JPH05144083A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To improve repetition characteristics by providing boundary control layers of an oxide restricted in a standard forming free energy value in contact with a thin recording film. CONSTITUTION:The boundary control layers 3, 5 are provided in contact with the thin recording film 4. The layers 3, 5 are physically and chemically stable and have the higher m. p. than the m. p. of the recording material and the higher softening temp. than the softening temp. thereof. The essential component consists of the oxide having the standard forming free energy value at 1000 deg.C ranging from 4000kJ/mol O2 to -800kJ/mol O2. The destruction of the film 4 by repetition is substantially prevented in this way and the good repetition characteristics are obtd.

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 in an information recording / reproducing apparatus using a laser beam, and more particularly to a rewritable optical disc.

[0002]

2. Description of the Related Art As an optical disc capable of recording, reproducing and erasing signals, a phase change type optical disc using a chalcogenide as a recording thin film material is known. In general, when the recording thin film material is in a crystalline state, it is set in an unrecorded state, and a signal is recorded by rapidly heating and quenching by laser irradiation to make it an amorphous state. Moreover, the recording signal is erased by re-crystallizing by rapid heating and slow cooling.

Recording thin film materials include, for example, Te, In,
It is general to use a material containing Sb, Se or the like as a main component, which undergoes a phase change between amorphous and crystals, or a substance which causes a reversible phase change between two different crystal structures.

Examples of the protective layer material include Al ₂ O ₃ and
SiO ₂ , SiO, Ta ₂ O ₅ , MoO ₃ , WO ₃ , ZnS, Zr
O ₂ , AlN, BN, SiNx, TiN, ZrN, PbF ₂ , M
Dielectrics such as gF ₂ or suitable combinations of these are known.

[0005]

The number of repetitions of recording / erasing of a phase change type optical disk is improved by optimizing the material of the recording thin film or the protective layer, the disk structure, the recording / erasing beam power, etc. It is not completely satisfactory.

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

[0007]

In order to solve the above 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, and the main component of this interface control layer is 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 structure is such that the interface control layer is provided in contact with the recording thin film, and the standard free energy of formation at 1000 ° C. of the main component of this interface control layer is from -400 kJ / mol O ₂ to -800.
By using a thermally stable oxide in the range of kJ / mol O ₂ , destruction of the recording thin film due to repetition is less likely to occur. That is, good repeatability can be obtained.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

A typical example of the structure of the recording medium of the present invention is shown in FIG.
Shown in. The laser light for recording, reproducing, and erasing is the substrate 1
Incident from the side.

The substrate 1 is made of resin such as PMMA or polycarbonate, or glass, and has a smooth surface. In the case of an optical disc, the substrate plane 10 is usually covered with spiral or concentric tracks to guide the laser light.

The interface control layers 3 and 5 are physically and chemically stable, that is, the melting point and softening temperature are higher than the melting point of the recording material, and the main free energy of formation is −400 kJ at 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 an appropriate combination thereof. The interface control layer may be either 3 or 5 depending on the case.

It is desirable that the materials of the protective layers 2 and 6 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 do not form a solid solution with the recording material. For example, Al ₂ O ₃ , SiOx, 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 or MgF ₂ or an appropriate combination thereof. 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. Further, if the protective layers 2 and 6 are made of different materials, there is an advantage that the degree of freedom in thermal and optical disc design is increased. Of course, the same material may be used. Further, the protective layer may have the same composition as that of the interface control layer.

The recording thin film 4 is a substance that reversibly changes its structure between a crystalline state and an amorphous state, such as Te or I.
It is made of a phase change material containing n, Se, etc. as main components. The well-known main components of phase change materials are Te-Sb-Ge and 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-
Examples thereof include Sb-Se and In-Se-Te.

The reflective layer 7 is made of a metal element such as Au, Al, Ni, Fe, Cr or an alloy thereof, and has a function of enhancing 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 by, for example, making the recording thin film 4 thicker to increase the light absorption efficiency. Alternatively, by alternately stacking the recording thin film and the protective layer a plurality of times, it is possible to improve the light absorption efficiency as a whole even if the thickness of one recording thin film is small.

The protective substrate 9 is formed by spin-coating a resin or laminating a resin plate, a glass plate, a metal plate or the like similar to the substrate with an adhesive 8. Further, a structure capable of recording, reproducing and erasing from both sides may be realized by bonding two sets of recording media with the intermediate substrate or the reflection layer inside by using an adhesive.

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

When the same signal pattern is repeatedly recorded in a specific area in various rewritable phase change type optical discs containing Te or In as a main component, the end of the area (the part where a series of signals have been written) is recorded. The phenomenon that the recording thin film breaks is observed. Hereinafter, this phenomenon is referred to as repeated deterioration at the end of the recording area. The phenomenon of repeated deterioration at the end of the recording area is that the recording thin film constituent elements slightly diffuse and move in the disk radial direction or the disk circumferential direction at the time of laser irradiation, and the diffusion movement amount of the recording thin film constituent element is increased by repeated laser irradiation. I think that this is due to the accumulation. Repeated deterioration at the end of the recording area
This is especially noticeable when the recording power is high. As a means for solving this phenomenon, an attempt was made to provide an interface control layer containing an oxide as a main component 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 was a thermally stable oxide whose standard free energy of formation at 1000 ° C was in the range of -400 kJ / mol O ₂ to -800 kJ / mol O ₂ . Only in this case, the repeated deterioration at the end of the recording area was reduced.

There are infinite combinations of phase change recording thin film compositions containing Te or In as a main component and capable of repeating recording and erasing, and the effect of the oxide interface control layer is experimentally confirmed for all of them. Is impossible. However, the main component of a well-known typical phase change recording thin film containing Te or In as the main component and capable of repeating recording and erasing is Te-S.
It can be roughly classified into b, Te-Ge, Te-Se, In-Te, In-Sb, and In-Se. When the effect of the interface control layer was examined on optical disks having typical recording thin film compositions in the above classification, the standard free energy of formation of the main component of the interface control layer at 1000 ° C was -400 kJ / mol O ₂ to -800 kJ /. Only when a thermally stable oxide in the range of mol O ₂ was used, the effect of suppressing repeated deterioration of recording and erasing was remarkable. From the experimental results, it was found that the oxide interface control layer having the above-mentioned physical properties was set as the main component of Te or In, and the recording / erasing repetitive deterioration of the phase-change recording thin film capable of recording / erasing was repeated. Can be judged to be effective in suppressing the repeated deterioration of the end portion of the recording area.

As described above, in the case of a erasable phase change type optical disk device, usually, the amorphous phase of the recording thin film corresponds to the recording signal and the crystalline phase corresponds to the erased state.
In some cases, two different optically distinguishable crystal states may be used for recording and erasing, respectively. In either 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 or raise the temperature above the phase transformation transition temperature by irradiation with a laser beam. In the molten state,
Alternatively, in the recording thin film in a high temperature state, the constituent elements of the recording thin film easily diffuse and move. That is, it can be said that in a phase-change type optical disc in which recording / erasing can be repeated, the recording thin film has a possibility of being repeatedly deteriorated due to its recording / erasing mechanism. When the interface control layer mainly composed of 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 is provided in contact with the recording thin film. The mechanism by which repeated deterioration is suppressed is not clear, but the reason is as follows. (1) When the standard free energy of formation of the oxide forming the interface control layer is too small, the bond between the metal element forming the oxide and oxygen is relatively small. Therefore, when the recording thin film melts at a high temperature due to laser irradiation, oxygen that originally constitutes the interface control layer is easily deprived by the element that constitutes the recording thin film. For example, stable oxides of Ge, Te, Sb, and In which are often used as constituent materials of recording thin films (GeO ₂ , respectively)
Comparing TeO ₂ , SbO ₂ and In ₂ O ₃ ), 1000 ° C
The standard free energy of formation for 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 constituting 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 (for example, Nippon Metal Journal VOl.52 (1988), pp72). That is, when the standard free energy of formation of the oxide forming the interface control layer is too small, it can be expected that the oxide interface control layer and the recording thin film easily react with each other. As a result, the composition of the recording thin film material changes as recording and erasing are repeated, and the initial repeatability cannot be obtained. Experimentally, when the standard free energy of formation of the oxide forming 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 melt recording thin film becomes small. At this time, for example, the temperature dependence of the interfacial tension at the interface between the two becomes extremely large. Therefore, it is considered that the substance forming the recording thin film is likely to move during melting. Experimentally, the standard free energy of formation of the oxide constituting the interface control layer was −80.
It is estimated that this is the case when the concentration is 0 kJ / molO ₂ or more.

The present invention will be described in detail below with reference to specific examples. Example 1 Ge ₂ Sb ₂ Te ₅ was selected as a typical recording thin film composition, and recording / erasing repetitive characteristics when an interface control layer made of various oxides was provided in contact with this recording thin film-especially repetitive The allowable range of the recording power with respect to was compared. Ge ₂ S
b ₂ Te ₅ is known as a material that can obtain good recording / erasing characteristics and repetitive characteristics (Japanese Laid-Open Patent Publication No. 62-209742).

FIG. 1 shows the disk structure. The substrate material is
5.25 inch diameter glass was used. Recording thin film thickness is 50 nm
Thus, the oxide interface control layer having a thickness of 3 nm sandwiches both sides thereof. Furthermore, silicon nitride (Si
_The protective layer consisting of ₃ N ₄ ) is sandwiched. The thickness of the protective layer was determined so as to obtain optically optimum characteristics. Specifically, the film thickness on the substrate side was 150 nm, and the film thickness was 200 nm on the recording thin film. Gold (Au) is used for the reflective layer material,
The film thickness was 20 nm. The formation of each layer was performed by the sputtering method.

Repeated recording / erasing tests were conducted using the disk having the above structure. Here, the laser beam (wavelength:
830 nm) and the relative speed of the disk is 14 m / sec, the pulse width is 50 ns, and the random data is overwritten by 2-7 modulation mark position recording. ) Was measured (the recording conditions for examining the recording / erasing characteristics in the following examples are based on this condition). At this time,
BER by changing recording / erasing power in steps of 0.2 mW
The change is measured, and the recording / erasing power that minimizes the BER value after repetition 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
Standard free energy of formation at 000 ° C is also shown.
Each physical property value was quoted from the Chemical Handbook, Revised 3rd 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, the standard free energy of formation at 1000 ° C is -400 kJ / molO ₂ to -800 kJ /.
It can be seen that the repeatability is 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 that constitutes 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 causes of the increase in BER due to repetition are waveform deterioration at the resync area (the area where a constant signal pattern is written every 16 bytes of data for signal synchronization) and the end of the recording area. These deteriorations were caused by the 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 repeating characteristics, the standard free energy of formation at 1000 ° C is -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 was provided on either side of the recording layer in contact with the recording layer, the standard free energy of formation at 1000 ° C was -400 kJ / mol O _2- 8
When the interface control layer was formed of a thermally stable oxide in the range of 00 kJ / mol O ₂ , the repeating characteristics were the best.

Next, the composition range of the recording thin film is widened to provide a thermally stable oxide interface control layer which has good crystallization / amorphization sensitivities and is in contact with the recording thin film. I investigated a configuration that would improve. As a result of the experiment, both the crystallization and the amorphization sensitivity are good.
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 the 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 repeatability was good when the interface control layer was formed of oxide.

As a result of further detailed examination of the Ge-Sb-Te composition range of the main component of the recording thin film, the range represented by (Ge ₂ Sb ₂ Te ₅ ) _x (GeSb ₂ Te ₄ ) _1-x 0 ≤ x ≤ 1 In the recording thin film set, the crystallization speed was particularly high, and at the same time, the deterioration of the end portion of the recording area due to repeated recording and erasing, that is, deterioration due to mass transfer was remarkable. A high crystallization speed is very preferable for a phase change type optical disc capable of overwriting. Therefore, the effect of suppressing repeated deterioration by providing the 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 Notable and important in the 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 repeatability was 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, such as 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 specific physical properties on both sides or one side of the Te recording thin film (specifically, the standard free energy of formation at 1000 ° C is -400 kJ / mol O ₂ to -800 kJ.
It was confirmed by an experiment that the provision of the interface control layer made of an oxide in the range of / mol O ₂ ) tends to improve the recording / erasing repetition characteristics. As an example, (Table 2) shows the repeating characteristics of an optical disk having a (InSb) ₂ Te recording thin film. The structure of the disk is such that the glass substrate and the recording thin film have a thickness of 40 nm, and an oxide interface control layer having a thickness of 3 nm sandwiches 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 optimum characteristics. Specifically, the film thickness on the substrate side was 150 nm, and the film thickness was 200 nm on the recording thin film. Gold (Au) was used as the reflective layer material, and the film thickness was 20 nm. The formation of each layer was performed by the sputtering method. The signal was recorded 10,000 times under the recording conditions shown in Example 1. When repeated recording is performed with the optimum power, the number of repetitions when the BER becomes larger than 1 × 10 ⁻⁵ is shown in (Table 2).

[0029]

[Table 2]

From Table 2, the standard free energy of formation at 1000 ° C is -400 kJ / molO ₂ to -800 kJ /.
It can be seen that the repeatability is 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 that constitutes 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 causes of the increase in BER due to repetition are waveform deterioration at the resync area (the area where a constant signal pattern is written every 16 bytes of data for signal synchronization) and the end of the recording area. These deteriorations were caused by the 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 repeating characteristics, the standard free energy of formation at 1000 ° C is -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. Further, in the case of providing only oxide interface control layer on either one side in contact with the recording layer also, (Table 2) results and similar, the standard free energy of formation at 1000 ° C from -400 kJ / mol O ₂ - 8
When the interface control layer was formed of a thermally stable oxide in the range of 00 kJ / mol O ₂ , the repeating characteristics were the best.

[0031]

The interface control layer is provided in contact with the recording thin film, and the standard free energy of formation of the main component of the interface control layer at 1000 ° C. is -400 kJ / mol O ₂ to -8.
By using a thermally stable oxide in the range of 00 kJ / mol O ₂ , destruction of the recording thin film due to repetition is less likely to occur. That is, good repeatability can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a 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]

 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

Claims (5)

[Claims] 1. A substrate, a recording thin film formed on the substrate and capable of reversibly shifting to a state having different optical characteristics by causing a phase change upon irradiation with a laser beam, and both sides of the recording thin film in contact with the recording thin film. Alternatively, in the optical information recording medium having at least one interface control layer formed on one side, the interface control layer has a standard free energy of formation of −400 kJ / mol O ₂ to −800 kJ / mol O ₂ at 1000 ° C. An optical information recording medium comprising an oxide in the range. 2. The oxide forming the interface control layer is Cr ₂ O.
_2. The optical element according to claim 1, wherein any one of five kinds of oxides of ₃ , SiO ₂ , Ta ₂ O ₅ , TiO ₂ , and V ₂ O ₃ or a combination of these oxides is used. Information recording medium. 3. The optical information recording medium according to claim 1, wherein the main component of the recording thin film is Te or In. 4. The main component of the recording thin film is Ge, Sb, Te,
The composition ratio of the main components is within the 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. An optical information recording medium according to the item. 5. The composition ratio of Ge, Sb and Te is 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.