JP2948899B2 - Optical recording medium and optical recording method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium and an optical recording method, and in particular, performs optical recording using a thin film of an alloy that changes its crystal structure by heating by laser light irradiation. The present invention relates to a medium and an optical recording method using the medium.

<Prior Art> As a large-capacity information recording medium, an optical recording medium such as an optical recording disk has attracted attention.

Examples of the optical recording medium include a rewritable type such as a phase-change optical recording medium and a magneto-optical recording medium, and a write-once type such as a pit-forming optical recording disk.

Of these, the phase-change optical recording medium uses a phase-change alloy whose recording film changes in crystal structure and changes in light reflectance by heating.

As a phase change alloy used for a phase change type optical recording medium, an Ag-Zn alloy or the like is used (Japanese Patent Laid-Open No. 61-1300).
No. 89 gazette).

However, a phase change type optical recording medium using an Ag-Zn alloy or the like for a recording film has a small difference in reflectivity due to a phase change, and cannot obtain a change in reflectivity required in the Compact Disc (CD) standard. Further, in the CD, the reflectance of the information carrying portion is lower than the reflectance of the non-bearing portion.However, when an Ag-Zn alloy is used, the reflectance is usually increased in the light irradiation portion, that is, in the recording portion. From this point, it is difficult to support the CD standard.

Therefore, it is impossible to use such a phase-change optical recording medium as a so-called write-once CD.

Under such circumstances, an optical recording disk satisfying the CD standard has been proposed (Japanese Patent Laid-Open No. 2-235789).

The publication discloses that Au, Al, Ag, Pt, Pd,
High reflectance layer composed of elements selected from Ni, Cr, Co and alloys containing these elements, laser wavelength 750-850nm
The low-reflectance layer composed of a material that is recognized in absorption is an optical information recording member laminated on the substrate surface in this order, and a chalcogen element such as Te is used as a constituent material of the low-reflectance layer. I have. The high reflectivity layer does not show absorption of laser light, and therefore cannot be used alone as a recording material.

In this optical information recording member, the chalcogen element constituting the low reflectivity layer reacts with the high reflectivity layer to form an alloy by irradiating recording light from the substrate surface side, that is, from the low reflectivity layer side, thereby forming an alloy. The light reflectance of the light irradiation part decreases. Then, reproduction light is irradiated through the substrate from the side opposite to the recording light, that is, from the back side of the substrate, and the change in the light reflectance is detected.

According to this configuration, a write-once CD can be obtained.

<Problems to be Solved by the Invention> In the optical information recording member described in JP-A-2-235789, the low-reflectance layer and the high-reflectance layer are formed by a sputtering method. When the optical disk having the above configuration was manufactured using the method and recording and reproduction were performed, the reflectance in the unrecorded portion was only about 14 to 16%, and the reflectance in the recorded portion was 10%. It only dropped to the extent. For this reason, it is impossible to reproduce not only by the CD standard but also by a drive device for a phase-change optical recording disk.

According to the study of the present inventors, when a low-reflectance layer made of Te is formed on a high-reflectivity layer made of Ag by a sputtering method, both layers are mutually diffused and an alloy or a mixture of Ag and Te is formed. It has been found that this is because a compound has been generated and is already in a recording state immediately after sputtering.

These results are obtained when the high-reflectance layer is formed to a thickness of about 500 mm, which allows recording at a linear velocity of 1.2 to 1.4 m / s according to the CD standard.

On the other hand, when the thickness of the high reflectivity layer is set to about 1000 °, the influence of mutual diffusion at the time of forming the low reflectivity layer is reduced, and the reflection from the high reflectivity layer in an unrecorded state can be sufficiently obtained. But,
In this case, it takes a long time for the two layers to diffuse each other, and it is impossible to perform recording even by irradiating a recording laser beam at a linear velocity of a CD standard.

Further, in this optical information recording member, since the recording light is irradiated from the front side of the substrate, it is necessary to turn the optical information recording member upside down and reversely rotate at the time of recording, and it is necessary to reverse the tracking polarity. Therefore, a dedicated driving device is required at the time of recording. The reason for irradiating the recording light from the low reflectance layer side is that the high reflection layer has a high melting point and requires extremely high recording power when irradiating from the back side of the substrate.

The present invention has been made under such circumstances,
It is an object of the present invention to provide an optical recording medium capable of reproducing data conforming to the CD standard, and an optical recording method for performing recording on the optical recording medium.

<Means for Solving the Problems> Such an object is achieved by the present invention of the following (1) to (7).

(1) having a phase change alloy thin film on a substrate surface, having a low melting point thin film on the phase change alloy thin film, wherein the phase change alloy thin film has at least one element selected from Group 1B of the periodic table A substrate containing, as a main component, at least one element selected from Group 2B of the periodic table; and the low melting point thin film containing, as a main component, at least one element selected from Te, Se, and S. An optical recording medium on which recording and reproduction are performed.

(2) The optical recording medium according to (1), wherein the phase change alloy thin film contains Ag and Zn as main components.

(3) The optical recording medium according to (1) or (2), wherein a value obtained by dividing the thickness of the low melting point thin film by the thickness of the phase change alloy thin film is 1 to 5.

(4) the thickness of the phase change alloy thin film is 300 to 700 mm,
The above (1), wherein the low melting point thin film has a thickness of 500 to 1500 °.
The optical recording medium according to any one of (1) to (3).

(5) The low melting point intermediate thin film between the substrate and the phase change alloy thin film, wherein the low melting point intermediate thin film contains at least one of Te, Se and S as a main component. The optical recording medium according to any one of 4).

(6) The optical recording medium according to the above (5), wherein the low melting point intermediate thin film has a thickness of 10 to 100 °.

(7) The optical recording medium according to any one of (1) to (6),
A non-rewritable recording portion in which light reflectance is changed by interdiffusion between the phase change alloy thin film and the low melting point thin film, and light reflectance is changed by a change in a crystal structure of the phase change alloy thin film. An optical recording method comprising: performing recording so as to have a rewritable recording unit.

<Operation> As shown in FIG. 1, the optical recording medium 1 of the present invention comprises:
A phase change alloy thin film 3 is provided on the surface of the substrate 2, and a low melting point thin film 4 is provided on the phase change alloy thin film 3.

When the recording laser beam is irradiated from the back side of the substrate 2, the phase change alloy thin film 3 and the low melting point thin film 4 are heated. By this heating, the constituent elements of the low melting point thin film 4 and the constituent elements of the phase change alloy thin film 3 are mutually diffused to form an alloy or a compound of these elements, and the light reflectance of the laser beam irradiated part is significantly reduced. .

Since this change in light reflectance is irreversible, it can be used as a write-once optical recording medium. The reflectivity of 780 nm light used for CDs drops from about 90% before laser light irradiation to about 20% or less after laser light irradiation. It can be used as

In addition, a phase change alloy thin film 3 having a hexagonal structure
When a recording laser beam of relatively low power is irradiated, the low melting point thin film 4 does not change, but the crystal structure of the phase change alloy thin film 3 changes to a bcc structure or amorphous, and the light reflectance increases. Since this change in light reflectance is reversible, it can be used as a rewritable optical disk.

The low melting point thin film 4 is formed on the phase change alloy thin film 3 by a vapor phase growth method such as a sputtering method as described later.
Since the 2B group element such as Zn in the phase change alloy thin film 3 acts as a locking element for preventing the diffusion of the constituent elements of the low melting point thin film 4 such as Te, even if the phase change alloy thin film 3 is as thin as about 500 °, the low melting point thin film is used. At the time of formation 4, almost no mutual diffusion occurs between the two thin films.

On the other hand, when the phase-change alloy thin film 3 is heated by the irradiation of the recording laser beam and then cooled, various crystal structures and crystal states such as bcc, hexagonal and amorphous can be selected for the phase-change alloy thin film 3. As a result, the interlocking of the 2B group elements such as Zn is released, and the mutual diffusion of both thin film constituent elements occurs rapidly. As described above, an alloy or a compound is formed, and the reflectance is reduced.

<Specific Configuration> Hereinafter, a specific configuration of the present invention will be described in detail.

 FIG. 1 shows a preferred embodiment of the optical recording medium of the present invention.

As shown in FIG. 1, the optical recording medium 1 has a phase change alloy thin film 3 on the surface of a substrate 2, a low melting point thin film 4 on the phase change alloy thin film 3, and a protective film on the low melting point thin film 4. 5

In the optical recording medium 1, the phase change alloy thin film 3
Is irradiated with the recording light and the reproduction light, the substrate 2 needs to be substantially transparent to these lights. For this reason, the material of the substrate 2 includes various types of glass, acrylic resin,
Various resins such as a polycarbonate resin, an epoxy resin, and a polyolefin resin may be used.

The shape and dimensions of the substrate 2 are not particularly limited, but are usually disk-shaped, and the thickness thereof is usually 0.5
About 3mm, diameter is about 50-360mm.

On the surface of the substrate 2, predetermined patterns such as pits or groups are provided as needed for tracking, addressing, and the like.

The phase change alloy thin film 3 contains at least one element selected from Group 1B and at least one element selected from Group 2B. Group 1B is preferably at least one selected from Cu, Ag and Au, and Group 2B is preferably at least one selected from Zn and Cd. Specifically, Ag is an alloy that provides a high reflectance and causes a sufficient change in reflectance depending on the cooling conditions after heating.
-Zn alloy, Cu-Zn alloy, Ag-Cd alloy, Au-Zn alloy and the like are preferable, and among them, Ag-
Zn alloys and Ag-Cd alloys are preferred.

The ratio of the group 1B element and the group 2B element in the phase change alloy thin film 3 may be appropriately set according to the required reflectance and the change rate thereof, but it is based on the total content of the group 1B element and the group 2B element. The proportion of group 1B elements is 40-60 atomic%, especially 45-55
Preferably, it is atomic%.

In addition, various elements of Sb, Sn, In, S, and Cu may be added to the phase change alloy thin film 3 as needed. Sb is
Since it has the effect of improving the mutual diffusion speed between the phase change alloy thin film 3 and the low melting point thin film 4, recording at lower power becomes possible, and the recording sensitivity is improved. Further, since Sn, In, and Cu have an effect of lowering the melting point of the phase change alloy thin film, the recording sensitivity can be improved by adding them.

When adding these elements, their total content is 1B
It is preferable that the content be 5 atomic% or less based on the total content of the group II element and the group IIB element. This is because if the content of the additional element is too large, the reflectance is significantly reduced.

The phase change alloy thin film 3 is preferably formed by a vapor phase growth method such as a sputtering method or a vapor deposition method.

When using the sputtering method, the pressure of the atmosphere during film formation is 1.
It is preferably 5 Pa or less, particularly preferably 0.5 to 1.0 Pa. When a phase change alloy thin film containing a Group 1B element and a Group 2B element is formed by a sputtering method, it is usually necessary to perform a heat treatment of heating to a temperature of about 300 ° C. or more and rapidly cooling. By such heat treatment, the phase change alloy thin film usually has a bcc structure and exhibits a reflectance of about 90% or more, and the CD
Compliance with standards becomes possible. When a resin is used as the substrate material, it is difficult to perform such a heat treatment after the phase change alloy thin film is formed. However, by sputtering at a pressure in the above range, a reflectance of about 90% or more can be obtained without heat treatment. Thus, a normal resin substrate can be used without any problem.

When the optical recording medium of the present invention is used as a normal phase-change type optical recording medium, a hexagonal structure is formed by forming a phase change alloy thin film 3 having a bcc structure and then performing a heat treatment at a low temperature of about 200 ° C. preferable. In this state, the CD
It can also be used as a corresponding write-once optical recording medium.

The phase change alloy thin film 3 is at least a binary alloy,
Usually, since various physical properties such as a melting point are different, when an alloy target is used in the sputtering method, it is preferable to shift a target composition from a target thin film composition as necessary. In the case where an evaporation method is used, it is preferable that each metal is independently used as an evaporation source.

The low melting point thin film 4 contains at least one element selected from Te, Se and S as a main component.

It is preferable that the low melting point thin film 4 is formed by a vapor phase growth method similarly to the phase change alloy thin film 3.

The low melting point thin film 4 may contain Sn as an additional element as needed. The content of these additional elements is
It is preferably at most 5 atomic% in order to maintain a low melting point.

 The melting point of the low melting point thin film 4 is about 200 to 400 ° C.

When a recording laser beam is irradiated from the phase change alloy thin film 3 side to the laminate of the phase change alloy thin film 3 and the low melting point thin film 4, the crystal structure of the phase change alloy thin film 3 changes, and the phase change alloy thin film 3
The constituent elements and the constituent elements of the low-melting-point thin film 4 are easily diffused with each other, and a compound or alloy of these elements is formed. The light reflectance is remarkably reduced, thereby enabling reproduction corresponding to the CD standard. At this time, the group 2B element such as Zn or Cd has an effect of assisting the diffusion of the low melting point thin film 4 constituent elements such as Te.

On the other hand, when the low melting point thin film 4 is formed by the vapor phase growth method, the phase change alloy thin film 3 does not mutually diffuse with the low melting point thin film 4. This is because the 2B group element such as Zn or Cd acts as a locking element for preventing the reaction between the low melting point thin film 4 constituent element such as Te and the 1B group element such as Ag, contrary to the recording laser beam irradiation. . For this reason, after sputtering, in an unrecorded state, a light reflectance corresponding to the CD standard is obtained.

If the phase change alloy thin film 3 is replaced with a mere reflective thin film such as an Ag thin film that does not cause a phase change due to heating, mutual diffusion occurs between the two thin films when the low melting point thin film 4 is formed by the vapor phase growth method. As a result, the reflectance corresponding to the CD standard cannot be obtained in the unrecorded portion.

The thickness of each thin film may be appropriately determined according to the target reflectance and the rate of change thereof, but in order to obtain high modulation, the thickness of the low melting point thin film 4 is set to the thickness of the phase change alloy thin film 3. Is preferably 1 to 5, particularly preferably 1 to 3.

The modulation is Is represented by Here, R _NON is the light reflectance of the unrecorded portion, and R is the light reflectance of the recorded portion, that is, the laser light irradiated portion.

Further, as a specific thickness, the phase change alloy thin film 3 is 300
It is preferably from 700 to 700, particularly preferably from 400 to 700. If the thickness of the phase change alloy thin film 3 is less than the above range, sufficient initial reflection of 70% or more cannot be obtained, and if it exceeds the above range, it takes time to diffuse the constituent elements of the low melting point thin film 4 and the recording sensitivity becomes poor. Will be enough.

Further, the thickness of the low melting point thin film 4 is 500 to 1500Å, especially 800
Preferably it is ~ 1200 °. If the thickness of the low melting point thin film 4 is less than the above range, the group 1B element such as Ag and the low melting point thin film 4
Since the unreacted phase change alloy thin film remains due to insufficient reaction with the constituent elements, a sufficient change in reflectance cannot be obtained.
If it exceeds the above range, the unreacted low-melting point thin film 4 remains, so that a sufficient change in reflectance cannot be obtained.

By setting the thickness of each thin film and their relationship as described above, a modulation of 70% or more can be obtained.

 A preferred embodiment of another aspect of the present invention is shown in FIG.

An optical recording medium 1 shown in FIG. 1 has a structure in which Te, Te is placed between a substrate 2 and a phase-change alloy thin film 3 of the optical recording medium 1 shown in FIG.
A low-melting intermediate thin film 6 containing at least one of Se and S as a main component is provided.

The low melting point intermediate thin film 6 has an endothermic effect, and also has the effect of improving the recording sensitivity because it lowers the melting point of the surface state of the phase change alloy thin film 3.

The thickness of the low-melting intermediate thin film 6 is 10 to 100 mm, particularly 30 to 70 mm.
Å is preferred.

When the thickness is less than the above range, a sufficient decrease in the melting point is not recognized, and when the thickness exceeds the above range, it is difficult to obtain a sufficient light reflectance in an unrecorded portion.

The protective film 5 is provided for improving scratch resistance and corrosion resistance, and is preferably made of various organic substances. , And is preferably made of a substance cured by radiation such as ultraviolet rays.

The thickness of the protective film 5 is usually about 0.1 to 100 μm,
It may be formed by a usual method such as spin coating, gravure coating, spray coating, and dipping.

In the above, the case where the present invention is applied to a single-sided recording type optical recording medium conforming to the CD standard has been described. However, the present invention is also applicable to a double-sided recording type optical recording medium.

When applied to a double-sided recording type optical recording medium, a pair of substrates 2 and 2 are bonded so that the phase-change alloy thin film 3 is enclosed.

In addition, a single-sided recording type may be employed, in which a protective plate is adhered on the protective film 5. In this case, as the protective plate, the same material as that of the substrate 2 may be usually used. However, the protective plate does not need to be transparent, and other materials may be used.

As described above, the optical recording medium of the present invention can be used as a write-once optical recording disk conforming to the CD standard, but it is necessary to prevent mutual diffusion between the phase change alloy thin film 3 and the low melting point thin film 4. By irradiating a low-power laser beam, it can be used as a normal phase-change optical recording disk.

Further, by controlling the power of the recording laser beam, a rewritable area and a non-rewritable area can be provided on one disc. However, in this case, in the rewritable region, the recording portion is formed by changing the phase change alloy thin film 3 from the hexagonal structure to the bcc structure or amorphous to increase the reflectivity. After forming the amorphous phase change alloy thin film 3
Heat treatment is performed at a low temperature of about 00 ° C. to form a hexagonal structure.

As a result, the hexagonal structure changes to a bcc structure or amorphous in the low-power laser beam irradiation part, and the reflectivity becomes 7
This increases from about 0% to about 90%, and a rewritable recording portion is formed. Then, in the high-power laser beam irradiating section, the above-mentioned mutual diffusion occurs, and the reflectivity decreases from about 70% to about 20% or less, thereby forming a non-rewritable recording section.

As a method of changing the phase change alloy thin film 3 from the bcc structure or the amorphous structure to the hexagonal structure, laser light irradiation of an appropriate intensity can be used in addition to the heat treatment described above.

<Example> Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

Example 1 A phase change alloy thin film 3, a low melting point thin film 4, and a protective film 5 of an ultraviolet curable resin were sequentially formed on the surface of a substrate 2,
Optical recording disk sample No. 1 having the configuration shown in the figure
Was prepared.

As the substrate 2, a disk-shaped polycarbonate resin having a diameter of 133 mm and a thickness of 1.2 mm, in which grooves were simultaneously formed by injection molding, was used.

The phase change alloy thin film 3 is an Ag—Zn alloy containing 50.0 atomic% of Ag, and formed to a thickness of 500 ° by a sputtering method. The pressure of the atmosphere during the sputtering was 0.9 Pa.

The low melting point thin film 4 is made of Te and has a thickness of 10
Formed at 00 °.

The protective film 5 was made of an ultraviolet-curable resin, and was applied by a spin coating method and then cured by irradiation with ultraviolet light. The thickness after curing was 5 μm.

The recording / reproducing characteristics of Sample No. 1 were measured.

A 20mW laser beam is applied for recording, and 5m for reproduction.
Irradiated with W laser light. The wavelength of the laser light was 780 nm.

As a result, the reflectivity of the unrecorded portion was 90%, and the reflectivity of the recorded portion was 21%, so that reproduction corresponding to the CD standard was possible.

Further, a phase change alloy thin film 3 and a low melting point thin film 4 were formed on a glass substrate having a thickness of 1.5 mm in the same manner as in Sample No. 1, and the spectral reflectance was measured with a spectrophotometer. This is shown in FIG. 3 as the initial reflectance.

Further, this was heated at 300 ° C. for 5 minutes, cooled in air, and the spectral reflectance was measured again. This is shown in FIG. 3 as the reflectance after heating.

As is clear from FIG. 3, the optical recording medium of the present invention
In an extremely wide wavelength range, a sufficiently high initial reflectance and a sufficient change in reflectance are obtained.

Example 2 Low-melting-point intermediate thin film 6 between substrate 2 and phase-change alloy thin film 3
An optical recording disk sample No. 2 having the configuration shown in FIG.

The low melting point intermediate thin film 6 was made of Te, and was formed to a thickness of 50 ° by a sputtering method.

Other configurations were the same as Sample No. 1.

When the recording and reproduction characteristics of sample No. 2 were measured, the reflectance of the unrecorded portion was 82%, and the reflectance of the recorded portion was 20%.
%, And playback compatible with the CD standard was possible.

Also, recording was possible even when the power of the laser light was reduced to 10 mW.

[Example 3] The composition of the phase change alloy thin film 3 was changed to Cu-Zn alloy or Ag-Cd.
An optical recording disk sample was prepared in the same manner as in each of the above examples except that the alloy was used.

Also, the composition of the low melting point thin film 4 was set to Se or S, and the other conditions were the same as those in the above-described embodiments to produce optical recording disk samples.

Further, the composition of the low melting point intermediate thin film 6 is set to Se or S,
Otherwise, an optical recording disk sample was manufactured in the same manner as in each of the above examples.

When the recording and reproduction characteristics of each of these samples were measured in the same manner as in the above-described embodiments, the same results as those in the above-described embodiments were obtained.

<Effects of the Invention> The optical recording medium of the present invention has a reflectivity of about 90% or more in the unrecorded area, and the reflection decreases to about 20% in the recorded area. It can be used as an optical recording disk.

Further, since the modulation is high as described above, a large reproduction signal can be obtained, and an error does not easily occur even if the accuracy and reliability of the driving device are low.

When a low-power laser beam is irradiated, the disk can be used as a normal phase-change optical recording disk, so that one disk can be provided with a rewritable area and a non-rewritable area. Moreover, since the ratio of these regions can be set arbitrarily by the user, a wide range of applications is possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are partial sectional views showing a preferred embodiment of the optical recording medium of the present invention. FIG. 3 is a graph showing the spectral reflectance of the optical recording medium of the present invention and its change. DESCRIPTION OF SYMBOLS 1 ... optical recording medium 2 ... substrate 3 ... phase change alloy thin film 4 ... low melting point thin film 5 ... protective film 6 ... low melting point intermediate thin film

Claims (7)

(57) [Claims] 1. A phase change alloy thin film on a substrate surface, a low melting point thin film on the phase change alloy thin film, wherein the phase change alloy thin film has at least one element selected from Group 1B of the periodic table. A low-melting point thin film containing at least one element selected from Te, Se and S as a main component; An optical recording medium on which recording and reproduction are performed through a substrate. 2. The optical recording medium according to claim 1, wherein said phase change alloy thin film contains Ag and Zn as main components. 3. The optical recording medium according to claim 1, wherein a value obtained by dividing the thickness of the low melting point thin film by the thickness of the phase change alloy thin film is 1 to 5. 4. The optical recording medium according to claim 1, wherein said phase change alloy thin film has a thickness of 300 to 700 °, and said low melting point thin film has a thickness of 500 to 1500 °. 5. A low melting point intermediate thin film between the substrate and the phase change alloy thin film, wherein the low melting point intermediate thin film contains at least one of Te, Se and S as a main component. 4. The optical recording medium according to any one of 4. 6. An optical recording medium according to claim 5, wherein said low melting point intermediate thin film has a thickness of 10 to 100 °. 7. The optical recording medium according to claim 1,
A non-rewritable recording portion in which light reflectance changes due to mutual diffusion between the phase change alloy thin film and the low melting point thin film, and light reflectance changes due to a change in the crystal structure of the phase change alloy thin film. An optical recording method comprising: performing recording so as to have a rewritable recording unit.