KR20000023546A - Phase change optical disk - Google Patents

Abstract

PURPOSE: An optical disk is provided to have a good overlap record characteristic and a good reiteration record endurance without a deterioration owing to a corrosion of a reflection layer. CONSTITUTION: An optical disk of a phase change type comprises a first dielectric layer,a second dielectric layer and a reflection layer which are sequentially formed on a transparent substrate. The reflection layer comprises a first reflection layer(34) consisting of a metal or an alloy having an electric negativity of 1.0 to 3.0, and a second reflection layer(35) consisting of Cu, Ag, or an alloy of the Cu and the Ag. The first reflection layer is located so as to be closely adhered to the second dielectric layer, and the second reflection layer is closely adhered to the first reflection layer and a protection layer(36).

Description

Phase change optical disk {PHASE CHANGE OPTICAL DISK}

The present invention relates to a phase change type optical disc, and more particularly, to a phase change type optical disc capable of freely recording and erasing and overlapping recording, and to a phase change type optical disk having improved corrosion resistance, repeated recording durability, and overlapping recording characteristics. will be.

A typical optical disk has a disk structure as shown mainly in Fig. 1, where 1 represents the information area of the disk. On the substrate 10 of the optical disc, as shown in Fig. 2, a pit 11, which is a mark for digital information, is formed on the track like a Morse code, and the reflective layer 12 and the protective layer 13 reflecting the laser beam thereon. ) Are formed one after the other.

The process of manufacturing the optical disk as described above is largely composed of the step of manufacturing a stamper (stamper) and the step of replicating the optical disk in large quantities by the manufactured stamper. The stamper is first made of a glass master having the same format as the optical disk, and then in the form of a mold for the obtained glass master. The optical disc produced in this way is a read only memory (ROM) which can only read the recorded contents of the recording layer.

On the other hand, with the rapid spread of CD-ROMs and the like, multimedia-related software programs including moving pictures, still images, and animations are rapidly spreading. Therefore, there is an urgent need for recording and reproducible recording media for effectively using such programs. In response to this demand, a write once write-once optical disc (CD-R) has been developed. However, the write-once optical disc has a fatal disadvantage that it is not possible to edit the recorded data freely and record new information because only one write-once is possible.

Accordingly, a slow-circuit type optical disc capable of erasing and rewriting (e.g., CD-RW (Compact Disc Rewritable)) has been developed. As a recording layer material, an optical magnetic disk using a magneto-optical material and a phase change optical disk using a phase change material have. Among these, the phase change type optical disc has a reproduction principle similar to that of a conventional CD.

The phase change type optical disc uses the principle that information is recorded and erased by controlling the heating temperature and the cooling rate of the material forming the recording layer to induce a reversible change between the crystalline structure and the amorphous structure. Conventional phase change type optical discs generally have a first dielectric layer 21, a recording layer 22, a second dielectric layer 23, a reflective layer 24, and a protective layer on a transparent substrate 20 as shown in FIG. 3. It has a structure in which 25 is sequentially stacked. Here, a track in which a recording signal is made is formed in the recording layer. When the laser beam is irradiated, the recording layer is reversibly changed from crystalline to amorphous or from amorphous to crystalline to repeat recording and erasing.

This phase change type optical disk is easier to superimpose recording than other optical disks using other recording methods, shortens the wavelength of the laser light to increase the recording density of the optical disk, and also because the optical system of the drive drive is simple, DVD-RAM (Digital Video) Disk random access memory).

On the other hand, the thickness of each layer constituting the phase change type optical disk is preferably formed as thin as possible. In this way, when the thickness of each layer is thin, not only the manufacturing cost is reduced but also the productivity is improved. However, in the case of the recording layer or the dielectric layer, it is very difficult to change arbitrarily because the optical characteristic changes very sensitively with the change of thickness.

In the case of the Al alloy mainly used as the reflective layer of the conventional phase change type optical disk, if the thickness of the reflective layer is reduced to a predetermined value or less, the recording property is deteriorated, and Ag has a disadvantage of poor corrosion resistance. Therefore, the conventional reflective layer has a disadvantage that the thickness thereof is considerably thick, but it cannot satisfy all of the proper corrosion resistance, recording characteristics, and repeat recording durability.

Accordingly, an object of the present invention is to solve the above problems, the first reflective layer made of a metal or alloy having an electronegativity of 1.9 to 3.0 and the second reflective layer made of Cu, Ag or alloys thereof having higher thermal conductivity than the first reflective layer. It is to provide a phase change type optical disk having a good superposition recording characteristics and repeat recording durability without deterioration due to corrosion of the reflective layer even by applying a double reflective layer comprising a.

1 is a view schematically showing an information area of a general optical disc,

FIG. 2 is an enlarged cross-sectional view taken along the line A-A 'of FIG. 1,

3 is a schematic cross-sectional view of a general phase change type optical disk stack structure,

4 is a schematic cross-sectional view of a phase change type optical disk according to an aspect of the present invention;

5 is a diagram schematically showing a superposition recording process in a phase change type optical disc,

6 is a graph showing the shape of the multi-pulse of the laser beam used in the embodiment of the present invention,

7 is a SEM photograph of the surface of the Ag reflective layer that is corroded during the environmental test of the phase change type optical disk to which the Ag reflective layer is applied.

FIG. 8 is a diagram showing a waveform of a reproduction signal after recording on a phase change type optical disk having an Al-Ti single reflection layer (thickness 750 kPa) according to Comparative Example 10;

9 is a view showing a preferred waveform for Figure 8,

FIG. 10 is a diagram showing the results of analyzing the heating and cooling behavior of the phase change optical disk of the comparative example including the Al-Ti single reflection layer through thermal characteristic simulation.

11 shows the results of the environmental resistance test in the case of applying the Ag single reflective layer (■) and in the case of using the Al-Ti layer as the first reflective layer and the Ag layer as the second reflective layer (Example 10) (●). It's a graph,

FIG. 12 is a graph showing changes in superposition recording jitter value and repeat recording durability according to the thickness of the Al-Cr alloy single reflecting layer used for the discs of Comparative Examples 15 to 18. FIG.

13 is a graph showing a change in recording power according to the thickness of the Al-Cr alloy single reflecting layer used for the disks of Comparative Examples 15 to 18,

FIG. 14 is a graph showing changes in superposition recording jitter value and repeat recording durability according to the thickness of the Cu second reflection layer used in the disks of Examples 15 to 19 and Comparative Example 19;

Fig. 15 is a graph showing the change in the jitter value of the repeat proxy of the phase change type optical discs manufactured in Example 20 (■) and Comparative Examples 22 (o) and 23 (o).

* <Description of the symbols for the main parts of the drawings>

1: Information area 10 of an optical disc 10: Polycarbonate substrate

11: Feet 12: Reflective layer 13: Shield

20: substrate 21: first dielectric layer 22: recording layer

23: second dielectric layer 24: reflective layer 25: protective film

30: substrate 31: first dielectric layer 32: recording layer

33: second dielectric layer 34: first reflective layer 35: second reflective layer 36: protective layer

According to the above object, in the present invention, in the phase change type optical disk including a first dielectric layer, a recording layer, a second dielectric layer and a reflective layer sequentially formed on a transparent substrate, the reflective layer is a metal having an electronegativity of 1.9 to 3.0 or And a first reflection layer made of an alloy and a second reflection layer made of Cu, Ag, or an alloy thereof, wherein the first reflection layer is in close contact with the second dielectric layer, and the second reflection layer is formed of the first reflection layer and the protective layer. Provides a phase-change type optical disc characterized in that it is in close contact.

A feature of the present invention is the use of the first reflective layer and the second reflective layer having a higher thermal conductivity than the first reflective layer, thereby exhibiting good corrosion resistance and superimposed recording characteristics even at a thin thickness, while improving repeat recording durability and reducing material costs in actual production. It is also possible to get along.

Hereinafter, the present invention will be described in more detail.

As shown in FIG. 4, the phase change type optical disk according to the present invention has a first dielectric layer 31, a recording layer 32, a second dielectric layer 33, and a first reflective layer 34 on a transparent substrate 30. ), The second reflection layer 35, and the protective layer 36 are laminated in this order.

The substrate used in the present invention can be produced by a method such as injection molding using a stamper using polycarbonate or the like, which is commonly used as a substrate material for an optical disk. Grooves formed on the substrate are designed for the width and depth of the servo required for recording and playback, especially when recording and playing both land and grooves for higher density. In order to prevent cross talk, the depth of the grooves should be set to λ / 5n to λ / 7n (λ: recording / reproducing light wavelength, n: refractive index of polycarbonate substrate).

Since the dielectric layer of the present invention must have light transmission characteristics and thermal durability, the material constituting the dielectric layer is a metal oxide, metal carbide, metal nitride, or a mixture thereof having an absorption coefficient close to zero and excellent in thermal stability. Materials commonly used for phase change type optical disc dielectric layers include ZnS-SiO ₂ (8: 2), AlN, GeN, and the like, which can be made into dielectric layers by conventional methods such as RF-sputtering. have. The thickness is preferably 300 to 3000 mV for the first dielectric layer and 50 to 500 mV for the second dielectric layer.

In the recording layer of the present invention, a material that can be easily amorphous and crystallized within a short time is used. Ge-Sb-Te, In-Sb-Te, Ag-In-Sb-, which are commonly used in the recording layer of a phase change type optical disk, are used. Chalcogen compounds, such as Te, Cr-Ge-Sb-Te alloy, and N-Ge-Sb-Te alloy, are used, and additional additive elements are sometimes introduced to improve properties. The recording layer may be formed into a recording layer by forming a film by a conventional method such as DC (direct current) sputtering. The thickness is preferably 100 to 1000 mm 3.

In the reflective layer, a metal material is used to improve the heat absorption effect and the light efficiency of the recording layer in amorphous form, and mainly a single element such as Al, Ag, Au, Cu or Cr, for recording sensitivity and oxidation resistance, Alloys containing small amounts of Ni, Ti, Si, Mg (e.g. Al-Ti (1.5 wt% Ti), Al alloys such as Al-Cr (Cr 2 atomic%), Ag such as Ag-Al, Ag-Mg Alloys, etc.) are used.

In the optical disk of the present invention, the first reflective layer forming material does not cause chemical reaction with the dielectric layer and uses a single metal or alloy having an electronegativity of 1.9 to 3.0, and the second reflective layer material has a thermal conductivity higher than that of the first reflective layer. High Cu, Ag or alloys thereof are used.

Specific examples of the first reflective layer forming material include Al, Au, W, Mo, Ni, Ge, Si, Pd, Sn, Rh, Pt, alloys thereof, and the like. In addition, the alloys used in the formation of the first and second reflection layers include Al, Au, Cu, Ag, W, Mo, Ni, Ge, Si, Fe, Cr, Co, Zr, Zn, Ti, Ta, Mg A metal component selected from the group consisting of, Pd, V, Nb, Hf, Sn, Sc, Rh, Pt, Mn and combinations thereof is added as the second component.

In general, the function required for the reflective layer is to cool the recording layer fast enough so that it can become amorphous during recording, and to allow it to be kept above a certain temperature for the time required for crystallization during erasing. In addition, it must have sufficient reflection characteristics for optical efficiency. It is Al alloy that has all these functions and is commonly used. However, in this case, there is a disadvantage in that the repeating proxy signal characteristic is degraded due to the thermal load applied to the reflective layer. As a result, Ag or Cu, which is a high thermal conductivity material, has been proposed, but both have problems in that the erase characteristic is not properly secured due to excessive thermal conductivity or a chemical reaction occurs with the dielectric layer.

In the present invention, the first reflective layer is a barrier for imparting cooling characteristics necessary for amorphization and crystallization, and thermal properties that can be maintained above a specific temperature, and inhibiting chemical reaction with the dielectric layer of the second reflective layer such as Ag or Cu. (barrier) to play a role. On the other hand, the second reflective layer to which a high thermal conductivity material such as Ag or Cu is applied serves to mitigate the thermal load imposed on the first reflective layer.

The thickness of the appropriate reflective layer depends on the combination of the materials constituting the selected first and second reflecting layers, the configuration of the recording layer and the recording flux, the type, composition and thickness of the dielectric layer. For example, when the recording layer is made of an Ag-In-Sb-Te alloy, a W, Si, Al alloy is used as the first reflection layer, and a Cu, Ag or Ag alloy is used as the second reflection layer, The thickness is 10 kPa or more, preferably 100 kPa or more, and the thickness of the second reflective layer is 250 kPa or more, preferably 450 kPa or more.

In the case where a Ge-Sb-Te alloy as a recording layer, an Al or Al alloy as a first reflection layer, and Cu or Ag as a second reflection layer are used for an optical disc for DVD-RAM, recording is performed under a recording flux of 6 m / s. When the characteristics were evaluated, the sum of the thicknesses of the first reflective layer and the second reflective layer is preferably 2000 GPa or less. The thickness of the first reflective layer is 1300 GPa or less, and the thickness of the second reflective layer is 10 GPa or more. The effect can be obtained. It is preferable that the thickness of a 2nd reflective layer is less than 800 GPa. In addition, when the type, composition, recording flux, etc. of the recording layer are changed, the effective reflective layer thickness also changes.

The thickness of each layer is preferably designed in combination so that the difference in reflectance when the recording layer is in an amorphous state and reflectance when in a crystalline state can be realized by 10% or more in order to exhibit sufficient modulation signal characteristics. In addition, it should be designed to have heating and cooling characteristics such that the recording layer can be kept above the crystallization temperature for a time required for crystallization during erasing while being sufficiently quenched to form a uniform amorphous mark as described above. At this time, the proper heating and cooling characteristics of the disk may be varied depending on the amorphous rate and the crystallization rate of the recording layer. Therefore, the appropriate thickness combination should be set in consideration of their correlation.

When recording simultaneously to land and groove, in order to suppress the phase difference caused by the difference in refractive index between the recorded amorphous mark and the crystal state matrix of the unrecorded portion and the decrease in signal amplitude caused by the interference caused by the phase difference, It is additionally necessary to design each layer thickness so that the reflectance is close to zero or the difference between the signal amplitude in the groove and the signal amplitude in the land caused by these interferences is minimized.

In addition, in order to shorten the production time of material costs in actual production, it is advantageous that the thickness of each layer is as thin as possible so that various properties are in a good range.

UV protective resin etc. are used normally as a protective layer.

In the phase change type optical disc of the present invention, the superimposed recording process is schematically shown in FIG. A high power laser beam is irradiated onto the recording layer to locally melt the recording layer, and then quenched to form an recording mark by amorphizing the irradiated portion. The recording mark here corresponds to a pit formed along the track of the reproduction-only optical disc. When the thus formed recording mark is irradiated with a laser beam having an output of about 1/3 to 1/2 of the power at the time of recording, a crystalline structure which is an erase area is formed to erase the recorded information. In order to make the shape of the recording mark uniform, it is preferable to use a multi pulse consisting of a series of several short pulses as the recording pulse.

In order to obtain good reproduction signal characteristics even after superimposing recording, an amorphous mark of uniform shape must be formed during recording and this amorphous mark must be sufficiently crystallized during erasing. In addition, the grain size of the recrystallized region should be as uniform as possible. In other words, the reflective layer takes away the heat of the portion of the recording layer melted by the laser incident light at a high speed, thereby helping to form the amorphous mark by having the melting portion of the recording layer have a high cooling rate.

In order to form a uniform amorphous mark, first, the recording layer heated above the melting point must be quenched. However, if the cooling rate is too fast, it may not be erased properly because it is not maintained for as long as necessary for crystallization during erasing. In other words, if the cooling rate of the recording layer is slow, recording is not performed properly. On the contrary, if the recording layer is too fast, erasing is not performed properly. For this reason, it is very important to design the cooling rate within the range in which both recording and erasing can be performed well in the structure design of the phase change type optical disk.

In phase change optical disks, the cooling rate is mainly determined by the thermal conductivity and thickness of each layer. Therefore, a good combination of the thickness and the selection of each of these layer materials can be achieved to show good overlapping recording characteristics. As an indicator of the superposition recording characteristic, jitter which means time deviation of the reproduction signal is used, and the lower the jitter, the better the signal characteristic.

Another characteristic required for a phase change optical disk is repeat recording durability. This means that deterioration does not occur in the reproduction signal characteristics even after repeated recording and erasing. It is known that deterioration due to repetitive recording in a phase change type optical disc is mainly caused by deformation or precipitation of the recording layer due to accumulation of thermal load. Therefore, in order to suppress deterioration, it is necessary to reduce this heat load as much as possible. This case also depends on the cooling characteristic of the recording layer, similarly to the above-mentioned superposition recording characteristic.

In this way, the physical properties of the reflective layer, which serves to cool the recording layer, play an important role in the recording characteristics of the optical disc. In the present invention, the reflective layer is constituted by a double layer to impart appropriate thermal characteristics.

The present invention will be described in detail with reference to Examples, but the present invention is not limited only to the following Examples.

Examples 1 to 15 and Comparative Examples 1 to 14 manufactured CD double-speed flux-change optical disks and evaluated their characteristics. Various performance evaluation of the optical disk manufactured therefrom was carried out by the following method:

(1) corrosion resistance

After leaving the sample for 100 hours at a temperature of 25 to 85 ° C. and a relative humidity of 50 to 95%, the recording and reproducing conditions were evaluated.

(2) recording characteristics

The optical disc was mounted on a CD-RW dedicated dynamic characteristic evaluator (manufactured by APEX, model name: Modular Media Tester (MMT)), and then rotated at 2.4 m / s to evaluate recording characteristics. At this time, the pulses of the laser beam for recording were multi-pulsed as shown in Fig. 6, and the recording power and the erasing power were fixed at 12.5 mW and 6.25 mW. At this time, the wavelength of the light source used was 780nm, NA of the objective lens was 0.55.

Initial recording characteristics were expressed as jitter values in one recording, and when the jitter value exceeded 20ns, it was determined that the recording signal characteristics were poor.

The superimposed recording characteristics were represented by jitter values when recorded 10 times, and when the jitter values exceeded 20ns, it was determined that the recording signal characteristics were poor.

Repeat recording endurance is an observation of recording characteristics deterioration while repeating recording and erasing. When multiple recordings are performed, the jitter value starts to increase to over 50% of the overlapping jitter value, that is, the jitter value after 10 overlapping recordings. The number of records is shown.

Example 1

By injection molding using a stamper, a 1.2 mm thick polycarbonate disk substrate was formed in which a spiral groove having a depth of 500 mm was formed.

ZnS-SiO ₂ (8: 2) was RF sputtered on the groove forming surface of the disk substrate to form a first dielectric layer having a thickness of 950 kPa. Subsequently, an Ag—In—Sb—Te alloy thin film was formed on the first dielectric layer to have a thickness of 200 μs by DC sputtering. Subsequently, ZnS-SiO ₂ (8: 2) was again RF sputtered to form a second dielectric layer having a thickness of 250 GPa, and then an Al-Ti alloy (Al 98.5 wt%, 1.5 wt% Ti) first reflective layer was formed to have a thickness of 50 GPa. It was. Thereafter, Ag was sputtered on top of the Al-Ti first reflection layer to form a second reflection layer having a thickness of 500 kHz. UV protective resin (brand name: SD17: DIC) was spin-coated as a protective layer.

In order to initialize the phase change type optical disk, the recording layer was crystallized by irradiating a semiconductor laser beam (wavelength: 830 nm) while rotating the disk on a high speed initialization device (POP-120, manufactured by Hitachi).

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 1.

Examples 2 and 3

Al-Ti alloy (98.5 weight% of Al, 1.5 weight% of Ti) It carried out by the same method as Example 1 except having set the thickness of the 1st reflective layer to 30 kPa and 10 kPa, respectively.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 1.

Example 4

The Al-Ti alloy (Al 98.5 wt%, Ti 1.5 wt%) was used as the first reflection layer in the same manner as in Example 1, except that Ag was formed to a thickness of 10 kPa and the second reflection layer was formed to be 250 kPa. .

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 1.

Example 5

The Al-Ti alloy (Al 98.5 wt%, Ti 1.5 wt%) was used as the first reflective layer in the same manner as in Example 1 except that 100 Ag was formed in the thickness of the second reflective layer. .

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 1.

Comparative Examples 1 to 7

The same procedure as in Example 1 was conducted except that only a single Ag reflective layer having a thickness of 1000 mV, 750 mV, 500 mV, 300 mV, 250 mV, 200 mV and 150 mV was formed without making the double layer.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 1.

Comparative Examples 8 to 12

The same method as in Example 1, except that a single reflective layer was formed without using the reflective layer as a double layer and forming only a single reflective layer having a thickness of 1500 mW, 1000 mW, 750 mW, 500 mW and 300 mW, respectively. It was carried out according to.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 1.

Comparative Examples 13 and 14

An optical disc of the present invention was prepared in the same manner as in Example 1 except that the thicknesses of the Al-Ti first reflection layer and the Ag second reflection layer were changed as shown in Table 1.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 1.

When the Al-Ti first reflection layer and the silver reflection layer were used (Comparative Example 13) and when the Cu first reflection layer and the second silver reflection layer were used (Comparative Example 14), the thickness of the second reflection layer was too thin. Good, but initial recording jitter value is higher than 20ns and poor recording signal characteristics

First (or single) reflector layer Second reflective layer Corrosion resistance Record Signal Characteristics Initial recording jitter (ns) material Thickness material Thickness Example 1 Al-Ti 50 Ag 500 Good Good 12 Example 2 Al-Ti 30 Ag 500 Good Good 12 Example 3 Al-Ti 10 Ag 500 Good Good 12 Example 4 Al-Ti 10 Ag 250 Good Good 13 Example 5 Al-Ti 100 Ag 400 Good Good 14 Comparative Example 1 Ag 1000 - - Bad Good 21 Comparative Example 2 Ag 750 - - Bad Good 19 Comparative Example 3 Ag 500 - - Bad Good 15 Comparative Example 4 Ag 300 - - Bad Good 18 Comparative Example 5 Ag 250 - - Bad Good 19 Comparative Example 6 Ag 200 - - Bad Bad 34 Comparative Example 7 Ag 150 - - Bad Not measurable - Comparative Example 8 Al-Ti 1500 - - Good Good 19 Comparative Example 9 Al-Ti 1000 - - Good Good 19 Comparative Example 10 Al-Ti 750 - - Good Bad 23 Comparative Example 11 Al-Ti 500 - - Good Not measurable - Comparative Example 12 Al-Ti 300 - - Good Not measurable - Comparative Example 13 Al-Ti 10 Ag 200 Good Bad 21 Comparative Example 14 Cu 10 Ag 200 Good Bad 23

As can be seen from the results of Table 1, the phase change type optical disks of the present invention according to Examples 1 to 9 had not only good recording signal characteristics and corrosion resistance but also very good initial recording jitter characteristics of 15 ns or less. .

On the other hand, when only one Ag reflective layer was formed, the Ag reflective layer had a thickness of 750 GPa or less, which is preferable in terms of productivity due to good recording characteristics, but poor in corrosion resistance. ) Has poor recording signal characteristics, initial recording characteristics and corrosion resistance. 7 is a SEM photograph of the surface of the corroded reflective layer during the environmental test of the phase change type optical disk to which the Ag single reflective layer is applied according to Comparative Example 3.

Further, when the Al-Ti reflective layer has a thickness of 1000 GPa or more (Comparative Examples 8 and 9), the corrosion resistance and the recording signal characteristics are good, but not only in terms of productivity, but also the initial recording characteristics are poor compared to those of the present invention. When the thicknesses of the Al-Ti reflecting layers were 750, 500, and 300 microseconds (Comparative Examples 10 to 12), the recording signal characteristics, initial recording jitter characteristics, and optical characteristics were all poor.

FIG. 8 is a diagram showing a waveform of a reproduced signal after recording on a phase change type optical disk having an Al-Ti single reflective layer (thickness 750 kPa) according to Comparative Example 10, which is different from the preferred waveform shown in FIG. Can be.

On the other hand, Figure 10 is a graph analyzing the thermal cooling behavior according to the Al-Ti reflective layer thickness in the phase change type optical disk having an Al-Ti reflective layer according to Comparative Examples 8 to 12, which was used in this simulation Physical properties and optical constants of each layer are shown in Table 2 below.

Each layer material Complex refractive index (780 nm) Thermal Conductivity (Joule / cm / sec / ℃) Specific heat (Joule / cm 3) First and second dielectric layers ZnS-SiO ₂ 2.05 + 0.00i 0.006 2.055 Recording layer Ag-In-Sb-Te 4.13 + 4.68i 0.0055 1.292 Reflective layer Al-Ti 2.54 + 7.82i 1.1 2.464

Referring to FIG. 10, it can be seen that as the thickness of the Al alloy reflective layer decreases, the cooling curve gradually decreases. Amorphization generally takes place at the point of cooling below the melting point after melting, at which time the cooling rate should be sufficient to allow for amorphous. However, decreasing the thickness of the Al alloy reflective layer means that the cooling rate of the recording layer is reduced by that amount, and if the cooling rate is reduced such that the recording layer is lower than the critical cooling rate necessary for amorphousization, the recording layer is not amorphous even if it is melted. Eventually there is a greater chance of crystallization. Therefore, it is not preferable because the recording characteristics become poor.

As can be seen from the above results, when only the existing Al-Ti alloy layer is used as a single reflecting layer, the thickness must be 1000 Å or more, which is disadvantageous in the manufacturing process. On the other hand, when the reflective layer is composed of a double layer as in the present invention, the physical properties are excellent even in a relatively thin thickness.

Example 6

By injection molding using a stamper, a 1.2 mm thick polycarbonate disk substrate was formed in which a spiral groove having a depth of 500 mm was formed.

ZnS-SiO ₂ (8: 2) was RF sputtered on the groove forming surface of the disk substrate to form a first dielectric layer having a thickness of 950 kPa. Subsequently, an Ag—In—Sb—Te alloy thin film was formed on the first dielectric layer to have a thickness of 200 μs by DC sputtering. Subsequently, ZnS-SiO ₂ (8: 2) was again RF sputtered to form a second dielectric layer with a thickness of 250 GPa, and then the Al-Ti first reflection layer was formed to a thickness of 500 GPa by the sputtering method. Finally, the Ag second reflection layer was formed into a film with a thickness of 500 GPa using DC sputtering. UV protective resin was spin-coated as a protective layer.

In order to initialize the phase change type optical disk, the recording layer was crystallized by irradiating a semiconductor laser beam (wavelength: 830 nm) while rotating the disk on a high speed initialization device (manufactured by Hitachi).

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 3.

Examples 7-11

An optical disk of the present invention was produced in the same manner as in Example 6 except that the thicknesses of the Al-Ti first reflection layer and the Ag second reflection layer were changed as shown in Table 3.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 3.

Examples 12 and 13

An optical disc of the present invention was produced in the same manner as in Example 6 except that the thicknesses of the W first reflecting layer and the Ag second reflecting layer were changed as shown in Table 3.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 3.

Example 14

An optical disk of the present invention was prepared in the same manner as in Example 10 except that the thicknesses of the Si first reflection layer and the Ag second reflection layer were changed as shown in Table 3.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 3.

First reflection layer Second reflective layer Corrosion resistance Record Signal Characteristics Initial recording characteristic (jitter / ns) Repeat Record Durability material Thickness material Thickness Example 6 Al-Ti 500 Ag 500 Good Good 19 > 2,000 Example 7 Al-Ti 400 Ag 500 Good Good 18 > 2,000 Example 8 Al-Ti 300 Ag 500 Good Good 19 > 2,000 Example 9 Al-Ti 200 Ag 500 Good Good 18 > 2,000 Example 10 Al-Ti 100 Ag 500 Good Good 18 > 1,800 Example 11 Al-Ti 100 Ag 450 Good Good 14 > 900 Example 12 W 100 Ag 500 Good Good 18 > 2,000 Example 13 W 500 Ag 500 Good Good 18 > 2,000 Example 14 Si 100 Ag 500 Good Good 18 > 1,100

As can be seen from Table 3, when the Ag layer is used as the second reflection layer and the Al-Ti layer is the first reflection layer according to the present invention, and the thickness is 100 kPa and 450 kPa, respectively, the corrosion resistance and the recording signal characteristics And not only the excellent initial recording characteristics, but also the repetitive recording durability was excellent.

11 is a diagram showing the results of an environmental test performed at 80 ° C. and 85% RH when an Ag single reflecting layer was applied (■) and when an Al-Ti layer was applied as the first reflective layer according to Example 10 (●). . In the case of the present invention, the jitter value is constant with time, whereas in the case of using an Ag monolayer, the jitter value increases rapidly after 10 hours.

Examples 15 to 20 and Comparative Examples 15 to 18 fabricated phase change optical disks for DVD-RAM and evaluated their characteristics. Various performance evaluation of the optical disk manufactured therefrom was carried out by the following method:

The optical disk was mounted on a dynamic characteristic evaluator (manufactured by Nakmichi, model name: OMS-2000), and then rotated at 6.0 m / s to evaluate recording characteristics. At this time, the shape of the pulse of the laser beam for recording was based on the DVD-RAM standard 1.0 (published by: DVD Forum). The wavelength of the light source used was 680 nm, and the NA of the objective lens was 0.60.

The superimposed recording characteristics were represented by jitter values during 10 recordings, and the repeated recording durability was observed by degrading recording characteristics while repeating recording and erasing. In other words, the number of recordings that started to increase to 50% or more of the jitter value after 10 overlapping recordings was shown.

P _p (mW) represents the power required for recording. In the overall judgment, the superimposed recording jitter value was 4.0 ns or less, the repeated recording durability was 100,000 or more, and a good value (o) was set.

Example 15

By injection molding using a stamper, a 0.6 mm thick polycarbonate disk substrate was formed in which a spiral groove having a depth of 70 nm was formed. At this time, the distance between the groove of the substrate and the adjacent groove is 1.48 μm, and the distance between the groove and the land is 0.74 μm corresponding to 1/2 thereof, and a header pit for address detection of each sector in the middle of the groove is provided. Was formed. Further, each groove was formed with a bend such that a wobble signal of the same frequency could be detected.

ZnS-SiO ₂ (8: 2) was RF sputtered on the groove-forming surface of the polycarbonate substrate to form a first dielectric layer having a thickness of 950 kPa. Subsequently, a Ge—Sb—Te alloy thin film was formed on the first dielectric layer to a thickness of 200 μs by DC sputtering. Subsequently, ZnS-SiO ₂ (8: 2) was again RF sputtered to form a second dielectric layer having a thickness of 140 kHz.

An Al—Cr first reflection layer was formed on the second dielectric to have a thickness of 500 kHz by RF sputtering. Finally, the Cu 2nd reflective layer was formed into a film with a 400-micrometer thickness using DC sputtering method. UV resin was spin-coated as a protective layer.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 4.

Examples 16-19

An optical disk of the present invention was manufactured in the same manner as in Example 1 except that the thicknesses of the Al-Cr first reflection layer and the Cu second reflection layer were changed as shown in Table 4.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 4.

Comparative Examples 15 to 18

The same procedure as in Example 16 was carried out, except that only a single reflective layer of 500-, 1000-, 1500-, and 2000-nm Al-Cr alloys (Al: 98at%, Cr: 2at%) was formed without double reflection layers. It was.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 4.

Comparative Examples 19 to 21

An optical disk of the present invention was prepared in the same manner as in Example 15 except that the thicknesses of the Al-Cr first reflection layer and the Cu second reflection layer were changed as shown in Table 4.

The characteristics of the manufactured optical disc were evaluated and the results are shown in Table 4.

First (single) reflector Second reflective layer Overwrite Jitter (ns) Repeat recording durability (times) P _P (mW) Judgment material Thickness material Thickness Example 16 Al-Cr 500 Cu 400 3.7 120,000 12.0 ○ Example 17 Al-Cr 500 Cu 500 3.8 120,000 12.6 ○ Example 18 Al-Cr 500 Cu 600 3.9 130,000 12.6 ○ Example 19 Al-Cr 1000 Cu 500 3.7 100,000 13.1 ○ Example 20 Al-Cr 500 Cu 700 4.0 140,000 12.6 ○ Comparative Example 15 Al-Cr 500 - - 3.8 2,000 10.8 × Comparative Example 16 Al-Cr 1000 - - 3.7 2,000 12.0 × Comparative Example 17 Al-Cr 1500 - - 3.6 50,000 12.2 × Comparative Example 18 Al-Cr 2000 - - 3.6 70,000 13.0 × Comparative Example 19 Al-Cr 500 Cu 800 4.7 - 12.6 × Comparative Example 20 Al-Cr 500 Cu 1000 4.6 - 12.8 × Comparative Example 21 Al-Cr 1500 Cu 500 3.8 50,000 12.2 ×

As can be seen from Table 4, according to the present invention, when Al-Cr is used as the first reflection layer and Cu is used as the second reflection layer, better corrosion resistance, recording signal characteristics, and initial recording than when only Al-Cr single reflection layer is used. Properties and repeat recording durability were shown.

FIG. 12 is a graph showing overlapping recording jitter and repeatable recording durability according to the thickness of the reflective layer of the optical disc employing the Al-Cr alloy single reflective layer according to Comparative Examples 15 to 18. FIG. In this case, even if the thickness is 2000Å or more, the repeat recording durability is only about 70,000 times. FIG. 13 is a graph showing the recording power according to the thickness of the reflecting layer of the optical disk employing the Al-Cr alloy single reflecting layer according to Comparative Examples 15 to 18. As the thickness increases, the power required for recording also increases, which is disadvantageous for practical use. Able to know. In addition, if the thickness of the reflective layer is excessively large, an increase in the material cost and an increase in the required deposition time causes a problem of reduced productivity. In addition, even in the case of employing the double reflecting layer, in the case of Comparative Examples 19 to 21, the thickness of each reflecting layer is out of the preferable range, and thus there is a disadvantage that the superimposition jitter value is high or the repeat recording durability is poor.

In contrast, in the case of employing the double reflective layer according to the present invention, as shown in Fig. 14, even if the Cu layer thickness is only 400 ns (total 900 ns of double reflecting layer thicknesses), it is possible to obtain repeat recording durability of 100,000 or more times. In addition, when the Cu thickness is limited to about 700 GPa or less, good superposition recording characteristics of jitter 4.0 GPa or less are exhibited. As a result, good repeat recording durability and overlapping recording characteristics can be exhibited, and material cost reduction and productivity improvement can be obtained.

Example 21

The composition of the GeSbTe recording layer is a composition around GeSb ₂ Te ₄ , a 500 Å thick AlCr alloy (Cr 2.0at%) as the first reflective layer and a 100 Å thick Cu layer as the second reflective layer, and a header pit as the substrate. ) And the optical disc of the present invention was produced in the same manner as in Example 16 except that the wobble was not formed.

Comparative Example 22

An optical disk was manufactured in the same manner as in Example 20 except that only a 500 µm thick AlCr alloy was used as the single reflective layer.

Comparative Example 23

An optical disk was produced in the same manner as in Example 21 except that a Cu layer having a thickness of 200 Hz was used as the second reflective layer.

The phase change type optical discs prepared in Example 20 (■) and Comparative Examples 22 (●) and 23 (▲) were recorded under the same conditions as the method disclosed in Example 16 except that the recording flux was 8.2 m / s. Then, the width jitter value of the reproduction signal corresponding to 3Tw was measured, and the result is shown in FIG. As can be seen from this, when the recording layer composition and the recording conditions are different, it shows a good effect even when the Cu second reflecting layer is 100 ms, and when the thickness is 200 ms, the jitter value is rather high.

The phase change type optical disc of the present invention exhibits excellent corrosion resistance, superimposed recording characteristics, and repeatable recording durability, and is therefore suitable as a slow ring type optical disk.

Claims (10)

In a phase change type optical disc including a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer sequentially formed on a transparent substrate, the reflective layer includes a first reflective layer and a Cu or a metal having an electronegativity of 1.9 to 3.0 and an alloy. And a second reflection layer made of Ag or an alloy thereof, wherein the first reflection layer is in close contact with the second dielectric layer, and the second reflection layer is in close contact with the first reflection layer and the protective layer. Changeable optical discs. The method of claim 1, And the first reflection layer is formed of a material selected from the group consisting of Al, Au, W, Mo, Ni, Ge, Si, Pd, Sn, Rh, Pt, and alloys thereof. The method of claim 2, The alloy is Al, Au, Cu, Ag, W, Mo, Ni, Ge, Si, Fe, Cr, Co, Zr, Zn, Ti, Ta, Mg, Pd, V, Nb, Hf, Sn, Sc, Rh And a metal component selected from the group consisting of Pt, Mn and mixtures thereof as a second component. The method of claim 1, Cu or Ag alloy forming the second reflection layer is Al, Au, Cu, Ag, W, Mo, Ni, Ge, Si, Fe, Cr, Co, Zr, Zn, Ti, Ta, Mg, Pd, V, Nb And a metal component selected from the group consisting of Hf, Sn, Sc, Rh, Pt, Mn and mixtures thereof as a second component. The method of claim 1, The recording layer is made of an Ag-In-Sb-Te alloy, the first reflection layer is made of a W, Si, or Al alloy having a thickness of 10 GPa or more, and the second reflection layer is made of a Cu, Ag, or Ag alloy having a thickness of 250 GPa or more. Phase change type optical disk characterized by. The method of claim 5, And a thickness of the first reflection layer is 100 GPa or more, and a thickness of the second reflection layer is 450 GPa or more. The method of claim 1, And the recording layer is made of a Ge-Sb-Te alloy, the first reflecting layer is made of Al or an Al alloy, and the second reflecting layer is made of Cu or Ag. The method of claim 1, A phase change type optical disc, characterized in that the total thickness of the two reflective layers is less than 2000Å. The method of claim 8, And a thickness of the first reflective layer is 1300 GPa or less, and a thickness of the second reflective layer is 10 GPa or more. The method of claim 9, A phase change type optical disc, wherein the thickness of the second reflection layer is less than 800 mm 3.