JP2903969B2 - 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 using a magneto-optical effect and a phase change medium using a reversible change in crystalline state.

[0003] The phase change medium does not require an external magnetic field, and can be recorded / erased 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 a 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 alloy thin film is often used. For example, Ge-Te system, Ge-Te-Sb
System, In-Sb-Te system, Ge-Sn-Te system alloy thin film and the like. In addition, almost the same materials and
By applying the layer structure, a write-once type phase change medium can be realized.
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.

[0005] When a phase change medium is used as a write-once type, unlike a perforated type, there is no ridge called a rim around the recording pits, so that the signal quality is excellent. There is an advantage that there is no need to do this. Generally, in a rewritable phase change recording medium, two different laser beam powers are used to realize 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.

[0006] 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 radiation layer for obtaining a sufficient cooling rate (supercooling rate).

[0007] Further, in order to prevent the recording layer from being deformed due to melting and volume change 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 above dielectric layer is important. The material of the dielectric layer is selected from the viewpoint that it is optically transparent to laser light, has a high melting point, softening point, and decomposition temperature, is easy to form, and has an appropriate thermal conductivity. Is done.

[0008]

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.

In a phase-change type optical disk, erasing of recording is performed 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.

[0010]

Means for Solving the Problems The present inventors have improved the relationship between the phase change recording layer and the second dielectric layer so as to increase the time during which the recording layer is kept at the crystallization temperature. It is possible to give a sufficient amount of heat at the crystallization temperature,
In particular, the present inventors have found that the medium is an optical recording medium suitable for short-wavelength recording of less than 600 nm, and arrived at the present invention.

[0011] The gist of the present invention is 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 in order. The thickness of the layer is 20-50 nm, the second dielectric layer is made of a material having a thermal conductivity of 1 × 10 ⁻³ pJ · μm ⁻¹ · K ⁻¹ · ns ⁻¹ or less, and has a thickness of 1 nm or more and less than 10 nm,
An optical information recording medium for recording and reproducing information using a laser beam having a wavelength of less than 600 nm, and a recording and reproducing method for recording and reproducing information using a laser having a wavelength of less than 600 nm using the medium. Is the way.

The phase change recording layer is made of GeSbTe, InSb
Te-based or the like is preferably used, and Sn, I is used for improving the crystallization speed, the easiness of amorphization, the crystal grain size, the storage stability and the like.
n, Ge, Pb, As, Se, Si, Bi, Au, T
i, Cu, Ag, Pt, Pd, Co, Ni, etc. may be added. If the thickness of the recording layer is less than 20 nm, the heat insulation property of the recording layer itself is reduced, and the formation of crystal nuclei for crystallization of the recording layer is suppressed to suppress crystallization, and furthermore, a sufficient contrast cannot be obtained. The problem arises.

On the other hand, when the thickness is more than 50 nm, mass transfer at the time of overwriting tends to occur and cracks in the recording layer tend to occur. The thickness of the recording layer is preferably 20 to 50 nm. The recording layer is provided on the substrate sandwiched between the dielectric layers,
A reflective layer, a protective layer made of an ultraviolet curable resin, or the like may be provided. The first and second dielectric layers are preferably transparent and have an optical constant n of 1.1, such as a mixture of zinc sulfide and silicon dioxide.
It is preferable to use a dielectric material having a coefficient of thermal expansion of not more than 9 to 2.4, k of 0 to 0.05, and 1.0 × 10 ⁻⁵ or less.

The thickness of the dielectric layer is 10 n for the second dielectric layer.
m and the first dielectric layer is preferably between 50 nm and 250 nm. The present invention is characterized in that the thickness of the second dielectric layer is less than 10 nm, which is much smaller than usual. The second dielectric layer has at least 1 n
m or more, and 5 nm or more in terms of manufacturing.

The second dielectric layer has a thermal conductivity of 1 × 10 ⁻³ p.
A material having a material of J · μm ^-1 · K ^-1 · ns ^-1 or less is used.
With such a thickness and thermal conductivity, heat can be quickly released from the recording layer through the second dielectric layer,
It is possible to increase the width of the recording layer maintained at the temperature for crystallization, and it is possible to increase the time for sufficiently crystallization.

The substrate of the recording medium in the present invention includes:
Glass, plastic, may be any of those provided with a photocurable resin on the glass, etc., since the dielectric layer used in the present invention has excellent heat resistance and has an effect of preventing thermal deformation of the substrate, It is possible to use a polycarbonate resin substrate generally used as an optical disk substrate at present.

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 a value in the bulk of a substance, but a 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.

[0019]

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%),
When the wavelength is 488 nm, the optical constants are n = 2.2 and k = 0.
155nm the first dielectric film, Ge ₂ Sb ₂ Te ₅ (composition expressed as a percentage) 30 nm recording layer, (ZnS)
_A second dielectric film having a composition of ₈₀ (SiO ₂ ) ₂₀ and an optical constant of n = 2.2 and k = 0 at a wavelength of 488 nm (thermal conductivity 3.5 × 10 ⁻⁴ pJ · μm ^−1. K ^-1 · ns ^-1 ) is 5n
m, an Al 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, 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 12 mW at a linear velocity of 10 m / sec, a recording frequency of 8.58 MHz at an erasing power of 6 mW, and a pulse width of 3
The C / N ratio when a signal of 8 nsec was recorded and the erasing ratio when DC power was applied to the erasing power were 56 dB, respectively.
It was 28 dB. Further, the erase power margin at an erase ratio of 20 dB or more was 4 mW.

[0021]

[0022]

Comparative Example 1 (ZnS) ₈₀ (Si
The composition of O ₂ ) ₂₀ has an optical constant of n when the wavelength is 488 nm.
= 2.2, k = 0, 160 nm, Ge
_{The 2} Sb ₂ Te ₅ recording film is made of 20 nm, (ZnS) ₈₀ (Si
The composition of O ₂ ) ₂₀ has an optical constant of n when the wavelength is 488 nm.
= 2.2, k = 0 (second thermal conductivity 3.5 ×
10 ⁻⁴ pJ · μm ⁻¹ · K ⁻¹ · ns ⁻¹ ) to 20 nm, Al
An 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 was in an amorphous state, the disk was crystallized with an Ar laser and initialized, and then the dynamic characteristics of the disk were evaluated by an evaluation device using a laser pickup having a wavelength of 488 nm. At a linear velocity of 10 m / sec, a recording power of 8 mW and an erasing power of 4
8.58 MHz recording frequency and 38 ns pulse width at mW
The C / N ratio when the signal of c was recorded and the erasing ratio when DC power was applied to the erasing power were 56 dB and 20 dB, respectively.
Met. Further, the erase power margin at an erase ratio of 20 dB or more was 0.3 mW. Reference Examples 1 to 3 Composition of (ZnS) ₈₀ (SiO ₂ ) ₂₀ (unit: mol%; thermal conductivity: 3.5 × 10 ⁻⁴ [pJ / μ) on a polycarbonate resin substrate
m / K / ns]) of the first dielectric film of 110 nm,
Ge ₂ Sb ₂ Te ₅ recording film having a thickness shown in FIG. 1, (ZnS)
₈₀ (SiO ₂ ) ₂₀ composition (thermal conductivity 3.5 × 10 ^-4 [p
J / μm / K / ns]), and a 200 nm thick second dielectric film and an Al alloy reflective film having the thicknesses shown in Table 1 were sequentially formed by sputtering. Further, an ultraviolet curable resin layer was provided on the reflective layer. Since the recording layer of the disk created as described above is in an amorphous state, the wavelength is 810 nm.
After performing crystallization and initialization with a bulk eraser using the LD as a light source, the dynamic characteristics of the disk were evaluated by an evaluation apparatus using a laser pickup having a wavelength of 780 nm (NA 0.55). At a linear velocity of 10 m / sec, the recording power and erasing power shown in Table 1 were used at a recording frequency of 4 MHz and a dut.
C / N ratio when a signal of y50% is recorded, and erase ratio 2
Table 1 shows the erase power margin of 0 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. Rather, in Reference Example 3 in which the film thickness and the thermal conductivity match the ranges specified in the present application, it can be seen that the recording and erasing powers are large and the sensitivity is poor.

[0025]

According to the optical information recording medium of the present invention, a recording / reproducing characteristic having a high C / N ratio and a good erasing ratio can be obtained with high sensitivity, particularly 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-4-263133 (JP, A) 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 Is 20-5
0 nm, and the second dielectric layer has a thermal conductivity of 1 × 10 ^−3.
a wavelength of 600 nm, which is made of a material of pJ · μm ^-1 · K ^-1 · ns ^-1 or less and has a film thickness of 1 nm or more and less than 10 nm.
For recording and reproducing information using laser light less than
The optical information recording medium. 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 first and second dielectric layers comprise zinc sulfide and
3. The composition according to claim 1, which has a composition of a mixture with silicon dioxide.
2. The optical information recording medium according to claim 1. 4. The first and second dielectric layers have an optical constant n
Is 1.9-2.4 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.