JPH0536113A - Optical recording medium - Google Patents

Abstract

PURPOSE:To attain an optical recording medium high in sensitivity, erasing rate, C/N and free from deterioration of characteristics, default with stable operation even if repeating recording and erasing many times by providing a specific optical thickness constituting thickness of the optical recording medium. CONSTITUTION:At least one or more layer of a dielectric layer is formed between a substrate and a recording layer in the optical recording medium and the optical thickness L1 of the dielectric layer is in a region expressed by the following formula. In formula ((mlambda/2) < L1 < (mlambda/2) + (lambda/4)), (m) is an integer between 1 and 3, lambda is wave length of recording light. Namely, by controlling thickness of the dielectric layer formed between the transparent substrate and the recording layer to the specific thickness expressed by the prescribed formula, the optical recording medium higher than heretofore in recording sensitivity is realized.

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 capable of recording, erasing and reproducing information by irradiating light.

In particular, the present invention relates to a rewritable phase-change type optical recording medium such as an optical disc, an optical card, an optical tape having a recording information erasing / rewriting function and capable of recording an information signal at high speed and high density. It is a thing.

[0003]

2. Description of the Related Art The conventional techniques for rewritable phase change type optical recording media are as follows.

These optical recording media have a recording layer containing tellurium as a main component, and during recording, a focused laser light pulse is irradiated to the recording layer in a crystalline state for a short time to partially melt the recording layer. To do. The melted portion is rapidly cooled by thermal diffusion and solidified to form a recording mark in an amorphous state. The light reflectance of this recording mark is lower than that of the crystalline state, and it can be optically reproduced as a recording signal.

Further, at the time of erasing, the recording mark portion is irradiated with a laser beam and heated to a temperature below the melting point of the recording layer and above the crystallization temperature to crystallize the recording mark in an amorphous state, and the original unrecorded state. Return to the state.

In this optical recording medium, a dielectric layer having heat resistance and translucency is usually provided on both sides of the recording layer to prevent the recording layer from being deformed or having an opening. Further, a metal reflective layer such as a light-reflective metal such as Al is provided on the dielectric layer on the side opposite to the light beam incident direction to improve the signal contrast at the time of reproduction by an optical interference effect, and at the same time, a non-reflecting effect by a cooling effect. Facilitates the formation of crystalline recording marks,
Moreover, a technique for improving the erasing characteristic and the repeating characteristic is known. In particular, the dielectric layer between the recording layer and the reflective layer is 20 nm thick.
The "quick cooling structure", which is made thin to a certain extent, is excellent in that it has little deterioration due to repeated recording rewriting, and has a wide erase power margin (T.Ohota et al, Japanese.
Jounal of Applied Physics, Vol 28 (1989) Suppl. 28-
3 pp123-128).

[0007]

A problem in the rewritable phase change type optical recording medium having the above-mentioned rapid cooling structure is that the recording sensitivity is low because the cooling effect of the reflective layer is large. That is, the irradiation power of light required for recording and erasing is large, the semiconductor laser of the optical head needs to have a high output, and the device cost becomes high. Moreover, in the case of a disc, the irradiation power of light is insufficient and recording is performed at high speed. There was a problem that it became difficult.

An object of the present invention is to provide an optical recording medium which has a high recording sensitivity, is less deteriorated in recording characteristics even if recording, erasing or rewriting operations are performed many times, and is excellent in recording characteristics and erasing characteristics. It is to be.

Another object of the present invention is to provide a long-life optical recording medium which is excellent in oxidation resistance and resistance to moist heat and has no defects even during long-term storage.

[0010]

According to the present invention, a recording layer, a dielectric layer and a reflection layer are provided on a transparent substrate, and information can be recorded, erased and reproduced by irradiating the recording layer with light. ,
In an optical recording medium in which information is recorded and erased by a phase change between an amorphous phase and a crystalline phase, at least one dielectric layer is provided between the substrate and the recording layer, and its optical The optical recording medium is characterized in that the thickness L1 is in the range represented by the following formula.

Formula mλ / 2 <L1 <mλ / 2 + λ / 4 where m represents an integer from 1 to 3, and λ is
Indicates the wavelength of recording light. According to the present invention, the thickness of the dielectric layer (hereinafter, referred to as the first dielectric layer) provided between the transparent substrate and the recording layer is set to a specific thickness represented by the above-mentioned formula, so that The present invention realizes an optical recording medium with high recording sensitivity.

The layer structure of the optical recording medium of the present invention includes, for example, a transparent substrate, a first dielectric layer, a recording layer, a second dielectric layer and a reflective layer which are laminated in this order. Not limited. However, light is assumed to enter from the transparent substrate side. On the reflective layer, other layers such as a resin layer such as an ultraviolet curable resin and an adhesive layer for adhering to another substrate may be provided as long as the effects of the present invention are not impaired.

The optical thickness L1 of the first dielectric layer in the present invention is represented by L1 = nd when the layer thickness of the first dielectric layer is d and the refractive index is n. When the first dielectric layer is a laminated body of a plurality of dielectric layers, it is represented by L1 = Σni di. Here, ni and di are the thickness and refractive index of the i-th layer. Therefore, the specific layer thickness d is adjusted according to the refractive index n of the dielectric.
By selecting, it is possible to adjust L1 to the value shown in the above equation.

The value of L1 is (m-1) λ / 2 + 1 /
When in the range of 4λ ≤ L1 ≤ mλ / 2,
There is a problem that the recording sensitivity is lower than that of the optical recording medium of the present invention having the same reflectance and having the layer thickness. Further, when m is 4 or more, the thickness of the first dielectric layer is large, so that it takes a long time to form the layer and the material cost is high, which is not practical.

Particularly, since the recording sensitivity can be increased, L1
Value of mλ / 2 + λ / 16 <L1 <mλ / 2 +
The range is preferably 3λ / 16 (where m is 1, 2, or 3).

It is preferable that the thickness of the first dielectric layer is in the range of the layer thickness where m in the formula is 1 or 2, since the time required for forming the layer can be shortened, and particularly m is 1. The range is more preferable for the above reason.

Further, the value of L1 is set to mλ / 2 + λ / 16 <
L1 <mλ / 2 + 3λ / 16 and m is 1
Alternatively, the range of 2 is more preferable because the sensitivity is high, the film thickness is thin, and the time required for forming the layer is short. As the material of the first dielectric layer of the present invention, ZnS, SiO ₂ which is substantially transparent at the recording light wavelength and whose refractive index is larger than that of the transparent substrate and smaller than that of the recording layer, Metal sulfides such as aluminum oxide, silicon nitride, ZrC, ZnSe, and ZnTe,
Examples thereof include metal compounds such as metal oxides, metal nitrides, metal carbides, metal selenides, metal tellurides, and mixtures thereof.

In particular, ZnS thin film, Si, Ge, Al, T
Thin films of oxides of metals such as i, Zr and Ta, Si and Al
A thin film of nitride such as, a thin film of carbide such as Ti, Zr, and Hf, and a film of a mixture of these compounds are preferable because of high heat resistance. Further, a mixture of these with a fluoride such as MgF ₂ is also preferable because the residual stress of the film is small. In particular, a mixed film of ZnS and SiO ₂ is preferable because deterioration of recording sensitivity, C / N, erasing rate, etc. does not easily occur even when recording and erasing are repeated.

The material of the second dielectric layer of the present invention may be the same as the material listed for the material of the first dielectric layer. Second
The material of the dielectric layer may be the same as or different from the material of the first dielectric layer. The thickness of the second dielectric layer is approximately 10 to 250 nm. About 10
The range of ˜50 nm is preferable because the range of erasing power (or bottom power) with which a good erasing rate can be obtained is wide.

The recording layer of the present invention is not particularly limited, but a Pd-Ge-Sb-Te alloy, Ni-G is used.
e-Sb-Te alloy, Ge-Sb-Te alloy, Co-G
e-Sb-Te alloy, In-Sb-Te alloy, Ag-I
Examples thereof include n-Sb-Te alloy and In-Se alloy.

Since the recording can be rewritten many times, Pd-Ge-Sb-Te alloy, Ni-Ge-Sb-
Te alloy, Ge-Sb-Te alloy, Co-Ge-Sb-
Te alloys are preferred.

In particular, Pd-Ge-Sb-Te alloy, Ge-
The Sb-Te alloy is preferable because it has a short erasing time, can be repeatedly recorded and erased many times, and has excellent recording characteristics such as C / N and erasing rate, and is particularly preferable for Pd-Ge-Sb-. Te alloy is preferable because it has excellent properties described above.

The thickness of the recording layer of the present invention is not particularly limited, but is preferably 10 to 100 nm. In particular, since the recording and erasing sensitivity is high and the recording and erasing can be performed many times, the thickness is preferably 10 nm or more and 30 nm or less.

Examples of the material of the reflective layer include metals, alloys, and mixtures of metals and metal compounds having light reflectivity. As the metal, Al, Au, Ag, Cu, Ti
However, as the metal compound to be mixed, Al, Si, T
Oxides such as i, nitrides, carbides such as Ti, Zr, and Hf can be used.

Metals such as Al and Au, and alloys containing these as the main components are preferable because they have high light reflectivity and high thermal conductivity. As an example of the above alloy, Al
Si, Mg, Cu, Pd, Ti, Cr, Hf, Ta,
At least one element such as Nb or Mn added in a total amount of 5 atomic% or less, 0.5 atomic% or more, or Au.
In addition, at least one element such as Cr, Ag, Cu, Pd, Pt, and Ni is added in a total amount of 20 atom% or less and 1 atom% or more.

Particularly, since the price of the material can be reduced,
An alloy containing Al as a main component is preferable, and in particular, since it has good corrosion resistance, the total amount of at least one metal selected from Ti, Cr, and Ta is 5 atomic% or less and 0.5 atomic% or more. The added alloy or the alloy in which 5% or less in total of Si and Mn are added to Al is preferable.

The thickness of the reflective layer is about 10 nm.
It is above 300 nm. It is preferably 50 nm or more and 200 nm or less because the recording sensitivity can be increased.

In particular, since the recording sensitivity is high, the one-beam overwrite can be performed at a high speed, the erasing rate is large, and the erasing characteristics are good, the main part of the optical recording medium can be constructed as follows. preferable.

That is, the dielectric layer is a mixed film of ZnS and SiO ₂ , and the mixing ratio of SiO ₂ is 15 to 35 mol%,
The refractive index at a recording wavelength of 830 nm is 2.1 to 2.3, and the thickness of the first dielectric layer is 220 nm to 270 n.
m, the second dielectric layer has a thickness of 10 nm to 30 nm, the recording layer has a thickness of 10 nm to 30 nm, and the reflective layer has a thickness of 50 nm to 150 nm. It is preferably in the range represented by the formula.

(Pdx Sby Te1-xy) 1-z (Te0.
5 Ge 0.5) z 0.01 ≦ x ≦ 0.1 0.35 ≦ y ≦ 0.65 0.2 ≦ z ≦ 0.4 where x, y, z and 0.5 are the atomic ratios of the respective elements. Represents

In the present invention, a transparent material is used as the substrate because recording is performed from the substrate side using a focused light beam for the purpose of avoiding the influence of dust, scratches on the substrate, and the like. Examples of such a material include glass, polycarbonate, polymethyl methacrylate, polyolefin resin, epoxy resin, and polyimide resin.

Particularly, a polycarbonate resin and an epoxy resin are preferable because they have small optical birefringence, small hygroscopicity, and easy molding. Epoxy resin is preferable when heat resistance is particularly required.

The thickness of the substrate is not particularly limited, but 0.01 mm to 5 mm is practical. 0.01 m
If it is less than m, even when recording with an optical beam focused from the substrate side, it is easily affected by dust, and if it is 5 mm or more,
It becomes difficult to increase the numerical aperture of the objective lens, and the irradiation light beam spot size becomes large, which makes it difficult to increase the recording density. The substrate may be flexible or rigid. The flexible substrate is used in a tape shape, a sheet shape, a card shape, or the like. The rigid substrate is used in a card shape or a disk shape. In addition, these substrates may have an air sandwich structure, an air incident structure, or a close-bonding structure by using two substrates after forming a recording layer and the like.

The light source used for recording on the optical recording medium of the present invention is a high-intensity light source such as laser light or strobe light. Particularly, the semiconductor laser light is capable of downsizing the light source, low power consumption, and modulation. Is preferable because it is easy.

Recording is performed by irradiating a crystalline recording layer with a laser light pulse or the like to form an amorphous recording mark. On the contrary, crystalline recording marks may be formed on the amorphous recording layer. Erasure can be performed by irradiating a laser beam to crystallize an amorphous recording mark or by amorphizing a crystalline recording mark.

A method of forming an amorphous recording mark at the time of recording and crystallizing at the time of erasing is preferable because the recording speed can be increased and the deformation of the recording layer is less likely to occur.

Further, the light intensity is made high (peak power) at the time of forming a recording mark and slightly weakened (bottom power) at the time of erasing, and the one-beam overwrite for rewriting by irradiating a light beam once is a rewriting. It is preferable because the required time is shortened.

Next, a method for manufacturing the optical recording medium of the present invention will be described. As a method for forming the recording layer, the dielectric layer, the reflective layer, etc. on the substrate, a known thin film forming method in vacuum,
For example, a vacuum vapor deposition method, an ion plating method, a sputtering method and the like can be mentioned. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled.

The thickness of the recording layer or the like to be formed can be easily controlled by monitoring the deposition state with a well-known technique such as a crystal oscillator film thickness meter.

The recording layer or the like may be formed with the substrate fixed, moved, or rotated. Since the in-plane uniformity of the film thickness is excellent, it is preferable to rotate the substrate on its own axis, and it is more preferable to combine the revolution.

Further, within a range that does not significantly impair the effects of the present invention, after forming a reflective layer or the like, a protective layer such as an ultraviolet curable resin may be provided as necessary to prevent scratches and deformation. .. Also, after forming the reflective layer,
Alternatively, after further forming the above-mentioned resin protective layer, the two substrates may be opposed to each other and adhered with an adhesive.

[0042]

EXAMPLES The present invention will be described below based on examples. (Analysis and measurement method) The compositions of the reflection layer and the recording layer were confirmed by ICP emission analysis (manufactured by Seiko Denshi Kogyo KK).
The carrier-to-noise ratio and the erasing rate (difference in reproduced carrier signal intensity after recording and after erasing) were measured by a spectrum analyzer.

The film thicknesses of the recording layer, the dielectric layer and the reflective layer were monitored by a crystal oscillator film thickness meter. Example 1 A substrate made of polycarbonate with spiral grooves having a thickness of 1.2 mm, a diameter of 13 cm, and a pitch of 1.6 μm is 3 per minute.
The recording layer, the dielectric layer, and the reflective layer were formed by a high frequency sputtering method while rotating at 0 revolutions.

First, the vacuum chamber was evacuated to 1 × 10 ^-5 Pa, and then SiO 2 in an Ar gas atmosphere of 2 × 10 ^-1 Pa.
ZnS containing 20 mol% of ₂ was sputtered to form a first dielectric layer having a thickness of 250 nm and a refractive index of 2.2 on the substrate. Then, an alloy target composed of Pd, Ge, Sb, and Te is sputtered to form the composition Pd1 Ge17 Sb26.
A recording layer having a film thickness of 20 nm of Te 56 (atomic%) was formed.
Further, a second dielectric layer of the same material as that of the first dielectric layer is formed in a thickness of 20n.
Then, a Mn0.01Si0.04Al0.95 alloy was sputtered thereon to form a reflection layer having a film thickness of 80 nm. Further, after the disk was taken out from the vacuum container, an acrylic ultraviolet curable resin was spin-coated on the reflective layer and cured by irradiation with ultraviolet rays to form a resin layer having a film thickness of 10 μm to obtain an optical recording medium of the present invention. ..

This optical recording medium was rotated at a linear velocity of 5.5 m / sec, and a semiconductor laser beam of wavelength 820 nm focused on an ellipse of 22 × 66 μm from the substrate side was irradiated under the condition that the film surface intensity was 1.1 W. The recording layer was crystallized and initialized. The reflectance on the land of this disc was measured to be 13.5%.
Met.

Then, under the condition of linear velocity of 6 m / sec, the numerical aperture of the objective lens is 0.5 and the wavelength of the semiconductor laser is 790 nm.
After performing overwriting recording 100 times with a semiconductor laser beam modulated under the conditions of a frequency of 3.7 MHz, a pulse width of 50 nsec, a peak power of 11 to 17 mW, and a bottom power of 4 to 9 mW using the optical head of 1., the reproduction power of 1.
Bandwidth 30kHz by irradiating 3mW semiconductor laser light
C / N was measured under the conditions of.

Further, this portion was irradiated with a semiconductor laser beam modulated at 1.4 MHz in the same manner as the above, and one-beam overwriting was performed. At this time, the erasing rate of 3.7 MHz was measured and the peak power was practically 12 mW or more. Enough 50 dB
The above C / N is obtained, and the bottom power is 4.5 to
At 7.5 mW, a practically sufficient erasing rate of 20 dB or more was obtained.

Further, under the conditions of peak power of 13 mW, bottom power of 6 mW and frequency of 3.7 MHz, one beam overwrite was repeated 1000 times and 100,000 times, and the same measurement was performed. The change in erasing rate was within 2 dB, and almost no deterioration was observed.

This optical recording medium was placed in an environment of 80 ° C. and 80% relative humidity for 1000 hours, and then the recorded portion was reproduced, but the change in C / N was less than 2 dB and hardly changed. Recording / erasing is performed again and C /
When N and the erasing rate were measured, there was almost no change and no increase in defects was observed.

Example 2 An optical recording medium having the same structure as in Example 1 was prepared except that the thickness of the first dielectric layer in Example 1 was 440 nm. When the C / N and the erasing rate of this optical recording medium were measured in the same manner as in Example 1, the reflectance was 13%, and the peak power was 11%.
A practically sufficient C / N of 50 dB or more can be obtained at mW or more, and a practically sufficient 2 at a bottom power of 5 to 7.5 mW.
An erase rate of 0 dB or more was obtained.

Example 3 An optical recording medium having the same structure as in Example 1 was prepared except that the recording layer in Example 1 was Ge22Sb23Te55. When the C / N and the erasing rate of this optical recording medium were measured in the same manner as in Example 1, the reflectance was 13%, and a practically sufficient C / N of 50 dB or more was obtained at a peak power of 12 mW or more, Moreover, the erasing rate of 20 dB or more, which is practically sufficient, was obtained at the bottom power of 5 to 7.5 mW.

Comparative Example 1 The thickness of the first dielectric layer of Example 1 was set outside the range of 18 of the present invention.
A conventional optical recording medium similar to that of Example 1 was manufactured except that the thickness was set to 0 nm. When this optical recording medium was measured in the same manner as in Example 1, the reflectance was 20% and the peak power was 15%.
A practically sufficient C / N of 50 dB or higher was obtained at mW or higher, and a practically sufficient erasing rate of 20 dB or higher was obtained at a bottom power of 5 to 9 mW. Compared to Examples 1 and 2, C / N5
Peak power during recording of 0 dB or more is 3 to 4 m
It was found that the optical recording media of Examples 1 and 2 of the present invention had much higher sensitivity than the optical recording media of the present Comparative Example.

Comparative Example 2 The thickness of the first dielectric layer of Example 1 was set to 36, which is outside the range of the present invention.
An optical recording medium similar to that of Example 1 was manufactured except that the thickness was set to 0 nm. When this optical recording medium was measured in the same manner as in Example 1, the reflectance was about 13%, which is almost the same as in Examples 1 and 2, but in order to obtain a practically sufficient C / N of 50 dB or more, 14
A peak power of mW was needed. As compared with Comparative Example 1, the recording sensitivity was about 1 mW, which was hardly improved, and the effect of improving the sensitivity was found to be much smaller than that of Examples 1 and 2.

[0054]

According to the present invention, since the thickness of the dielectric layer of the optical recording medium is set to a specific optical thickness, the following effects can be obtained. (1) High sensitivity, high erasing rate and C / N. (2) Even if recording and erasing are repeated a number of times, the operation is stable and there is almost no deterioration of characteristics or occurrence of defects. (3) Excellent resistance to moist heat and oxidation, and long life. (4) It can be easily manufactured by the sputtering method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoya Seo 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Toray Co., Ltd. Shiga Plant

Claims (1)

Claim: What is claimed is: 1. A transparent substrate having a recording layer, a dielectric layer, and a reflective layer, the information being recorded, erased, and reproduced by irradiating the recording layer with light. Recording and erasing
An optical recording medium that is formed by a phase change between an amorphous phase and a crystalline phase, has at least one dielectric layer between the substrate and the recording layer, and has an optical thickness L1 of the following formula: An optical recording medium characterized by being in a range represented by. Formula mλ / 2 <L1 <mλ / 2 + λ / 4 where m represents an integer from 1 to 3, and λ is
Indicates the wavelength of recording light.