JPH0522592B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a laser recording medium. More specifically, the present invention relates to a laser recording medium suitable for recording information by irradiating a laser beam and causing an optical change in the irradiated area.

Conventional technology In recent years, with the remarkable progress in laser technology, the possibility of various applications using coherent light has been pursued. It is expected to be a useful technology in a wide range of fields such as processing, medical, and chemical reaction applications.
Rapid development and research has been carried out, and some have already been put into practical use.

Among these, optical recording media that utilize the good focusing properties of laser light, such as laser disks, have recently attracted attention as media for high-density information recording. Such optical recording media can be broadly divided into rewritable media, which allows different information to be written on the same medium any number of times, and fixed recording media, in which information can be written only once. Magnetic materials, photochromic materials, amorphous materials, thermoplastic materials, electro-optic crystals, etc., and the latter include ablative materials, photopolymer materials,
Silver salt materials, photoresist materials, etc. are known.

Conventionally, as a method of recording information on these materials using a laser beam, a method is known in which information is recorded by causing holes or deformation locally in a metal film, a pigment film, or the like. However, in such an embodiment, once recorded information cannot be erased, it is used as a so-called write-once optical recording medium.

On the other hand, as a rewritable optical recording medium, Te, Te and Bi, Sb, which utilize the phase transition between crystal and amorphous, are used.
VO ₂ , SmS, etc., which utilize metal-semiconductor phase transition, are known.

Among these, in recording media using Te-based materials and alloys of Te, Bi, Sb, etc., repeated recording and erasing, that is, repeated crystal-to-amorphous phase transitions, cause phase separation and loss of rewriting performance. It is known that This phase separation reduces the amount of doping in the alloy and
This can be prevented by increasing the amount of Te, Bi, or Sb. However, when the amount of doping is reduced, a problem arises in that the amorphous lifetime is shortened and the material transitions to an amorphous state within a short period of time at room temperature.

On the other hand, media using VO ₂ or SmS have large volume changes due to transition, which easily causes deformation and cracking of the film, and the hysteresis effect caused by heat is used for repeated recording and erasing. It has the disadvantage that a thermal bias such as cooling to below room temperature must be applied.

Problems to be Solved by the Invention As mentioned above, along with the recent remarkable technological developments regarding lasers, optical recording media are also facing a new phase. However, with conventional optical recording media, it is impossible to erase information once recorded (fixed recording type materials), and even with rewritable media, phase separation occurs when information is repeatedly recorded and erased. There remained various problems that needed to be improved, such as the drying process and the need for extra operations (for example, cooling treatment).

Therefore, it is extremely important to develop a new recording medium that does not exhibit these drawbacks in order to increase the reliability of the recording medium and increase demand for it.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an optical recording medium that does not exhibit the drawbacks of conventional optical recording media as described above and allows repeated recording and erasing.

Means for Solving the Problems In view of the above-mentioned current state of laser beam recording media, the present inventors aimed to obtain an optical recording medium that does not exhibit the various drawbacks of conventional products and can be repeatedly recorded and erased. As a result of various studies and studies, it was found that it is extremely advantageous to provide two or more relatively thin Bi or Sb layers in order to achieve the above object, and the present invention was completed.

That is, the laser beam recording medium of the present invention includes a substrate, at least two dielectric layers as recording medium layers provided on the substrate, and at least two dielectric layers provided on the substrate.
Bi layers or Sb layers, each of the Bi layers or Sb layers is sandwiched between the dielectric layers and alternately arranged with the dielectric layers on the substrate.

In addition to Bi, the Bi layer contains Bi containing 90 atomic% or more of Bi.
Alloys can be used, and the Sb layer can be made of other than Sb.
An Sb alloy containing 90 atomic % or more of Sb can be used and similar effects can be expected.
These can be formed by vapor deposition, sputtering, or the like.

Here, as the substrate, plastics such as polycarbonate or acrylic resin, metals such as Al, or glass are used.

Further, as the dielectric layer, an inorganic vapor deposited film, an inorganic sputtered film, an organic vapor deposited film, an organic sputtered film, or a plasma polymerized film can be used. Of these, inorganic vapor deposited films and inorganic sputtered films include
_SiO2 , _SiO , _Al2O3 , _{Y2O3 , WO3} , _{Ta2O5 ,
Cr2O3} , _CeO2 , _{TeO2 , MoO3} , _In2O3 , _{GeO2 ,}
Oxide films such as _TiO2 , fluoride films such as _MgF2 , _PbF2 , _{CeF3 ,} nitride films such as AlN, _Si3N4 ,
A sulfide film such as ZuS can be applied.

As the organic vapor deposited film, a polymer vapor deposited film such as polyethylene, polyvinylidene fluoride, or polyphenylene sulfide, or a low molecular vapor deposited film such as Cu phthalocyanine or fluorescein can be applied.

As a plasma polymerized film, olefin compounds such as ethylene, aromatic compounds such as styrene, 6
Polymerized films obtained from various organic compounds such as fluorine-containing compounds such as propylene fluoride, nitrogen-containing compounds such as acrylonitrile, Si-containing compounds such as hexamethyldisiloxane, and organometallic compounds such as tetramethyltin can be applied. .

In the laser recording medium of the present invention, a light reflecting layer can also be provided on the recording medium layer or at the interface between the substrate and the recording medium layer, that is, for example, between the substrate and the dielectric layer.

The laser recording medium of the present invention can have a configuration as shown in FIGS. 1 and 2, for example.
For example, the medium in FIG. 1 includes a substrate 1, a dielectric layer 2 formed thereon, and a Bi or Sb layer provided on the dielectric layer, or a Bi or Sb layer containing 90 atomic percent of Bi or Sb.
Alloy layer 3 containing the above (hereinafter referred to as recording layer for simplicity), dielectric layers 4 and 6, and recording layer provided by sequentially forming a dielectric layer and a recording layer thereon in this order. It consists of 5. Further, the embodiment shown in FIG. 2 is an example in which a light reflecting layer 7 is provided on the recording medium. For this light-reflecting layer, conventionally known materials and forming methods can be used as they are, and there are no particular limitations.

Effect The laser recording medium of the present invention uses a recording layer of Bi or Bi alloy, Sb or Sb alloy,
It is characterized by a multi-layered structure in which this and dielectric layers are alternately sandwiched together, and this structure makes it possible to reduce the amount of amorphous compared to the conventional one-layered structure without lamination. Since the quality life is significantly extended, a stable recording medium that does not undergo phase separation and has a long amorphous life can be provided.

Generally, a dielectric layer 2 in contact with the substrate 1 is provided with a substrate 1
If you want to provide a function as a heat insulating layer to prevent heat leakage to the media, it is desirable to have a film thickness of about 50 nm or more, and the top dielectric layer should also be used to suppress the deformation of the medium. It is preferable to use the film with a thickness of about 50 nm or more. Other dielectric layers may be used as long as they can separate the recording layers 3 and 5.
A film thickness of about 5 nm or more is sufficient.

In addition to the function of achieving the separation of the Bi layer, etc. mentioned above, the dielectric layer also has the function of preventing these deformations, which may occur during many repetitions of recording/erasing cycles. Certain types of agglomeration and fusion between recording medium particles are prevented to maintain the particle size of the particles in a fine state.

On the other hand, the recording layers 3 and 5 are formed by vapor deposition or sputtering, and their thickness is preferably 10 nm or less. It has been found that by forming such a relatively thin film, the amorphous lifetime of Bi or Sb can be sufficiently long at room temperature. In other words, the crystallization temperature becomes higher as the film thickness of Bi and Bb becomes thinner. Therefore, as the film thickness of Bi and Sb becomes thinner, the lifetime of the amorphous state of Bi and Sb at room temperature becomes longer, but the recording/erasing sensitivity due to crystallization decreases, so the film thickness of Bi and Sb decreases. A suitable film thickness is 3 to 10 nm.

On the other hand, instead of Bi and Sb, Bi alloy or
When using an Sb alloy, the crystallization temperature is originally higher than that of Bi and Sb alone, so a sufficiently long amorphous life can be obtained by making the film thickness 30 nm or less, and the lower limit is set for the same reason as above. The film thickness is required to be 5 nm or more.
It is suitable that the wavelength is within the range of ~30 nm.

Note that this Bi and Sb compound has a composition that does not cause phase separation, that is, Bi and Sb atoms are 90%
Contains atomic% or more, Pb, Sn, In, As, Se, Ge,
Examples include those doped with 10 atomic % or less of at least one element selected from the group consisting of Si, S, and Sb (when Bi is used as the base).

Some elements of the above alloy components, such as Sn and
By using Ge, In, Se, and the like, it is possible to obtain a recording medium that not only exhibits excellent recording and erasing characteristics but also has a high erasing speed, like the other materials. Therefore, it is possible to speed up recording and erasing.

Although the examples in FIGS. 1 and 2 show a recording medium having only two recording layers, it is possible to configure a laser recording medium with only one recording layer.
However, it is difficult to obtain sufficient contrast with one layer, and a sandwich structure including two or more recording layers is suitable.

Furthermore, as shown in FIG. 2, a light reflecting layer 7 is provided on the dielectric layer 6, and the film thickness of the dielectric layer is controlled.
By minimizing the reflection intensity at the recording wavelength, it is possible to increase the absorption rate of the recording laser beam and improve the sensitivity. In this case, in addition to a metal film such as Al, Au, or Ag, a Bi or Sb film itself can also be used as the light reflection layer.

Next, a method of recording and erasing information by irradiating the recording medium of the present invention with a laser beam will be described.

First, since the Bi or Sb layer is in a crystalline state after it has been deposited, Bi or Sb is crystallized by irradiating it with a strong laser beam with a short pulse width and heating it above the melting point of Bi or Sb, followed by rapid cooling. A phase transition occurs from a crystalline state to an amorphous state, and information is recorded through this amorphous state.

On the other hand, the information recorded as described above can be reproduced by irradiating a laser beam weak enough not to cause amorphization or crystallization and detecting its reflected intensity or transmitted intensity.

In addition, by irradiating this amorphous part with a laser beam that is weaker than the laser beam used for recording but stronger than the reproduction beam for a relatively long period of time, a phase transition from amorphous to crystalline is caused. Information can be deleted.

When using Bi-based alloy or Sb-based alloy layer,
After deposition, it is in an amorphous state. Therefore, it is possible to record by crystallization and erase by amorphization, or to crystallize in advance by heat treatment, record by amorphization, and erase by crystallization. You can also do that.

Furthermore, in the examples described above, recording is generally performed by laser irradiation from the substrate side, but it is also possible to provide a light reflective layer between the substrate 1 and the dielectric layer 2 and irradiate the laser beam from the recording medium side. It can also be done.

Examples Next, the recording medium of the present invention will be described in more detail with reference to Examples.

Example 1 Using polymethyl methacrylate as the substrate,
On top of this, SiO ₂ was deposited to a thickness of 20n by electron beam evaporation.
Bi layers were deposited to a thickness of 5 nm, and Bi was deposited to a thickness of 5 nm using a resistance heating evaporation method.
A recording medium of the present invention provided with layers was produced. however,
The thickness of the uppermost SiO ₂ dielectric layer was 100 nm.
Recording and erasing experiments were conducted on this recording medium using a semiconductor laser with a wavelength of 850 nm. Laser irradiation is performed through the substrate with a laser beam diameter of 1.6 μm, and the laser power is 6 m on the recording medium.
Amorphization occurred at W and a pulse width of 80 ns, and crystallization occurred at a laser power of 4 mW and a pulse width of 400 ns.
For reproduction, laser power is 1mW and pulse width is 500ns.
No change was observed in the recording medium. Moreover, it was confirmed that the same signal output as the initial value was maintained even after more than 10 ⁴ recording/playback experiments. Furthermore, it was found that the amorphous Bi remained stable without crystallization even when stored at 40°C for more than one month.

Example 2 The operation of Example 1 was repeated, and Sb was used instead of Bi film.
A similar recording medium was fabricated using a vapor-deposited film, and this one had a laser power of 15 mW and a pulse width of 15 mW.
Amorphousization occurs in 100ns, laser power 6mW,
Crystallization occurred with a pulse width of 500 ns. When reproduction was performed with a laser power of 1 mW and a pulse width of 500 ns, no change was observed in the recorded state. Moreover,
10 It was confirmed that the same signal output as the initial value was maintained even after ^four or more recording/playback experiments.

Example 3 Repeat the operation of Example 1 and use Bi instead of
Recording media of the present invention were produced using Bi ₉₀ Sn ₅ Ge ₅ , Bi ₉₀ In ₅ Se ₅ , and Bi ₉₀ Pb ₅ As ₅ , respectively. The recording and erasing characteristics of this material were almost the same as those of the recording medium of Example 1, but in erasing, the laser power was 4 m
W, a tendency for the erasing speed to become faster was observed, with crystallization occurring at a pulse width of 300 ns. Regarding stability, no crystallization was observed even after storage at 40°C for more than 2 months, indicating that the product was even more stable than that of Example 1.

Example 4 The operation of Example 2 was repeated to obtain a recording medium having the same structure. However, instead of Sb, Sb ₉₀ Sn ₅ Ge ₅ ,
One using Sb ₉₀ In ₅ Se ₅ and Sb ₉₀ Pb ₅ As ₅ was produced. The recording/erasing characteristics of this product were almost the same as those of Example 2, but the laser power was 6 m.
W, a tendency for the erasing speed to become faster was observed, with crystallization occurring at a pulse width of 400 ns. In addition, no crystals were observed even when the material was stored in an amorphous state at 40° C. for two months, thus confirming that it is extremely stable as an amorphous material at room temperature.

Example 5 The procedure of Example 1 was repeated. However, when we produced a recording medium using electron beam evaporated films of Y ₂ O ₃ , Ta ₂ O ₅ , Al ₂ O ₃ , SiO, CeF ₃ and Cr ₂ O ₃ as dielectric layers instead of SiO ₂ , This product showed the same values as those of Example 1 in terms of recording and erasing characteristics. Also, instead of SiO ₂ PbF ₂ , GeO ₂ ,
The same was true when vapor deposited films of MoO ₃ , MgF ₂ and TeO ₂ were used as dielectric layers.

Example 6 A recording medium of the present invention was produced in the same manner as in Example 1 except that a plasma polymerized film of tetramethyltin was used instead of SiO ₂ as the dielectric film. In this case, the polymer film thickness of the top layer was 200 nm. In this recording medium, amorphization occurs at a laser power of 5 mW and a pulse width of 6 ns, and the laser power is 3 mW.
Crystallization occurred with a pulse width of 40 ns. Reproduction was performed with a laser power of 1 mW and a pulse width of 500 ns, but no change was observed in the recorded state. Furthermore, this thing
10 It was confirmed that the same signal output as the initial value was maintained even after ^four or more recording/playback experiments.

Example 7 Two types of recording media were manufactured in the same manner as in Example 6 except that a polyimide sputtered film and a Cu phthalocyanine vapor-deposited film were used instead of the tetramethyltin plasma polymerized film as the dielectric layer. did. These gave the same results as Example 3 in terms of recording/erasing characteristics, but after 10 ³ times of recording/erasing.
After the extinction experiment, irreversible changes occurred in these media.

Example 8 A recording medium was produced in which two Bi layers were provided in Example 1, the top layer had a SiO ₂ film thickness of 150 nm, and an Al vapor deposited film with a thickness of 50 nm was provided thereon as a light emitting film. In this medium, the laser power is 6 mW,
Amorphization occurred with a pulse width of 70 ns, and crystallization occurred with a laser power of 3 mW and a pulse width of 400 ns.

Effects of the Invention As explained in detail above, in the laser beam recording medium with the laminated structure of the present invention, the characteristics of the medium can be controlled by controlling the film thickness of the Bi or Sb or Bi alloy or Sb alloy layer. It has the advantage of good reproducibility of media characteristics.
Furthermore, since Bi, Sb, or a Bi alloy or Sb alloy containing 90 atomic percent or more of Bi or Sb is used, a medium with high sensitivity and excellent contrast is provided.
In addition, the recording medium of the present invention does not cause phase separation and has a long life in the amorphous state, and the dielectric layer prevents deformation of the medium, and the particle size of Bi, Sb, Bi compound, and Sb compound is small. Because it remains minute and does not change, it can be used as a laser recording medium that can be repeatedly recorded and erased.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing the structure of a recording medium according to the present invention, and FIG. 2 is a schematic cross-sectional view showing the structure of a recording medium according to another aspect of the present invention. (Main reference numbers), 1... Board, 2, 4, 6...
...dielectric layer, 3,5...Bi or Sb layer or
Bi alloy or Sb containing 90 atomic% or more of Bi or Sb
Alloy layer, 7... light reflective layer.

Claims (1)

[Claims] 1. A substrate, at least two dielectric layers as recording medium layers provided on the substrate, and at least two
the Bi layer or the Sb layer, and the Bi layer or the Sb layer.
1. A laser recording medium characterized in that each of the layers is sandwiched between the dielectric layers and alternately provided with the dielectric layers on the substrate. 2 A Bi alloy layer containing 90 atomic % or more of Bi is used instead of the Bi layer, or an Sb alloy layer containing 90 atomic % or more of Sb is used instead of the Sb layer. The laser recording medium according to scope 1. 3. The laser recording medium according to claim 1 or 2, characterized in that a light reflective layer is provided on the recording medium layer or at the interface between the substrate and the recording medium layer.