JP2000207771A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-sensitivity optical recording medium by setting the gap Tauc corresponding to the energy gap in an amorphous state to a specified range in an amorphous phase of a recording material, esp., after forming films. SOLUTION: Using a recording material having a gap Tauc obtained from the light absorption spectrum due to transition of its amorphous phase between bands or an optical gap of 0.18-0.58 eV, a recording medium capable of efficiently absorbing red or blue-green semiconductor laser lights at a high sensitivity and easily initially crystallizable is realized. The material having a gap Tauc ranging from 0.18 eV to 0.58 eV is mainly composed of Ag, In, Sb, Te, Ho and N, esp. N controls the gap Tauc which is changeable by the N quantity according to designs, thus leading to a high sensitivity, improved preserve characteristics, improved repetition characteristic, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change optical recording medium applicable to the field of rewritable optical recording media.

[0002]

2. Description of the Related Art As one of optical recording media capable of recording, reproducing and erasing information by irradiating a laser beam, so-called phase-change optical recording utilizing a transition between a crystal and an amorphous phase or between a crystal and a crystal phase. The medium is well known. This is characterized in that overwriting with a single beam is possible and the optical system on the drive side is simpler, and is applied as a computer-related or audio-visual recording medium. GeTe,
GeTeSe, GeTeS, GeSeS, GeSeS
b, GeAsSe, InTe, SeTe, SeAs, G
e-Te- (Sn, Au, Pd), GeTeSeSb,
GeTeSb, Ag-In-Sb-Te and the like are available. Further, as disclosed in JP-A-57-208648, there has been proposed a recording layer in which a recording layer is embedded in a base material such as SiO ₂ to suppress irreversible changes in the recording material. Ag-In-Sb-Te has high sensitivity and a feature in which an amorphous portion has a clear contour, and has been developed as a recording layer for mark edge recording. (JP-A-2-37
466, JP-A-2-171325, JP-A-2-41
No. 5581, JP-A-4-141485). Furthermore, (Sb-Ag-Te) (Ge-T)
e) system has also been developed (Japanese Patent Laid-Open No. 1-143838), and ABSbGeTe (A is Co, Ti, Ni, V,
Materials such as Cr and B (Tl, I, Na) have also been proposed (Japanese Patent Application Laid-Open No. 7-14798). Optical recording media using these recording layers include those having a multilayer structure having a reflective layer, a first protective layer, and a second protective layer. In this optical recording medium, the repetitive recording characteristics are improved, Are important issues, for example, the modulation degree, the predetermined reflectance, and the like. Regarding this problem, Japanese Patent Application Laid-Open No. Hei 4-1 describes that the addition of nitrogen or the like to the recording layer suppresses the flow of the recording layer and contributes to the improvement of repetitive recording characteristics.
1336, JP-A-4-10980, JP-A-4-16
No. 383, JP-A-4-10979, JP-A-4-521
No. 88 and JP-A-4-52189. However, in an optical recording system having a relatively low recording linear velocity at a low price or an optical recording medium used as an optical recording medium (CD-RW) which is compatible with reproduction from a CD, the flow of the recording layer, Due to problems such as film peeling due to thermal shock at the time of laser irradiation or deterioration of the metal used for the reflective layer, the number of repetitive recordings remains at the level of several thousand times, and when frequently rewriting is done with peripheral devices of computers etc. Had a problem. Further, in order to further reduce the price of the drive, it is required to improve the recording sensitivity. Furthermore, the conventional recording medium does not take into account the easiness of initial crystallization, and has a problem that characteristics such as jitter are deteriorated because initialization is difficult even though repetition characteristics and recording sensitivity are good.

[0003]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of the above situation, and a first object of the present invention is to provide an optical recording medium having high recording sensitivity. is there. A second object of the present invention is to provide an optical recording medium having high recording sensitivity, good repetition characteristics, and easy initial crystallization. It is a further object of the present invention to provide an optical recording medium which has high sensitivity, good repetition characteristics, easy initial crystallization, and can be used for a light source in a short wavelength range to a long wavelength range.

[0004]

According to the present invention, (1)
"In an optical recording material that records, reproduces, and erases information by irradiating the recording material with electromagnetic waves such as a laser and changing its optical constant, the amorphous phase of the recording material, especially the amorphous state after film formation, Ta corresponding to energy gap
An optical recording material having a uc gap in the range of 0.18 eV to 0.58 eV. ”, (2)“ Wavelength 1 ”
The square root (α · E) ^1/2 of the product of the absorption coefficient α for each wavelength of the recording material in the range of 000 nm to 400 nm and the energy E corresponding to the wavelength is 260 [cm].
The optical recording material according to the above (1), wherein the optical recording material is in the range of ^-1 / 2.eV ^1/2 ] to 650 [cm ^-1 / 2.eV ^1/2 ]. (3) "A recording material having a Tauc gap in the range of 0.18 eV to 0.58 eV is composed of Ag, In, Sb, Te, Ho, and N, and in particular, the element that controls the Tauc gap is N. (4) Ag having a Tauc gap in the range of 0.18 eV to 0.58 eV.
(3) The optical recording material according to the above (3), wherein the crystallization temperature of the recording material composed of In, Sb, Te, Ho and N increases as the Tauc gap increases. And (5) “Ag, In, Sb, Te, and H having a Tauc gap in the range of 0.18 eV to 0.58 eV.”
The crystallization temperature of the recording material composed of o and N is 165 ° C.
(3) characterized in that the temperature is between
The optical recording material described in the above item. (6) “Ag and In with Tauc gap in the range of 0.18 eV to 0.58 eV”
The real part and the imaginary part of the complex refractive index of the amorphous phase of the recording material composed of Sb, Te, Ho and N have a wavelength of 450 nm.
(3) The optical recording material according to the above (3), wherein the Tauc gap becomes smaller as the Tauc gap becomes larger in a range from 1 to 800 nm. (7) “Ag with Tauc gap in the range of 0.18 eV to 0.58 eV”
Real part n of the complex refractive index of the amorphous phase of the recording material composed of Al, In, Sb, Te, Ho, and N, especially the amorphous phase after film formation
And the value of the imaginary part k is 3.6 ≦ n at a wavelength of 630 nm.
The optical recording material according to the above (3), wherein the optical recording material is in the range of ≦ 4.3 and 1.5 ≦ k ≦ 2.5. ”, (8)
"A recording material composed of Ag, In, Sb, Te, Ho, and N having a Tauc gap in the range of 0.18 eV to 0.58 eV is made of Bi-Ge, Bi-Si, Gd-G
(3) The optical recording material as described in (3) above, wherein at least one compound selected from oxides of a is added. (9) “Ag, In, Sb, Te, and H having a Tauc gap in the range of 0.18 eV to 0.58 eV.”
Item (3), wherein the proportion of at least one oxide of Bi-Ge, Bi-Si, and Gd-Ga added to the recording material composed of o and N is 5 mol% or less. The optical recording material according to the above. Is provided.

That is, in the recording material according to the first aspect of the present invention, the Tauc gap or the optical gap determined from the light absorption spectrum accompanying the transition between the bands of the amorphous phase is from 0.18 eV to 0.58 eV. By using this recording material, a recording medium with high sensitivity and easy initial crystallization can be realized. This is because the existing red semiconductor laser or blue-green semiconductor laser light can be efficiently absorbed when the Tauc gap of the recording material is between the Tauc gaps. When the Tauc gap is 0.18 eV or less, the crystallization temperature is lowered and storage characteristics are deteriorated as described later. On the other hand, if the Tauc gap exceeds 0.58 eV, the crystallization temperature rises, making initial crystallization difficult.

[0006] In the recording material according to the above (2), the Tauc gap is 0.18 eV to 0.58 eV.
, The absorption coefficient α for each wavelength of the recording material in the wavelength range of 1000 nm to 400 nm.
And the square root of the product of the energy E corresponding to the wavelength (α
・ E) ^1/2 is 260 [cm ^-1/2 · eV ^1/2 ] to 650
[Cm ^−1/2 · eV ^1/2 ]. This makes it possible to provide a recording medium with high sensitivity and easy initial crystallization.

[0007] In the recording material of the above item (3), the Tauc gap is from 0.18 eV to 0.58 eV.
Ag, In, Sb, Te, and H
It is mainly composed of o and N. In particular, N is a material for controlling the Tauc gap, and the Tauc gap can be changed according to the design by the amount of N. Specifically, it is to increase sensitivity, improve storage characteristics, and improve repetition characteristics. Of course, the Tauc gap is controlled by A
It is also possible by changing each composition ratio of g, In, Sb, Te, Ho, and N, and other compounds, for example, Ag-Sn-Sb-Te-Ho-N, Cu-Sn-
Sb-Te-Ho-N, Ag-Pb-Sb-Te-Ho
-N, Ag-In-Sn-Sb-Te-Ho-N, Ag
-In-Pb-Sb-Te-Ho-N, Cu-In-S
n-Bi-Te-Ho-N, Ag-In-Sn-Bi-
Te-Ho-N, Ag-In-Pb-Bi-Te-Ho
-N, Ag-In-Sn-As-Te-Ho-N, and In of these elements were selected from Ga, Te was selected from Se and S, and Ho was selected from Pr, Ce, and Nd. It may be replaced by at least one element. This Ho, P
The elements r, Ce, and Nd have the effect of reducing the thermal expansion of the recording material, and improve the repetition characteristics.

Further, in the recording material of the above (4) and (5), the Tauc gap is 0.18 eV.
Ag, In, Sb, and T in the range of
The crystallization temperature of the recording material composed of e, Ho and N is T
It is characterized in that the auc gap increases as the width increases. Therefore, since the crystallization temperature can be controlled by controlling the Tauc gap, the storage characteristics of the recording material and the initial crystallization can be facilitated. As a specific control method, it is easiest to control the amount of N. The crystallization temperature at this time is between 165 ° C. and 253 ° C. with respect to the range of the Tauc gap. If the crystallization temperature is lower than this, the storage characteristics deteriorate, and
At temperatures higher than this, initialization becomes extremely difficult.

Further, in the recording material according to the above items (6) and (7), the recording material comprises Ag, In, Sb, Te, Ho, and N having a Tauc gap in a range of 0.18 eV to 0.58 eV. Complex refractive index of the amorphous phase after forming the recording material to be formed (n ^c = n + ik, n is a real part, and k is an imaginary part)
The values of the real part n and the imaginary part k of the
It has a tendency to become smaller as the Tauc gap increases between wavelengths of nm, and between 3.6 ≦ n ≦ 4.3 and 1.5 ≦ k ≦ 2.5 for the wavelength of 630 nm. It is characterized by. In general, the complex refractive index of a material tends to decrease as its energy gap increases, but the element composed of Ag, In, Sb, Te, Ho, and N has a clear relationship. In particular, the Tauc gap is from 0.18 eV to 0.58
Between eV, for n = 630 nm, n greatly changes between 3.6 and 4.3 and k between 1.5 and 2.5. Here, this is the complex refractive index of the amorphous phase obtained by forming this material by a method such as sputtering.
The large change in the refractive index with respect to the change in the c gap means that when this is used as a recording material, the optical characteristics such as the reflectance can be freely controlled, so that the recording medium can be easily designed and the recording medium having a large degree of modulation can be obtained. Can be provided.

Further, in the recording material according to the above (8) or (9), the Tauc gap is 0.18 eV.
, In, Sb, and Te in the range of 0.58 eV to
Bi-Ge, Bi on the recording material composed of
At least one compound selected from oxides of -Si and Gd-Ga is added. These include, for example, Al ₂ O ₃ , Bi ₄ Ge ₃ O ₁₂ , Bi ₁₂ GeO ₂₀ ,
Using a compound such as Gd ₃ Ga ₅ O ₁₂ or LiNbO ₃ as a sputtering target, a film is formed by sputtering with the above-mentioned recording material composed of Ag, In, Sb, Te, and Ho. At this time, the ratio of these oxides is 5 mol% or less. By the introduction of this oxide, mass transfer during melting of the recording film is suppressed, and the repetition characteristics are improved. Although the reason is not clear, it is considered that the viscosity of the recording material at the time of melting is increased. However, when the content is 5 mol% or more, the sensitivity decreases. Preferably 1 mol% to 3 mol% is good.

[0011]

EXAMPLES The present invention will be described more specifically with reference to the following examples.

Example 1 A lower heat-resistant protective layer, a recording layer, and an upper heat-resistant protective layer having the structure shown in Table 1 were formed on a polycarbonate substrate having a track pitch of 1.0 μm, a depth of 500 mm, a grooved thickness of 1.2 mm, and a diameter of 120 μm. The reflection heat radiation layer was sequentially laminated by a sputtering method to prepare a phase change recording medium. At this time, in order to prepare a sample for measuring the Tauc gap, crystallization temperature, and complex refractive index of the recording film, only the recording layer was separately provided on the glass substrate at 2000 °. Recording material is A
A target composed of g, In, Sb, Te, and Ho and having the composition shown in Table 1 was prepared, and a recording film was prepared by a sputtering method. Then, at the time of film formation, nitrogen was added at 0.5 SCCM.
The recording film was doped with nitrogen by flowing. The protective layer is made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ , and the reflective heat radiation layer is made of A
1 alloy was used. Here, the characteristics as a CD-RW are evaluated. Of course, the DVD-RAM and the blue light source (λ =
(400 nm or more).

[0013]

[Table 1]

Example 2 A recording medium was prepared in exactly the same manner as in Example 1 except that the recording layer was sputtered with nitrogen at 1 SCCM during film formation.

Example 3 A recording medium was prepared in exactly the same manner as in Example 1 except that the recording layer was sputtered with 2 SCCM of nitrogen during film formation.

Example 4 A recording medium was prepared in exactly the same manner as in Example 1 except that the recording layer was sputtered with nitrogen at 3 SCCM during film formation.

Example 5 A recording medium was prepared in exactly the same manner as in Example 1 except that the recording layer was sputtered with nitrogen at 4 SCCM during film formation.

Example 6 A recording medium was prepared in exactly the same manner as in Example 1 except that the recording layer was sputtered with nitrogen at 5 SCCM during film formation.

Example 7 As a recording layer, a target having 98 mol% of (Ag _3.0 In _6.0 Sb ₆₁ Te ₂₉ Ho ₁ ) and 2 mol% of (Bi ₄ Ge ₃ O ₁₂ ) was used. A recording medium was prepared in exactly the same manner as in Example 1 except that the above conditions were satisfied.

Example 8 A target having 98 mol% of (Ag _3.0 In _6.0 Sb ₆₁ Te ₂₉ Ho ₁ ) and 2 mol% of (Gd ₃ Ga ₅ O ₁₂ ) was used as a recording layer. A recording medium was prepared in exactly the same manner as in Example 1 except that the above conditions were satisfied.

[Evaluation] (1) The square root (α · E) ^1/2 of the product of the Tauc gap of the recording material used in each embodiment, the absorption coefficient α for each wavelength, and the energy E corresponding to that wavelength. It was determined from the measurement of the spectral absorbance. The results are shown in FIG. 1 (however, in Examples 7 and 8).
Are excluded) and Table 2. (2) Similarly, the real part n and the imaginary part k of the spectral refractive index of each recording material are shown in FIG. 2 (excluding Examples 1, 7, and 8). Table 2 shows the values at 630 nm. (3) Table 2 shows the crystallization temperature of each recording material. (4) Next, the disk characteristics of the recording medium were evaluated. After initializing the recording medium, overwrite repetitive recording is performed in an EFM random pattern at a linear velocity of 1.4 m / s,
The evaluation was made based on the recording power dependence of the jitter of the 3T signal at that time. Note that the linear velocity during reproduction is 2.8 m / s. The results are shown in Tables 2 and 3. Here, a high-output semiconductor laser was used for the initial crystallization of the recording medium. The easiness of the initialization is displayed in three stages of A, B, and C. A is very easy to initialize, C is difficult to initialize, and B is between A and C. The results are also shown in Tables 3, 4, 5,
6, 7, 8, 9, and 10 are shown.

[0022]

[Table 2]

[0023]

[Table 3] (Example 1)

[0024]

[Table 4] (Example 2)

[0025]

[Table 5] (Example 3)

[0026]

[Table 6] (Example 4)

[0027]

[Table 7] (Example 5)

[0028]

Table 8 (Example 6)

[0029]

Table 9 (Example 7)

[0030]

Table 10 (Example 8)

From the above, it can be seen from Table 2 that the Tauc gap increases as the nitrogen flow rate during film formation increases. The crystallization temperature increases as the Tauc gap increases. The complex refractive indexes n and k are Tauc
It can be seen that the larger the gap, the smaller the gap. On the other hand, from Tables 3, 4, 5, 6, 7, 8, 9, and 10, initial crystallization can be performed relatively easily up to a Tauc gap of 0.58 eV, but becomes extremely difficult when the Tauc gap is larger than this. Further, the recording sensitivity is better as the Tauc gap is smaller, but the sensitivity decreases when the Tauc gap becomes 0.58 eV or more. On the other hand, (Bi ₄
It can be seen that the system to which (Ge ₃ O ₁₂ ) and (Gd ₃ Ga ₅ O ₁₂ ) of Example 8 are added has significantly improved repetition characteristics. Although specific examples are not shown, Ag, In, S
When Ho is removed from b, Te, Ho, and N, the repetition characteristics deteriorate.

[0032]

As is apparent from the detailed and specific description, the optical recording medium according to claims 1 and 2 has a Tauc gap of 0.18 eV to 0.58 eV of the recording material constituting the recording layer. Within this range, initial crystallization can be easily achieved, and the recording sensitivity is excellent. Further, it is possible to provide a recording medium compatible with blue, for example, a GaN-based semiconductor laser. Further, in the optical recording medium of claim 3, the recording material constituting the recording layer is made of Ag, In, Sb, Te, and H.
N is a material consisting of o and N and controlling the Tauc gap of this material, and by this control, an excellent recording medium can be provided. Further, in the optical recording medium according to claims 4 and 5, the Tauc gap of the recording material constituting the recording layer is 0.18.
In the range of eV to 0.58 eV, since the crystallization temperature is in the range of 165 ° C. to 253 ° C., it is possible to provide a recording medium in which initial crystallization is easily performed. Furthermore, in the optical recording medium according to the sixth and eighth aspects, the values of the real part and the imaginary part of the complex refractive index of the recording material constituting the recording layer are changed from a wavelength of 450 nm to 38 as the value of the Tauc gap increases.
Since the complex refractive index tends to be smaller at a constant size within the range of 00 nm and changes in the Tauc gap, the recording medium having a large degree of modulation for light of 450 nm to 3800 nm can be provided. Further, the optical recording medium according to claim 7 or 8 has a Tauc gap of 0.18 eV to 0.58 as an optical recording material constituting the recording layer.
It is repeated by adding at least one compound selected from oxides of Bi-Ge, Bi-Si, and Gd-Ga to a material composed of Ag, In, Sb, Te, Ho, and N in the range of eV. It has an extremely excellent effect of being excellent in characteristics.

[Brief description of the drawings]

FIG. 1 is a diagram showing the Tauc gap dependence of the light absorption coefficient of the optical recording material (amorphous phase) of the present invention.

FIG. 2 is a diagram showing a spectral complex refractive index with respect to a Tauc gap of a recording material (amorphous phase) of the present invention.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoshiyuki Kageyama 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 2H111 EA04 EA12 EA23 EA31 EA33 EA43 FA01 FB05 FB09 FB10 FB12 FB17 FB20 FB21 FB24 FB25 FB30 5D029 JA01 JB16 JB35 JB47 JC05 JC09 JC11 JC18 JC20

Claims (9)

[Claims] 1. A recording material which undergoes a phase transition between a crystalline phase and an amorphous phase upon irradiation with an electromagnetic wave, has a Tauc gap corresponding to the energy gap of the amorphous phase in the range of 0.18 eV to 0.58 eV. An optical recording material, characterized in that: 2. The square root (α · E) of the product of the absorption coefficient α for each wavelength of the optical recording material in the wavelength range of 1000 nm to 400 nm and the energy E corresponding to the wavelength.
^1/2 from ^{260cm -1/2 · eV 1/2 650cm -1/2 ·} e
2. The optical recording material according to claim 1, wherein the optical recording material is in the range of V1 ^{/ 2} . 3. A recording material having a Tauc gap in a range of 0.18 eV to 0.58 eV is composed of Ag, In, and S.
2. The element comprising b, Te, Ho, and N, wherein the element controlling the Tauc gap is N.
The optical recording material according to the above. 4. Ag, In, Sb, Te, and H having a Tauc gap in a range of 0.18 eV to 0.58 eV.
The crystallization temperature of the recording material composed of o and N is Tauc
4. The optical recording material according to claim 3, wherein the gap increases as the gap increases. 5. Ag, In, Sb, Te, and H having a Tauc gap in the range of 0.18 eV to 0.58 eV.
The crystallization temperature of the recording material composed of o and N is 165 ° C.
4. The optical recording material according to claim 3, wherein the temperature is in the range of from 253.degree. 6. Ag, In, Sb, Te, and H having a Tauc gap in a range of 0.18 eV to 0.58 eV.
The values of the real part and the imaginary part of the complex refractive index of the amorphous phase of the optical recording material composed of o and N are from 450 nm to 800 nm.
4. The optical recording material according to claim 3, wherein the gap decreases as the Tauc gap increases. 7. Ag, In, Sb, Te, and H having a Tauc gap in a range of 0.18 eV to 0.58 eV.
When the values of the real part n and the imaginary part k of the complex refractive index of the amorphous phase of the optical recording material composed of o and N are 630 nm,
4. The optical recording material according to claim 3, wherein the range is 3.6 ≦ n ≦ 4.3 and 1.5 ≦ k ≦ 2.5. 8. Ag, In, Sb, Te, and H having a Tauc gap in a range of 0.18 eV to 0.58 eV.
Bi-Ge, Bi are used for the optical recording material composed of o and N.
4. The optical recording material according to claim 3, wherein at least one compound selected from the group consisting of -Si and Gd-Ga oxides is added. 9. Ag, In, Sb, Te, and H having a Tauc gap in a range of 0.18 eV to 0.58 eV.
4. The composition according to claim 3, wherein the proportion of at least one kind of Bi-Ge, Bi-Si, Gd-Ga oxide added to the optical recording material composed of o and N is 5 mol% or less. Optical recording material.