JP2002222541A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase-change type optical recording medium which can be used as a write-once type and on which high density recording can be performed. SOLUTION: The optical recording medium having a phase-change type recording layer where recording is performed so that the shortest recording mark is formed which has a length of 0.4 λ/NA when the wavelength of recording light and the numerical aperture of the object lens of a recording optical system are expressed by λand NA, respectively, and a circular or an oval shape and consisting of a DRAW type medium wherein recording information can not be erased or rewrited in the used minimum linear velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical recording medium having a phase-change recording layer and used as a write-once medium.

[0002]

2. Description of the Related Art In recent years, optical recording media capable of high-density recording have attracted attention. Optical recording media include write-once media that can be recorded only once and cannot be rewritten, and rewritable media that can be repeatedly recorded.

[0003] A write-once medium is not suitable for recording an official document or the like in which information falsification is a problem since the recorded information cannot be rewritten. As a write-once medium, a medium using an organic dye as a recording material is widely used. However, when an organic dye is used as a recording material, recording sensitivity tends to be insufficient when high-speed recording is performed by increasing the linear velocity of a medium, and it is difficult to achieve a high transfer rate. In addition, since organic dyes have relatively steep spectral absorption characteristics and spectral reflection characteristics, recording and
It is necessary to use an organic dye corresponding to the reproduction wavelength. Therefore, for example, when there is an upper format that uses recording / reproducing light of a shorter wavelength, there is a problem that recording / reproducing light for the upper format cannot perform recording / reproducing on a medium of a lower format. In addition, recording of short wavelength
There is also a problem that it is difficult to design and obtain an organic dye corresponding to reproduction light.

On the other hand, phase change type rewritable optical recording media perform recording by changing the crystal state of a recording layer by irradiating a laser beam, and the recording is accompanied by such a state change. Reproduction is performed by detecting a change in the reflectance of the recording layer. In a phase-change type medium that can be rewritten by overwriting, a crystalline recording layer is irradiated with a laser beam having a recording power level to be melted, and is rapidly cooled from a molten state to form an amorphous recording mark. When erasing, irradiate a laser beam at the erasing power level to raise the temperature to a temperature higher than the crystallization temperature of the recording layer and lower than the melting point,
Then, the amorphous recording mark is crystallized by slow cooling. Therefore, overwriting is possible by irradiating a single laser beam while modulating the intensity.

A medium having a phase change type recording layer can be used as a write-once type medium in addition to the above-mentioned rewritable type. When used as a write-once medium, it is necessary that an amorphous recording mark once formed cannot be erased or rewritten.

[0006] In a write-once medium using an organic dye, the organic dye is decomposed during recording. Therefore, in general, it is said that the linear velocity during recording to double the power of the recording laser beam is required to be 2 ^1/2 times. On the other hand, when a phase-change medium is used as a write-once medium, the portion irradiated with the recording laser beam may reach the melting point. Since the recording layer instantaneously absorbs the laser beam and reaches the melting point, the power of the recording laser beam does not largely depend on the linear velocity during recording. Therefore, even if the linear velocity during recording is doubled,
There is an advantage that the power of the recording laser beam can be slightly increased.

However, no effective proposal has been made for utilizing a phase change type medium as a write-once type medium.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase change type optical recording medium which can be used as a write-once type and can perform high-density recording.

[0009]

This object is achieved by any one of the following constitutions (1) to (5). (1) Assuming that the wavelength of the recording light is λ and the numerical aperture of the objective lens of the recording optical system is NA, the shortest recording mark whose length is 0.4λ / NA or less and which is circular or oblong. An optical recording medium which is a write-once medium having a phase-change type recording layer on which recording is performed so as to form erasable information and in which recorded information cannot be erased or rewritten at a minimum linear velocity used. (2) the elements except for the Sb and Te expressed in M, represents an atomic ratio of the recording layer constituent elements in the formula _{I (Sb x Te 1-x} ) 1-y M y, the minimum linear velocity to be used Vmin (M / s), 0.5 ≦ x ≦ y / 2 + 0.02Vmin + 0.57 and x
The optical recording medium according to the above (1), wherein ≦ 0.9 and 0 ≦ y ≦ 0.4. (3) The optical recording medium according to the above (1) or (2), wherein recording is performed such that a recrystallization region does not exist around the recording mark. (4) The above-mentioned (1) to (3) in which recorded information cannot be erased or rewritten at a linear velocity of 3.49 m / s or more.
An optical recording medium according to any of the above. (5) The optical recording medium according to any one of the above (1) to (3), wherein erasing or rewriting of recorded information is impossible at a linear velocity of 1.2 m / s or more.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A phase change type medium is required to have an improved recording density whether it is a rewritable type or a write-once type.
However, when the recording mark length is shortened for performing high-density recording, a reduction in reproduction output and an increase in jitter are likely to occur.
On the other hand, Japanese Patent Application Laid-Open No. 2000-231725 proposes that the shape of the shortest recording mark is controlled to improve the reproduction output reduction and jitter increase accompanying high-density recording. This publication describes an optical recording method in which at least a part of the rear end is convex toward the front end, specifically, a bat-shaped shortest recording mark. Such a bat-like shortest recording mark can be formed by controlling recording conditions. When the recording laser beam is irradiated to the crystallized recording layer, the irradiated area is melted. When the laser beam is moved away, the melted area is rapidly cooled to form an amorphous recording mark. At this time, if the cooling rate near the rear end of the molten region is controlled by controlling the intensity modulation pattern of the laser beam, the latter half of the molten region can be recrystallized. As a result, only the first half of the molten region becomes amorphous, and a bat-like amorphous recording mark is formed.

According to the method described in the publication, the recording mark width can be made relatively large with respect to the recording mark length, thereby suppressing a decrease in the reproduction output due to the shortening of the recording mark length. Therefore, in the publication, when the wavelength of the recording light is λ and the numerical aperture of the objective lens of the recording optical system is NA, even if the length of the shortest recording mark is shortened to 0.4λ / NA or less, a sufficient recording mark can be obtained. The width can be secured, and as a result, a sufficient reproduction output is obtained. In this publication, jitter is reduced by making the shortest recording mark into this shape.

The present inventors have proposed a write-once phase change medium by providing a recording layer having a relatively low crystallization rate and making the linear velocity used relatively high, as disclosed in
As in the case of the rewritable medium described in the embodiment of JP-A-0-231725, the length of the shortest recording mark is 0.4λ / N.
The recording conditions were set so that the temperature was less than or equal to A and the rear part of the molten region was recrystallized. However, in this case, unlike the rewritable medium described in Japanese Patent Application Laid-Open No. 2000-231725, the jitter increased.

The cause of the increase in jitter in the above experiment for performing high-density recording on a write-once medium is considered as follows. In order to use a phase change medium as a write-once medium, in the above experiment, a recording layer having a relatively low crystallization rate was provided, and the linear velocity used was relatively high. However, under these conditions, the melted recording layer is unlikely to recrystallize. As a result, the recrystallization of the latter half of the melted region is not performed stably, and as a result, the position of the trailing edge of the recording mark tends to vary, and the shape of the recording mark tends to vary. The effect of these variations is relatively greater as the recording marks are shorter. Therefore, the length of the shortest recording mark is 0.4λ /
When the length is shorter than NA, the jitter of the shortest signal increases, and the jitter of the shortest signal strongly influences the jitter of the entire recording signal.

On the basis of such experimental results, the present inventors performed recording under the condition of suppressing the recrystallization of the latter half of the melted area of the recording layer in order to prevent the variation of the recording mark shape.
Variations in the shape of the recording marks were prevented. Specifically, the crystallization speed of the recording layer and the thermal design of the medium are controlled in accordance with the recording linear velocity so that the recording sensitivity can be sufficiently secured and the shape of the shortest recording mark is circular or oval. At the same time, optimal recording conditions were set. However, if the shortest recording mark is simply circular or oval, the reproduction output will be low. Therefore, in the present invention, the composition of the recording layer is selected so that the crystallization speed is relatively slow and the change in reflectance between the crystal and the amorphous phase is large. Thereby, the present invention provides a phase change type medium having a recording layer having a crystallization rate that can be used as a write-once medium, and having a small jitter when performing high-density recording and a sufficiently high reproduction output. It was realized.

In the present invention, a sufficient reproduction output is obtained when high-density recording is performed, when the shortest recording mark length is 0.4λ / NA or less. carrier to noise ratio) is 45 dB or more, preferably 48 dB or more.

By the way, Japanese Patent Application Laid-Open No. 2000-23172 is disclosed.
FIG. 5 and FIG. 6 of JP-A No. 5 describe a substantially circular recording mark as a comparative example. These recording marks are formed by making the recording power relatively low to prevent recrystallization of the latter half of the melted area during recording. The composition of the recording layer the recording mark is formed (atomic ratio), as shown in paragraph 0071 and paragraph 0052 of the _{publication, Ag a In b Sb c Te} a = 0.07 in _d, b = 0. 05, c = 0.59, d = 0.29, and in the form of (Sb _x Te _1-x ) _1-y (Ag, In) _y , x = 0.67 and y = 0.12. Further, the circular recording mark is formed at a linear velocity of 1.2 m / s. The recording layer of this composition has a linear velocity of 1.2 m /
You can erase with s. In the medium of the present invention that cannot be erased at a linear velocity of 1.2 m / s, x representing the Sb content is smaller, so that the reproduction output is higher.

In the medium of the present invention, when an amorphous recording mark is formed, it is preferable that a recrystallization region does not exist around the recording mark. Conventional phase change recording media are disclosed in JP-A-9-7176 (see FIG. 2) and JP-A-4-366.
As described in Japanese Patent No. 424 (see FIG. 2), a recrystallized region exists around an amorphous recording mark. This recrystallization region is formed by the mechanism described below.

The beam spot of the laser beam used for recording on the optical recording medium is substantially circular, and the energy distribution in the beam spot is a Gaussian distribution. Therefore, when the recording laser beam is irradiated to the phase-change type recording layer, the temperature of the irradiated portion becomes higher in the central portion than in the peripheral portion, and heat is transmitted from the central portion of the irradiated portion to the peripheral portion after the irradiation. As a result, the cooling rate in the peripheral part of the irradiation site becomes slow, and the peripheral part is gradually cooled. Therefore, even if the peripheral portion is once melted, it does not become amorphous but returns to crystalline again. By such an operation, a recrystallized region is formed around the amorphous recording mark.

The crystal grain size in the recrystallized region thus formed is different from the crystal grain size formed by initializing the recording layer (entire crystallization) and formed by an erasing operation. Also different from the crystal grain size. When the crystal grain size is different, the light reflectance is also different. As a result, the outer edge of the recording mark becomes unclear, resulting in deterioration of the reproduction characteristics. In particular, in mark edge recording where it is necessary to detect the edge position of a recording mark, jitter becomes worse if the length of the recording mark or the state of the edge becomes unclear.

On the other hand, in a preferred embodiment of the present invention, since there is no recrystallized region around the recording mark, the signal quality is improved and the jitter can be reduced.
In order to prevent recrystallization around the recording mark, the composition of the recording layer and / or the thermal design of the medium may be appropriately controlled.

As described above, Japanese Patent Laid-Open Publication No. 2000-231725 describes a substantially circular recording mark as a comparative example. In the medium used in this comparative example, the composition of the recording layer and the thermal design of the medium were selected so that rewriting at a linear velocity of 3.5 m / s was possible. At a speed of 1.2 m / s, it does not become a write-once type, and recrystallization around a recording mark is likely to occur. In fact, in FIGS. 5 and 6 of the publication, a recrystallized region made of a crystalline material different from the unrecorded crystalline material is observed around the substantially circular recording mark.

The present invention is particularly suitable for a type of medium in which an amorphous recording mark is formed on a crystalline recording layer. However, the present invention is also applicable to a medium in which a crystalline recording mark is formed on an amorphous recording layer.

Next, a configuration example of the medium of the present invention will be described.

FIG . 1 shows an example of the structure of the optical recording medium of the present invention. This optical recording medium has a first dielectric layer 31, a recording layer 4, a second dielectric layer 32, a reflective layer 5, and a protective layer 6 on a translucent substrate 2 in this order. Is incident through the translucent substrate 2.

The light-transmitting substrate 2 light-transmitting substrate 2 has a light-transmitting property with respect to the laser beam for recording or reproduction. The thickness of the translucent substrate 2 is usually
The thickness may be 0.2 to 1.2 mm, preferably 0.4 to 1.2 mm. The translucent substrate 2 may be made of resin, but may be made of glass. A groove (guide groove) 21 usually provided in the optical recording medium is a region present on the near side as viewed from the laser beam incident side, and a region existing between adjacent grooves is a land 22.

In the present invention, lands and / or grooves can be used as recording tracks.

First dielectric layer 31 and second dielectric layer 32 These dielectric layers prevent the recording layer from being oxidized or deteriorated, and also block or release heat transmitted from the recording layer during recording. This protects the translucent substrate 2. Also,
By providing these dielectric layers, the degree of modulation can be improved. Each dielectric layer may have a configuration in which two or more dielectric layers having different compositions are stacked.

As the dielectric used for these dielectric layers, for example, various compounds containing at least one metal component selected from Si, Ge, Zn, Al, rare earth elements and the like are preferable. The compound is preferably an oxide, a nitride or a sulfide, and a mixture containing two or more of these compounds can also be used.

The thicknesses of the first dielectric layer and the second dielectric layer may be appropriately determined so as to sufficiently obtain a protective effect and a modulation degree improving effect. The thickness is preferably 30 to 300 nm, more preferably 50 to 2 nm.
50 nm, and the thickness of the second dielectric layer 32 is preferably 1
0 to 50 nm.

Each dielectric layer is preferably formed by a sputtering method.

Recording Layer 4 The composition of the recording layer is not particularly limited, and may be appropriately selected from various phase change materials, but preferably contains at least Sb and Te. The recording layer composed of only Sb and Te has a low crystallization temperature of about 130 ° C. and has insufficient storage reliability. Therefore, it is preferable to add another element to improve the crystallization temperature. In this case, the additional elements include In, Ag, Au, Bi, Se, Al, P, Ge,
H, Si, C, V, W, Ta, Zn, Ti, Sn, P
At least one selected from b, Pd and rare earth elements (Sc, Y and lanthanoids) is preferred. Of these, the effect of improving storage reliability is particularly high,
At least one selected from the group consisting of rare earth elements, Ag, In and Ge is preferable.

As the composition containing Sb and Te used in the write-once type recording layer, the following is preferable. Represents an element other than the Sb and Te in M, it represents an atomic ratio of the recording layer constituent element formula _{I (Sb x Te 1-x} ) in _1-y M _y, the minimum linear velocity medium is used Vmin (m / s), the range of x and y in the above formula I is 0.5 ≦ x ≦ y / 2 + 0.02Vmin + 0.57 and x
≦ 0.9, 0 ≦ y ≦ 0.4, preferably y / 2 + 0.02Vmin + 0.5 ≦ x ≦ y / 2 + 0.0
2Vmin + 0.57, x ≦ 0.9, and 0 ≦ y ≦ 0.4.

In the above formula I, x representing the content of Sb
Is too small, the crystallization speed becomes too slow, so that it is difficult to initialize the recording layer. On the other hand, x is y / 2 + 0.0
If it exceeds 2 Vmin + 0.57, erasing (crystallization) becomes possible at the linear velocity Vmin, and it cannot be used as a write-once medium. Also, when x is large, especially when it exceeds 0.9, the difference in reflectance between the crystalline state and the amorphous state is small, and the reproduction output is low. Therefore, by setting x within the above range, an appropriate crystallization speed can be obtained as a recording layer of the write-once medium, and the reproduction output can be sufficiently increased.

Note that x ≦ y / 2 + 0.02 Vmin + 0.
The relationship 57 was determined experimentally by the following procedure. First,
Erasure was attempted at various linear velocities for each of a plurality of media having different x and / or y, and a critical linear velocity at which erasure was impossible in each medium was determined. Next, the relationship between the critical linear velocity and x and y was expressed as a linear expression. When the critical linear velocity is represented by V, this linear expression is x = y / 2 + 0.02V + 0.57.

In the present specification, the minimum linear velocity Vmin at which the medium is used is defined as a standard linear velocity (1 × speed) in a standard to which the medium of the present invention belongs or a standard having high compatibility with the medium of the present invention. Or its minimum value. For example, since the reference linear velocity of a CD-R known as a write-once compact disc and a CD-RW known as a rewritable compact disc is 1.2 to 1.4 m / s, the CD-R or CD-RW is used.
When the medium of the present invention is used as a write-once medium having high compatibility with the above, Vmin is 1.2 m / s. DVD
(Digital Versatile Disk) Of the optical disks known as the standard, the write-once type DVD-R and the rewritable type DVD-RW have a reference linear velocity of 3.49 m / s.
When the medium of the present invention is used as a write-once medium having high compatibility with VD-R or DVD-RW, Vmin is 3.
It is 49 m / s. Generally, in an optical disk drive, it is extremely rare that an erasing operation or a rewriting operation is performed at a linear velocity lower than 1 × speed after a writing operation, and erasing or rewriting becomes easier as the linear velocity becomes lower. The composition of the layer is limited based on Vmin.

In the present invention, the minimum linear velocity used is not particularly limited. However, since the initialization linear velocity generally needs to be lower than the recording linear velocity, a recording layer optimized for a low recording linear velocity requires a significantly lower initialization linear velocity, and the productivity of the medium is reduced. It will be lower. Also, the recording layer optimized for extremely low linear velocity,
Initialization may not be possible. On the other hand, if the recording linear velocity is too high, it is difficult to keep the surface run-out within an allowable range unless the medium has extremely good mechanical accuracy, or the vibration of the motor for driving the medium becomes large, so that the medium becomes stable. Recording is difficult. for that reason,
The minimum linear velocity used is usually between 1 and 20 m / s, in particular 1
It is preferably in the range of 15 to 15 m / s.

The element M is not particularly limited, but it is preferable to select at least one of the above-mentioned elements exhibiting the effect of improving storage reliability. If y representing the content of the element M is too large, the reproduction output will be low.

The thickness of the recording layer is preferably more than 4 nm and 50 nm
Hereinafter, it is more preferably 5 to 30 nm. If the recording layer is too thin, growth of the crystal phase becomes difficult, and crystallization becomes difficult. On the other hand, if the recording layer is too thick, the heat capacity of the recording layer becomes large, so that recording becomes difficult and the reproduction output decreases.

The recording layer is preferably formed by a sputtering method.

In the present invention, the structure of the recording layer is not particularly limited. For example, the present invention is applicable to a medium having a multilayered recording layer described in JP-A-8-221814 and JP-A-10-226173.

Reflective Layer 5 In the present invention, the material constituting the reflective layer is not particularly limited, and is usually Al, Au, Ag, Pt, Cu, Ni, Cr, T
It may be made of a single metal or semimetal such as i or Si, or an alloy containing one or more of these.

The thickness of the reflection layer is usually preferably from 10 to 300 nm. If the thickness is less than the above range, it becomes difficult to obtain a sufficient reflectance. Further, even if the ratio exceeds the above range, the improvement of the reflectance is small, which is disadvantageous in cost. The reflective layer is preferably formed by a vapor phase growth method such as a sputtering method or an evaporation method.

Protective Layer 6 The protective layer 6 is provided for improving scratch resistance and corrosion resistance. This protective layer is preferably composed of various organic substances, and in particular, it is preferably composed of a substance obtained by curing a radiation-curable compound or a composition thereof with an electron beam, radiation such as ultraviolet rays. . The thickness of the protective layer is usually about 0.1 to 100 μm, and may be formed by a usual method such as spin coating, gravure coating, spray coating, and dipping.

FIG . 2 shows an example of the structure of the optical recording medium of the present invention. This optical recording medium includes a reflective layer 5, a second dielectric layer 32, a recording layer 4, a first layer
It is formed by laminating a dielectric layer 31 and a translucent substrate 2 in this order. Laser light for recording or reproduction enters through the translucent substrate 2. Note that an intermediate layer made of a dielectric material may be provided between the support base 20 and the reflection layer 5.

As the translucent substrate 2 in this configuration example, a resin plate or a glass plate having the same thickness as the translucent substrate 2 in FIG. 1 may be used. However, the high NA of the recording / reproducing optical system
In order to achieve a high recording density by the formation, it is preferable to make the light-transmitting substrate 2 thin. In this case, the thickness of the light-transmitting substrate is preferably selected from the range of 30 to 300 μm. If the light-transmitting substrate is too thin, the optical effect of dust adhering to the surface of the light-transmitting substrate increases. on the other hand,
If the translucent substrate is too thick, it is difficult to achieve a high recording density by increasing the NA.

To make the light-transmitting substrate 2 thin, for example, a light-transmitting sheet made of a light-transmitting resin is attached to the first dielectric layer 31 with various adhesives or adhesives to form a light-transmitting substrate. Alternatively, a light-transmitting resin layer may be formed directly on the first dielectric layer 31 using a coating method to form a light-transmitting substrate.

The support base 20 is provided to maintain the rigidity of the medium. The thickness and the constituent material of the support base 20 may be the same as those of the translucent base 2 in the configuration example shown in FIG. 1, and may be transparent or opaque. As shown in the figure, the groove 21 can be formed by transferring a groove provided in the support base 20 to each layer formed thereon.

In the medium having the structure shown in FIG. 2, the surface roughness of the reflection layer on the laser beam incident side tends to increase due to crystal growth when the reflection layer 5 is formed. As the surface roughness increases, the reproduction noise increases. Therefore, it is preferable to reduce the crystal grain size of the reflective layer or to form the reflective layer as an amorphous layer. To do this, Ag or A
A reflective layer containing l as a main component and containing the above-mentioned additive element is preferable.

Since the thermal conductivity of the reflective layer decreases as the crystal grain size decreases, if the reflective layer is amorphous, it is difficult to obtain a sufficient cooling rate during recording. Therefore, it is preferable to first form the reflective layer as an amorphous layer and then perform a heat treatment to crystallize the layer. Once formed as an amorphous layer and then crystallized, the surface roughness in the amorphous state can be substantially maintained, and the thermal conductivity can be improved by crystallization.

The other layers are the same as in the configuration example shown in FIG.

[0051]

EXAMPLE 1 A groove (width 0.2 μm, depth 20 nm,
A disc-shaped polycarbonate plate having a diameter of 120 mm and a thickness of 0.6 mm simultaneously formed with a pitch of 0.74 μm) is used as the light-transmitting substrate 2, and the first dielectric layer 31, the recording layer 4, and the second dielectric The layer 32, the reflective layer 5, and the protective layer 6 were formed in the following procedure, and an optical recording disk sample No. 1 having the configuration shown in FIG. 1 was obtained.

The first dielectric layer 31 is made of Z
Using nS (80 mol%)-SiO ₂ (20 mol%)
It was formed by a sputtering method in an Ar atmosphere. First
The thickness of the dielectric layer 31 was 90 nm.

The recording layer 4 was formed by a sputtering method in an Ar atmosphere. The composition (atomic ratio) of the recording layer 4 was (Sb _0.67 Te _0.33 ) _0.9 (In _0.4 Ag _0.6 ) _0.1 . The thickness of the recording layer 4 was 20 nm.

The second dielectric layer 32 has a Z target as a target.
Using nS (50 mol%)-SiO ₂ (50 mol%)
It was formed by a sputtering method in an Ar atmosphere. Second
The thickness of the dielectric layer 32 was 20 nm.

The reflection layer 5 was made of Al-1.
A 7 mol% Cr alloy was formed by a sputtering method in an Ar atmosphere. The thickness of the reflection layer 5 was 100 nm.

The protective layer 6 was formed by applying an ultraviolet curable resin by a spin coating method and then curing the resin by irradiation with ultraviolet light. The thickness of the protective layer after curing was 5 μm.

The sample No. 1 thus produced was initialized. Initialization was performed at a linear velocity of 2 m / s using a bulk eraser.

For this sample No. 1, using an optical recording medium evaluation device (DDU-1000 manufactured by Pulstec), a laser wavelength λ: 635 nm, a numerical aperture NA: 0.6, a recording signal: EFM plus (8-16) ) Modulated single signal (3T signal which is the shortest signal) and random signal, Linear velocity: 3.5m / s (Shortest signal length: 0.38λ / N)
A) Under the conditions of (1) and (2), the shortest signal and the random signal were each recorded once, and then the recorded information was reproduced with a reproduction power of 0.9 mW.

Here, the intensity modulation pattern of the laser beam during recording will be described. Generally, when recording on a phase-change optical recording medium, recording light is not radiated in a DC manner corresponding to the length of a recording mark.
As described in 155945, multi-pulse recording is generally performed. FIG. 3 shows an example of a recording waveform in multi-pulse recording. In this specification, the recording waveform means a drive signal pattern for intensity-modulating the recording light. FIG. 3 shows the NRZI signal 5
A T signal and a recording waveform corresponding to the 5T signal are shown. In FIG. 3, Pw is the recording power, and Pb is the bias power. Pb is usually called an erasing power in a recording system capable of overwriting. This recording waveform has a recording pulse portion for forming a recording mark and a DC portion connecting the recording pulse portions. The recording pulse section has a structure in which a combination of an upward pulse (intensity Pw) and a subsequent downward pulse (intensity Pb) is repeated, and as a whole, rises from Pb and returns to Pb. In FIG. 3, Ttop is the width of the leading upward pulse, and Tmp is the width of another upward pulse (also called a multi-pulse). These pulse widths are represented by values standardized by the reference clock width (1T).

In this embodiment, using such a recording waveform, recording was performed under the following conditions: recording power Pw: 9 mW, bias power Pb: 0.5 mW, Ttop: 0.6 T, Tmp: 0.35 T. In the shortest signal (3T signal), the number of upward pulses in the recording pulse portion was one, and the width was Ttop. These recording conditions are optimal recording conditions that minimize clock jitter.

After recording, the shortest signal was measured for CNR using a spectrum analyzer (manufactured by Advantest) to find that it was 49.1 dB. When the clock jitter and the reproduction output of the random signal were measured, they were 8.5% and 1.04 V, respectively. If the clock jitter is 9% or less, it is possible to reproduce a signal having no practical problem. However, if the clock jitter exceeds 13%, especially if it exceeds 15%, many errors occur. Disappears. The clock jitter is determined by measuring the reproduced signal using a time interval analyzer (manufactured by Yokogawa Electric Corporation) and determining the “signal fluctuation (σ)”.
And σ / Tw (%). Tw is the detection window width. The reproduction output was measured with an analog oscilloscope.

Next, the track on which the signal was recorded was irradiated with a DC laser beam having an output of 2 to 7 mW at a linear velocity of 3.5 m / s to try to erase the recording mark. When CNR was measured after irradiation, a signal attenuation of 16.5 dB at the maximum was observed in the shortest signal. On the other hand, in the track on which the random signal was recorded, the ratio of the reproduction output after irradiation to the reproduction output before DC laser beam irradiation was 0.29.

Next, a random signal was recorded at a linear velocity of 3.5 m / s on the track irradiated with the DC laser beam, and its clock jitter was measured. Proved impossible to use.

In this sample, since the erasing rate by the irradiation of the DC laser beam corresponding to the erasing light is low, the clock jitter when a random signal is recorded after the irradiation is extremely large. Therefore, this sample cannot rewrite information.

The power of the DC laser beam was 7 mW
As the height was increased, the recording layer was melted and became amorphous after laser beam irradiation. That is, even if the laser power was increased, recrystallization of the recording layer was impossible.

After the initialization, the random signal was overwritten in the area where the random signal was recorded under the above conditions, and the clock jitter was measured under the same conditions. Then, the clock jitter could not be measured (more than 20%). Yes, signal reproduction was impossible.

After recording under the above conditions, the sample No.
When the recording layer 1 was observed with a transmission electron microscope,
As shown in FIG. 4, the shortest recording mark was almost circular. In FIG. 4, no recrystallized area is observed around the recording mark.

COMPARATIVE EXAMPLE 1 The thickness of the first dielectric layer was set to 120 nm, and the thickness of the second
Sample No. 2 was produced in the same manner as in Example 1, except that the thickness of the sample No. was changed to 50 nm.

The shortest signal and the random signal were recorded on Sample No. 2 in the same manner as in Example 1 except that the recording power Pw was changed to 8 mW, and the CNR, reproduction output and jitter were measured. As a result, the CNR of the shortest signal was 49 dB, the reproduction output of the random signal was 0.98 V, and the jitter was 1
It was 0%. That is, as compared with Example 1, the CNR was the same, but the jitter was large.

The sample No. 2 was used in Example 1
When irradiation with a DC laser beam was performed in the same manner as in the above, the carrier attenuation of the shortest signal was 18 dB or less. When re-recording was performed after the irradiation of the DC laser beam, the clock jitter of the re-recorded signal exceeded 15%.

Observation of the recording layer of Sample No. 2 with a transmission electron microscope revealed that the shortest recording mark was not circular but had a rounded trailing edge, and the vicinity of the trailing edge was recrystallized. . It is considered that the deterioration of the jitter occurred because the degree of recrystallization greatly varied from recording mark to recording mark.

The composition of the recording layer for comparison between the write-once medium and the rewritable medium was (Sb _0.7 Te _0.3 ) _0.9 (In _0.4 Ag _0.6 ) _0.1 except that the composition was the same as that of sample No. 1 of Example 1.
Sample No. 3 was prepared. Sample No. 3 has a recording layer with a higher crystallization speed than Sample No. 1, and thus can be rewritten at a linear velocity of 3.5 m / s.

After recording a random signal on the sample No. 1 and the sample No. 3 in the same manner as in the first embodiment,
Perform a playback operation in the recording area of the random signal,
The highest reflection level obtained at this time was defined as Rini. Next, an erasing operation of irradiating a DC laser beam at the same linear velocity as that at the time of recording was performed. FIG. 5 shows the relationship between the power of the irradiated DC laser light (DC erasing power) and the linear velocity V during irradiation.
Shown in Next, a reproducing operation is performed in the DC laser light irradiation area, and the highest reflection level obtained at this time is Rtop, the lowest reflection level is Rbottom, and (Rtop +
Rbottom) / 2Rini. FIG. 5 shows the results. The reflection level was measured by an optical recording medium evaluation device (DDU-1000 manufactured by Pulstec).

In FIG. 5, sample No. 3 satisfies (Rtop + Rbottom) / 2Rini ≧ 1 when the linear velocity is 3.5 m / s and the DC laser beam power is 3 mW or more. At all linear velocities of 5 m / s or more, (Rtop + Rbottom) / 2Rini <1 regardless of the power of the DC laser beam.

In each of these cases, after irradiating a DC laser beam of 3 mW or more, a random signal was recorded again under the same conditions as the first recording, and the clock jitter was measured.
In sample No. 3, it was 8 to 9%, and in sample No. 1, it was 16.8 to 20%. That is, sample No. 3
Can be rewritten at a linear velocity of 3.5 m / s, and sample No. 1 cannot be rewritten at a linear velocity of 3.5 to 14 m / s.

Comparative Sample No. 4 for Recrystallization around Recording Marks (Example) An optical recording disk sample No. 4 was manufactured in the following procedure. Translucent substrate 2, first dielectric layer 31, and protective layer 6
Were the same as Sample No. 1, respectively.

The recording layer 4 was formed by a sputtering method in an Ar atmosphere. The composition (atomic ratio) of the recording layer 4 was (Sb _0.68 Te _0.32 ) _0.92 (In _0.4 Ag _0.6 ) _0.08 . The thickness of the recording layer 4 was 20 nm.

The second dielectric layer 32 is composed of A
It was formed by sputtering in an Ar atmosphere using l ₂ O ₃ . The thickness of the second dielectric layer 32 was 20 nm.

The reflection layer 5 was made of Ag ₉₈ Pd as a target.
₁ Cu ₁ was formed by a sputtering method in an Ar atmosphere. The thickness of the reflection layer 5 was 75 nm.

Sample No. 5 (Comparative Example) The second dielectric layer 32 was made of ZnS (50 mol%)-SiO
₂ (50 mol%), and the reflective layer 5 is made of Al-1.7
A sample was prepared in the same manner as in Sample No. 4 except that the sample was composed of mol% Cr.

Evaluation The recording layer of each sample was initialized in the same manner as in Example 1. Then, for each sample, the shortest signal and the random signal were recorded once under the same conditions as in Example 1 except that the recording power Pw was set to 13 mW, and then the recorded information was reproduced.

For each sample after recording, a transmission electron micrograph of the recording layer was taken in the same manner as in Example 1.
A photograph of Sample No. 5 is shown in FIG. The recording mark in FIG. 6 is substantially circular or oblong. In FIG. 6, there is a recrystallized area around the recording mark that is clearly different from the crystalline state of the unrecorded area. The width of this recrystallized region was 50 μm. In addition, the area of the shooting field in FIG.
It is the same as the area of the shooting field in FIG. On the other hand, sample No. 4
In the transmission electron micrograph, no recrystallized region was observed around the circular recording mark as in FIG.

For each sample after recording, CNR and clock jitter were measured in the same manner as in Example 1. As a result, the CNR of the shortest signal is 51d in sample No. 4.
B, 50 dB in sample No. 5. The clock jitter of the shortest signal was 6% in sample No. 4 and 7.5% in sample No. 5. The clock jitter of the random signal is 8% for sample No. 4, and
In o.5, it was 10%.

From this result, it can be seen that when no recrystallized area exists around the recording mark, the CNR increases and the jitter decreases.

Next, each sample was inspected in the same manner as in Example 1 to determine whether it was a write-once medium. As a result, each sample was the sample No. of Example 1.
As in the case of No. 1, it was confirmed that the medium functions as a write-once medium at a linear velocity of 3.5 m / s.

[0086]

According to the present invention, there is provided a write-once phase change type medium having a small jitter when performing high-density recording.
In addition, a medium having a sufficiently high reproduction output is realized.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view illustrating a configuration example of an optical recording medium of the present invention.

FIG. 2 is a partial cross-sectional view illustrating a configuration example of an optical recording medium according to the present invention.

FIG. 3 is a graph showing a 5T signal and its recording waveform.

FIG. 4 is a drawing substitute photograph showing a crystal structure, and is a transmission electron micrograph of a recording layer.

FIG. 5 shows DC erasing power and (Rtop + Rbottom) / 2Ri
6 is a graph showing a relationship with ni.

FIG. 6 is a drawing substitute photograph showing a crystal structure, and is a transmission electron microscope photograph of a recording layer having a recrystallized region around a recording mark.

[Explanation of symbols]

 2 Translucent Substrate 20 Support Substrate 21 Groove 22 Land 31 First Dielectric Layer 32 Second Dielectric Layer 4 Recording Layer 5 Reflective Layer 6 Protective Layer

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hajime Utsunomiya 1-1-13 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (72) Inventor Toshiki Aoi 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK F term in the company (reference) 2H111 EA03 EA23 EA31 FA12 FA14 FA23 FB09 FB12 FB30 5D029 JA01 JB45 JB47 5D090 AA01 BB03 CC01 CC04 CC12 DD01

Claims (5)

[Claims] When the wavelength of a recording light is λ and the numerical aperture of an objective lens of a recording optical system is NA, the length is 0.4λ /
It has a phase-change type recording layer in which recording is performed so that the shortest recording mark that is less than or equal to NA and that is circular or oval is formed. An optical recording medium that is a write-once medium that cannot be read. 2. A represents an element other than the Sb and Te in M, represents an atomic ratio of the recording layer constituent element formula _{I (Sb x Te 1-x} ) in _1-y M _y, the minimum linear velocity to be used Is Vmin (m / s), 0.5 ≦ x ≦ y / 2 + 0.02Vmin + 0.57 and x
The optical recording medium according to claim 1, wherein ≤ 0.9 and 0 ≤ y ≤ 0.4. 3. The optical recording medium according to claim 1, wherein recording is performed such that a recrystallization region does not exist around the recording mark. 4. The recording information cannot be erased or rewritten at a linear velocity of 3.49 m / s or more.
An optical recording medium according to any of the above. 5. The optical recording medium according to claim 1, wherein erasing or rewriting of recorded information is impossible at a linear velocity of 1.2 m / s or more.