, Cu-AJ/, -N
Claim 1, characterized in that the film is an amorphous film containing 5 to 40 atomic percent each of carbon and hydrogen in at least one kind of alloy selected from +, Cu-Zn-8i, and Cu-Zn-8i. Optical information recording medium. (3) The recording film changes from an amorphous film to a martensitic phase consisting only of shape memory alloy components when gas components containing carbon and hydrogen evaporate due to the heat generated by the light beam irradiation in the area irradiated with the recording light beam. Along with changing to a crystalline film,
3. The optical information recording medium according to claim 1, wherein the crystalline film portion expands under pressure due to evaporation of the gas component to form a convex portion. (4) The recording film is such that the crystalline film portion in which convex portions are formed during recording melts due to the heat generated by irradiation with the erasing light beam, which has a stronger power than the recording light beam, and the convex portions disappear. An optical information recording medium according to claim 3, characterized in that: (5) Convex portions are formed in the recording film by evoking the memorized convex shape in the crystalline film portion by heat generated by irradiation with a re-recording light beam having approximately the same power as the recording light beam. The optical information recording medium according to claim 4, characterized in that: