JP3049864B2 - Optical information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium used for an information recording / reproducing apparatus using a laser beam, and more particularly to a rewritable phase change optical disk.

[0002]

2. Description of the Related Art As an optical disk capable of recording, reproducing and erasing signals, a phase-change optical disk using a chalcogenide as a recording thin film material is known. Generally, a signal is recorded by setting the recording thin film material in a crystalline state to an unrecorded state and rapidly heating and quenching by laser irradiation to make the recording thin film amorphous. In addition, the crystal becomes a crystalline state again by rapid heating and slow cooling, and the recorded signal is erased.

As recording thin film materials, for example, Te, In,
It is common to use a material which is mainly composed of Sb, Se and the like and which changes phase between an amorphous and a crystal, or a substance which reversibly changes phase between two different types of crystal structures.

As a material for the protective layer, for example, Al 2 O 3,
SiO2, SiO, Ta2 O5, MoO3, WO3, ZnS, Zr
O2, AlN, BN, SiNx, TiN, ZrN, PbF2, M
Dielectrics such as gF2 or suitable combinations thereof are known.

On the other hand, the recording format of an optical disc is
CLV (Constant Linear Velocity) method, CAV (Co
nstant Angular Velocity) method and M-CAV (Mod
Unified CAV) is common. Especially CAV method, M
-In the CAV method, the rotation speed of the spindle motor is constant,
There is an advantage that the access time is shorter than the CLV method.

[0006] CAV method or M-type
When recording by the CAV method, the linear velocity at the laser irradiation position is faster on the outer circumference than on the inner circumference of the disc. That is, the time for the laser beam to cross one point on the disk is shorter on the outer circumference than on the inner circumference. Therefore, in order to obtain good recording / erasing characteristics for both the inner and outer circumferences, it is general to appropriately select the recording / erasing power and the laser irradiation pulse width according to the recording radius.

[0007]

SUMMARY OF THE INVENTION A phase change optical disk has C
In the case of recording by the AV method or the M-CAV method, the repetition characteristics of recording / erasing differ depending on the recording radius even if the recording / erasing power and the laser irradiation pulse width are appropriately selected according to the recording radius. In other words, in a disk whose structure is adjusted so that the repetition characteristics become higher at a linear velocity corresponding to the inner periphery, the repetition characteristics are worse on the outer periphery than on the inner periphery. Conversely, in a disk whose structure is adjusted so that the repetition characteristics become higher at a linear velocity corresponding to the outer periphery, the repetition characteristics are worse at the inner periphery than at the outer periphery.

It is an object of the present invention to provide an optical information recording medium having good recording / erasing repetition characteristics regardless of the inner and outer peripheries of a recording area.

[0009]

According to the present invention, there is provided a crystallization suppressing layer or a crystallization promoting layer in contact with a recording thin film of a phase change type optical information recording medium.
The recording thin film and crystal per unit area of the recording thin film interface
Contact area of the crystallization suppression layer, or between the recording thin film and the crystallization promoting layer.
Either of the contact areas changes in the radial direction of the recording thin film formation area.
It is obtained so as to reduction. At this time, when the crystallization suppression layer is provided, the contact area between the recording thin film and the crystallization suppression layer per unit area of the recording thin film interface increases from the outer peripheral side to the inner peripheral side of the recording thin film formation region. this is so
When a crystallization promoting layer is provided, the contact area between the recording thin film and the crystallization promoting layer per unit area of the recording thin film interface is increased from the inner peripheral side to the outer peripheral side of the recording thin film forming region. Preferably .

[0010]

When a crystallization suppressing layer or a crystallization promoting layer is provided in contact with a recording thin film of a phase-change type optical information recording medium, and a crystallization suppressing layer is provided, a unit area per unit area of a recording thin film interface is provided. In the case where the contact area between the recording thin film and the crystallization suppressing layer is increased from the outer peripheral side to the inner peripheral side of the recording thin film forming region and the crystallization promoting layer is provided, the recording per unit area of the recording thin film interface is performed. By increasing the contact area between the thin film and the crystallization promoting layer from the inner peripheral side to the outer peripheral side of the recording thin film forming region, good recording / erasing repetition characteristics can be obtained regardless of the inner and outer periphery of the recording region. .

[0011]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 shows a typical structural example of the recording medium of the present invention.
Shown in The laser beam for recording, reproducing and erasing is applied to the substrate 1
From the side.

As the substrate 1, a resin having a smooth surface such as a resin such as PMMA or polycarbonate or glass is used. In the case of an optical disk, the substrate plane 9 is usually covered with spiral or concentric tracks for guiding laser light.

The material of the protective layers 2 and 4 is preferably physically and chemically stable, that is, has a higher melting point and softening temperature than the melting point of the recording material, and does not form a solid solution with the recording material. For example, Al2 O3, SiOx, Ta2 O5, MoO3, WO
3, ZrO2, ZnS, AlNx, BN, SiNx, Tin, Zr
It is made of a dielectric material such as N, PbF2, MgF2, or an appropriate combination thereof. The protective layer need not be transparent in the dielectric. For example, it may be formed of ZnTe having a light absorbing property for visible light and infrared light. Further, when the protective layers 2 and 4 are formed of different materials, there is an advantage that the degree of freedom of thermal and optical disc design is increased. Of course, they may be formed of the same material.

The recording thin film 3 is made of a material that reversibly changes its structure between a crystalline state and an amorphous state, for example, Te or I.
It is made of a phase change material containing n, Se and the like as main components. The main components of well-known phase change materials are Te-Sb-Ge, Te-
Ge, Te-Ge-Sn, Te-Ge-Sn-Au, Sb-Te, Sb-S
e-Te, In-Te, In-Se, In-Se-Tl, In-Sb, In-
Sb-Se, In-Se-Te, and the like.

The crystallization control layer (crystallization suppression layer or crystallization promoting layer) 5 is formed discontinuously between the recording thin film 3 and the protective layer 2 (or 4), and is formed in an amorphous state. In the case where is crystallized by irradiation of a laser beam, it plays a role of controlling the crystallization process. The recording thin film is in contact with both the protective layer and the crystallization control layer.

Here, as the rate of contact with the interface of the recording thin film per unit area increases, the crystallization of the recording thin film becomes more difficult, and the crystallization cannot be performed unless the laser irradiation time is long (crystallization control). Is referred to as a crystallization suppressing layer as compared with the protective layer.

Further, as the ratio of contact with the recording thin film interface per unit area increases, the crystallization of the recording thin film becomes easier, and crystallization can be performed with a shorter laser irradiation time (crystallization control). The layer is referred to as a crystallization promoting layer, as compared to the protective layer.

The crystallization suppression layer is formed such that the contact area between the recording thin film and the crystallization suppression layer per unit area of the recording thin film interface increases from the outer peripheral side to the inner peripheral side of the recording thin film forming region. The crystallization promoting layer is formed such that the contact area between the recording thin film and the crystallization promoting layer per unit area of the interface of the recording thin film increases from the inner peripheral side to the outer peripheral side of the recording thin film forming region. As a result, good erasing characteristics and repetition characteristics of recording / erasing can be obtained regardless of the inner and outer circumferences of the disk (linear velocity).

The constituent materials and film forming conditions of the crystallization suppressing layer or the crystallization promoting layer 5 vary depending on the combination of the protective layer and the recording thin film 3. For example, Al2 O3, SiOx,
Oxides such as Ta2 O5, ZrO2, AlNx, BN, NbN, S
It is composed of a nitride such as iNx, an element such as B or C, or an appropriate combination thereof.

The reflection layer 6 is made of a metal element such as Au, Al, Ni, Fe, or Cr, or an alloy thereof, and functions to increase the light absorption efficiency of the recording thin film. However, it is also possible to adopt a configuration in which the reflective layer 6 is not provided, for example, by increasing the thickness of the recording thin film 3 to improve the light absorption efficiency. Alternatively, by adopting a configuration in which the recording thin film and the protective layer are alternately stacked a plurality of times, the light absorption efficiency can be increased as a whole even if the film thickness per recording thin film is small.

The protective substrate 8 is formed by spin-coating a resin or by bonding a resin plate, a glass plate, a metal plate, or the like similar to the substrate using an adhesive 7. Furthermore, a structure in which recording, reproduction, and erasing can be performed from both surfaces may be performed by bonding two sets of recording media using an adhesive with the intermediate substrate or the reflective layer inside.

The recording thin film, protective layer, and crystallization control layer are usually formed by an electron beam evaporation method, a sputtering method, an ion plating method, a CVD method, a laser sputtering method, or the like.

Hereinafter, the present invention will be described in detail with specific examples. (Example 1) A sample disk was prepared by selecting a Ge ₂ Sb ₂ Te ₅ composition as a recording thin film, and recording / erasing characteristics were examined at different linear velocities. The Ge ₂ Sb ₂ Te ₅ composition is known as a material capable of obtaining good recording / erasing characteristics and repetition characteristics (JP-A-62-209742).

FIG. 1A shows a disk structure. Substrate 1
Is 8 inch diameter glass and the recording area is φ80 ~
φ200. On the substrate 1, the composition is ZnS-20mol% Si.
O ₂ protective layer 2, crystallization suppressing layer 5 made of silicon nitride (Si ₃ N ₄ ), Ge ₂ Sb ₂ Te ₅ recording thin film 3, ZnS-20 mol% Si
An O ₂ protective layer 4 and an Au reflective layer 6 are sequentially laminated. Recording thin film 3
Was 50 nm in thickness. The thicknesses of the protective layers 2 and 4 were determined so as to obtain optically optimal characteristics. Specifically, the film thickness on the substrate 1 side was 150 nm, and the film thickness on the recording thin film 3 was 200 nm. The reflection layer 6 is made of gold (Au) and has a thickness of 20 n.
m. Each layer was formed by a sputtering method.

The crystallization suppression layer 5 has a maximum thickness of 2 nm,
On the inner peripheral side (φ80 to φ90) of the recording area, the crystallization suppressing layer 5 covers 80% or more of the interface of the protective layer 2, and the continuity of the crystallization suppressing layer 5 itself decreases toward the outer peripheral side. On the outer peripheral side (φ190 to φ200) of the recording area, the crystallization suppression layer 5 covers 20% or less of the interface of the protective layer 2. Specifically, the crystallization suppression layer 5 was formed using a slit having a large aperture ratio on the inner periphery, and the continuity of the crystallization suppression layer 5 in the disk radial direction was controlled. At the stage when the crystallization suppression layer 5 was formed, the surface state was observed using an STM (scanning tunnel microscope).

FIG. 2 shows a distribution state of the crystallization suppressing layer 5 covering the protective layer 2. FIG. 2A shows the outer peripheral side of the recording area (φ1
95)).
I have. As shown in this figure, the crystallization suppression layer 5 is
Are discontinuously and sparsely formed. FIG. 2 (b) is a record.
Of the crystallization suppression layer 5 on the inner peripheral side of the region (around φ85)
This shows the distribution state. As shown in FIG.
The control layer 5 (shaded area) is continuously and densely formed on the inner peripheral side.
ing. Rotate the disk with the above configuration at 2400 rpm, φ
The recording / erasing characteristics were examined in the area of 195 and the area of φ85. The relative speeds of the laser beam (wavelength: 830 nm) and the disk are 24.5 m / s and 10.7 m / s, respectively. Record
The frequency of the erase signal was set to 8 MHz and 5 MHz, and overwriting was performed 100,000 times (overwrite recording). At this time, even after repetition, the C / N is 50 dB or more, and the erasure rate is 25 dB.
Combinations of the recording / erasing powers that could maintain the above are shown by circles in the table of FIG. FIG. 3A shows a recording medium.
It is the result on the outer peripheral side of the body (φ195), and (b)
The result on the inner circumference side (φ85) is shown . A value of C / N of 50 dB or more and an erasing rate of 25 dB or more are sufficiently practical values for digital recording. From FIG. 3, this implementation
The example recording medium has a wide power range
It can be seen that good recording / erasing repetition characteristics were obtained.

Further, a disk in which the crystallization suppressing layer was formed between the recording thin film and the protective layer on the reflection layer side, and a crystallization suppressing layer was formed on both sides of the recording thin film. The same recording / erasing characteristics as described above were also examined for the disc.

As a result, in each case, it was found that good recording / erasing repetition characteristics were obtained in a wide power range regardless of the inner and outer circumferences.

In order to confirm the effect of the crystallization suppressing layer provided in Example 1, a disk having no crystallization suppressing layer was prepared, and the recording / erasing characteristics were examined under the same conditions as in Example 1. The structure of the sample disk is exactly the same as that of Example 1 except that the crystallization suppression layer is not formed. Since the crystallization suppressing layer of Example 1 is sufficiently thin, both disks can be regarded as having equivalent optical and thermal structures.

FIG. 4 shows a combination of recording / erasing powers in which the C / N is maintained at 50 dB or more and the erasing rate is maintained at 25 dB or more even after recording / erasing is repeated 100,000 times in the area of φ195 and the area of φ85. Are respectively shown. 4 and 3
Comparing (Example 1), the following can be said.

Good repetition characteristics are exhibited at the outer periphery. -In the inner periphery, without the crystallization suppressing layer, the power range showing good repetition characteristics becomes narrow. In particular, the repetition characteristics on the low recording power side deteriorate.

As a result of TEM observation of the laser irradiated portion, when recording / erasing is performed at a low linear velocity, a large recording mark (amorphous mark) is produced even at a low recording power when a crystallization suppressing layer is present. On the other hand, it was found that when the crystallization suppressing layer was not present, a sufficiently large recording mark could not be formed unless the recording power was higher.

The crystallization suppressing layer, which is in contact with the recording thin film in a larger area on the inner peripheral side, makes it difficult to form crystal nuclei during the crystallization process of the recording thin film, or to reduce the crystal growth rate after crystallization. By suppressing this, sufficient recording characteristics can be ensured even at the inner circumference where the linear velocity is low, and as a result, the recording / erasing repetition characteristics are also improved. What is important here is that the presence of the crystallization suppressing layer controls the crystallization characteristics according to the linear velocity without substantially changing the optical structure and the thermal structure of the disk.

(Embodiment 2) In Embodiment 1, a disk using a crystallization suppressing layer was described. Next, in a third embodiment, a disk using a crystallization promoting layer will be described.
Here, a Ge ₄ Sb ₅ Te ₁₀ composition is selected as the recording thin film.
Ge ₄ Sb ₅ Te ₁₀ has a slightly slower crystallization rate than the Ge ₂ Sb ₂ Te ₅ composition, but exhibits good recording / erasing characteristics and repetition characteristics (Japanese Patent Application Laid-Open No. 62-209742).

FIG. 1B shows a disk structure. Substrate 1
Is made of glass of φ130, and the recording area is φ60-φ.
128. A silicon nitride (Si ₃ N ₄ ) protective layer, a crystallization promoting layer 10 made of tantalum oxide (Ta ₂ O ₅ ), a Ge ₄ Sb ₅ Te ₁₀ recording thin film 3, a Si ₃ N ₄ protective layer, and an Au
The reflection layers 6 are sequentially laminated. The thickness of the recording thin film 3 was 30 nm. The thickness of the protective layer was determined so as to obtain optically optimal characteristics. Specifically, the film thickness on the substrate 1 side is 150 n
m, 100 nm on the recording thin film 3. The reflective layer 6 was made of gold (Au) and had a thickness of 20 nm. Each layer was formed by a sputtering method.

The maximum thickness of the crystallization promoting layer 10 is 2 nm.
On the outer peripheral side (φ120 to φ128) of the recording area, the crystallization promoting layer 10 covers 80% or more of the interface of the protective layer, and the continuity of the crystallization promoting layer 10 itself decreases as it approaches the inner peripheral side. On the inner circumference side (φ60 to φ70) of the recording area, the crystallization promoting layer 10 covers 20% or less of the interface of the protective layer. Specifically, the crystallization-promoting layer 10 was formed using a slit having a large aperture ratio on the outer periphery, and the degree of continuity of the crystallization-promoting layer 10 in the disk radial direction was controlled. At the stage when the crystallization promoting layer 10 was formed, the surface state was observed using STM. FIG. 5 shows a distribution state of the crystallization promoting layer 10 covering the protective layer.

FIG . 5A shows the outer peripheral side of the recording area (φ12
5)).
I have. As shown in this figure, the crystallization promoting layer 10 (shaded area)
Is continuously formed on the outer peripheral side. In FIG.
(B) shows a crystal on the inner circumference side (around φ65) of the recording area.
3 shows a distribution state of the activation promoting layer 10. As shown in this figure
Thus, the crystallization promoting layer 10 is discontinuously and sparsely formed on the inner peripheral side.
Has been established. The disk having the above configuration was rotated at 1800 rpm, and the recording / erasing characteristics were examined in the area of φ65 and the area of φ125. The relative speeds of the laser beam (wavelength: 830 nm) and the disk are 6.5 m / s and 11.8 m / s, respectively.
The frequency of the recording / erasing signal is 5 MHz, 3 MHz, and 1
Overwriting (overwrite recording) was performed 100,000 times. At this time,
Combinations of recording / erasing powers that can maintain the C / N at 50 dB or more and the erasing rate at 25 dB or more even after the repetition are indicated by circles in the table of FIG. (A) of FIG.
This is the result on the outer peripheral side (φ125) of the recording medium,
(B) shows the result on the inner circumference side (φ65) .
The values of C / N of 50 dB or more and the erasure rate of 25 dB or more are sufficiently practical values for digital recording. Fig. 6
Thus, it can be seen that in the recording medium of this example , good recording / erasing repetition characteristics were obtained in a wide power range regardless of the inner and outer circumferences.

Further, the crystallization promoting layer 10 comprises the recording thin film 3
And a disk formed so as to be between the protective layer on the reflective layer 6 side and a disk formed so that the crystallization promoting layer 10 is on both sides of the recording thin film 3 in the same manner as described above. The characteristics were investigated. As a result, in any case, good recording and
It was found that erasing repetition characteristics were obtained.

In order to confirm the effect of the crystallization promoting layer 10 provided in Example 2, a disk having no crystallization promoting layer 10 was prepared, and the recording / erasing characteristics were examined under the same conditions as in Example 2. The structure of the sample disk is exactly the same as that of Example 3 except that the crystallization promoting layer 10 is not formed. Since the crystallization promoting layer 10 of the second embodiment is sufficiently thin, both disks can be considered to have equivalent optical and thermal structures. FIG.
In the area of φ65 and the area of φ125, the C / N is still 50 dB even after recording / erasing is repeated 100,000 times.
The combinations of the recording and erasing powers at which the erasing rate is maintained at 25 dB or more are described above. 7 and 6 (Example 2), the following can be said.

Good repetition characteristics are exhibited at the inner circumference. -In the outer periphery, without the crystallization promoting layer 10, the power range showing good repetition characteristics becomes narrow. In particular, the repetition characteristics on the low erase power side deteriorate.

As a result of TEM (transmission electron microscope) observation of the laser irradiation part, when erasing is performed at a high linear velocity, and when the crystallization promoting layer 10 is present, sufficient crystallization (erasing) is performed even with a low erasing power. On the other hand, when the crystallization accelerating layer 10 was not present, it was found that crystallization could not form a sufficiently large recording mark unless the erasing power was higher.

The crystallization-promoting layer, which is in contact with the recording thin film over a larger area on the outer peripheral side, makes it easier to form crystal nuclei in the process of crystallization of the recording thin film, or to increase the crystal growth rate after crystallization. By doing so, sufficient erasing characteristics can be ensured even at the outer periphery where the linear velocity is high, and as a result, the repetition characteristics of recording / erasing are improved. What is important here is that the presence of the crystallization promoting layer controls the crystallization characteristics according to the linear velocity without substantially changing the optical structure and the thermal structure of the disk.

[0044]

According to the present invention, a crystallization suppressing layer or a crystallization promoting layer is provided in contact with a recording thin film of a phase change type optical information recording medium, and
When the crystallization suppression layer is provided, the contact area between the recording thin film and the crystallization suppression layer per unit area of the interface of the recording thin film is increased from the outer peripheral side to the inner peripheral side of the recording thin film forming region, and the crystallization is suppressed. When the accelerating layer is provided, the contact area between the recording thin film and the crystallization accelerating layer per unit area of the interface of the recording thin film is increased from the inner peripheral side to the outer peripheral side of the recording thin film forming area, thereby increasing the recording area. Irrespective of the inner and outer peripheries, good recording / erasing repetition characteristics are obtained.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view illustrating a structure of an optical information recording medium according to a first embodiment of the present invention. FIG. 1B is a cross-sectional view illustrating a structure of an optical information recording medium according to a second embodiment of the present invention.

FIG. 2 (a) is a view of a distribution state of a crystallization suppression layer near φ195 observed with a scanning tunneling microscope, and FIG. 2 (b) is a view of a distribution state of a crystallization suppression layer near φ85 observed with a scanning tunneling microscope.

FIG. 3A shows φ1 of a disk having a crystallization suppression layer.
FIG. 9B shows a cycle characteristic for a combination of recording / erasing powers around 95. FIG. 10B shows a cycle characteristic for a combination of recording / erasing powers near φ85 of a disk having a crystallization suppression layer.

FIG. 4 (a) shows the φ of a disk without a crystallization suppression layer.
FIG. 4B shows the cycle characteristics for a combination of recording / erasing powers around 195. FIG. 5B shows the cycle characteristics for a combination of recording / erasing powers near φ85 of a disk having no crystallization suppression layer.

FIG. 5 (a) is a view of a distribution state of a crystallization promoting layer near φ125 observed by a scanning tunneling microscope. FIG. 5 (b) is a view of a distribution state of a crystallization promotion layer near φ65 observed by a scanning tunneling microscope.

FIG. 6 (a) shows φ1 of a disk having a crystallization promoting layer.
FIG. 4B shows the cycle characteristics for a combination of recording and erasing powers near 25, and FIG. 6B shows the cycle characteristics for a combination of recording and erasing powers near φ65 of a disk having a crystallization promoting layer.

FIG. 7 (a) shows the φ of a disk having no crystallization promoting layer.
FIG. 7B shows the cycle characteristics for a combination of recording / erasing powers around 195. FIG. 9B shows the cycle characteristics for a combination of recording / erasing powers near φ85 of a disk having no crystallization promoting layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Protective layer 3 Recording thin film 4 Protective layer 5 Crystallization suppressing layer 6 Reflective layer 7 Adhesive layer 8 Protective substrate 9 Substrate plane 10 Crystallization promoting layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-42654 (JP, A) JP-A-61-292239 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G11B 7/24 533

Claims (2)

(57) [Claims] 1. A disk-shaped substrate, a recording thin film formed on the disk-shaped substrate and capable of undergoing a phase change by irradiation with a laser beam and reversibly shifting to a state having different optical characteristics, the contact area between the an optical information recording medium comprising a suppressing crystallization suppressing layer crystallization of the recording thin film, per unit area, the recording thin film and the crystallization inhibiting layer Te is, the optical information recording From the outer circumference of the media to the inner
An optical information recording medium characterized by being continuously increasing toward the circumferential side . 2. A disk-shaped substrate, and said disk-shaped substrate
Formed on the surface and undergoes a phase change
Recording thin film capable of reversibly moving to a state with different optical properties
Promotes crystallization of the recording thin film in contact with the recording thin film
An optical information recording medium comprising a crystallization promoting layer
Thus, the recording thin film and the crystallization promoting
The area of contact with the coating layer is
An optical information recording medium, which continuously increases toward the circumferential side .