JP2000348380A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical recording medium improved in C/N ratio and mechanical strength, excellent in jitter characteristic and chemical stability when heated and subsequently improved in durability to repeatedly recording, erasing and reproducing. SOLUTION: This optical recording medium is provided with a recording layer 3 to be amorphous or crystalline by phase transition corresponding to the output of irradiated light and a reflecting layer 5 formed successively on a transparent substrate. A first transparent dielectric layer 2 and a second transparent dielectric layer 4 based on the oxide having 1.5 or higher refractive index and zinc sulfide are laminated on at least one interface of the recording layer 3. By this constitution, the refractive indexes of the transparent dielectric layers are enlarged and the enhancement effect of the light is increased at the transparent dielectric layers. Since the signal intensity is enlarged when reproduced, the C/N ratio is improved and the jitter characteristic becomes excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording layer having a phase change between an amorphous state and a crystalline state according to the output of a light beam such as a laser beam to be irradiated. The present invention relates to a rewritable optical recording medium which records and reproduces digital information by utilizing the difference in reflectance of the optical recording medium.

[0002]

2. Description of the Related Art FIG. 1 is a partial sectional view of a conventional rewritable optical recording medium M1 utilizing a phase transition (hereinafter referred to as a medium M1). In FIG. 1, reference numeral 1 denotes a disk-shaped substrate made of a resin such as polycarbonate, glass, or the like;
First transparent dielectric layer made of S-SiO ₂ or the like, 3 GeT
e, a recording layer capable of phase-change into two states of amorphous or crystalline, 4 a second transparent dielectric layer made of ZnS-SiO ₂ or the like, 5 a reflective layer made of a high reflectivity material such as Al It is.

In such a rewritable medium M1, the recording layer 3 has a different light reflectance between a crystalline state and an amorphous state, and generally has a higher reflectance in the crystalline state. There are many. The operating principle of the medium M1 is as follows. First, all the recording bits of the recording layer 3 are crystallized. That is, initialization is performed in a state where the reflectance is high. For writing information, a laser beam pulse-modulated to two types of laser power is irradiated while rotating the medium M1, and the recording layer is irradiated with a high-power (about 10 to 20 mW) laser beam. The material becomes higher than the melting points of the three materials, and is melted and rapidly cooled to become amorphous. on the other hand,
A recording bit irradiated with a laser beam of medium output (about 5 to 10 mW) is heated to a crystallization-possible temperature range equal to or lower than the melting point and then cooled to a crystalline state.

[0004] The above-mentioned writing operation can be performed directly after the old information remains, and each recording bit changes to a state corresponding to the new information. That is, overwriting by overwriting (Over Write, hereinafter abbreviated as OW) is possible. Reproduction is performed by irradiating a low-output (about 1 to 2 mW) laser beam for reading to determine whether the phase is a crystalline phase having a high reflectivity or an amorphous phase having a low reflectivity. read.

The material of the recording layer 3 is Te, S
A chalcogenide of a material containing one element of e and S is suitable, and the chalcogenide has a feature that it easily becomes amorphous. Specifically, GeTe-based materials, GeSbT
e-based materials, InSeTlCo-based materials, InSbTe-based materials, and the like.

Conventionally, such a phase change type medium M
1, the optical information recording medium in which a first dielectric protective layer, a phase change type recording layer, a second dielectric protective layer, and a reflective layer are sequentially formed on a transparent substrate, wherein the second dielectric protective layer is formed of Zn.
A film which is excellent in repetition characteristics and stability over time by using a mixed film of S and silicon oxide or tantalum oxide has been proposed (conventional example 1: JP-A-4-358332).

As a second conventional example, in an optical information recording medium in which a first dielectric protective layer, a phase-change recording layer, a second dielectric protective layer, and a reflective layer are sequentially formed on a transparent substrate, (2) The dielectric protective layer is composed of a high compressive stress layer and a low compressive stress layer on the recording layer side, the high compressive stress layer is tantalum oxide, and the low compressive stress layer is made of a mixture of ZnS and silicon oxide or tantalum oxide. By becoming, repetition characteristics,
A material having excellent aging stability has been proposed (conventional example 2:
JP-A-4-358334).

As a third conventional example, a first protective film, a second protective film, a third protective film, a phase-change recording thin film, a fourth protective film, a fifth protective film, An optical recording medium in which a sixth protective film and a reflective layer are sequentially formed, wherein the first, third, fourth, and sixth protective films are a mixed film of ZnS and SiO ₂ , so that recording and erasing can be performed. It is known that the cycle characteristics and the erasing power margin can be widened (conventional example 3: JP-A-5-144082).

Conventional Example 4 is an optical recording medium in which a first protective film, a phase-change recording film, a second protective film, and a reflective film are sequentially formed on a transparent substrate, Protective film is Z
It is known that a film composed of a mixed film of nS and SiO ₂ is improved in mechanical strength and has a large effect on repetition of recording / erasing a large number of times (conventional example 4: JP-A-6-4 / 1994).
904).

As Conventional Example 5, a substrate, an optically active layer,
A heat-resistant protective layer provided on one interface of the optically active layer,
The heat-resistant protective layer is made of a crystalline chalcogenide such as ZnS;
There is known an optical information recording member which can increase the sensitivity to incident light power at the time of recording and increase the number of repetitions of recording / erasing by containing a vitrified oxide such as iO ₂ ( Conventional Example 5: Japanese Patent Publication No. 6-908
No. 08).

As a conventional example 6, a transparent substrate, a first protective layer, a recording layer, a second protective layer, and a reflective layer are sequentially formed, and at least the first protective layer is a mixture of zinc sulfide and titanium oxide. There is known an optical information recording medium in which the erasing rate at the time of overwriting is improved, the jitter value can be reduced, the productivity is good, and the manufacturing cost is reduced (Conventional Example 6: See JP-A-7-262615).

A prior art example 7 is an optical information recording medium in which a first dielectric layer, a phase change type recording layer, and a second dielectric layer are laminated on a substrate, wherein the first dielectric layer And at least one of the second dielectric layer and the second dielectric layer is made of a mixture of ZnS and silicon oxynitride, thereby increasing the mechanical strength and improving the overwrite cycle. 198712).

[0013]

[SUMMARY OF THE INVENTION However, the optical recording medium using a dielectric layer made of ZnS and primarily SiO ₂ Metropolitan as have been proposed, but they have the following problems Was. In the above conventional example 1, the dielectric protection layer made of a mixed film of ZnS and silicon oxide or ZnS and tantalum oxide is used. However, in the case of ZnS and silicon oxide, the jitter characteristic of the recording bit is insufficient,
In the case of nS and tantalum oxide, the quality is easily deteriorated by oxidation, so that the reliability is reduced. Further, also in Conventional Example 2, a dielectric protection layer made of a mixed film of ZnS and silicon oxide or ZnS and tantalum oxide was used, and had the same problems as Conventional Example 1.

In Conventional Example 3, the protective film is made of ZnS and SiO ₂
, And has a considerable multilayer structure of eight layers, so that the jitter characteristics are insufficient and the manufacturing cost increases. Conventional Example 4, Conventional Example 5
Further, in the conventional example 7, a mixed film of ZnS and SiO ₂ is used for the protective film, and there is a problem that the jitter characteristic is deteriorated.

In the conventional example 6, the protective layer is composed of a mixture of zinc sulfide and titanium oxide. Since the particle diameter of zinc sulfide and titanium oxide is large, noise during reproduction is large and the C / N ratio is low. There was a problem of deterioration.

Accordingly, the present invention has been completed in view of the above circumstances, and aims to improve mechanical strength, improve chemical stability, and increase signal strength (amplitude) during reproduction. Therefore, the object is to improve the C / N ratio and the jitter characteristics, and to further suppress deterioration due to repeated recording and reproduction.

[0017]

The optical recording medium of the present invention comprises:
On a transparent substrate, a recording layer and a reflective layer, which change into an amorphous or crystalline phase in accordance with the output of irradiation light, are provided, and at least one interface of the recording layer has a refractive index of 1.5 or more. And a transparent dielectric layer containing zinc oxide and zinc sulfide as main components.

According to the present invention, the refractive index of the transparent dielectric layer is increased by the above configuration, and as a result, the enhancement effect due to the light interference effect in the transparent dielectric layer is increased, and the signal intensity (amplitude) at the time of reproduction is increased. Therefore, the C / N ratio is improved, and the jitter characteristics are improved. Further, since the mechanical strength is improved and the chemical stability at the time of heating is excellent, the durability against repeated recording, erasing and reproduction is also enhanced.

In the present invention, preferably, the oxide having a refractive index of 1.5 or more contains zirconium oxide or aluminum oxide as a main component.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The medium of the present invention will be described below. The basic configuration of the medium of the present invention is the same as that of FIG. In the figure, 1 is a disk-shaped transparent substrate made of polycarbonate, polyolefin, epoxy resin, acrylic resin, glass, tempered glass having a resin layer formed on the surface, translucent ceramic, etc., and 2 has a refractive index of 1.5 or more. Is a first transparent dielectric layer mainly composed of an oxide and zinc sulfide, 3 is a phase-change recording layer, 4 is a second transparent dielectric layer of the same material as the first transparent dielectric layer 2, and 5 is Al , Al-Ti alloy, Al-Cr alloy or the like.

In the present invention, the recording layer 3 is made of GeTe, G
Materials made of chalcogenides such as eSbTe, InSeTlCo, InSbTe, etc. are preferred, and GeTe, G
eSbTe is preferable in that it can be rewritten a large number of times, can be crystallized in a short time when crystallized, and has high stability in an amorphous state.

[0022] In _{addition, Ge a Sb b Te c (} a + b + c =
100 at%), 5 at (atomic)% ≦ a ≦ 7
0 at% is good, and when a <5 at%, the crystallization speed is low,
When 70 at% <a, the amorphous state becomes unstable. 0at
% ≦ b ≦ 50 at% is good, and if 50 at% <b, the amorphous state becomes unstable. 40 at% ≦ c ≦ 70 at% is good, and if c <40 at%, the crystallization temperature becomes too high, and
Even when 0 at% <c, the crystallization temperature is too high. In particular, Ge ₂ Sb ₂ Te ₅ or GeSb ₂ Te ₄ is preferable, in which case the crystallization speed is high and the erasing characteristics at a high linear velocity are good.

The thickness of the recording layer 3 is preferably 5 to 50 nm, and if it is less than 5 nm, the reflectance difference between the crystalline state and the amorphous state becomes small. Deterioration increases. More preferably, it is 10 to 40 nm.

The composition of the first transparent dielectric layer 2 and the second transparent dielectric layer 4 is mainly composed of an oxide having a refractive index of 1.5 or more and zinc sulfide (ZnS).
O ₂ , ZnS · Al ₂ O ₃ . (ZnS) _d (Zr
When O ₂ ) _e (d + e = 100 mol%), d = 5
The content is preferably 0 to 95 mol%, and when d <50 mol%, the refractive index is reduced, and it becomes difficult to obtain an enhancement effect due to light interference. When d> 95 mol%, (ZnS) _d (ZrO ₂ ) _e
The size of the particles increases, and noise during reproduction increases.
Further, it is preferable that e = 5 to 50 mol%, and when e <5 mol%, the particle size of the (ZnS) _d (ZrO ₂ ) _e particle becomes large and the noise at the time of reproduction becomes large. And the enhancement effect is reduced. ZnS ・
The same applies to the case of Al ₂ O ₃ .

Further it may be added Ma composed of an oxide such as ZnS · ZrO _2, when expressed as _{ZnS · (ZrO 2 Ma),} Ma is silicon oxide (SiO _2), aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC), titanium nitride (TiN), titanium carbide (TiC), aluminum nitride (AlN), zirconium carbide (ZrC), oxidation At least one of yttrium (Y ₂ O ₃ ), magnesium oxide (MgO), nickel oxide (NiO), boron oxide (B ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), and calcium oxide (CaO) Including. The addition of these substances Ma improves the durability against repeated recording and reproduction.

On the other hand, in the case of ZnS.Al ₂ O ₃ , similarly, the above-mentioned Ma except aluminum oxide (Al ₂ O ₃ ) may be added.

The amount of the Ma, when the relative ZrO ₂ and _{(ZrO 2) 100-f (} Ma) f, f = 0~5
0 mol% is preferable, and when f> 50 mol%, the refractive indices of the first transparent dielectric layer 2 and the second transparent dielectric layer 4 become small,
The signal strength during reproduction is reduced. The same applies to the case of ZnS.Al ₂ O ₃ .

The thickness of the first transparent dielectric layer 2 of the present invention is 10
0 ° to 2500 ° is good, and if it is less than 100 °, the enhancement effect becomes small, and if it exceeds 2500 °, the film forming time becomes too long and the productivity is lowered. Second transparent dielectric layer 4
The thickness is preferably from 10 to 500 °, and if it is less than 10 °, uniform film formation becomes difficult, and if it exceeds 500 °, the durability against repeated recording and reproduction deteriorates.

In the above embodiment, light is transmitted to the transparent substrate 1.
Although the configuration in which light is incident from the side has been described, the present invention is also applicable to a medium M2 in which light is incident from the recording layer 3 side as shown in FIG. In the figure, 11 is a disk-shaped transparent substrate, 12 is a reflective layer, 13 is a second transparent dielectric layer, 1
Reference numeral 4 denotes a phase-change type recording layer, and reference numeral 15 denotes a first transparent dielectric layer. The order of film formation is different from that in FIG. 1, but the materials and thicknesses thereof are the same as those in FIG.

Further, ZnS, Al ₂ O ₃ , ZrO ₂ , TiO ₂ , Si related to the material of the transparent dielectric layer of the present invention.
Table 1 shows the refractive index, melting point, and Young's modulus of O ₂ , ZnS · ZrO ₂ , and ZnS · Al ₂ O ₃ .

[0031]

[Table 1]

From Table 1, it can be seen that ZnS, Al ₂ O ₃ , Zr
O ₂ and TiO _{2 have} a higher refractive index than SiO ₂ and Al
It can be seen that the melting points and Young's modulus of ₂ O ₃ and ZrO ₂ are higher than that of SiO ₂ . Therefore, Al ₂ O ₃ and ZrO are added to ZnS.
By mixing _{2 and the} like, the effects of the present invention described above can be obtained as a result. In Table 1, ZnS / ZrO was used.
_2. The data of the refractive index and the melting point of ZnS.Al ₂ O ₃ are blurred due to the deviation of the composition ratio of O and the like and the film forming conditions when the film is formed by the sputtering method.

Thus, in the optical recording medium of the present invention, the refractive index of the transparent dielectric layer is increased, and as a result, the effect of enhancing light in the transparent dielectric layer is increased, and the signal intensity during reproduction is increased. / N ratio is improved, and jitter characteristics are improved. Further, since the mechanical strength is improved and the chemical stability at the time of heating is excellent, it has the effect of increasing the durability against repeated recording, erasing, and reproduction.

In the present invention, the recording capacity may be doubled by laminating each of the above layers on both sides of the transparent substrate 1 or by bonding two transparent substrates 1 each having the above layer on one side. The present invention is not limited to the light intensity modulation method for pulse-modulating a laser beam, but may be applied to a heating method using energy beams such as an electron beam and an electromagnetic wave. The media M1 and M2 of the present invention are phase-change rewritable optical disks, and are CD-RW (Compact Disc).
ReWritable), DVD-RW (Digital Versatile Di)
It can be applied to optical disks such as sc ReWritable).

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0036]

Embodiments of the present invention will be described below.

Example 1 The medium M1 (optical disk) shown in FIG. 1 was constructed as follows. The following layers were sequentially formed on the main surface of a 3.5-inch diameter disk-shaped transparent substrate 1 made of polycarbonate by magnetron sputtering.

The first transparent dielectric layer 2 made of various materials (Table 2) having a thickness of about 1200 °, a thickness of about 200 °, and Ge ₂ Sb
₂ Te ₅ recording layer 3 made of a film thickness of about 200 Å, the second transparent dielectric layer 4 made of the same material as the first transparent dielectric layer 2 is the reflective layer 16 made of a film thickness of about 1500 Å, Al-Cr alloy .

When the materials of the first transparent dielectric layer 2 and the second transparent dielectric layer 4 are changed as shown in Table 2, the C / N
Table 2 shows the measurement results of the ratio (dB), the jitter (%) after performing the OW for 10 times, and the jitter (%) after performing the OW for 10,000 times. In addition, C / N ratio (dB)
Was measured as follows. The linear velocity of the track of the optical disc is set to 6.18 m / s, and a laser beam pulse-modulated to 13 mW (corresponding to amorphous) and 5 mW (corresponding to crystalline) at a light wavelength of 830 nm is emitted at 4.91 MH.
This is obtained from the reproduced signal intensity when recording was performed at z and reproduced with a 1 mW laser beam. Also, the measurement of jitter
This is a measurement of the jitter of the reproduced signal after performing the same recording 10 times and the jitter of the reproduced signal after performing 10,000 times. In Table 2, the amount of Ma added was ZrO
₂ or mol% based on Al ₂ O ₃ .

Further, the first transparent dielectric layer 2 and the second transparent dielectric layer 4 are made of ZnS. (ZrO ₂ Ma) and ZnS. (Al ₂
O ₃ Ma) and the addition amount of Ma was less than 50 mol% at around 50 mol%, the C / N ratio (dB), 10
Table 3 shows the results of measuring the jitter (%) after performing OW for 10,000 times and the jitter (%) after performing OW for 10,000 times. As also comparative examples, a first transparent dielectric layer 2 and the second transparent dielectric layer 4 that a ZnS · SiO _2, in the same manner as in Table 3, a first transparent dielectric layer 2 second transparent dielectric The body layer 4 is made of ZnS · (ZrO ₂ Ma) and ZnS · (Al ₂ O ₃
Ma) and the addition amount of Ma was set to 50 mol% at around 50 mol%.
Table 4 shows the result of measuring the C / N ratio and the jitter after performing OW for 10 times and the jitter after performing OW for 10,000 times.

[0041]

[Table 2]

[0042]

[Table 3]

[0043]

[Table 4]

As shown in Table 2, in the present invention, the C / N ratio was 50.1 dB or more, and the jitter after recording 10 times was 8.6%.
Hereinafter, the jitter after recording 10,000 times shows an excellent characteristic of 9.8% or less, and among those containing the additive component Ma, M
NO without a. Some of the properties were better than 1. In Table 3, the C / N ratio was 47.1 dB or more, and the jitter after 10 times of recording was 8.6% or less, and the jitter after 10,000 times of recording was 9.9% or less. In contrast, in the comparative example of Table 4, the C / N ratio was 45.8 to 48.7 dB, the jitter after recording 10 times was 9.6 to 12.5%, and the jitter after recording 10,000 times was 11. It deteriorated to 8 to 15.6%.

[0045]

According to the present invention, a transparent dielectric layer mainly composed of an oxide having a refractive index of 1.5 or more and zinc sulfide is laminated on at least one interface of a phase change type recording layer.
The refractive index of the transparent dielectric layer increases, and as a result, the effect of enhancing light in the transparent dielectric layer increases, and the signal intensity during reproduction increases, so that the C / N ratio improves and the jitter characteristics improve. . Further, since the mechanical strength is improved and the chemical stability at a high temperature is excellent, the effect of increasing the durability against repeated recording, erasing, and reproduction is also obtained.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of an optical recording medium M1 of the present invention.

FIG. 2 is a partial cross-sectional view of the optical recording medium M2 of the present invention.

[Explanation of symbols]

 1: transparent substrate 2: first transparent dielectric layer 3: recording layer 4: second transparent dielectric layer 5: reflective layer

Claims (2)

[Claims] A recording layer and a reflection layer, which change into an amorphous or crystalline phase in accordance with the output of irradiation light, are provided on a transparent substrate, and at least one interface of the recording layer has a refractive index. An optical recording medium characterized in that a transparent dielectric layer mainly composed of an oxide of at least 1.5 and zinc sulfide is laminated. 2. An optical recording medium according to claim 1, wherein said oxide having a refractive index of 1.5 or more contains zirconium oxide or aluminum oxide as a main component.