KR20010010365A - Phase change optical disc - Google Patents

Abstract

PURPOSE: A phase changed type optical disk is provided to improve the corrosion resistance, the overlapped recording characteristic, the cross erase characteristic and a repeated recording durability by introducing a corrosion resistant inserting layer between an upper dielectric layer and a reflecting layer. CONSTITUTION: A phase changed type optical disk comprises first/second lower dielectric layers(31,32), a recording layer(33), an upper dielectric layer(34), a corrosion resistant inserting layer(35), first/second reflecting layers(36,37) and a protecting layer(38) on a transparent substrate(30). A material of the corrosion resistant inserting layer is an oxide or a nitride such as ZnS-SiO2, AlN, Si3N4, Al2O3 and so on. The materials are not reacted with Ge/N/Al alloys. A thickness of the corrosion resistant inserting layer is 50-500angstroms. The corrosion resistant inserting layer is formed by an RF(Radio Frequency) sputtering method.

Description

Phase change type optical disc {PHASE CHANGE OPTICAL DISC}

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. Relates to a fluorescent disk.

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), the step of replicating the transparent resin substrate in a large amount by the manufactured stamper and the step of forming a thin film such as a reflective layer thereon. The stamper is made by first producing a glass master having the same format as the optical disk, and then plating Ni thereon. 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-ROM 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. 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).

As an example of the development of a phase change type optical disk, PCT Patent Application Publication No. WO97 / 34298 discloses a ZnS-SiO forming a lower dielectric layer by further forming a GeN dielectric insertion layer between a recording layer and a ZnS-SiO ₂ dielectric layer underneath. _It is disclosed that sulfur, which is a member of ₂ , is suppressed from being diffused into the recording layer, and the crystallization of the recording layer is promoted by using GeN in the dielectric layer on the recording layer. However, in this case, corrosion resistance and repeated recording durability are significantly reduced. There is this.

Accordingly, an object of the present invention is to form a lower dielectric layer into a double layer in order to solve the above problems, and to introduce a corrosion resistant insertion layer between the upper dielectric layer and the reflective layer, thereby providing corrosion resistance, superimposed recording characteristics, cross erasing characteristics, and repeatable recording durability. All of these provide an improved phase change type optical disk.

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,

4 is a schematic cross-sectional view of a phase change optical disk of the present invention;

5 is a graph showing the recording characteristics of the phase change type optical disks prepared according to Example 1 and Comparative Example 1,

FIG. 6 is a graph showing recording characteristics of phase change type optical disks prepared according to Comparative Examples 1, 6, and 7. FIG.

* <Explanation of symbols for main parts of drawing>

1: Information area of the optical disc

DESCRIPTION OF SYMBOLS 10 Polycarbonate substrate 11: Feet 12: Reflective layer 13: Protective film

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

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

30: substrate 31: first lower dielectric layer 32: second lower dielectric layer

33: recording layer 34: upper dielectric layer 35: corrosion resistant insertion layer

36: first reflection layer 37: second reflection layer 38: protective layer

In accordance with the above object, in the present invention, in a phase change optical disk including a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective layer sequentially formed on a transparent substrate, the lower dielectric layer has a double layer structure and is disposed between the upper dielectric layer and the reflective layer. Provided is a phase change type optical disk, wherein the corrosion resistant insertion layer is formed.

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

As shown in FIG. 4, a phase change type optical disc according to an aspect of the present invention has a first lower dielectric layer 31, a second lower dielectric layer 32, and a recording layer 33 on a transparent substrate 30. The upper dielectric layer 34, the corrosion resistant insertion layer 35, the first reflective layer 36, the second reflective layer 37, and the protective layer 38 are sequentially stacked.

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. The dielectric layer of the phase change type optical disc of the present invention includes a lower dielectric layer formed below the recording layer and an upper dielectric layer formed above the recording layer, wherein the lower dielectric layer is formed on the first lower dielectric layer and the first lower dielectric layer. It consists of two lower dielectric layers.

Suitable materials for use in the lower dielectric layer include ZnS-SiO ₂ , AlN, GeN, silicon oxide, silicon nitride, aluminum oxide, metal oxides, metal carbides, mixtures thereof, and the like, including RF sputtering, The dielectric layer may be manufactured by conventional methods such as reactive sputtering. The thickness is preferably 500 to 3000 mV for the first lower dielectric layer, 10 to 500 mV for the second lower dielectric layer, and 10 to 500 mV for the upper dielectric layer. Preferably the first lower dielectric layer is ZnS-SiO ₂ and the second lower dielectric layer is made of GeN or silicon nitride.

The upper dielectric layer is preferably GeN, silicon nitride, or the like, and may also be formed by conventional methods such as radio-frequency sputtering.

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, alloys, Cr-Ge-Sb-Te alloys and N-Ge-Sb-Te alloys 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, etc. (e.g., Al-Ti (1.5 wt% Ti), Al alloys such as Al-Cr (Cr 2 atomic%), Ag alloys such as Ag-Al, Ag-Mg, etc. ) Is used. In this case, it is preferable that the reflecting layer is made of a first reflecting layer and a second reflecting layer having a higher thermal conductivity than the first reflecting layer, and it is particularly preferable that the first reflecting layer is Al alloy and the second reflecting layer is Cu. Further, the total thickness of the two reflective layers is preferably 2000 kPa or less, more preferably 1300 kPa or less, and the thickness of the second reflective layer is 350 to 700 kPa.

In the present invention, a corrosion resistant insertion layer is formed between the reflective layer and the upper dielectric layer. Materials used in the corrosion resistant interlayers include oxides or nitrides such as ZnS—SiO ₂ , AlN, Si ₃ N ₄ , Al ₂ O ₃ , which are known to not react with Ge, N, or Al alloys. The corrosion resistant insertion layer has a thickness of 50 to 500 kPa. The corrosion resistant interlayer can be deposited by conventional methods such as RF sputtering.

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 a phase change type optical disc, a laser beam of high power is irradiated to the recording layer, the recording layer is locally melted, and then quenched, and the irradiated portion is amorphous to form a recording mark. 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 characteristics of the recording layer, similarly to the above-mentioned superposition recording characteristics, and it is advantageous to have a quench structure as much as possible.

In addition, there is a cross erase prevention characteristic. The cross erase phenomenon occurs when the track interval at which information is recorded for high density recording to increase the information storage capacity, and means that the recording marks of adjacent tracks are erased by the row of the track in which recording is performed. In order to prevent this, it is necessary to suppress heat diffusion to adjacent tracks. This case also depends on the cooling rate of the recording layer, such as repeat durability, and it is advantageous to have a quench structure.

In summary, it can be seen that even if the cooling structure of the disc is designed within the range of good overlapping recording, the improvement of the repeat recording durability and the cross erase characteristic can be limited to some extent.

As described above, the conventional phase change type optical disc has a problem in that the repetitive recording endurance and the cross erase characteristic cannot be improved by a certain level or more when each layer of the disc is designed in a range showing good overlap recording characteristics. That is, when the disc cooling structure is designed as a quench structure in order to improve the repeat recording durability and cross erase characteristics, there is a problem that the erasure is not particularly realized when the superimposed recording characteristics are implemented. This is due to the insufficient crystallization temperature and its holding time necessary for erasing the recorded amorphous marks as described above due to the high cooling rate. Therefore, it is important to maintain a good superimposition characteristic while having a high cooling structure.

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

Example 1

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 space | interval between the groove of a board | substrate and an adjacent groove was 1.40-1.48 micrometers, and the space | interval between a groove and a land was 0.70-0.74 micrometer corresponding to 1/2. 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 disk substrate to form a first lower dielectric layer with a thickness of 830 Å. Reactive sputtering of Ge alloys (GeMo, GeCr, etc.) and N ₂ was formed thereon to form a GeN second lower dielectric layer having a thickness of 200 kHz.

Subsequently, a Ge—Sb—Te based alloy thin film is formed on the second lower dielectric layer by DC sputtering to a thickness of 200 μs, and a GeN upper dielectric layer having a thickness of 100 μs is formed on the ZnS-SiO on the same method as described above. ₂ (8: 2) was RF sputtered to form a corrosion resistant insertion layer at 100 kPa.

Subsequently, an AlCr first reflection layer and a Cu second reflection layer were formed to have a thickness of 300 mW and 700 mW by DC sputtering, respectively. The protective layer was cured after spin coating a UV curable resin (trade name: SD17: DIC).

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.

Example 2

The same procedure as in Example 1 was carried out except that the thicknesses of the AlCr first reflection layer and the Cu second reflection layer were both 500 kPa.

Comparative Example 1

The same procedure as in Example 1 was conducted except that the ZnS-SiO ₂ corrosion resistant insertion layer was not formed.

Comparative Example 2

The same process as in Example 1 was conducted except that the GeN second lower dielectric layer and the ZnS-SiO ₂ corrosion resistant insertion layer were not formed.

Comparative Example 3

The same process as in Example 1 was conducted except that the ZnS-SiO ₂ first lower dielectric layer and the ZnS-SiO ₂ corrosion resistant insertion layer were not formed.

Comparative Example 4

The same procedure as in Example 1 was carried out except that the thickness of the GeN second lower dielectric layer was 50 mW, without forming a ZnS-SiO ₂ corrosion resistant insertion layer.

Comparative Example 5

The same procedure as in Example 1 was carried out except that the thickness of the GeN second lower dielectric layer was 200 mW, without forming a ZnS-SiO ₂ corrosion resistant insertion layer.

Comparative Example 6

Without applying the GeN second lower dielectric layer and the ZnS-SiO ₂ corrosion resistant interlayer, the lower dielectric layer is a 950 Å thick ZnS-SiO ₂ single layer, the upper dielectric layer is 120 Å thick ZnS-SiO ₂ , and the first reflective layer The same process as in Example 1 was carried out except that the thicknesses of the second and second reflective layers were 500 mW and 100 mW, respectively.

Comparative Example 7

The same procedure as in Comparative Example 6 was carried out except that the thickness of the Cu second reflective layer was changed to 400 GPa.

After evaluating the characteristics of the manufactured optical disc as follows, the results are shown in Table 1.

(1) Overlap recording characteristics

The optical disc was mounted on a CD-RW dedicated dynamic characteristics evaluator (manufacturer: Nakamichi, model name: OMS-2000), and then rotated at 8.2 m / s and mounted on a track of 3T to 14T (T _w = 28.6㎱). After recording a signal of a random pattern, the jitter value of the reproduction signal with respect to a certain clock was evaluated. The wavelength of the light source used for pickup of the dynamics evaluator was 680 nm, and the NA of the objective lens was 0.60.

The jitter means a signal deviation of the reproduction signal, and the lower the signal quality, the better the signal characteristics. After 10 or more recordings, it was determined that the jitter value was 4.0 dB or less.

(2) repeated recording durability

After multiple repetitive recordings of the same power on the same track of the optical disc, 3T jitter values of the reproduction signals were measured. At this time, the number of times that the 3T jitter value began to exceed 4.0 ms was set as the number of times that can be repeatedly recorded. At this time, when the jitter value exceeded 4.0 ms after 10 overlapping recordings, the repeated recording durability evaluation had no meaning, and thus was excluded.

It was determined that the repetitive recording count was 100,000 or more.

(3) corrosion resistance

After leaving the sample for 24 hours at a temperature of 80 ° C. and a relative humidity of 85%, it was evaluated that it was satisfactory that no corrosion phenomenon occurred on the surface of the disk.

(4) cross erase

After 10 recordings were recorded on the groove tracks, 10 times were recorded on both adjacent land tracks at 1.3 times the power recorded on the groove tracks. At this time, the increase rate of the jitter value before and after recording adjacent tracks was measured. In this case, when the 10th superposition recording characteristic is 4.0 ms or more, the cross erase characteristic evaluation has no meaning and is excluded from the evaluation.

It was determined that the jitter increase rate was 20% or less.

Superposition recording characteristic Corrosion resistance Repeat Record Durability Cross cancellation characteristic Example 1 Good Good Good Good Example 2 Good Good Good Good Comparative Example 1 Good Bad Bad Good Comparative Example 2 Bad Bad Bad - Comparative Example 3 Bad Bad Bad - Comparative Example 4 Good Bad Bad Good Comparative Example 5 Good Bad Bad Good Comparative Example 6 Good Good Bad Bad Comparative Example 7 Bad Good Good -

As can be seen from the results of Table 1, the phase change type optical discs of the present invention according to Examples 1 and 2 were excellent in all of the superposition recording characteristics, corrosion resistance, repeated recording durability and cross erasing characteristics. On the other hand, the disc according to the comparative example having a configuration outside the scope of the present invention was generally poor in the above characteristics.

In particular, FIG. 5 shows the recording characteristics of the phase change disks according to Example 1 and Comparative Example 1, and it can be seen that in Comparative Example 1, the jitter value increased significantly after 10 overlapping recordings. 6 shows recording characteristics of the phase change disks according to Comparative Examples 1, 6 and 7, and it can be seen that the repeat recording durability is very poor.

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

Claims (7)

A phase change optical disk comprising a lower dielectric layer, a recording layer, an upper dielectric layer, and a reflective layer sequentially formed on a transparent substrate, wherein the lower dielectric layer has a double layer structure, and a corrosion resistant insertion layer is formed between the upper dielectric layer and the reflective layer. Phase change type optical disk characterized by. The method of claim 1, The corrosion resistant insertion layer is ZnS-SiO ₂ , AlN, Si ₃ N ₄ or Al ₂ O ₃ A phase change type optical disk, characterized in that. The method of claim 1, The lower dielectric layer is formed of ZnS—SiO ₂ , a first lower dielectric layer made of silicon oxide, aluminum oxide, silicon nitride, a metal oxide, a metal carbide, or a mixture thereof, and a GeN or silicon nitride formed on the first lower dielectric layer A phase change type optical disc comprising a lower dielectric layer. The method of claim 1, And the reflecting layer comprises a first reflecting layer and a second reflecting layer having a higher thermal conductivity than the first reflecting layer. The method of claim 4, wherein And wherein the first reflective layer is an Al alloy and the second reflective layer is Cu. The method of claim 5, 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 6, The thickness of the first reflective layer is 1300Å or less, the thickness of the second reflective layer is 350 to 700Å, the phase change type optical disk, characterized in that.