JP3289716B2 - Phase change optical disk - 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 for recording / reproducing information by irradiating a laser beam, and more particularly, to recording by changing a phase state in a recording layer and an amorphous state of the recording layer. The present invention relates to a phase change disk that reproduces information by using a difference in optical characteristics between a crystal and a crystal state.

[0002]

2. Description of the Related Art Magneto-optical disks and phase change disks have been provided as optical information recording media utilizing recent optical technology. Of these, the phase-change disk records information by changing the recording layer between a crystalline state and an amorphous state,
Further, information is reproduced by utilizing a difference in light reflectance or light transmittance between the crystalline state and the amorphous state of the recording layer. In a conventional phase change optical disk, Aa is generally higher than Ac. Therefore, when the pitch of the recording track of the phase-change optical disk is narrowed for higher density, when a certain recording track is irradiated with a laser beam to change the phase of the recording layer, information is recorded. In addition, the temperature rise and crystallization due to light absorption, that is, so-called cross erase, occurs in the amorphous recording mark having a high light absorption rate existing in the adjacent recording track.

Therefore, in order to prevent such cross erasure, it is considered effective to make the light absorption rate Aa in the amorphous state lower than the light absorption rate Ac in the crystalline state. . As far as the point where Aa is lower than Ac is described, for example, JP-A-1-149238 and JP-A-7-93804, Proceedings of the 5th Phase Change Recording Workshop Symposium P92-94. There are the techniques described. However, in these techniques, especially for a short wavelength light source, Aa is changed to Aa while keeping the difference between Ra and Rc large.
It is difficult to make it significantly lower than c.

[0004]

The conventional phase-change optical disk has a structure in which the heat load is increased, so that the number of times that information can be rewritten is small, and it is greatly limited especially at a low linear velocity. There is also a problem. For example, the above-mentioned 5th Phase Change Recording Research Group Symposium Proceedings P94
In the configuration example shown in Fig. 1, an absorbing reflective layer (ultra-thin gold thin film) is provided directly above the substrate, so that during recording of information, the reflective layer absorbs laser light and is heated, and immediately below the reflective layer. The heat load is applied to the substrate, and the number of times of rewriting information repeatedly is limited. In particular, at low linear velocities of 8 m / s or less, there has been a problem that the number of repetitive rewrites is greatly limited.

An object of the present invention is to provide a phase change optical disk which suppresses cross erasure and has excellent repetition characteristics.

[0006]

According to the phase change optical disk of the present invention, a first dielectric layer, a second dielectric layer, a third dielectric layer, a recording layer, a fourth dielectric layer, and a reflective layer are sequentially formed on a substrate. And a refractive index n2 of the second dielectric layer and a refractive index n3 of the third dielectric layer.
Satisfies the relationship n2 <n3, and the absorptance in the amorphous state is lower than the absorptivity in the crystalline state. In the present invention, it is preferable that the refractive index n1 of the first dielectric layer and the refractive index n2 of the second dielectric layer satisfy a relationship of n1> n2.

Here, in the phase change optical disk of the present invention, when the wavelength of a light source used for recording and reproducing information is λ, the refractive index of the first dielectric layer at the wavelength λ is larger than 1.7. That the reflection layer has A
u, Al, Ti, Cu, Cr and their alloys, and the thickness of the reflective layer is 40 nm.
The thickness is preferably not less than 300 nm and not more than 300 nm.

In the present invention, the refractive indices n2 and n3 of the second and third dielectric layers formed between the substrate and the recording layer are set to n3
By satisfying the relationship of> n2, Ra in the recording layer can be made higher than Rc, and Aa can be made lower than Ac. Further, among the first, second and third dielectric layers formed between the substrate and the recording layer, the respective refractive indices n1 and n2 of the first and second dielectric layers are defined as n1> n2. By satisfying, it is possible to increase the degree of freedom of the film thickness of each layer. Furthermore, in the present invention, since there is no light absorbing layer between the recording layer and the substrate, the temperature rise near the substrate surface is suppressed, the thermal load on the substrate is reduced, and the repetition characteristics of rewriting are improved. can do.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a cross-sectional structure of a phase change optical disc of the present invention. A first dielectric layer 11, a second dielectric layer 12, a third dielectric layer 13, a recording layer 15, a fourth dielectric layer 14, and a reflective layer 16 are laminated on a transparent substrate 10 in this order. .

FIG. 2 shows the relationship between Aa and the change in the ratio of n3 / n2.
Is obtained by an optical calculation by the matrix method, and if the relationship of n2 <n3 is satisfied, Aa becomes Ac
It turns out that it becomes lower. Further, it is preferable that the refractive index n1 of the first dielectric layer and the refractive index n2 of the second dielectric layer satisfy a relationship of n1> n2. Even if the relationship of n1> n2 is not satisfied, it is not impossible to realize Aa <Ac, but if n1 = n2 or n1 <n2, the film of the fourth dielectric layer that can realize Aa <Ac The thickness is limited, and it is difficult to secure repetition characteristics. FIG. 3 shows the lower limit of the thickness of the fourth dielectric layer capable of realizing Aa <AC obtained by optical calculation using a matrix method. When n1 ≦ n2, the thickness of the fourth dielectric layer is 90 nm.
It turns out that it must be at least. In order to improve the repetition characteristics, the thickness of the fourth dielectric layer is as small as possible.
Since it is desirably 60 nm or less, it is preferable to satisfy the relationship of n1> n2.

As described above, by making the light absorption coefficient Aa in the amorphous state of the recording layer lower than the light absorption coefficient Ac in the crystalline state, as shown in FIG. When recording information by forming a recording mark M1 by irradiating a laser beam spot SP on the groove T1, the recording layer 15 is centered on the recording track T1 by the thermal energy of the laser light. Has a temperature distribution as shown in FIG. For this reason, if the recording marks M2 and M3 in the amorphous state in which information is recorded on the adjacent recording tracks (lands) T2 and T3 exist, these recording marks M2 and M3 become spots of the laser light. SP
Affected by temperature. However, at this time, the light absorption rate Aa of the recording marks M2 and M3 which are in an amorphous state is lower than the light absorption rate Ac of the crystalline state of the track T1 on which recording is performed.
3, the amount of absorption of the laser beam is reduced, its temperature rise is suppressed, and the recording marks M2 and M3 are erased.
That is, cross erasure is prevented.

Here, when the refractive index n1 of the first dielectric layer 11 and the refractive index n0 of the substrate 10 are the same, the substrate 10 and the first
The dielectric layer 11 becomes optically identical, and the R
Since the optical interference effect of making a higher than Rc cannot be obtained, the refractive index n1 of the first dielectric layer 11 needs to be larger than the refractive index n0 of the substrate 10. Since the refractive index of a plastic substrate or a glass substrate is generally about 1.5, n
1 must be greater than 1.7.

In this configuration, the substrate 10 and the recording layer 15
Since there is no light absorbing layer between the substrate and the substrate, the temperature rise near the surface of the substrate 10 can be suppressed, the thermal load on the substrate can be reduced, and the repetition characteristics of rewriting can be improved. The reflective layer 16 is made of a metal material for increasing heat dissipation and improving repetition characteristics, and its thickness is desirably 40 nm or more and 300 nm or less. This is because if the thickness of the reflective layer 16 is 40 nm or less, sufficient heat dissipation cannot be obtained, and the repetition characteristics deteriorate, and if the thickness of the reflective layer 16 is 300 nm or more, the reflective layer is easily peeled.

[0014]

Embodiments of the present invention will be described below. Referring to FIG. 1, first substrate 10 is made of polycarbonate,
60 nm of ZnS—SiO ₂ as the dielectric layer 11,
SiO ₂ is 90 nm as the dielectric layer 12, ZnS—SiO ₂ is 50 nm as the third dielectric layer 13, Ge ₂ Sb ₂ Te ₅ is 12 nm as the recording layer 15, and the third dielectric layer 13 is formed.
The ZnS-SiO ₂ 40nm, an Al as a reflective layer 16 formed sequentially change optical discs are laminated by sputtering 120nm as. Here, the third dielectric layer 1
The refractive index n of 3 (ZnS—SiO ₂ ) is 2.1, and the refractive index n of the second dielectric layer 12 (SiO ₂ ) is 1.5. The pitch of the guide groove of the recording track (track pitch) was 1.1 μm as shown in FIG.

In this phase change optical disk, the recording layer 15
The light absorption of each of the crystalline state and the amorphous state was measured, and found to be 90% for Ac and 60% for Aa. Then, this phase change optical disk is rotated at a linear velocity of 5 m / s, and
The measurement was performed using an optical head having a numerical aperture of an objective lens of 0.6 nm and a numerical aperture of 0.6. First, 1MHz, duty on the land
= 50%, a 1.5 MHz signal and a duty = 50% signal were repeatedly recorded in adjacent groove portions on both sides, and the carrier change of the 1 MHz signal was measured. As is apparent from FIG. 5, even if information is repeatedly rewritten in the adjacent groove portion, the 1 MHz signal is not affected at all. FIG. 5 shows the carrier Ci of the 1 MHz signal measured without recording information on the adjacent track and the carrier C of the 1 MHz signal measured after repeatedly recording a 1.5 MHz signal on the adjacent track a predetermined number of times.
1 (Ci-Cl). When a signal of 1 MHz and duty = 50% was repeatedly recorded using this phase change optical disk, no change in the carrier or noise of the 1 MHz signal was observed up to 500,000 times.

A second embodiment will be described. The substrate 10 is made of polycarbonate, and the first dielectric layer 11 is made of Zn.
S is 100 nm and SiN is 50 as the second dielectric layer 12.
80 nm, ZnS of 80 nm as the third dielectric layer 13, 15 nm of GeSb ₂ Te ₄ as the recording layer 15, 20 nm of ZnS—SiO ₂ as the fourth dielectric layer 14, and the reflective layer 16
A phase change optical disk was formed by sequentially laminating 100 nm of Al by sputtering. Here, the refractive index of the second dielectric layer (SiN) is 1.9, and the refractive indexes of the first dielectric layer 11 and the third dielectric layer 13 (ZnS) are 2.3. The pitch of the guide groove of the recording track (track pitch) was 1.1 μm as shown in FIG.

In this phase change optical disk, Ac in the recording layer 15 was 85% and Aa was 65%. The disk was rotated at a linear velocity of 5 m / s, and the measurement was performed using an optical head having a wavelength of 660 nm and a numerical aperture of the objective lens of 0.6. As in the previous embodiment, first, 1 MHz, d
After recording a signal of duty = 50%, a signal of 1.5 MHz and a signal of duty = 50% were repeatedly recorded on adjacent glue portions, and a change in carrier of a 1 MHz signal was measured. Also in this embodiment, the 1 MHz signal was not affected at all. Using this phase change optical disk, 1MH
When a signal of z, duty = 50% was repeatedly recorded, no change in carrier or noise was observed up to 500,000 times.

Another embodiment will be described. The substrate 10 is made of polycarbonate, and the first dielectric layer 11 is made of SiN.
00 nm, 20 n of SiO ₂ as the second dielectric layer 12
m, ZnS is 100 nm as the third dielectric layer 13, GeSb ₂ Te ₄ is 13 nm as the recording layer 15, ZnS—SiO ₂ is 50 nm as the fourth dielectric layer 14, and the reflection layer 26
Al was successively laminated in a thickness of 100 nm by sparing. Here, the refractive index of ZnS was 2.3, the refractive index of SiN was 1.9, and the refractive index of SiO ₂ was 1.5. The track pitch is 1.1 μm as in the above embodiments.
And

In this phase change optical disk, Ac in the recording layer 15 was 80% and Aa was 60%. The disk was rotated at a linear velocity of 5 m / s, and the measurement was performed using an optical head having a wavelength of 860 nm and a numerical aperture of the objective lens of 0.6. As in the previous embodiment, 1 MHz, dut
After the signal of y = 50% was recorded, the signal of 1.5 MHz and the signal of duty = 50% were repeatedly recorded in the adjacent groove portions, and the change of the carrier of the signal of 1 MHz was measured. Again, the 1 MHz signal was not affected at all. Using this phase change optical disk, 1MHz,
When the signal of duty = 50% was repeatedly recorded, 5
No change in carrier or noise was observed up to 10,000 times.

Here, the material of each dielectric layer, recording layer and reflection layer constituting the phase change optical disk of the present invention is not limited to those of the above-described embodiment. Particularly, as the reflective layer, Au, Ti, Cu, Cr other than the above-described embodiment.
It is also possible to use Al and their alloys, Al and their alloys.

[0021]

As described above, according to the present invention, it is possible to suppress cross erasure on adjacent recording tracks during recording and to improve the recording density by narrowing the track pitch of the recording tracks. Further, in the present invention, since there is no light absorbing layer between the recording layer and the substrate, the temperature rise near the substrate surface is suppressed, and the thermal load on the substrate is reduced.
Repetition characteristics of rewriting can be improved. Further, in the present invention, since the absorptance of the recording layer in the amorphous state is reduced, it is possible to prevent data from being erased even when the reproduction laser light fluctuates and the power becomes high, When the wavelength of the light source is further shortened, it is possible to prevent data from being erased by the reproduction laser beam.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a phase change optical disk according to the present invention.

FIG. 2 is a diagram illustrating an example of optical characteristics of a phase change optical disc according to the present invention.

FIG. 3 shows a first example of the phase change optical disc according to the present invention.
FIG. 9 is a diagram illustrating a relationship between a refractive index ratio of a second dielectric layer and a film thickness of a fourth dielectric layer on the condition that Ac> Aa.

FIG. 4 is a diagram showing a temperature rise when recording is performed.

FIG. 5 is a diagram showing a cross erase characteristic.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Substrate 11 1st dielectric layer 12 2nd dielectric layer 13 3rd dielectric layer 14 4th dielectric layer 15 recording layer 16 reflection layer

Claims (3)

(57) [Claims] 1. A phase-change optical disc comprising a first dielectric layer, a second dielectric layer, a third dielectric layer, a recording layer, a fourth dielectric layer, and a reflective layer sequentially laminated on a substrate. When the refractive index n2 of the second dielectric layer and the refractive index n3 of the third dielectric layer satisfy the relationship of n2 <n3, the absorptivity of the recording layer in the amorphous state is lower than the absorptivity of the recording layer in the crystalline state. and, wherein the first refractive index n2 of the refractive index n1 of the dielectric layer a second dielectric layer meets the relation of n1> n2, the thickness of the reflective layer
A phase-change optical disk , wherein is greater than or equal to 40 nm and less than or equal to 300 nm. 2. The method according to claim 1, wherein said reflective layer is made of Au, Al, Ti, C.
2. The phase change optical disk according to claim 1, wherein u, Cr and their alloys are used. 3. The phase-change optical disk according to claim 1, wherein the substrate is a plastic substrate, and the first dielectric layer is a layer containing ZnS.