JP2903970B2 - Optical recording medium and recording / reproducing method using the same - 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 recording medium capable of recording, reproducing, and erasing information at a high speed and at a high density by irradiation with a laser beam or the like, and a recording / reproducing method using the same.

[0002]

2. Description of the Related Art In recent years, an optical disk using a laser beam has been developed as a recording medium that meets the demand for an increase in the amount of information and a high density and high speed of recording and reproduction. Optical discs include a write-once type, which allows recording only once, and a rewritable type, which allows recording and erasing as many times as possible.

Examples of the rewritable optical disk include a magneto-optical recording medium utilizing a magneto-optical effect and a phase change medium utilizing a reversible change in crystalline state. The phase change medium does not require an external magnetic field, and can record and erase only by modulating the power of laser light. Furthermore, there is an advantage that one-beam overwriting in which erasing and re-recording are performed simultaneously with a single beam is possible.

In the phase change recording method capable of one-beam overwriting, it is general that a recording bit is formed by amorphizing a recording film, and erasing is performed by crystallization. As a recording layer material used in such a phase change recording method, a chalcogen-based alloy thin film is often used. For example, Ge-Te system, Ge-Te-
Sb-based, In-Sb-Te-based, Ge-Sn-Te-based alloy thin films and the like can be mentioned.

[0005] A write-once type phase change medium can be realized by applying almost the same material and layer structure as the rewritable type. In this case, since the reversibility is not used, information can be recorded and stored for a longer period of time, and in principle, semi-permanent storage is possible. When a phase change medium is used as a write-once type,
Unlike the perforated type, there is an advantage that a signal rim is not formed around the recording pit, so that the signal quality is excellent, and no air gap is required above the recording layer, so that an air sandwich structure is not required.

Generally, in a rewritable phase change recording medium,
Two different laser light powers are used to achieve different crystal states. This method will be described by taking as an example a case in which amorphous pits are recorded and erased by crystallization in the crystallized initial state. The crystallization is performed by heating the recording layer to a temperature sufficiently higher than the crystallization temperature of the recording layer and lower than the melting point. In this case, the recording layer is sandwiched between dielectric layers, or an elliptical beam that is long in the beam moving direction is used so that the cooling rate becomes slow enough to sufficiently crystallize.

On the other hand, the amorphization is performed by heating the recording layer to a temperature higher than the melting point and rapidly cooling the recording layer. in this case,
The dielectric layer also has a function as a heat dissipation layer for obtaining a sufficient cooling rate (supercooling rate). Further, in order to prevent deformation due to melting and volume change of the recording layer in the heating / cooling process as described above, to prevent thermal damage to the plastic substrate, and to prevent deterioration of the recording layer due to moisture, the dielectric layer is used. Body layer is important.

The material of the dielectric layer is such that it is optically transparent to laser light, has a high melting point, softening point, and decomposition temperature, is easy to form, and has a suitable thermal conductivity. Selected from a viewpoint.

[0009]

The beam diameter of a laser assumed to be a Gaussian beam is 0.82 × λ ÷ NA (λ
Is the wavelength, and NA is the numerical aperture of the lens. Therefore, when a laser having a short wavelength such as 600 nm or less is used for high-density recording, the beam spot diameter becomes small.

[0010] In a phase-change type optical disk, recording is erased by annealing and crystallizing amorphous bits in a recording layer at a crystallization temperature. However, when the beam spot diameter is small, the recording layer is over the crystallization temperature. The problem is that the time for which crystallization is not maintained is shortened and crystallization does not work well.

[0011]

Means for Solving the Problems The present inventors can extend the time during which the recording layer is maintained at a temperature higher than the crystallization temperature by optimizing the thermal conductivity of the second dielectric layer. Was found. As a result, it has been found that heat can be sufficiently applied to the recording layer at a temperature higher than the crystallization temperature, and that the optical recording medium is particularly suitable for short-wavelength recording of less than 600 nm.
The present invention has been reached.

The gist of the present invention is to provide an optical information recording medium having a first dielectric layer, a phase change recording layer, a second dielectric layer and a reflective layer on a substrate, wherein The thickness of the layer is set to 15 to 50 nm, and the second dielectric layer has a thermal conductivity of 5.0 × 10 ⁻⁴ −7.39 × 10 ⁻³ pJ · μm ^−1.
A layer having a wavelength of less than 600 nm using K ^-1 ns ^-1 and having a thickness of the second dielectric layer of 10 to 250 nm;
An optical information recording medium for recording / reproducing information using laser light, and a recording / reproducing method characterized by recording / reproducing information using a laser beam having a wavelength of less than 600 nm.

The phase change recording layer is made of GeSbTe, InSb
Te type or the like is preferably used. For improving the crystallization speed, the easiness of amorphization, the crystal grain size, the storage stability, etc., Sn,
In, Ge, Pb, As, Se, Si, Bi, Au, T
i, Cu, Ag, Pt, Pd, Co, Ni, etc. may be added. When the thickness of the recording layer is less than 15 nm, the heat insulation property of the recording layer itself is reduced, and crystal nucleus formation for crystallization of the recording layer is suppressed to suppress crystallization, and furthermore, sufficient contrast cannot be obtained. The problem arises.

On the other hand, when the thickness is larger than 50 nm, mass transfer at the time of overwriting tends to occur. The thickness of the recording layer is 1
5 to 50 nm is preferred. The recording layer is provided on the substrate with the dielectric layer interposed therebetween. However, a reflective layer, a protective layer made of an ultraviolet curable resin, and the like may be further provided. The first and second dielectric layers are transparent, such as tantalum oxide, having an optical constant n of 1.5 to 2.4, k of 0 to 0.05, and a thermal expansion coefficient of 1.
It is preferable to use a dielectric material of 0 × 10 ⁻⁵ or less.

The second dielectric layer has a thermal conductivity of 5.0 × 1.
In ^{0 -4 -7.39 × 10 -3 pJ ·} μm -1 · K -1 · ns -1
It is necessary that there is. Thermal conductivity of 5.0 × 10 ^-4 pJ
By making it larger than μm ^-1 · K ^-1 · ns ^-1 , heat is quickly released from the recording layer through the second dielectric layer, so that the recording layer is maintained at a temperature for crystallization. It is possible to increase the width.

As a result, sufficient time for crystallization can be obtained, and the erasing characteristics can be improved.
The second dielectric layer has a thickness of 10 to 250 nm. Second
If the thickness of the dielectric layer is less than 10 nm, it is not possible to suppress mass transfer of the recording layer caused by repeated overwriting.

On the other hand, if the thickness of the second dielectric layer exceeds 250 nm, cracks tend to occur. The first dielectric layer preferably has a thickness of 50 to 250 nm. As the substrate of the recording medium in the present invention, glass, plastic,
It may be any of those provided with a photocurable resin on glass, but the dielectric layer used in the present invention has excellent heat resistance,
Since there is an effect of preventing thermal deformation of the substrate, it is possible to use a polycarbonate resin substrate generally used at present as an optical disk substrate.

The reflection layer is made of Al and an Al alloy, Au, A
g, it is preferable to use a substance having high thermal conductivity,
The thickness is usually selected in the range of 100 to 200 nm.
The recording layer, the dielectric layer, and the reflection layer are formed by a sputtering method or the like. It is desirable to form a film using an in-line apparatus in which a target for a recording film, a target for a dielectric film, and if necessary, a target for a reflective layer material are installed in the same vacuum chamber, from the viewpoint of preventing oxidation and contamination between layers. It is also excellent in productivity.

The thermal conductivity described in the present invention is not the bulk value of a substance but the thermal conductivity of a thin film. Methods for measuring the thermal conductivity of thin films are described in C. Lambropoul
os, et. al. , J. et al. Appl. Phys. , 6
6,4230 (1989); Hatta, et. a
l. Rev., Rev .. Sci. Instrum. , 56,16
43 (1985); Horie, et. al. ,
MitsubishiKasei R & D Review
w, 4 (2), 68 (1990) and the like. Specifically, a thermal conductivity measuring device using a photo-ac excitation method may be used.

[0020]

The present invention will be described in detail with reference to the following examples. Example 1 (ZnS) ₈₀ (Si
O ₂ ) ₂₀ (the numbers indicate the component ratio and the unit is mol%),
At a wavelength of 488 nm, the first dielectric film having an optical constant of n = 2.2 and k = 0 is 160 nm, the Ge ₂ Sb ₂ Te ₅ (composition is shown by ratio) recording film is 30 nm, and the Ta ₂ O ₅ ( Thermal conductivity 7.39 × 10 ^-3 pJ · μm ^-1 · K ^-1 · ns ^-1 , wavelength 4
The second dielectric film having an optical constant at 88 nm of n = 2.2 and k = 0) is 20 nm, and the Al alloy reflection film is 200 n.
m, and formed sequentially by a sputtering method. Further, an ultraviolet curable resin layer was provided on the reflective layer.

Since the recording layer of the disk prepared as described above is in an amorphous state, the disk is crystallized with an Ar laser and initialized, and then the dynamic characteristics of the disk are evaluated by an evaluation apparatus using a laser pickup having a wavelength of 488 nm. did. A recording power of 14 mW at a linear velocity of 10 m / s, a recording frequency of 8.58 MHz at an erasing power of 7 mW, and a pulse width of 38 n
The C / N ratio when a signal of sec was recorded and the erasing ratio when erasing power was applied by DC irradiation were 51 dB and 24 dB, respectively.
dB. Further, the erase power margin at an erase ratio of 20 dB or more was 2 mW.

Example 2 (ZnS) ₈₀ (Si) was coated on a polycarbonate resin substrate.
O ₂ ) ₂₀ composition, optical constant n = 2 at wavelength 488 nm.
2, 160 nm thick first dielectric film with k = 0, Ge ₂ Sb ₂
The Te ₅ recording film is formed of 30 nm, SiO ₂ (thermal conductivity 5.40 ×
^{10 -3 pJ · μm - 1 ·} K -1 · ns -1, the optical constants n = 1.6 at a wavelength of 488nm, k = 0) the second dielectric film 20nm made of, 200 nm of Al alloy reflective film , By sputtering. Further, an ultraviolet curable resin layer was provided on the reflective layer.

Since the recording layer of the disk prepared as described above is in an amorphous state, the disk is crystallized with an Ar laser and initialized, and then the dynamic characteristics of the disk are evaluated by an evaluation device using a laser pickup having a wavelength of 488 nm. did. A recording power of 15 mW at a linear velocity of 10 m / s, a recording frequency of 8.58 MHz at an erasing power of 7 mW, and a pulse width of 38 n
The C / N ratio when a signal of sec was recorded and the erasing ratio when DC power was applied to the erasing power were 49 dB and 24 dB, respectively.
dB. Further, the erase power margin at an erase ratio of 20 dB or more was 3 mW.

Comparative Example 1 (ZnS) ₈₀ (Si
O ₂ ) ₂₀ composition, optical constant n = 2 at wavelength 488 nm.
2, 160 nm thick first dielectric film with k = 0, Ge ₂ Sb ₂
Te ₅ recording film _{20nm, (ZnS) 80 (SiO} 2)
₂₀ (Thermal conductivity 3.5 × 10 ^-4 pJ-μm ^-1 · K ^-1 · ns
⁻¹ , optical constant at wavelength 488 nm n = 2.2, k = 0)
A second dielectric film of 20 nm and an Al alloy reflective film of 200 nm were sequentially formed by sputtering. Further, an ultraviolet curable resin layer was provided on the reflective layer.

Since the recording layer of the disk prepared as described above is in an amorphous state, the disk is crystallized with an Ar laser and initialized, and then the dynamic characteristics of the disk are evaluated by an evaluation device using a laser pickup having a wavelength of 488 nm. did. A recording power of 8 mW at a linear velocity of 10 m / s, a recording frequency of 8.58 MHz at an erasing power of 4 mW, and a pulse width of 38 ns
The C / N ratio when the ec signal was recorded and the erasing ratio when the erasing power was applied by DC irradiation were 56 dB and 20 d, respectively.
B. Further, the erase power margin at an erase ratio of 20 dB or more was 0.3 mW. Reference Examples 1 and 2 Composition of (ZnS) ₈₀ (SiO ₂ ) ₂₀ (unit: mol%; thermal conductivity: 3.5 × 10 ⁻⁴ [pJ /
μm / K / ns]), a Ge ₂ Sb ₂ Te ₅ recording film having a thickness of 110 nm and a thickness shown in Table 1 and a Ta ₂ O film thickness of 110 nm.
₅ (Thermal conductivity 7.39 × 10 ⁻³ [pJ / μm / K / n
s]: The composition of Reference Example 1) or (ZnS) ₈₀ (SiO ₂ ) ₂₀ (Thermal conductivity 3.5 × 10 ⁻⁴ [pJ / μm / K / ns]: Reference Example 2) and shown in Table 1. A second dielectric film of thickness A
An l-alloy reflective film was formed in order of 200 nm by a sputtering method. Further, an ultraviolet curable resin layer was provided on the reflective layer. Since the recording layer of the disk prepared as described above is in an amorphous state, it is crystallized and initialized by a bulk eraser using an LD of 810 nm as a light source, and then a laser pickup of 780 nm (NA 0.55) is used. The dynamic characteristics of the disk were evaluated using the evaluation device. Table 1 shows a C / N ratio when a signal having a recording frequency of 4 MHz and a duty of 50% was recorded at a recording power and an erasing power shown in Table 1 at a linear velocity of 10 m / sec, and an erasing power margin of an erasing ratio of 20 dB or more. .

[Table 1] From Table 1, it can be seen that in recording / reproducing at a wavelength of about 750 to 900 nm, there is no large difference in the erasing margin regardless of whether it is within the range of the film thickness and thermal conductivity specified in the present application. I understand.

[0026]

According to the optical information recording medium of the present invention, a recording / reproducing characteristic with a good erasing ratio can be obtained by using a light source having a laser wavelength of 600 nm or less.

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI G11B 7/24 538 G11B 7/24 538C (72) Inventor Horie Tatsukazu 1000 Kamoshita-cho, Midori-ku, Yokohama-shi, Kanagawa Prefecture Mitsubishi Chemical Corporation Research Institute (56) References JP-A-3-241539 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7/24 535 G11B 7/24 538

Claims (6)

(57) [Claims] 1. An optical information recording medium having a first dielectric layer, a phase change recording layer, a second dielectric layer, and a reflective layer on a substrate, wherein the thickness of the phase change recording layer is 15-5
0 nm, and the thermal conductivity of the second dielectric layer is 5.0 ×
10 ^-4 -7.39 × 10 ^-3 pJ · μm ^-1 · K ^-1 · ns ^-1
And the thickness of the second dielectric layer is 10-25.
Using laser light with a wavelength of less than 600 nm, which is 0 nm
Optical information recording medium for recording and reproducing information. 2. A phase change recording layer comprising a GeSbTe-based or I
2. The optical information recording device according to claim 1, wherein the optical information recording device is an nSbTe system.
Medium. 3. The method of claim 1, wherein the first and second dielectric layers are tantalum oxide.
The optical information recording medium according to claim 1, wherein the medium comprises an optical information recording medium.
body. 4. The first and second dielectric layers have an optical constant n
Is 1.5-2.4 and k is 0-0.05.
An optical device according to any one of claims 1 to 3, wherein the optical device comprises a body.
Information recording medium. 5. The reflective layer has a thickness of 100 to 200 nm.
The optical information recording device according to any one of claims 1 to 4,
Recording medium. 6. The method according to claim 1, wherein
Laser with wavelength less than 600nm for optical information recording medium
-Recording and reproduction of information using light
Recording and playback method.