JP2000043414A - Phase change type optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a phase change type optical recording medium having excellent repeating overwriting characteristics by suppressing an increase in jitters of both a leading edge and a trailing edge of a recording mark without deviation. SOLUTION: An Sb-Te-Ge alloy is used for a recording layer. A composition of the alloy is selected to one value of composition point group contained in a rectangular region surrounded by straight lines A-A (first line), B-B (second line), C-C (third line) and E-E (fourth line) on a triangular coordinate graph representing the composition (mol.%). The composition of the region is specified with respect to a film constitution containing a recording layer film thickness. Further, the composition of the recording layer is specified in relation to the laser wavelength and a recording speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical information recording medium for recording and reproducing information using light, and more particularly to a phase change type optical recording medium.

[0002]

2. Description of the Related Art Optical information recording media are always required to record at higher speeds and with larger capacities. For this reason,
For example, techniques such as land / groove recording and mark edge recording have been proposed for higher density. A phase-change optical recording medium uses a reversible structural change (a phase change) between an amorphous state and a crystalline state of a substance caused by light irradiation, mainly laser irradiation, for recording information. Medium. In addition, this phase-change optical recording medium records another piece of information while erasing the information once recorded in order to erase and record the recorded information at high speed (overwrite: Ov
er write).
However, in the repetition of erasure / recording, stable operation is indispensable. Further, the number of repetitions of the erasing / recording is required to be as large as possible.

[0003] Many studies have been made on phase-change optical recording media as rewritable optical disks. A typical disk configuration is a polycarbonate transparent substrate, ZnS.Si.
O ₂ first transparent dielectric film (first protective layer), Ge—Sb—
It has a laminated structure of a recording layer of a Te alloy, a second transparent dielectric film (second protective layer) of ZnS / SiO ₂ , a reflective layer of an Al alloy, and an ultraviolet-curable organic resin coating layer (resin protective layer).

As a means for improving the recording repetition characteristics of a phase-change type optical recording medium using a means of heating and raising the temperature of a thin film to melt and quench or a method of heating and gradual cooling, the phase separation between GeTe and Sb ₂ Te ₃ is suppressed. Examination of composition (JP-A-63-228433)
And study of means to prevent mechanical damage (Japanese Patent Laid-Open No. 7-3070)
No. 36). These techniques have improved the repetitive overwrite characteristics of the phase-change optical recording medium. However, in recent years, in a rewritable disc of high-density recording such as a track width of 0.8 μm or less and a minimum recording mark size of 0.5 μm or less, repetitive recording (overwriting) is performed due to mark edge recording. ), The degree of adverse effect on signal quality due to mark edge deterioration has been increasing. Also,
Since the system margin on the drive side is also reduced, the C / N ratio (signal amplitude to noise ratio) and the average jitter, which have been repeatedly evaluated for the overwrite characteristics, are not sufficient. Edge (leading edge) and trailing edge of the mark (trailing edge)
It has become important to evaluate and improve the jitter independently. In other words, even if it seems that the system margin can be taken with the root mean square jitter of both, the jitter of either the leading edge (leading edge) or the trailing edge (trailing edge) is worse than the system margin. And both show the same tendency,
In addition, there is a demand for a phase-change optical recording medium having a square mean overwrite of 100,000 passes and no practical deterioration.

As described above, the phase-change type optical recording medium uses a means for heating and raising the temperature of the thin film and rapidly cooling and melting or heating and gradually cooling the thin film. Very sensitive to changes in mark heating time and temperature. In the prior art, it was insufficient to suppress the deterioration of the jitter at the leading edge (leading edge) and trailing edge (trailing edge) of the mark corresponding to the difference between these conditions.

For example, Japanese Patent Application Laid-Open No. 63-22843 mentioned above.
Even if the composition of the recording layer is limited as disclosed in Japanese Patent Publication No. 3 (1993) -1995, the jitter at the leading edge (leading edge) and trailing edge (trailing edge) of the mark is independently large depending on the thickness of the recording layer and the thickness of the second protective film. However, it was insufficient to achieve the above-mentioned object, and the linear velocity of the recording drive and the change in the spot size of the laser were also insufficient.

[0007]

In a high-density phase change type optical recording medium on the premise of mark edge recording, a so-called "write strategy" in which the power of a laser beam used for recording is controlled by a predetermined pulse waveform. Attempts have been made to reduce distortion. However, this write strategy does not suppress changes on the medium side due to repeated overwriting. As the mark edge distortion, the leading edge of the mark (leading edge) caused by a change in crystal grain size or a change in the atomic arrangement due to repeated melting before mechanical damage due to the above-described repeated heating and deterioration due to segregation of the recording layer composition. ) And degradation of the trailing edge (trailing edge).

In view of such circumstances, the present invention provides an excellent phase-change type optical recording medium in which jitter at the leading edge (leading edge) and trailing edge (trailing edge) of a mark due to repeated overwriting is not deteriorated. The purpose is to:

It is another object of the present invention to provide a phase-change optical recording medium in which either the leading edge or the trailing edge does not start to deteriorate in repeated overwriting.

Still another object of the present invention is to provide a high-density phase-change optical recording medium having good repetition durability.

In particular, it is an object of the present invention to optimize the composition of the alloy used for the recording layer in relation to the structure of each layer constituting the phase change type optical recording medium and the thickness of each layer.

Still another object of the present invention is to optimize the composition of the alloy used for the recording layer in consideration of the mark heating time, and to determine the leading edge (leading edge) or trailing edge (trailing edge) of the mark by repeated overwriting. An object of the present invention is to provide an excellent phase change type optical recording medium without jitter deterioration. Specifically, it is to optimize the composition of the alloy used for the recording layer in consideration of the linear velocity of the recording drive and the spot size of the laser.

[0013]

In order to achieve the above-mentioned object, many experiments and studies have been made, and in relation to the structure of each layer constituting the phase change type optical recording medium, the S
The composition (mol%) of the b-Te-Ge alloy was optimized. That is, a first feature of the present invention is that a transparent substrate, a first protective layer disposed on the transparent substrate, and a Sb-Te film having a thickness of 20 to 35 nm disposed on the first protective layer.
A recording layer comprising a Ge alloy, on which marks are recorded by a laser beam, a second protective layer having a thickness of 16 to 23 nm disposed on the recording layer, and disposed on the second protective layer; A phase-change optical recording medium comprising at least a reflective layer having a thickness of 100 to 250 nm, wherein the composition (mol%) of the Sb-Te-Ge alloy used for the recording layer is related to the thickness of each of the above layers. Is set as follows. That is, S according to the first feature of the present invention.
The b-Te-Ge alloy has a point Sb _22.8 Ge _21.5 Te _55.7 and a point Sb in the triangular coordinate graph representing the composition (mol%).
_A first straight line passing through _26.0 Ge _20.5 Te _53.5 and a point Sb _22.0 Ge _22.7
A second straight line passing through Te _55.3 and point Sb _26.0 Ge _21.5 Te _52.5 , and a point
Sb _26.2 Ge _20.0 Te _{53 .8} and the point Sb _23.0 Ge _24.0 third through Te _53.0
And straight, the point Sb _20.0 Ge _25.0 Te _55.0 and the point Sb _{24 .0} Ge _20.0 Te
The composition is set so as to be a composition in a rectangular area surrounded by a fourth straight line passing through _56.0 .

[0014] The composition of the Sb-Te-Ge alloy is closely related to the crystallization rate of the alloy. This is because the structure of each layer and the film thickness of each layer constituting the phase change type optical recording medium greatly depend on the melting temperature and the cooling rate of the recording layer, and thus need to be determined in relation to the alloy composition. For example, when the second protective layer is made thicker, the thermal conductivity of the reflective layer serving as a heat sink deteriorates, and the cooling rate decreases.
Conversely, if the thickness of the second protective layer is reduced, the cooling rate of the recording layer is too high and the recording sensitivity is reduced. Therefore, it is necessary to select an optimal thickness of the second protective layer in relation to the composition of the alloy. The same applies to the other layers. That is, the Sb-Te- used for the recording layer
If the composition of the Ge alloy is selected within a certain range, the structure of each layer and the film thickness of each layer constituting the phase change type optical recording medium will determine the optimum values. Conversely, if the structure of each layer and the film thickness of each layer constituting the phase change type optical recording medium are determined, Sb-T
The composition of the e-Ge alloy can take only a value within a certain range.

According to the first feature of the present invention, the composition of the Sb-Te-Ge alloy used for the recording layer is determined in relation to the structure of each layer constituting the phase change type optical recording medium and the thickness of each layer. Because of the optimization, it is possible to provide an excellent phase change type optical recording medium free from deterioration of jitter at the leading edge (leading edge) and trailing edge (trailing edge) of the mark due to repeated overwriting.

A second feature of the present invention resides in that a transparent substrate, a first protective layer disposed on the transparent substrate, and a point Sb on the triangular coordinate graph disposed on the first protective layer.
_22.8 Ge _21.5 Te _56.7 and a first straight line passing through the point Sb _26.0 Ge _20.5 Te _53.5, point Sb _22.0 Ge _22.7 Te _{55 .3} and the point Sb _26.0 Ge _21.5 Te _52.5
A recording layer made of an Sb—Te—Ge alloy having a composition (mol%) sandwiched between a second straight line passing through the recording layer, a second protective layer disposed on the recording layer, A phase change type optical recording medium comprising at least a reflective layer disposed on a protective layer, wherein the Sb-T
The composition of the e-Ge alloy is set as follows in consideration of the heating time by laser light for forming a mark on the recording layer. That is, when the wavelength of the laser beam is λ (nm), the aperture ratio of the objective lens through which the laser beam passes is NA, and the recording linear velocity by the laser beam is L (m / s), the second feature of the present invention. The composition of the Sb-Te-Ge alloy according to the following is: (i) If (λ / NA) / L <180, the point Sb _26.2 Ge _20.0 Te
A third straight line passing through the _53.8 and the point Sb _23.0 Ge _{24. 0} Te _53.0,
Value of the region between the point Sb _24.5 Ge _20.0 Te _55.5 and the fifth straight line passing through the point Sb _20.0 Ge _25.5 Te _54.5 ; (ii) the point Sb _20.0 Ge when (λ / NA) / L> 180 _25.0 Te
_45.0 straight line passing through _55.0 and point Sb _24.0 Ge _20.0 Te _56.0 , and point
The value between Sb _25.5 Ge _20.0 Te _54.5 and the sixth straight line passing through the point Sb _22.3 Ge _24.0 Te _53.7 is set.

As described in the first feature, Sb-Te-
The composition of the Ge alloy is closely related to the crystallization rate of the alloy. The structure of each layer constituting the phase change type optical recording medium and the film thickness of each layer are related to the melting temperature and the cooling rate of the recording layer, and at the same time, the heating time of the laser light for forming the mark and the laser light The wavelength λ (nm) and the recording linear velocity L (m / s) by the laser beam are also closely related to the melting temperature and cooling rate of the recording layer. Further, the spot size of the laser beam and the aperture ratio NA of the objective lens through which the laser beam passes also relate to the melting temperature and cooling rate of the recording layer. For this reason,
Performing fast (short mark heating time) recording in a composition region with a low crystallization rate leads to the leading edge of the mark (leading edge).
Although the influence of the poor crystallization is small, jitter deterioration due to the poor crystallization appears at the trailing edge (trailing edge). Conversely, if recording is performed slowly in a composition region where the crystallization speed is high, crystallization is likely to proceed, and in particular, the jitter at the leading edge of the mark (leading edge) is deteriorated. Therefore, as described above, Sb-Te-Ge is determined according to the value of (λ / NA) / L.
By selecting the composition of the alloy, it is possible to provide an excellent phase change type optical recording medium without deterioration of jitter at the leading edge (leading edge) or trailing edge (trailing edge) of the mark due to repeated overwriting.

In the above first and second features, marks of different lengths are recorded on the recording layer according to information,
It is preferable to use a write strategy in which the laser beam is controlled so as to be a combination of at least one or more pulses having a predetermined pulse width, and the length of the mark to be formed is determined by the combination of the pulses. For example, the shortest mark may be written with a single pulse, and the long mark may be selected with the number of pulses according to its length.
Specifically, the laser light has a maximum power (peak power)
, A plurality of pulses including three types of pulses having ternary outputs of a recording power, a bias power (erase power) smaller than this, and a smaller read power (read power), For writing, a mark having a desired length may be formed on the recording layer by combining a plurality of recording power pulses. The pulse width of the recording power is
Two or more types may be prepared and appropriately combined. By employing such a write strategy, it is possible to provide a phase-change optical recording medium capable of stably performing overwrite repetition operations more times.

In the above first and second features, even if the recording layer contains a small amount of elements other than the Sb-Te-Ge alloy, the composition of the Sb-Te-Ge alloy is not limited to the above value. I don't care. That is, other elements such as the fourth and fifth elements may be included in the recording layer as long as the recording layer substantially exhibits the characteristics as the Sb-Te-Ge alloy of the present invention.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a cross section of a phase-change optical recording medium according to an embodiment of the present invention. As shown in FIG. 1, in a phase-change optical recording medium according to an embodiment of the present invention, a first protective layer 12 is formed on a transparent substrate 11. Further, on the first protective layer 12, the recording layer 1
3, a second protective layer 14 and a reflective layer 15 are sequentially deposited, and an ultraviolet curable resin protective layer 16 is formed on the uppermost layer.

Here, the transparent substrate 11 has a DVD-RAM
A 0.6 mm thick substrate for (2.6 GB) is used. The transparent substrate 11 is made of polycarbonate, has a track pitch of 0.74 μm, and records data on both lands and grooves. The first protective layer is preferably a transparent dielectric film in an amorphous state. For example, amorphous ZnS-S
An iO ₂ film (ZnS: SiO ₂ = 80: 20 mol%) may be used. The thickness is preferably 90 nm to 100 nm,
For example, it may be 95 nm. The second protective layer is also a transparent dielectric film in an amorphous state, for example, amorphous ZnS—SiO _2.
(ZnS: SiO ₂ = 80: 20 mol%) may be used. The film thickness is preferably 16 nm to 23 nm, and may be, for example, about 16 nm. The reflective layer 15 may use an AlCr alloy film (Al: Cr = 97: 3 mol%). The thickness is preferably 100 nm to 250 nm, for example, 25 nm.
The thickness may be set to 0 nm. The UV-curable resin protective layer may have a thickness of about 2 μm.

The recording layer 13 is an alloy comprising three elements of Sb, Te and Ge, and has a thickness of 20 nm to 35 nm.
nm is preferred. In the embodiment of the present invention, the composition of the Sb-Te-Ge alloy is a composition selected from a composition point group included in a fixed composition region indicated by a rectangle as shown in FIGS. Have.

FIG. 2 is a triangular coordinate graph showing the entire Sb-Te-Ge alloy system. The composition region targeted by the present invention belongs to a triangular region painted black. FIG. 2 shows a compound line connecting GeTe and Sb ₂ Te ₃ . FIG. 3 is a partial triangular coordinate graph in which a black triangular region in FIG. 2 is enlarged and shows a preferable region for the Sb-Te-Ge alloy of the present invention. That is, in the embodiment of the present invention, Sb, T
In the partial triangular coordinate graph shown in FIG. 3, the compositions (mol%) of the three elements e and Ge are represented by straight lines AA (first straight line),
Straight line BB (second straight line), straight line CC (third straight line)
And a composition point group included in a rectangular area surrounded by a straight line EE (a fourth straight line). Here: (a) Straight line AA (first straight line) is Sb _22.8 Ge _21.5 Te
_A straight line passing through a point a which is _55.7 and a point b which is Sb _26.0 Ge _20.5 Te _53.5 ; (b) a straight line BB (second straight line) is Sb _22.0 Ge _22.7 Te
_A straight line passing through a point c which is _55.3 and a point d which is Sb _26.0 Ge _21.5 Te _52.5 ; (c) a straight line CC (third straight line) is Sb _26.2 Ge _20.0 Te
There a a a point switch and Sb _23.0 Ge _24.0 preparative point is Te _{53.0 53.8} a straight line; (d) a straight line E-E (fourth straight line) is, Sb _20.0 Ge _25.0 Te
This is a straight line passing through the point e at _55.0 and the point Sb _24.0 Ge _20.0 Te _56.0 .

By selecting an Sb-Te-Ge alloy having a composition located inside the rectangular area hatched by oblique lines in FIG. 3, jitter at the leading edge (leading edge) and trailing edge (trailing edge) of the mark due to repeated overwriting is repeated. An excellent phase-change optical recording medium with little difference in tendency and no deterioration can be provided. This is as shown in FIG.
This is because the crystallization speed of the compound line connecting GeTe and Sb ₂ Te ₃ is the fastest, and the crystallization speed becomes slower as the distance increases. That is, each film thickness in the film configuration shown in FIG. 1 is greatly related to the melting temperature and the cooling rate of the recording layer 13. For example, when the second protective layer 14 is thickened, the thermal conductivity to the reflective layer 15 serving as a heat sink is increased. It deteriorates and the cooling rate decreases. Conversely, if the thickness of the second protective layer 14 is reduced, the cooling rate of the recording layer 13 is too high, and the recording sensitivity is reduced. If the mark heating time is defined as a holding time equal to or longer than the crystallization temperature, if the cooling rate of the recording layer 13 is too high, the crystallization temperature holding time becomes short. That is, in the embodiment of the present invention, in relation to the thickness of each layer,
The optimum Sb-Te-Ge alloy composition is selected. Therefore, when an Sb-Te-Ge alloy having a composition located inside the rectangular region hatched by oblique lines in FIG. 3 is used, the thickness of the recording layer is preferably 20 to 35 nm, particularly preferably 22 to 28 nm. When the thickness is less than 20 nm, sufficient recording characteristics cannot be obtained, and when the thickness is more than 35 nm, the recording sensitivity becomes insufficient or the recording layer easily flows and the repetition durability is lowered.

Similarly, when an Sb-Te-Ge alloy having a composition located inside the rectangular area hatched by oblique lines in FIG. 3 is selected as the material of the recording layer 13, the first protective layer 12
Is 90 to 100 nm, and the thickness of the second protective layer 14 is 1
It is required that the thickness be 6 to 22 nm. When the first protective layer 12 is thinner than 90 nm, the heat given to the recording layer 13 also damages the transparent substrate 11, which is not preferable. On the other hand, when the film thickness of the first protective layer 12 is larger than 100 nm, the optical characteristics change due to the effect of the film thickness, so that the recording characteristics of the recording layer 13 deteriorate. 16 nm of the second protective layer 14
When the recording layer 13 is thinner, the heat applied to the recording layer 13 is
When the thickness is larger than 22 nm, the heat applied to the recording layer 13 is not released to the outside, and the recording layer 13 is easily deteriorated. As the thickness of the reflective layer,
The reason why the thickness is preferably 150 to 350 nm is that when the thickness is smaller than 150 nm, the corrosion resistance is deteriorated, and when the thickness is larger than 350 nm, the recording sensitivity is deteriorated.

When recording is performed quickly (with a short mark heating time) in a composition region having a low crystallization speed, the influence on the leading edge (leading edge) of the mark is small, but the jitter deteriorates due to poor crystallization at the trailing edge (trailing edge). Conversely, if slow recording is performed in a composition region where the crystallization speed is high, crystallization is likely to proceed, especially the leading edge of the mark (leading edge).
Jitter becomes worse. Therefore, it is clear that the composition of the recording layer 13 used in the phase-change medium cannot exist independently of the linear velocity of recording or the laser wavelength, and is significant only when the relation between them is defined.

This will be specifically described with reference to FIGS. FIGS. 4 and 5 are partial triangular coordinate graphs having vertexes of 30 mol% of Sb, 60 mol% of Te, and 30 mol% of Ge as in FIG. First, the wavelength of a laser beam (recording laser wavelength) for recording a mark on the recording layer is λ.
(Nm), NA is the aperture ratio of the objective lens through which this laser light passes, and L (m /
T = (λ / NA) / L (1) is defined as s). Then, depending on whether T defined as above is larger or smaller than 180, the optimum Sb-T
The composition region of the e-Ge alloy will be described. (I) In the case of T <180, as shown in FIG.
A (first straight line) and the straight line B-B sandwiched (second straight line), further the linear C-C (third straight line) and Sb _{24 .5} Ge _20.0
The composition of an Sb-Te-Ge alloy using a region α sandwiched between a straight line FF (fifth straight line) passing through a point (Te _55.5) and a point (Sb _20.0 Ge _25.5 Te _54.5 ) Is preferred.

(Ii) On the other hand, when T> 180, as shown in FIG. 5, a straight line AA (first straight line) and a straight line BB
(Second straight line), a straight line D passing through a point あ る which is Sb _25.5 Ge _20.0 Te _54.5 and a point で which is Sb _22.3 Ge _24.0 Te _53.7
It is preferable that the region β sandwiched between -D (sixth straight line) and EE (fourth straight line) be a composition of the Sb-Te-Ge alloy used for the recording layer.

As described above, by selecting the composition in relation to the value of T, the leading edge (leading edge) or trailing edge (trailing edge) of the mark due to repetitive overwriting can be obtained.
An excellent phase-change type optical recording medium having little difference in jitter tendency and no deterioration.

(Embodiment) Next, as shown in FIG.
Samples # 1 to # 5 as examples in a rectangular area surrounded by A, BB, CC, and EE, and samples # 11, # 12, and # as comparative examples outside the rectangular area. 13 is recorded, reproduced, and erased, and the leading edge (leading edge: L
E) Jitter and trailing edge (trailing edge: TE)
Was measured. Here, FIG. 6 is a partial triangular coordinate graph having Sb 28 mol%, Te 59 mol%, and Ge 27 mol% as vertices.

The recording layer was formed on a transparent substrate by magnetron sputtering while revolving the substrate on its own axis. The thickness of the recording layer 13 is 23 nm.

That is, sample numbers # 1 to # 5 and # 1
When the phase change type optical recording media of Nos. 1 to # 13 is set on an optical disk drive, the linear velocity is 6 m when T> 180 is set.
/ S so that the linear velocity is 8 m at the setting of T <180.
/ S was set as the number of revolutions. The NA was measured using a semiconductor laser having a wavelength of 0.6 and a wavelength of 650 nm, using a write strategy (control waveform of laser power) as shown in FIG.

FIG. 7A shows a mark written by the write strategy of FIG. 7C. FIG. 7B shows a write waveform (recording waveform), where τ = 34 ns and three write pulses of pulse widths 11τ, 5τ, and 3τ are shown. Corresponding to the three write pulses having the pulse widths 11τ, 5τ, and 3τ, three marks having different lengths as shown in FIG. 7A are formed. FIG. 7C shows a write strategy, that is, a specific time change of the power of the laser beam for realizing the write waveform of FIG. 7B. As shown in FIG. 7C, the laser beam has a maximum power (peak power), a recording power, a bias power (erasing power) smaller than the recording power, and a read power (read power) smaller than the recording power. It is composed of three types of pulses having ternary outputs. Then, FIG.
The formation of each mark of different length as shown in
A combination of pulse trains (multi-pulse) as shown in FIG. 7C is used.

In the measurements of the following Examples and Comparative Examples, the peak power (recording power) and the bias power (erasing power) were respectively set to optimum powers, and overwriting of the random signal was repeated 100,000 times. And the read power (read power) was 1 mW. Then, the leading edge (LE) and trailing edge (TE) jitters were measured up to 100,000 repetitions. The evaluated radius is about 2
5 mm, and one track of an arbitrary groove in the innermost data zone was used.

Specifically, as shown in FIG. 1, the recording layer 13 was irradiated with a multi-pulse laser beam via the transparent substrate 11 and the first protective layer 12. That is, a laser beam having the maximum output (recording power) narrowed down through a lens or the like is irradiated for a predetermined number of pulses, and the recording layer 13 is heated to a temperature equal to or higher than its melting point and once melted (about 500 to 600 ° C.). As shown in FIG. 7, the number of pulses of the multi-pulse is changed according to the length of the mark. Subsequently, the power of the laser beam is turned off, the recording layer is rapidly cooled, and a mark is formed in an amorphous state.

On the other hand, at the end of the recording, as shown in FIG. 7C, a laser beam with a weak erasing power (bias power) is irradiated to raise the temperature to a temperature lower than the melting point, thereby forming an amorphous mark. Is crystallized. Reading is performed with a laser beam having a lower read power (reading power).

In FIG. 8, the quality of the leading edge jitter (LE) and the trailing edge jitter (TE) according to the number of repetitions (overwriting times) up to 100,000 times are indicated by ○, Δ, and ×. FIG. 8 also shows the composition (mol%) of the recording layer of each sample and the thickness of each film constituting the phase-change optical recording medium. FIG. 8 also shows the results for samples (Comparative Examples) # 14, # 15, and # 16 in which the thicknesses of the recording layers of Samples # 1, # 3, and # 5 and the first and second protective layers were changed. Was.
The thickness of each layer shown in FIG. 8 was adjusted by changing the sputtering time.

The judgment of ○, Δ, × was made as follows. That is, as shown in FIG. 9, the progress of the jitter of the leading and trailing edges of the mark due to the overwriting of the random signal with respect to the number of repetitions is represented by the leading edge (LE) and the trailing edge (T
E) and changes in three graphs showing the root mean square jitter. If the leading edge jitter (LE) differs from the trailing edge jitter (TE) by a maximum of 5% or more in the course of up to 100,000 times as shown in FIG.
E shows a cross. Similarly, when the trailing edge jitter (TE) is worse than the leading edge jitter (LE) as shown in FIG. As shown in FIG. 10 (a), both LE and TE show the same tendency, and the jitter after 100,000 times is 13% or less in a root mean square. Further, although a slight difference was observed in the tendency of LE and TE, the case where the jitter after 100,000 times was less than 13% in the root mean square was indicated by Δ. In addition, the case where the difference between LE and TE does not exceed 5% at the maximum in the course of up to 100,000 times is defined as Δ. Jitter converts the signal after binarization into TA320 manufactured by Yokogawa Electric Corporation.
Clock to data using A
Was measured. That is, the difference between the LE and TE of the clock pulse and the LE and TE of the data pulse was obtained, and the fluctuation of the pulse position was examined.

Returning to the description of the table shown in FIG. FIG.
In the examples of sample numbers # 1 to # 3 in which the composition of the recording layer is in the region α as shown in FIG.
Both E and TE show good results. On the other hand, T = 13
In the case of sample No. 5, it can be seen that in the examples of sample numbers # 1 and # 2, the jitter at the trailing edge of the mark is slightly deteriorated due to insufficient crystallization time. As is clear from the overwrite repetition characteristic in the case of T = 181 in the example of sample number # 3 shown in FIG. 10A, if the composition of the recording layer is in the region α, L
It can be seen that E and TE show the same tendency, and that each jitter is less than 13% even after overwriting 100,000 times. In the examples of sample numbers # 4 and # 5 in which the composition of the recording layer is in the region β, when T = 181, the crystallization is apt to proceed, and for example, the crystal is formed by the first cooling pulse of 5τ (= 5 × 34 ns) or more. LE due to
The jitter on the side is slightly worse. At T = 135, both LE and TE showed very good results.

It can be seen that, in the region α and the region β, the film thickness configuration of the present invention shows good overwriting with little difference between the LE and TE jitter tendency. Thus, T
When the composition region is set by the value of
Excellent results with little jitter difference of E are obtained.

On the other hand, in the comparative example of sample No. # 11 deviating from the regions α and β of the present invention, when T = 181, both LE and TE deteriorate. Although the crystallization rate is lower than that in the example of Sample No. # 5, it is considered that the crystallization rate in the solid phase is sharply reduced.
In the comparative example of sample number # 12, T = 181 and T = 13
In each case of 5, the LE deteriorated. Here, FIG.
Shows the overwrite repetition characteristics when T = 135 in the comparative example of sample number # 12. It can be seen that the TE jitter hardly changes, but only the LE jitter increases as the number of overwrites increases. As a result, the root-mean-square jitter is 13 after 100,000 times overwriting.
%. In the comparative example of sample number # 13 shown in FIG. 9B, TE was deteriorated in any case of T due to deterioration of the erasing rate due to insufficient crystallization. It is clear that only the TE jitter tends to increase.

Sample Nos. # 14, # 15, and # 1 having the same recording layer composition as the embodiments of Sample Nos. # 1, # 3, and # 5
With respect to Comparative Example 6, the following can be understood. In the comparative example of sample number # 14, the cooling was too slow, and the TE jitter deteriorated relatively quickly, resulting in the deterioration of the jitter in the early period of overwriting repetition. The comparative example of sample # 15 has the same composition as the example of # 3, and FIG.
Is the film thickness shown in FIG. In the sample of # 15, sufficient recording characteristics were not obtained because the recording layer thickness was too thin, and as shown in FIG. 10 (b), both LE and TE deteriorated in the early period of repeated overwriting. Results. Here, FIG. 10B shows the overwrite repetition characteristics when T = 135 in the comparative example of # 15. The comparative example of sample number # 16 had the same recording layer composition as the example of # 5, and the film thickness was formed as shown in FIG. Sample number #
In Comparative Example No. 16, the reflective layer was thick, the quenching structure was passed, the recording sensitivity was poor, and the LE was considered to be deteriorated due to the short crystallization temperature holding time.

From the above examination results, the phase change type optical recording comprising the phase change recording layer having the relationship between the recording linear velocity and the laser wavelength within the composition range of the present invention and the film constitution of the present invention including this recording layer. It has been clarified that the recording medium has no difference in the tendency of jitter between the leading edge and the trailing edge of the mark when recording / erasing (overwriting) is repeated. Also, it was found that no increase in jitter was observed even after 100,000 repetitions, and that particularly excellent durability was exhibited.

[0044]

According to the present invention, it is possible to provide a phase change type optical recording medium having no difference in jitter tendency between a leading edge (leading edge) and a trailing edge (trailing edge) of a mark.

According to the present invention, there is provided a phase change type optical recording medium in which either the leading edge (leading edge) or the trailing edge (trailing edge) of the mark does not start to deteriorate in repeated overwriting. can do.

Further, according to the present invention, it is possible to provide a phase-change type optical recording medium capable of stably performing overwrite repetition operations more times.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a phase-change optical recording medium according to an embodiment of the present invention.

FIG. 2 is a triangular coordinate graph showing the composition of an Sb—Te—Ge alloy system.

FIG. 3 shows Sb used for a recording layer according to an embodiment of the present invention.
It is a partial triangular coordinate graph which expands and shows the composition region of -Te-Ge alloy system.

FIG. 4 is a partial triangular coordinate graph showing an optimal Sb—Te—Ge alloy-based composition region used for the recording layer when the recording linear velocity is high.

FIG. 5 is a partial triangular coordinate graph showing an optimal Sb—Te—Ge alloy-based composition region used for a recording layer when the recording linear velocity is low.

FIG. 6 is a partial triangular coordinate graph showing a relationship between a recording layer region of each sample and a composition region of the present invention.

FIG. 7 is a diagram illustrating a write strategy using multi-pulses.

8 shows details of the composition and thickness of the recording layer of each sample shown in FIG. 6, and the leading edge (LE) of each sample when a random signal is overwritten up to 100,000 times. 6 is a table showing measurement results of a trailing edge (TE) jitter.

FIG. 9A shows a comparative example of sample number # 12,
(B) is a diagram showing a measurement result of jitter when a random signal is overwritten up to 100,000 times in the comparative example of sample number # 13.

FIG. 10 (a) shows the jitter of the example of sample number # 3, and FIG. 10 (b) shows the jitter of the comparative example of sample number # 15 when the random signal was overwritten up to 100,000 times. It is a figure showing a measurement result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Transparent substrate 12 1st protective layer 13 Recording layer 14 2nd protective layer 15 Reflective layer 16 UV curable resin protective layer

Claims (3)

[Claims] 1. A transparent substrate, a first protective layer disposed on the transparent substrate, and a film thickness of 20 to 35 nm disposed on the first protective layer.
A recording layer on which a mark is recorded by a laser beam, a second protective layer having a thickness of 16 to 23 nm disposed on the recording layer, and an upper part of the second protective layer Film thickness of 100 to 250
a reflective layer having a thickness of at least 3 nm, and the Sb-Te-Ge alloy has a composition passing through points Sb _22.8 Ge _21.5 Te _55.7 and Sb _26.0 Ge _20.5 Te _53.5 in a triangular coordinate graph representing the composition (mol%). 1 line and point Sb _22.0 Ge
_22.7 Te _55.3 and a second straight line passing through the point Sb _26.0 Ge _21.5 Te _52.5, and a third straight line passing through the point Sb _26.2 Ge _{20 .0} Te _53.8 and the point Sb _23.0 Ge _24.0 Te _53.0, point Sb _20.0 Ge _25.0 Te _55.0 and point Sb _24.0 Ge
A phase-change optical recording medium having a composition in a rectangular area surrounded by a fourth straight line passing through _20.0 Te _56.0 . 2. A transparent substrate, a first protective layer disposed on the transparent substrate, and points Sb _22.8 Ge _21.5 Te _56.7 and Sb in the triangular coordinate graph disposed on the first protective layer. _A first straight line passing through _26.0 Ge _20.5 Te _53.5 , a point Sb _22.0 Ge _22.7 Te _55.3 and a point Sb _26.0 Ge
_A recording layer composed of an Sb-Te-Ge alloy having a composition (mol%) of a region sandwiched between a second straight line passing through _21.5 Te _52.5 , a second protective layer disposed on the recording layer, And a reflective layer disposed on the second protective layer. Further, a wavelength of a laser beam for recording a mark on the recording layer is λ (nm), and an objective lens through which the laser beam is transmitted. The aperture ratio is NA, and the recording linear velocity by the laser light is L.
(m / s), the composition of the Sb-Te-Ge alloy is:
When (λ / NA) / L <180, point Sb _26.2 Ge _20.0 Te _53.8 and point
A third straight line passing through Sb _23.0 Ge _24.0 Te _53.0 and a point Sb _24.5 Ge
_This is the value of the area between the _20.0 Te _55.5 and the fifth straight line passing through the point Sb _20.0 Ge _25.5 Te _54.5 . When (λ / NA) / L> 180, the point Sb _20.0 Ge _25.0 Te _55.0 and the point A fourth straight line passing through Sb _24.0 Ge _20.0 Te _56.0 , a point Sb _25.5 Ge _20.0 Te _54.5 and a point Sb _22.3 Ge
A phase-change optical recording medium characterized by being a value between a sixth straight line passing through _24.0 Te _53.7 . 3. A mark having a different length according to information is recorded on the recording layer, and the laser beam is controlled to be a combination of at least one or more pulses having a predetermined pulse width. 3. The phase-change optical recording medium according to claim 1, wherein the length of the mark is determined by a combination of the pulses.