JP2990901B2 - Optical information recording medium - 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 information recording medium used for an information recording / reproducing apparatus using a laser beam, and more particularly to a rewritable optical disk.

[0002]

2. Description of the Related Art As an optical disk capable of recording, reproducing and erasing signals, a phase-change optical disk using a chalcogenide as a recording thin film material is known. Generally, a signal is recorded by setting the recording thin film material in a crystalline state to an unrecorded state and rapidly heating and quenching by laser irradiation to make the recording thin film amorphous. In addition, the crystal becomes a crystalline state again by rapid heating and slow cooling, and the recorded signal is erased.

As recording thin film materials, for example, Te, In,
It is common to use a material which is mainly composed of Sb, Se and the like and which changes phase between an amorphous and a crystal, or a substance which reversibly changes phase between two different types of crystal structures.

As a material for the protective layer, for example, Al ₂ O ₃ ,
SiO ₂ , SiO, Ta ₂ O ₅ , MoO ₃ , WO ₃ , ZnS, Zr
O ₂ , AlN, BN, SiNx, TiN, ZrN, PbF ₂ , M
dielectric or of suitable combinations of such gF ₂ are known.

[0005]

The number of repetitions of recording / erasing of a phase change type optical disk can be improved by optimizing the material of the recording thin film and the protective layer, the disk configuration, the recording / erasing beam power, etc. It is not fully satisfactory.

An object of the present invention is to provide an optical information recording medium having improved recording / erasing repetition characteristics.

[0007]

In order to solve the above-mentioned problems, the present invention has a structure in which an interface control layer is provided in contact with a recording thin film of a phase change type optical information recording medium. Is a thermally stable oxide having a standard free energy of formation at 1000 ° C. in the range of −400 kJ / mol O ₂ to −800 kJ / mol O ₂ .

[0008]

The interface has a structure in which an interface control layer is provided in contact with the recording thin film. The main component of the interface control layer has a standard free energy of formation at 1000 ° C. of from −400 kJ / mol O ₂ to −800.
By using a thermally stable oxide in the range of kJ / mol O _2, the recording thin film is less likely to be broken by repetition. That is, good repetition characteristics can be obtained.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

FIG. 1 shows a typical structure example of the recording medium of the present invention.
Shown in The laser beam for recording, reproducing and erasing is applied to the substrate 1
From the side.

As the substrate 1, a resin having a smooth surface such as resin such as PMMA or polycarbonate or glass is used. In the case of an optical disk, the substrate plane 10 is usually covered with spiral or concentric tracks for guiding laser light.

The interface control layers 3 and 5 are physically and chemically stable, that is, have a melting point and a softening temperature higher than the melting point of the recording material, and have a standard free energy of formation of -400 kJ when the main component is 1000 ° C. / mol O ₂ to -800 kJ / m
It consists of oxides in the range of ol O ₂ . For example, Cr
₂ O ₃ , MnO, NbO, NbO ₂ , SiO ₂ , Ta ₂ O ₅ , TiO
₂ , VO ₂ , V ₂ O ₃ , V ₂ O ₅ , ZnO or a suitable combination thereof. In some cases, the interface control layer may be only one of 3 or 5.

It is desirable that the material of the protective layers 2 and 6 is physically and chemically stable, that is, has a melting point and a softening temperature higher than the melting point of the recording material and does not form a solid solution with the recording material. For example, Al ₂ O ₃ , SiO x, Ta ₂ O ₅ , MoO ₃ , WO
_{3, ZnS, ZrO 2, AlNx} , BN, SiNx, TiN, Zr
It is made of a dielectric material such as N, PbF ₂ , MgF ₂ or an appropriate combination of these. The protective layer need not be dielectric or transparent. For example, it may be formed of ZnTe having a light absorbing property for visible light and infrared light. In addition, when the protective layers 2 and 6 are formed of different materials, there is an advantage that the degree of freedom in thermal and optical disc design is increased. Of course, they may be formed of the same material. Further, the protective layer may have the same composition as the interface control layer.

The recording thin film 4 is made of a material which reversibly changes its structure between a crystalline state and an amorphous state, for example, Te or I.
It is made of a phase change material containing n, Se and the like as main components. The main components of well-known phase change materials are Te-Sb-Ge, Te-
Ge, Te-Ge-Sn, Te-Ge-Sn-Au, Sb-Te, Sb-S
e-Te, In-Te, In-Se, In-Se-Tl, In-Sb, In-
Sb-Se, In-Se-Te, and the like.

The reflection layer 7 is made of a metal element such as Au, Al, Ni, Fe, or Cr, or an alloy thereof, and functions to increase the light absorption efficiency of the recording thin film. However, it is also possible to adopt a configuration in which the reflective layer 7 is not provided, for example, by increasing the thickness of the recording thin film 4 to improve the light absorption efficiency. Alternatively, by adopting a configuration in which the recording thin film and the protective layer are alternately stacked a plurality of times, the light absorption efficiency can be increased as a whole even if the film thickness per recording thin film is small.

The protective substrate 9 is formed by spin-coating a resin, or by bonding a resin plate, a glass plate, a metal plate, or the like similar to the substrate using an adhesive 8. Furthermore, a structure in which recording, reproduction, and erasing can be performed from both surfaces may be performed by bonding two sets of recording media using an adhesive with the intermediate substrate or the reflective layer inside.

The recording thin film and the protective layer are usually formed by electron beam evaporation, sputtering, ion plating, CV
It is formed by a D method, a laser sputtering method, or the like.

In various rewritable phase-change optical disks mainly composed of Te or In, when the same signal pattern is repeatedly recorded in a specific area, the end of the area (the part where a series of signals has been written) , A phenomenon in which the recording thin film is broken is observed. Hereinafter, this phenomenon is referred to as repetitive deterioration at the end of the recording area. The phenomenon of repetitive degradation at the end of the recording area is that during laser irradiation, the constituent elements of the recording thin film slightly diffuse and move in the radial direction of the disk or in the circumferential direction of the disk, and the amount of diffusion and movement of the constituent elements of the recording thin film by repeated laser irradiation is reduced. It is thought to be due to the addition. Repeated deterioration at the end of the recording area
This is particularly noticeable when the recording power is high. As a means for solving this phenomenon, an attempt was made to provide an interface control layer mainly composed of an oxide in contact with the recording thin film. As a result, the main component of the interface control layer provided in contact with the recording thin film is a thermally stable oxide whose standard free energy of formation at 1000 ° C. is in the range of −400 kJ / mol O ₂ to −800 kJ / mol O ₂ . Only when the above condition was satisfied, the repeated deterioration at the end of the recording area was reduced.

There are infinite combinations of phase change type recording thin film compositions containing Te or In as a main component and capable of repeating recording / erasing, and the effect of the oxide interface control layer is experimentally confirmed for all of them. It is impossible. However, the main component of a typical phase-change type recording thin film which has been publicly known and which can be repeatedly recorded and erased with Te or In as a main component is Te-S
b, Te-Ge, Te-Se, In-Te, In-Sb, and In-Se. When the effect of the interface control layer on the optical disc having a recording thin film composition representative of the above classification was examined, the main component of the interface control layer was found to have a standard free energy of formation at 1000 ° C of from −400 kJ / mol O ₂ to −800 kJ / mol. Only when a thermally stable oxide in the range of mol O ₂ was used, the effect of suppressing repeated deterioration of recording / erasing was remarkable. From the experimental results, it was found that the provision of the oxide interface control layer having the above-mentioned physical properties indicates that the recording / erasing repetitive deterioration of a phase-change recording thin film containing Te or In as a main component and capable of repeating recording / erasing-more specifically Can be determined to be effective in suppressing the repetitive deterioration of the end portion of the recording area.

As described above, usually, in the case of an erasable phase-change optical disk device, the amorphous phase of the recording thin film is made to correspond to the recording signal, and the crystalline phase is made to correspond to the erased state.
In some cases, two different optically identifiable crystal states are associated with recording and erasing, respectively. In any case, of the two optically distinguishable recording thin film states,
In order to obtain at least one of the states, it is necessary to melt the recording thin film by laser beam irradiation or to raise the temperature of the recording thin film to a transition temperature or higher. Molten state,
Alternatively, in a recording thin film in a high temperature state, the constituent elements of the recording thin film easily diffuse and move. In other words, it can be said that a phase change type optical disk capable of repeating recording / erasing inherently has a possibility that the recording thin film is repeatedly deteriorated due to its recording / erasing mechanism. When the standard free energy of 1000 ° C was provided in contact with the interface control layer mainly composed of thermally stable oxide in the range of -400 kJ / mol O ₂ of -800kJ / mol O ₂ in the recording thin film The mechanism by which the deterioration is repeatedly suppressed is not well understood, but the reason is considered as follows. (1) When the standard free energy of formation of the oxide constituting the interface control layer is too small, the bond between the metal element constituting the oxide and oxygen is relatively small. Therefore, when the recording thin film is melted by the laser irradiation at a high temperature, oxygen which originally constituted the interface control layer is easily taken away by the elements constituting the recording thin film. For example, stable oxides of Ge, Te, Sb, and In (GeO ₂ ,
(TeO ₂ , SbO ₂ , In ₂ O ₃ )
Is the largest when GeO ₂ (hex) is about −350 kJ / mol O ₂ (bulk literature value). Therefore, the standard free energy of formation at 1000 ° C. is −
If the interface control layer is formed of an oxide smaller than 350 kJ / mol O ₂ and Sb is present in the recording thin film, the oxygen forming the interface control layer is converted to Sb when the recording thin film is melted at a high temperature by laser irradiation. Expected to be robbed. or,
The wettability between the oxide layer (in this case, the interface control layer) and the molten metal (in this case, the recording thin film material) tends to increase as the standard free energy of formation of the oxide decreases. Journal VOl. 52 (1988), pp 72). That is, when the standard free energy of formation of the oxide constituting the interface control layer is too small, it can be expected that the oxide interface control layer and the recording thin film easily react. As a result, the composition of the recording thin film material changes as recording and erasing are repeated, and the initial repetition characteristics cannot be obtained. Experimentally, when the standard free energy of formation of the oxide constituting the interface control layer is -400 kJ / mol O ₂ or less,
It is assumed that this is the case. (2) When the standard free energy of formation of the oxide constituting the interface control layer is too large, the wettability between the oxide interface control layer and the melted recording thin film becomes small. At this time, it is considered that the material constituting the recording thin film is likely to move during melting because, for example, the temperature dependency of the interfacial tension at the interface between the two becomes extremely large. Experimentally, the standard free energy of formation of the oxide constituting the interface control layer is -80.
It is assumed that the case of 0 kJ / mol O ₂ or more corresponds to this.

Hereinafter, the present invention will be described in detail with specific examples. Example 1 Ge ₂ Sb ₂ Te ₅ was selected as a typical recording thin film composition, and the recording / erasing repetition characteristics when an interface control layer made of various oxides was provided in contact with the recording thin film—particularly, repetition Were compared with respect to the allowable range of the recording power. Ge ₂ S
b ₂ Te ₅ is known as a material from which good recording / erasing characteristics and repetition characteristics can be obtained (JP-A-62-209742).

FIG. 1 shows a disk structure. The material of the substrate is
The glass was 5.25 inches in diameter. The thickness of the recording thin film is 50 nm
The oxide interface control layer having a thickness of 3 nm sandwiches both sides of the oxide interface control layer. In addition, silicon nitride (Si
Protective layer of ₃ N ₄₎ is sandwiched. The thickness of the protective layer was determined so as to obtain optically optimal characteristics. Specifically, the film thickness on the substrate side was 150 nm, and 200 nm on the recording thin film. Gold (Au) is used for the reflective layer material,
The film thickness was 20 nm. Each layer was formed by a sputtering method.

A recording / erasing repeated test was performed using the disk having the above configuration. Here, the laser beam (wavelength:
830 nm) and the relative speed of the disk is 14 m / sec. The pulse width of 50 ns is used to overwrite (overwrite) 2-7 modulation mark position recording of random data. ) Was measured (the recording conditions for examining the recording / erasing characteristics in the following examples follow these conditions). At this time,
BER by changing recording / erasing power in increments of 0.2 mW
The change is measured, and the recording / erasing power at which the BER value after the repetition becomes the minimum is called the optimum power. Table 1 shows the number of repetitions when the BER becomes larger than 1 × 10 ⁻⁵ when the recording is repeatedly performed with the optimum power and the recording / erasing power that is 15% higher than the optimum power.
Table 1 shows the melting point of the oxide of the interface control layer material, and 1
The standard free energy of formation at 000 ° C is also shown.
Each physical property value was quoted from the Chemical Handbook, 3rd revised edition, Basic Edition, and the Iron and Steel Handbook, 3rd Edition (edited by the Iron and Steel Institute of Japan).

[0024]

[Table 1]

From Table 1, it can be seen that the standard free energy of formation at 1000 ° C. is from −400 kJ / mol O ₂ to −800 kJ / mol.
It can be seen that the repetition characteristics are good when the interface control layer is formed of a thermally stable oxide in the range of mol O ₂ . The standard free energy of formation of the oxide constituting the interface control layer is -400 kJ / mol O ₂ or less (here, CoO, Ge
O _2, SnO _2, if the WO _2), the main cause of the increase in BER due to the repetition, the deterioration of the reproduction waveform due to an increase in noise to be the main cause, it was found from the waveform observation using an oscilloscope. On the other hand, when the standard free energy of formation of the oxide constituting the interface control layer is -800 kJ / mol O ₂ or more (here, CeO ₂ , Dy ₂ O ₃ , Gd ₂ O ₃ , MgO, Y ₂ O ₃ )
The main cause of the increase in BER due to repetition was a resync area (an area where a fixed signal pattern was written every 16 bytes of data for synchronizing signals) and a waveform deterioration in a recording area end portion. These deteriorations were caused by mass transfer of the recording thin film material. From these results, when the interface control layer is provided in contact with the recording thin film for the purpose of improving the repetition characteristics, the standard free energy of formation at 1000 ° C. is from −400 kJ / mol O ₂ to −800 kJ / mol O _2.
It can be concluded that the interface control layer should be formed of a thermally stable oxide in the range of The interface control layer may be composed of a plurality of oxides. Also, when the oxide interface control layer is provided on only one side in contact with the recording layer, the standard free energy of formation at 1000 ° C. is from −400 kJ / mol O ₂ , similarly to the result of (Table 1). 8
When the interface control layer was formed of a thermally stable oxide in the range of 00 kJ / mol O ₂ , the repetition characteristics were the best.

Next, by increasing the composition range of the recording thin film and providing a thermally stable oxide interface control layer in contact with the recording thin film, which has both good crystallization and amorphization sensitivity, the repetition characteristics are improved. A configuration that improves is investigated. As a result of the experiment, both the crystallization and the amorphization sensitivity were good (the heating time necessary for crystallization was 10
0 nsec or less) and the recording area end portion is unlikely to be degraded at the time of repetition of recording / erasing, when the composition range of the Ge—Sb—Te main component is (Ge) _x (Sb) _y (Te) _z 0.10 ≦ x ≦ 0.35 0.10 ≦ y 0.45 ≦ z ≦ 0.65 x + y + z = 1. The composition range of the Ge—Sb—Te main component is a range surrounded by A, B, C, D, and E in FIG. Even when providing the oxide interface control layers in contact with the recording thin film having the above composition range, thermally standard free energy is in the range of -400 kJ / Molo ₂ of -800kJ / mol O ₂ at 1000 ° C, stable It was experimentally confirmed that the repetition characteristics were good when the interface control layer was formed of an oxide.

As a result of further study of the Ge—Sb—Te composition range of the main component of the recording thin film, it was found that (Ge ₂ Sb ₂ Te ₅ ) _x (GeSb ₂ Te ₄ ) _1−x 0 ≦ x ≦ 1 In the recording thin film group, the crystallization speed was particularly high, and at the same time, the deterioration of the end portion of the recording area due to repetitive recording / erasing, that is, the deterioration due to mass transfer was remarkable. A high crystallization rate is very preferable for a rewritable phase-change optical disk. Therefore, the effect of suppressing repetitive deterioration by providing an interface control layer made of an oxide having an appropriate standard free energy of formation in contact with the recording thin film is (Ge ₂ Sb ₂ Te ₅ ) _x (GeSb ₂ Te ₄ ) _{1 -x} 0 ≦ x ≦ 1 Significant and important in composition.

Example 2 In Example 1, the standard free energy of formation at 1000 ° C. was −40 on both sides or one side of the Ge—Sb—Te recording thin film.
It was shown that the repetition characteristics were improved when the interface control layer was formed of a thermally stable oxide in the range of 0 kJ / mol O ₂ to -800 kJ / mol O ₂ . In addition, a recording thin film containing Te or In as a main component, for example, Te-Ge, Te-Ge-Sn,
Te-Ge-Sn-Au, Sb-Te, Sb-Se-Te, In-Te, I
n-Se, In-Se-Tl, In-Sb, In-Sb-Se, In-Se-
An oxide having a specific physical property value on both sides or one side of the Te recording thin film (specifically, the standard free energy of formation at 1000 ° C. is from −400 kJ / mol O ₂ to −800 kJ).
It was confirmed by experiments that the recording / erasing repetition characteristics tended to be improved by providing an interface control layer made of an oxide in the range of / mol O ₂ ). As an example, Table 2 shows the repetition characteristics of an optical disk having a (InSb) ₂ Te recording thin film. The disc has a glass substrate, a recording thin film having a thickness of 40 nm, and an oxide interface control layer having a thickness of 3 nm sandwiching both sides thereof. Further, a protective layer made of silicon nitride (Si ₃ N ₄ ) is sandwiched on both sides thereof. The thickness of the protective layer was determined so as to obtain optically optimal characteristics. Specifically, the film thickness on the substrate side was 150 nm, and 200 nm on the recording thin film. Gold (Au) was used for the reflective layer material, and the film thickness was 20 nm. Each layer was formed by a sputtering method. The signal was recorded 10,000 times under the recording conditions shown in Example 1. Table 2 shows the number of repetitions when the BER became larger than 1 × 10 ⁻⁵ when the recording was repeatedly performed with the optimum power.

[0029]

[Table 2]

According to Table 2, the standard free energy of formation at 1000 ° C. is from −400 kJ / mol O ₂ to −800 kJ / mol.
It can be seen that the repetition characteristics are good when the interface control layer is formed of a thermally stable oxide in the range of mol O ₂ . The standard free energy of formation of the oxide constituting the interface control layer is -400 kJ / mol O ₂ or less (here, CoO, Ge
O _2, SnO _2, if the WO _2), the main cause of the increase in BER due to the repetition, the deterioration of the reproduction waveform due to an increase in noise to be the main cause, it was found from the waveform observation using an oscilloscope. On the other hand, when the standard free energy of formation of the oxide constituting the interface control layer is -800 kJ / mol O ₂ or more (here, CeO ₂ , Dy ₂ O ₃ , Gd ₂ O ₃ , MgO, Y ₂ O ₃ )
The main cause of the increase in BER due to repetition was a resync area (an area where a fixed signal pattern was written every 16 bytes of data for synchronizing signals) and a waveform deterioration in a recording area end portion. These deteriorations were caused by mass transfer of the recording thin film material. From these results, when the interface control layer is provided in contact with the recording thin film for the purpose of improving the repetition characteristics, the standard free energy of formation at 1000 ° C. is from −400 kJ / mol O ₂ to −800 kJ / mol O _2.
It can be concluded that the interface control layer should be formed of a thermally stable oxide in the range of The interface control layer may be composed of a plurality of oxides. Also, when the oxide interface control layer is provided on only one side in contact with the recording layer, the standard free energy of formation at 1000 ° C. is from −400 kJ / mol O ₂ , similarly to the result of (Table 2). 8
When the interface control layer was formed of a thermally stable oxide in the range of 00 kJ / mol O ₂ , the repetition characteristics were the best.

[0031]

According to the present invention, the interface control layer is provided in contact with the recording thin film, and the main component of the interface control layer has a standard free energy of formation at 1000 ° C. of −400 kJ / mol O ₂ to −8.
By using a thermally stable oxide in the range of 00 kJ / mol O _2, the recording thin film is less likely to be broken by repetition. That is, good repetition characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the structure of a recording medium according to an embodiment of the present invention.

FIG. 2 is a diagram showing a main component composition range of a recording thin film containing Ge-Sb-Te as a main component.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Protective layer 3 Interface control layer 4 Recording thin film 5 Interface control layer 6 Protective layer 7 Reflective layer 8 Adhesive layer 9 Protective substrate 10 Substrate plane

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-125343 (JP, A) JP-A-2-195537 (JP, A) JP-A-3-181029 (JP, A) 88147 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 7/24 533

Claims (4)

(57) [Claims] 1. A substrate, a recording thin film formed on the substrate and capable of undergoing a phase change by irradiation with a laser beam and reversibly shifting to a state having different optical characteristics, and both sides of the recording thin film
An optical information recording medium comprising two protective layers formed on the recording medium, wherein an interface control layer is provided on at least one of the recording thin film and the two protective layers; But,
Standard free energy of formation at 1000 ° C. is −400
An oxide in the range of kJ / mol O ₂ to -800 kJ / mol O ₂ , which is composed of one of two kinds of oxides, Ta ₂ O ₅ and V ₂ O ₃ , or a combination of these oxides. An optical information recording medium characterized by the above-mentioned. 2. The recording film according to claim 1, wherein the main component of the recording thin film is Te or In.
The optical information recording medium according to claim 1, wherein: 3. The recording film according to claim 1, wherein said recording thin film is mainly composed of Ge, Sb, T
e , and the composition ratio of the main component is within a range represented by (Ge) _x (Sb) _y (Te) _z 0.10 ≦ x ≦ 0.35 0.10 ≦ y 0.45 ≦ z ≦ 0.65 x + y + z = 1 The optical information recording medium according to claim 1, wherein: 4. The recording thin film has three layers of Ge, Sb, and Te.
Includes components, the composition ratio of the three components, characterized in that in the range represented by _{(Ge 2 Sb 2 Te 5)} x (GeSb 2 Te 4) 1-x 0 ≦ x ≦ 1 The optical information recording medium according to claim 1.