JPS6166696A - Laser recording medium - Google Patents

Abstract

PURPOSE:To obtain a repeatedly recordable, erasable, highly sensitive laser recording medium with high contrast by providing dielectric layers and recording medium layers consisting of either Bi layer or Sb layer sandwiched between said dielectric layers on a substrate. CONSTITUTION:More than two dielectric layers (e.g. SiO2 film, etc.), recording medium layers consisting of either Bi layer or Sb layer 3, 5 sandwiched between said dielectric layers 2, 4, 6, are provided on a substrate 1 (e.g.: plastic sheet, etc.). Further preferably a light reflecting layer (e.g.: Al film, etc.) 7 is provided on the recording medium layer or the boundary between the substrate and the recording medium layer. Of a Bi alloy layer containing more than 90 atom o/o of bismuth is used in the Bi layer and a Sb alloy layer containing more than 90atom o/o of antimony in the Sb layer, it is possible to accelerate the recording and erasing speed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to laser recording media. 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 pursuit of various application possibilities using coherent light has resulted in improvements in optical communications, optical recording/reproduction, optical measurement, and the development of various products. It is expected to be a useful technology in a wide variety of fields, including processing, medical, and chemical reaction applications, and has been rapidly developed and researched, with some already putting it into practical use.

Among these, recently, optical recording media that utilize the good focusing properties of laser light, such as laser discs, have been attracting 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 only be written once. Magneto-optic materials, photochromic materials, amorphous materials, thermoplastic materials, electro-optic crystals, etc. are known, and among the latter, 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 locally causing holes or deformation 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, rewritable optical recording media include those that use Te or alloys of Te and Bi, Sb, etc. that utilize a crystal-amorphous phase transition, and those that utilize a metal-semiconductor phase transition.
0□, SmS, etc. are known.

Among these, in recording media using Te-based materials and alloys of Te and B1, Sb, etc., repeated recording and erasing, that is, repeated crystal-amorphous interphase transitions, cause phase separation and impair rewritability. It is known.

This phase separation can be prevented by reducing the amount of doping in the alloy and increasing the amount of Te, 8i, 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, in media using ■0□, SmS, there is a large volume change due to the transition, and the film is easily deformed and cracked, and the hysteresis effect due to heat is used for repeated recording and erasing. It has the disadvantage that a thermal bias must be applied, such as cooling it below room temperature.

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. Various problems remain that need to be improved, including the fact that the process is difficult to maintain, and that extra operations (for example, cooling treatment) are required.

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 have obtained an optical recording medium that does not exhibit the various drawbacks of conventional products and can be repeatedly recorded and erased. As much as possible, consider
As a result of research, 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 has a substrate, at least two dielectric layers and at least two Bi layers or Sb layers as recording medium layers provided on the substrate, and the Bi layer Alternatively, each of the Sb layers is sandwiched between the dielectric layers and arranged alternately with the dielectric layers on the substrate.

In addition to Bi, the Bi layer contains Bi containing 90 atomic percent or more of Bi.
A gold alloy can be used, and the Sb layer can be made of Sb as well as Sb.
An Sb gold alloy containing 90 atomic % or more of b 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 AI, 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. Among these, S 102.5iO1AI20 is used as an inorganic vapor deposited film and an inorganic sputtered film.
3, Y2O3, WO3, Ta205, Cr, 03, Ce
O2, Tea, , M2O3, In2O3, GaO2, T
Oxide films such as iO2, MgF2, PbFz, CeF3
A fluoride film such as AIN, a nitride film such as Si, N, or a sulfide film such as ZnS can be used.

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

As the plasma polymerized film, olefin compounds such as ethylene, aromatic compounds such as styrene, fluorine-containing compounds such as hexafluorinated propylene, nitrogen-containing compounds such as acrylonitrile, Si-containing compounds such as hexamethyldisiloxane, and tetramethyltin are used. Polymerized films obtained from various organic compounds such as organometallic compounds such as

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 B1 or Sb layer provided on the dielectric layer, or an alloy containing 90 atomic percent or more of Bi or Sb. Consisting of layer 3 (hereinafter referred to as recording layer for simplicity), dielectric layers 4 and 6 and recording layer 5 provided by sequentially forming a dielectric layer and a recording layer thereon in this order. has been done. -Also, 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.

Function The laser recording medium of the present invention is characterized by using a Bi or Bi gold alloy, Sb or Sb gold alloy recording layer, and having a sandwich-type multilayer structure in which this and a dielectric layer are alternately arranged. By adopting this configuration, compared to the conventional one which has a single layer structure without lamination,
Since the amorphous lifetime is significantly extended, a stable recording medium that does not cause phase separation and has a long amorphous lifetime can be provided.

Generally, when it is desired to give the dielectric layer 2 in contact with the substrate 1 a function as a heat insulating layer to prevent heat leakage to the substrate 1,
It is desirable to use a film thickness of about 50 nm or more, and the uppermost dielectric layer is preferably used with a film thickness of about 50 nm or more in order to suppress deformation of the medium.

The dielectric layer other than this only needs to be able to separate the recording layer 3.5, and therefore, 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, and as a result, the dielectric layer 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 layer 3.5 is formed by vapor deposition or sputtering, and its film thickness is preferably 10 nm or less. It has been found that by forming such a relatively thin film thickness, the amorphous life of 81 or Sb can be sufficiently long at room temperature. In other words, the crystallization temperature 1t increases as the film thickness of Bi and Sb 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 since the sensitivity of recording and erasing due to crystallization decreases, the film thickness of Bi and Sb decreases. A suitable thickness is 3 to 10 nm.

On the other hand, instead of Bi and Sb, Bi gold alloy or Sb
When a gold alloy is used, since the crystallization temperature is originally higher than that of Bi and Sb alone, a sufficiently long amorphous life can be obtained by making the film thickness 30 nm or less, and the lower limit is 5 nm for the same reason as above. Since the thickness is required to be above, it is suitable that the film thickness is within the range of 5 to 30 nm.

Note that this 81 and Sb compound has a composition that does not cause phase separation, that is, it contains 90 at% or more of Bi and Sb atoms, and contains Pb, Sn, In, As, 5eSG.
e,,Si,S.

Examples include those doped with 10 atomic % or less of at least one element selected from the group consisting of Sb (when based on Bi).

Some of the elements of the above alloying components, such as Sn and Ge.

By using 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 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 type structure including two or more recording layers is suitable.

Furthermore, as shown in FIG. 2, a light reflecting layer 7 is formed on the dielectric layer 6.
By providing a dielectric layer and controlling the thickness of the dielectric layer to minimize 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, the light reflecting layer may be a metal film such as Al, Au, or Ag, or a Bi or Sb film.

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 81 or Sb layer is in a crystalline state after being deposited, it is irradiated with a strong laser beam with a short pulse width.
By heating above the melting point of i or Sb and rapidly cooling it, B1 or Sb undergoes a phase transition from crystalline to amorphous,
Information is recorded by this amorphization.

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 a Bi-based alloy or Sbb alloy layer is used, the layer is in an amorphous state after being deposited. Therefore, it is also possible to record by crystallization and erase by amorphization, or to crystallize in advance by heat treatment, record by amorphization, and erase by crystallization.

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.

EXAMPLE Next, the recording medium of the present invention will be described in more detail with Example 1.

Example 1 Using polymethyl methacrylate as a substrate, SiC2 was deposited on it to a thickness of 20 nm by electron beam evaporation, B1 was deposited to a thickness of 5 m by a resistance heating evaporation method, and so on. A recording medium of the present invention having four B1 layers was produced. However, the film thickness of the uppermost 8102 dielectric layer was 1100 nm. Recording and erasing experiments were conducted on this recording medium using a semiconductor laser with a wavelength of 850 nm. Laser irradiation was performed through the substrate with a laser beam diameter of 1.6 μm, and amorphization occurred at a laser power of 5 mW and a pulse width of 80 ns on the recording medium, and the laser power was 4 mW.

Crystallization occurred with a pulse width of 400 ns. When reproduction was performed with a laser power of 1 m□ and a pulse width of 500 ns, 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 104 or more recording/reproducing experiments. In addition, the amorphous Bi is 4
It was found that the product is stable, with no crystallization observed even when stored at 0°C for more than 1 month.

Example 2 A similar recording medium was produced by repeating the operations in Example 1 and using an Sbb deposited film instead of the B1 film. This medium became amorphous at a laser power of 15 mW and a pulse width of 100 ns. , laser power [3 mW, pulse width 500
Crystallization occurred in ns. Playback with laser power of 1mW
When the recording was performed with a pulse width of 500 ns, no change was observed in the recording state. Moreover, it was confirmed that the same signal output as the initial value was maintained even after more than 104 recording/reproducing experiments.

Example 3 Repeat the operation of Example 1 and use B15aSn instead of B1.
sGes, B15oln5Ses, 81 gaPbsA
Recording media of the present invention using each of ss were produced. The recording/erasing characteristics of this medium were almost the same as those of the recording medium of Example 1, but there was a tendency for the erasing speed to become faster, with crystallization occurring at a laser power of 4 mW and a pulse width of 300 ns. In addition, 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 a similar configuration. However, instead of Sb, 5bsoSnsGes, 5b
One using sonsSes, 5klsoPbsASs was produced.

The recording/erasing characteristics of this product were almost the same as those of the product of Example 2, but the laser power was 5 mW and the pulse width was 400.
There was a tendency for the erasing speed to become faster, such as crystallization occurring at ns. Moreover, no crystallization was observed even when the amorphous state was stored at 40° C. for 2 months, and therefore, it was confirmed that it is extremely stable as an amorphous state at room temperature.

Example 5 The procedure of Example 1 was repeated. However, instead of SiC2, Y2O3, TazOs, Al2O3, S10, CeF
When we produced a recording medium using an electron beam evaporated film of Cr2O3 and Cr2O3 as a dielectric layer, this product was able to perform recording and recording.
The erasing characteristics showed values similar to those of Example 1.

Also, instead of SiC2, PbF2, GeO□, MOO
3. The same result was obtained when a vapor deposited film of MgF2 and TeO□ was used as a dielectric layer.

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 SiC2 as the dielectric film. In this case, the polymer film thickness of the top layer was 200 nm. In this recording medium, amorphization occurred at a laser power of 5 mL and a pulse width of 60 ns, and crystallization occurred at a laser power of 3 mW and a pulse width of 400 ns. Reproduction is performed using a laser power of 1 mW and a pulse width of 500 ns.
However, there was no change in the recording status. It was confirmed that this device maintained the same signal output as the initial value even after 104 or more recording/reproducing 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. . These gave the same results as Example 3 in terms of recording/erasing characteristics, but
After 03 recording/erasing experiments, irreversible changes occurred in these media.

Example 8 Two Bi layers were provided in Example 1, and the top layer of Si
A recording medium was prepared in which the O2 film thickness was 150 nm, and a 50 nm thick A1 vapor deposited film was provided thereon as a light reflecting film. In this medium, the laser power was 6 mW and the pulse width was 70 mW.
Amorphization occurred in ns, and the laser power was 3ml.

Crystallization occurred with a pulse width of 400 ns.

Effects of the Invention As explained in detail above, in the laser beam recording medium of the laminated structure of the present invention, the characteristics of the medium can be controlled by controlling the thickness of the B1 or Sb or 81 alloy or Sb alloy layer. It has the advantage of good reproducibility of media characteristics. Furthermore, B1, Sb or B1
or 81 alloy containing 90 atomic% or more of Sb or Sb
Since it uses a gold alloy, it provides a medium with high sensitivity and excellent contrast. In addition, the recording medium of the present invention does not cause phase separation and has a long life in an amorphous state, the dielectric layer prevents deformation of the medium, and the particle size of the B15SbSBi compound and Sb compound can be changed while remaining fine. 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 Substrate, 2.4.6 Dielectric layer, 3.5 B1 or Sb layer or 8i alloy or Sb alloy layer containing 90 atomic % or more of Bl or Sb, 7 Light reflective layer Patent applicant Japan Telegraph and Telephone Public Corporation Representative Patent Attorney Masahiko Arai Figure 1

Claims (3)

[Claims] (1) It has a substrate, at least two dielectric layers as recording medium layers provided on the substrate, and at least two Bi layers or Sb layers, each of the Bi layers or Sb layers being 1. A laser recording medium characterized in that the medium is sandwiched between dielectric layers and alternately provided with the dielectric layers on the substrate. (2) A patent characterized in that 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. A laser recording medium according to claim 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.