JPH03224789A - information recording medium - Google Patents

Abstract

PURPOSE:To prevent the generation of characteristic deterioration even when overlight operation is repeated by forming a recording layer, which reversibly generates a phase change between a crystal phase and an amorphous phase corresponding to a condition of the irradiation energy of laser beam, from a specific ternary alloy. CONSTITUTION:A data recording medium is constituted of a substrate 1 and the recording layer 3 provided on the substrate 1 and generating a phase change reversibly between an crystal phase and an amorphous phase corresponding to a condition of the irradiation energy of laser beam when receiving the irradia tion with laser beam. The recording layer 3 is composed of a ternary alloy having the same composition as an alloy {(InSb) (100-Y)/200TeY/100}100-Z (Sb2Te3)Z (wherein Y and Z are set to 20<=Y<=45, 0<=Z<=60 as well as 25<=Y<=35 and 60<=Z<=80) of Sb2Te3 and IN50-X/2Sb50-X/2TeX (wherein X is 20<=X<=45). The rapidly crystallizing characteristics and characteristics easy to become amor phous possessed by the alloy In50-X/2Sb50-X/2TeX are put to practical use and the stable amorphous characteristics of the compound Sb2Te3 can be obtained. Since Sb2Te3 has a stable composition, the composition of the ternary alloy is not changed even when overlight operation is repeated.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Field of Application) The present invention provides a method for forming a crystalline phase and an amorphous phase by alternately irradiating a light beam such as a laser beam while changing the irradiation conditions. has recording layers that are reversibly formed alternately with a predetermined width, and the information recorded on the recording layer can be read from the difference in the intensity of the optical signal that passes through the different phases formed in the recording layer. Regarding information recording media that can be used.

(Prior Art) Phase-change type optical disc materials in which light transmittance depends on the solid phase have been known as optical disk materials that can store information at high density and allow information to be erased and written at any time.

When this phase-change material is irradiated with a laser beam by changing the irradiation conditions, such as irradiation energy, irradiation intensity, or irradiation time, the irradiated area reversibly changes between different phases.

Examples of the above phase change material include tellurium (Te).
, germanium (Ge), these compounds T
Semiconductors, semiconductor compounds, or intermetallic compounds such as eGe, InSe, a compound of indium (In) and selenium (Se), 5bSe, a compound of antimony (sb> and selenium), or SbTe, a compound of antimony and tellurium. It has been known.

When the above material is irradiated with a laser beam, it forms either a crystalline phase or an amorphous phase depending on the irradiation conditions, and the above two states have a complex refractive index N=n (1 -ik) (where n is the refractive index and k is the absorption index). That is, since not only the refraction (J-n) but also the absorption index exhibit different values depending on the phase, light incident on the material exhibits different transmittance.

Therefore, the idea of using a material with the above characteristics as an optical memory that can erase and write information was 5Rovsh 1n.
It has been proposed by Sky et al. (Metal fu
rgical TransacNons 2.641 (
1971) ).

According to this proposal, a laser beam with varying irradiation conditions is alternately irradiated onto the disk while rotating a disk sandwiching a recording layer made of the above material, so that crystalline and amorphous phases are arranged alternately. A predetermined phase pattern is reversibly formed. Next, a reproduction laser beam with low irradiation energy is sequentially irradiated onto the crystalline phase and the amorphous phase. The irradiated reproduction laser beam alternately passes through either the crystalline phase or the amorphous phase, and then is reflected by a reflective layer appropriately provided at the rear.Then, the reflected reproduction laser beam is used as a reproduction signal as appropriate. The information consisting of the above-mentioned phase pattern is reproduced by converting the information using a photoelectric converter and determining the phase state based on the difference in transmittance corresponding to the phase.

More specifically, when recording information on a recording layer made of the above-mentioned material, a laser beam with high power and short pulse width that can heat the recording layer to a temperature exceeding its melting point is irradiated,
The irradiated portion is then melted and rapidly cooled to form a recording mark made of an amorphous phase. In addition, when erasing information recorded in the recording layer, a laser beam with a relatively long pulse width and a power that can heat the recording layer material to a temperature exceeding the crystallization temperature (lower than the melting point) is irradiated. The irradiated area is then slowly cooled, and the amorphous phase changes to a crystalline phase. That is, the recorded mark is erased.

In recording and erasing such information, a laser beam with a circular spot is used to melt and rapidly cool the irradiated area to make it amorphous, and a laser beam with an oblong spot is used to slowly cool and crystallize the irradiated area. A two-beam system that is used independently of each other is adopted.

However, in the above two-beam method, the optical system for irradiating the laser beam becomes complicated. In particular, it is difficult to make a laser beam with an oblong spot follow a spiral track inside the disk, which is made up of alternating amorphous and crystalline phases as the disk with the recording layer sandwiched therein rotates. Yes, a complicated servo machine is required.

Therefore, research is being conducted on a one-beam system in which information is recorded and erased using one laser beam.

In this 1-beam system, there is only a single laser beam source that follows the track on the disc, so it is easy to erase information already recorded on the recording layer and then override it by writing new information. I can do it.

That is, one laser beam irradiated from a single laser beam source is power modulated to two levels of power, that is, the power level Pe of the erasing laser beam or the power level Pw of the recording laser beam (Pe < P w ). However, the above two types of laser beams are alternately irradiated with a predetermined width onto a recording layer on which information has already been recorded, thereby erasing old information and overwriting new information at the same time.

This method of overriding with a single beam laser is called a 1-beam override method, and it eliminates the need for a complicated servo mechanism, which is a disadvantage of the 2-beam method mentioned above.
It is easy to set the position of the laser beam.

However, when applying the one-beam override method to a phase change recording layer, other difficulties arise.

That is, since the rotational speed of the disk at which a phase pattern consisting of an amorphous phase and a crystalline phase is to be formed is constant, the laser beam irradiated onto the recording layer at predetermined intervals in order to form an amorphous phase or a crystalline phase. The time during which the beam heat is released is the time during which the disk moves through the predetermined distance. In other words, the emission time of the laser beam heat does not depend on the phase formed, and whether the portion of the recording layer irradiated with the laser beam becomes an amorphous phase or a crystalline phase depends on the power of the irradiated laser beam. Determined only by size.

Therefore, since crystallization must be performed in a time as short as that required for amorphization, it is not possible to perform crystallization by taking a sufficient time for slow cooling to erase information.

Furthermore, when recording information, it is difficult to change the end portion of a portion where a recording mark made of an amorphous phase is to be formed into an amorphous phase. The reason for this is that some of the heat given to the recording layer by the erasing laser beam irradiated to form the crystalline phase immediately before the formation of the amorphous phase remains without being radiated, and this residual heat causes the above-mentioned This is because the rapid cooling of the end portion where the recording mark is to be formed is impaired.

Therefore, it becomes impossible to alternately form amorphous phases and crystalline phases with a predetermined width, which causes incorrect information to be read.

Therefore, in recent years, indium (In), antimony (sb>), and tellurium (Te) have been used as materials to which the above-mentioned one-beam override method can be applied to the phase change recording layer.
An alloy consisting of is attracting attention. This base alloy can be applied to the one-hime overwrite method by appropriately selecting the composition.

That is, according to the experiments of the present inventor, an alloy formed by adding 20 to 45 atomic % of tellurium to the compound InSb, in other words, an alloy formed by adding 20 to 45 atomic % of tellurium, in other words, X atomic % of Te, 50-X/2 atomic % of In, and 5
I n 50-X/2 consisting of 0-X/2 atomic % sb
S b %O-X/2T e X (however, 20≦
It is within the range of X≦45. ) by using an alloy material having the composition represented by as the recording layer, the compound I n
Obtain tellurium's property of easily becoming amorphous (hereinafter referred to as easy amorphous property) while taking advantage of Sb's property of quickly crystallizing (hereinafter referred to as high-speed crystallization property). I can do it. In other words, it is possible to overcome the problems of the one-beam override method, which are the need to crystallize in a short time and the need to become amorphous without rapid cooling.

In addition, since it is easily amorphous due to the above-mentioned property of making it easy to become amorphous, it is possible to make it amorphous even if the power of the recording laser beam, which requires the highest power, is turned off. Therefore, the optical system can be downsized, economical, and easy to handle.

However, the above I n 50-X/2S b 5
Since the recording layer made of 0-X/2TeX is an alloy, the bonding force between atoms is weak and there is a problem in the stability of the composition. Therefore, when the recording layer is repeatedly melted and rapidly cooled in the overriding operation, the alloy composition of the overridden portion gradually changes, that is, it segregates, and the above-mentioned high-speed crystallization characteristics and easy-to-amorphous characteristics deteriorate. There was a problem with it being put away.

On the other hand, Sb2Te, which is a compound with a stable composition, is considered as a material for the recording layer.

In other words, when Sb2Te is used as the recording layer material, the amorphous phase formed by recording laser beam irradiation is stable (hereinafter referred to as amorphous stability characteristic). It has the property of easily changing into an amorphous phase even if some of the heat from the beam remains, that is, it has the property of easily becoming amorphous.

Furthermore, since Sb and Te are compounds, their compositions do not change even if they are repeatedly melted and rapidly cooled in the overrite operation, so the above-mentioned amorphous stability characteristics and easy amorphousization characteristics of Sb2Te do not deteriorate.

However, when attempting to form a crystalline phase by using Sb or Te3 as the recording layer material and irradiating it with an erasing laser beam, the crystallization speed is very slow at approximately IIJs. That is, when overriding is performed, the amorphous phase that should be crystallized remains unerased, resulting in a disadvantage that the erasing rate of old information becomes poor.

(Problems to be Solved by the Invention) As described above, when the recording layer is irradiated with a laser beam using the two-beam method to form an amorphous phase and a crystalline phase, a desired phase can be obtained. The problem was that a complicated servo mechanism was required to determine the beam irradiation position.

Therefore, when the one-beam override method is applied, although the servo mechanism described above is simplified, crystallization must be performed in a time comparable to that required for amorphousization. Further, it is difficult to change the end portion of a recording mark made of an amorphous phase to an amorphous phase.

As a result, there was a problem in that incorrect information was read.

In order to solve this problem, we developed In 50-X/2S b 50-X, which has good high-speed crystallization characteristics and easy amorphization characteristics.
It was considered to apply /2TeX to the material of the recording layer, but there was a problem that when the recording layer was repeatedly melted and rapidly cooled in an alloy lick override operation, the material would segregate and the above characteristics would deteriorate. .

On the other hand, when the compounds Sb and Te are used in the recording layer, the amorphous stability and easy amorphous properties of 5b2Tei do not deteriorate even after repeated override operations, but the crystallization speed is slow and the information There was a problem that the erasure rate was poor.

Therefore, the present invention solves the above-mentioned problems of the prior art, and its purpose is to achieve high-speed crystallization characteristics and easy amorphousization characteristics without requiring a complicated sabot machine tank. It is an object of the present invention to provide an information recording medium which has good override characteristics and which does not deteriorate even if an override operation is repeated.

[Structure of the Invention] (Means for Solving the Problems) The present invention for solving the above-mentioned problems includes a substrate, and a light beam provided on the substrate that responds to the irradiation energy conditions when irradiated with a light beam. In an information recording medium comprising a recording layer whose phase changes reversibly between a crystalline phase and an amorphous phase, the recording layer comprises Sb, Te, and In 50-X/2.
S b 50-X/2T e x (in the formula, X is 20≦X
≦45) ((InSb) +too−
n/zoo Tey/loo) too-z
(Sb 2 Te=>2 (in the formula, Y and Z are 20≦Y
≦45 and 0≦Z≦60, and 25≦Y≦35 and 60
It is characterized by being made of a ternary alloy having the same composition as (Z≦80).

(Function) In the information recording medium of the present invention, the recording layer is made of indium (Indium).
>, antimony (Sb), and tellurium (Te) in the above-mentioned composition ratio, that is, ((TnSb)noo-v+7□oo
Tey, z+oo ) +oo-z (Sb2Te3
) (in the formula, Y and Z are 20≦Y≦45 and 0≦Z≦60,
and 25≦Y≦35 and 60 (Z≦80), so the alloy 1n5°-X7□sb.

-The property of quickly crystallizing and easily becoming amorphous that X7□Tex is utilized, and the compound 5b
The stable amorphous properties of 2Tei can also be obtained.

Further, since Sb and Te have stable compositions, there is no change in the composition of the ternary alloy constituting the recording layer even if the override operation is repeated.

The reason is that Sb2Te, which has a stable composition, is alloy I n
50-X/2Sb 5G-X/2T e x , so even if the recording layer melts during override, the alloy I n 50-X/2S b that constitutes this recording layer
50-x/zTexJ, the alloy I n , o-X/
2S b 50-X/2T e The constituent atoms of 2S b 50-X/2T e
This is because exchange with atoms of x is impaired and segregation does not occur.

Therefore, even if the recording layer is alternately irradiated with light beams under different conditions for overriding at any time, and crystalline phases and amorphous phases are alternately and reversibly formed with a predetermined width, the complex refractive index of each phase N=n
(1-ik> (where ■ is the refractive index and k is the absorption index)
always shows a stable constant value. That is, the light absorption rate of each phase is constant.

This means that the transmittance of an optical signal incident on the recording layer for reading a phase pattern consisting of a crystalline phase and an amorphous phase is always constant. Therefore, the phase pattern formed on the recording layer can always be accurately read from the difference in transmittance of optical signals incident on the recording layer.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an information recording medium according to an embodiment of the present invention.

As shown in the figure, the information recording medium of this embodiment includes a substrate 1 through which recording and erasing laser beams and information reproducing laser beams are transmitted, a thermally stable protective layer 2 provided on the substrate 1, and a thermally stable protective layer 2 provided on the substrate 1. A recording layer 3 provided on the protective layer 2 and recording information, and a recording layer 3 provided on the recording layer 3 together with the protective layer 2.
It is composed of a protective layer 4 that seals and protects the information, a reflective layer 5 laminated on the protective layer 4 to reflect the information reproducing laser beam, and a resin layer 6 provided on the reflective layer 5.

Here, the substrate 1 is a disk-shaped substrate with a diameter of 5 inches made of polycarbonate, which is a material that does not change easily over time.

The recording layer 3 is made of indium (In) and antimony (sb
> and a ternary alloy of tellurium (Te) formed to a thickness of 20OA, and the compound Sb2Te, tellurium at X atomic %, indium at 50-X/2 atomic %, and antimony at 50X/2 atomic % Alloy I n 5G-
X/2S b 50-X/2T e (However, X is expressed in atomic % and is within the range of 20≦X≦45.)
has the same composition as that of a predetermined ratio as described below.

The recording layer 3 made of the above ternary alloy has a melting point (50
The protective layer 2.4 is heated to a temperature exceeding 0 to 600° C.), and then laser beam heat is emitted to the protective layer 2.4 to make it amorphous and form an amorphous phase 7. Further, when the recording layer 3 is irradiated with an erasing laser beam having a predetermined power level, it is heated to a temperature exceeding the crystallization temperature, and then the laser beam heat is emitted to the protective layer 2.4, causing crystallization.
This forms a crystal phase 8.

The protective layer 2.4 is a dielectric material with a thickness of 100 OA made of aluminum oxide (A120) crystal, which is thermally stable (melting point is about 1300°C) and transparent to the laser beam. This protects the recording layer 3 sandwiched between the protective layers 2 and 4. That is, the protective layer 2.4 seals the recording layer 3 with a thermally stable material, so that
A recording or erasing laser beam is irradiated onto the recording layer 3 to prevent the formation of a cavity when the irradiated portion evaporates. In addition, the protective layers 2 and 4 are heated to the extent that the recording layer 3 heated by the laser beam irradiation is heated to an extent exceeding the melting point or crystallization temperature, and the heat is radiated to form an amorphous phase or a crystalline phase. It has conductivity and appropriately absorbs heat from the recording layer 3 that has been heated. Further, when a recording/reproducing laser beam made of a semiconductor laser with a wavelength of 830 nm is irradiated onto the recording layer 3, reflected by the recording layer 3 and the reflective layer 5, and then emitted from the substrate 1, the protective layer 4 protects the recording layer 3. An optical propagation distance is given to only one of the laser beams that passes through the layer 4, that is, the laser beam reflected by the reflective layer 5, and the two emitted laser beams are enhanced by causing interference, and the intensity of this laser beam is measured. Make it easy.

In this example, the reflective layer 5 is made of gold (with a thickness of 100 OA).
It consists of a thin film of Au).

The resin layer 6 is formed from an ultraviolet curing resin having a thickness of 10 μm, and prevents scratches from occurring on the surface.

Next, a method for manufacturing an information recording medium having the above configuration will be described.

First, a disk-shaped substrate 1 is made of aluminum oxide (Al□
0. ) is placed in a vacuum chamber of a sputtering apparatus having a target such as the target, and then the inside of the chamber is brought to a high vacuum using an appropriate vacuum device.

Next, argon gas is introduced into the chamber, and radio frequency power (hereinafter referred to as RIF) is applied to sputter the aluminum oxide target using the argon gas to form a protective layer 2 on the substrate 1. do.

Next, while maintaining the argon gas atmosphere inside the chamber, the compound Sb2Te3 and the alloy In were added.

X/2S b , 0-X/2Te X (However, X
is expressed in atomic % and falls within the range of 20≦X≦45. ) are simultaneously sputtered with argon gas to form the recording layer 3.

Here, the sputtering amount of each target sputtered in the above operation is prepared in advance, and t! A recording layer 3 having a desired composition can be obtained.

Note that the above targets may be alternately sputter-linked.

In addition, since the target compound or alloy is deposited on the protective layer 2 in atomic units during sputtering,
The same thing will happen if indium (In), antimony (Sb), and tellurium (Te) are sputtered simultaneously using separate target materials.

Next, a protective layer 4 is formed in the same manner as the protective layer 2.

Next, a reflective layer 5 is laminated by sputtering by applying R and F powers to a gold (Au> target).

Finally, the disk obtained by the above operation is taken out from the sputtering device, then set in a spinner, and after spin-coding the ultraviolet curable resin, it is irradiated with ultraviolet rays and cured to form the resin layer 6.

Using the method for manufacturing an information recording medium explained above, three samples consisting of sample A group to sample F group were prepared within the composition range 9 of the recording layer material of the information recording medium in this example shown in FIG.
One disc sample was created.

Sample A group ・ ((I n S b ) o,, 5/□Te a45)
too-Z(Sbz Te,)z z=0.20.40.60.80.100 atomic% Sample B group ((I n S b > 0.60/2T e O, 4
01100-Z(Sb2Te,)z2=0.20.40.60.80 atomic% Sample C group ((I n S b ) 0.65/2TeO, 15)
Ioo-Z(Sb2Tei)z2=0.20.40.60.80 atomic% Sample D group
・((I n5b) 0.70/2T60.90) +0
O-Z(Sbz Te3)z z=0.20.40.60.80 atomic% Sample E group
; ((I n S b ) o, tszzTe O,25
+ 100-Z (Sb, Te,)z z=0.20.40-60.80 atomic% Sample F group
: ((T n S b ) 0.110/2 T e O,
20) Io. -Z(Sbz Te,)z z=0.20.40.60.80 atomic%, that is, in sample A group, I n qo-xyxs b , o-xyzT
A compound with X=45% was used as ex.

Similarly, for sample 8 group, X = 40 atomic%, for sample C group, X = 35 atomic%, and for sample 0 group, X = 30 atomic%.
atomic %, X = 25 atomic % for sample E group, sample F
In the group, a compound containing X-20 atom % was used.

Next, initialization of the information recording medium obtained in this way,
Information override and information reproduction will be explained.

The recording layer 3 is formed by sputtering and is rapidly cooled when deposited on the substrate 1, so that it becomes an amorphous phase.

Therefore, in order to form an amorphous recording mark having a predetermined width, the entire recording layer 3 must undergo a phase change to a crystalline phase, which is the initialization of the information recording medium.

In this example, a disk sample produced by the above-described manufacturing method was rotated at 180 Or, p, +n, and a continuously emitted laser beam with a power of 14 mW was applied to a predetermined area of the recording layer in a spiral shape. track was irradiated and the above initialization was performed.

Here, since the amorphous phase formed on the substrate 1 by sputtering is very thermally stable, a recording laser beam with a particularly high power of 14 mW was used. Further, in order to completely crystallize the recording layer, the same track was irradiated with laser light three times.

After initialization is completed, a phase pattern in which amorphous phases and crystalline phases are alternately arranged with a predetermined width is formed along the track, and information can be obtained by reading this phase pattern. Formation of the phase pattern described above is information override.

In this example, as shown in FIG. 3, a recording laser beam with the highest power level Pw: 14 mW and a lower power level Pa=8 mW than this recording laser beam are used.
A W erasing laser beam was used. In other words, 4MH
The above two types of laser beams were switched at equal time intervals with a period corresponding to 2 or 5M82 frequency, that is, a period consisting of the reciprocal of the frequency, and then these laser beams were irradiated onto the tracks of the recording layer to perform the above overriding.

That is, since the disk is rotating at a predetermined speed, the portion irradiated with, for example, a recording laser beam becomes an amorphous phase and a recording mark is formed. Next, when the laser beam is switched to irradiation with the erasing laser beam after the switching cycle has elapsed, the amorphous phase moves, and the new irradiated area becomes crystalline when irradiated with the erasing laser beam. . In this way, a phase pattern is formed in which the amorphous phase and the crystalline phase are alternately arranged with a predetermined width corresponding to the switching period of the laser beam.

Note that at the time of first overriding, initialization has already been performed and the recording layer is in a crystal phase, so there is no need to use the erasing laser beam, and it is sufficient to intermittently irradiate only the recording laser beam.

Since the power level is switched at equal intervals, the duty ratio is 50%.

After the override is completed, the recording layer 3 is irradiated with a reproduction laser beam whose irradiation energy is low enough not to cause a phase change even if the recording layer 3 is irradiated, and then the amorphous phase and the crystalline phase are alternately transmitted. The phase pattern is read by measuring the difference in energy intensity of the laser beam. This phase pattern in which amorphous phases and crystalline phases are alternately arranged with a predetermined width can be regarded as data consisting of a binary code series, and this data is obtained as information written in the recording layer. This is information reproduction.

In this example, a semiconductor laser beam (wavelength: 830 nm) with a power level of 0°8 mW was used as the laser beam for reproduction.
m) was used. That is, the laser beam is incident on the protective layer 2.4 and the recording layer 3 from the substrate 1, and the laser beam is applied to the recording layer 3 and the reflective layer 5.
The laser beam reflected by the recording layer 3 and the protective layer 2.
4 was transmitted through the substrate 1, and the reflected light emitted from the substrate 1 was detected by a photoelectric conversion element. The detected reflected light is transmitted to A/A as a reproduction signal.
D-converted and the above sample A on a spectroanalyzer
The frequency distribution was measured for each disk sample in group or sample F group.

In other words, the reproduced signal transmitted through the amorphous phase or the crystalline phase is
Since each of the above phases is formed by switching the laser beam power at a frequency of 4 MHz or 5 MHz, the energy intensity fluctuates based on the unique transmittance of each phase to the laser, and the period of the fluctuation is the switching period of the laser beam power. matches. In short, the playback signal is 4MHz
Or the frequency will be 5MHz.

Next, measure the C/N value from the measured frequency distribution,
The information recorded on the recording layer of each disc sample was reproduced.

Here, the C/N value is the ratio of the magnitude of a reproduced signal having a specific frequency (4 MHz or 5 MHz) to the magnitude of noise having various frequencies, and is expressed in logarithmic decibel (dB) units.

C/N values measured in FIG. 4 (A> to FIG. 4 (F)),
The results of evaluating the characteristics of disk samples using the degree of erasure determined from this C/N value are shown for each sample group.

In the figure, the horizontal axis is In, 0-X/2S b 50
-X/2T shows the same composition as the alloy composition of e8 and Sb2Te, and the left end of the horizontal axis is In 50-X/2S b
The right end of the horizontal axis corresponds to the composition of only Sb2Te3, and the right end of the horizontal axis corresponds to the composition of only Sb2Te3. The vertical axis on the left side represents the C/N value and corresponds to a polygonal line connecting each data with a solid line, and the vertical axis on the right side represents the degree of erasure and corresponds to a polygonal line connecting each data with a broken line.

Here, the degree of erasure is defined as follows. That is, the first recording is performed using a recording laser beam with a frequency of initialization fJJ4MHz, and the C/N value of the reproduced signal 10 obtained as shown in FIG.
When overriding is performed by changing the phase pattern using the recording and erasing laser beams of the z frequency, as shown in FIG. When the /N value is, for example, B, the degree of erasure is the value of B-A obtained by logarithmizing the ratio of the magnitude of the erased remaining signal 11 to the magnitude of the reproduced signal 10.

Further, FIG. 5(B) shows the C/N value C of the reproduced signal 12 corresponding to the information newly written by the above-mentioned override, and this C/N value C is displayed in FIG.

Returning to Figure 4, in all sample groups, Sb2T
There is a tendency for the C/N value to decrease and the erasure degree to approach zero as the composition approaches the composition of .e.

This means that it is no longer possible to obtain a clear reproduced signal, and there is a greater possibility that erroneous signals will be picked up.

The reason for this tendency is that, as explained in the prior art, the crystallization rate, that is, the information erasing rate of Sb2Te compounds is slow, and as the composition approaches Sb and Te, the amorphous phase that should be crystallized is This is because the data will remain without being deleted.

Therefore, the phase pattern of the amorphous phase and the crystalline phase collapses, and the frequency of the reproduced signal that reads this phase pattern becomes different from the frequency corresponding to the power switching period of the laser beam, and the C/N value of the reproduced signal becomes to degrade. In addition, the degree of erasure B-A also deteriorates due to the deterioration of the C/N value A and the increase in the C/N value B due to the increase in the remaining erase signal 11 caused by the amorphous phase that remains unerased.

However, alloy I n , o-xy2s b rh
In the region where the influence of o-xyxT e8 contributes, that is, sample A group and sample F group, the compound Sb2Te is 60
At % or less, in the composition range where the compounds Sb and Te are at most 80 atomic % in Sample 8 Group to Sample 8 Group, alloy I n 5G-X/2S b 50-X/2T e
The high-speed crystallization property and easy-to-amorphize property of x are utilized, and the C/N value and erasing degree show excellent values. That is, C
/N value shows a value of 35 dB or more, and the cancellation degree is -20 dB.
The following values are obtained, and a clear reproduced signal can be obtained, and the possibility of picking up erroneous signals is greatly reduced.

Next, Figure 6 shows the results when overriding was repeated many times for all sample groups by alternately using a 4 MHz frequency recording and erasing laser beam and a 5 MHz frequency recording and erasing laser beam. show.

That is, as shown in FIG. 6 by extracting and enlarging the composition range 9 of the recording layer material of the information recording medium shown in FIG. The results of the evaluation were shown.

For example, for a disk sample that maintained a C/N value of 45 dB or more even after repeated overrides over 100,000 times, a symbol ◎ indicating excellent quality will be placed at its composition position, and a C/N value of 35 dB or more will be maintained under the same conditions as above. Disk samples that have been overridden are marked with a symbol ○ to indicate good, disc samples that maintain a C/N value of 35 dB or more until overriding is repeated 1000 to 1T times are marked with a symbol . Disc samples with a value of 35 dB or less are marked with a symbol indicating a defect.

Considering the characteristic evaluation when overriding is repeated many times as shown in Figure 6, and the characteristic evaluation considering the C/N value and erasure degree after the first override as shown in Figure 4, the alloy Ins. -8/2S b , 0-X/
The compound Sb, T
(I n S
b > +100-Yl/200 TeY/10(1)
10a-z (Sb2Te1)z (However, Y
, Z is expressed in atomic %, 20≦Y≦45 and 0≦
It is within the range of Z≦60. ) In the composition range of the In-5b-Te ternary alloy having the same composition as the composition shown in FIG.

That is, the C/N value maintains 35 dB until the override is repeated 1000 to 1T times, and the degree of cancellation remains 120 dB.
It shows a value of dB or less, and not only can a clear reproduced signal be obtained, but also the possibility of picking up an erroneous signal is greatly reduced.

In addition, in sample C group to sample 8 group, the compound *S
Even in the composition range in which b2Te accounts for 60 to 80 atomic %, the C/N value and erasure degree similarly exhibit excellent values.

In particular, in sample group 8, the compound Sb2Te ranged from 4O to 6
Composition range occupied by 0 atom%, compound Sb2 in sample C group
A composition range in which Te accounts for 20 to 60 at%, a composition range in which compounds Sb and Te account for 20 to 40 at% in sample 0 group and sample 8 group, and a composition range in which compound 5bzTe accounts for 40 at% in sample F group. Even after overriding over 100,000 times, the C/N value remains 4.
Since it maintains 5 dB or more, it is possible to obtain a very clear reproduced signal when applied as a material for a phase change type recording layer in a one-beam override system.

The reason why the C/N value and erasing degree show such excellent values is that Sb, Te, and In alloy have a stable composition. -X/2
Since it is between S b 5゜-X72TeX, the alloy I n , 0-X/2S b
5G-X/IT e x is the alloy I n , o-xyx
s b , o-X/2T e x constituent atoms in other alloys In 50-X/2S b 5G-X/27 e X
This is because exchange with other atoms is impaired and segregation does not occur.

Therefore, compounds Sb, Te3 alone or alloy I
n 5G-X/2S b 50-X/2T e x
(However, X is expressed in atomic%, 20≦X≦45
is within the range of ) alone, that is, high-speed crystallization properties and easy amorphous properties that are always stably obtained even after repeated overrides, can be achieved by using compounds Sb, T
e, and alloy 1 n 50-X/2S b 50-X/2
It can be obtained by suitably preparing the alloy composition to be the same as that of Te8.

In the above description, the protective layer 2 and the resin layer 6 are provided in the information recording medium of this example, but they are not necessarily necessary.

In addition, in this example, in order to evaluate the characteristics of the information recording medium,
The power pattern of the laser beam shown in Fig. 4 was obtained by switching the power of the laser beam with a frequency of 4 MHz or 5 MHz, and the recording layer was irradiated with the laser beam at a duty ratio of 50%. can be changed freely without being limited to the above, and the duty ratio may also be changed in the same way.

The present invention is not limited to the above-described embodiments, but can be implemented in any appropriate manner by making appropriate design changes.

[Effects of the Invention] As explained above, according to the present invention, when a substrate is provided on the substrate and is irradiated with a light beam, a crystalline phase or an amorphous phase is formed depending on the irradiation conditions such as the irradiation energy. In an information recording medium comprising a recording layer whose phase changes reversibly to
-X/2S b , 0-X/2T eX (where X is 2
0≦X≦45)) ((I n S b )
+100-Yl/200 TeY/1001 too
-Z(Sb2Te,)z (in the formula, Y-Z is 20≦Y≦
45 and 0≦Z≦60, and 25≦Y≦35 and 60×z≦80), and the compositionally stable compounds Sb and Te are alloy 1n. -X
7□Sb,. -X72TeX, so the alloy Ins when overriding. -X7□Sb 5G-
Since changing the constituent atoms of the The override characteristics represented by the easy-to-change characteristics are good, and the override characteristics do not deteriorate even if the override operation is repeated.

[Brief explanation of drawings]

FIG. 1 shows a cross-sectional view of an information recording medium according to an embodiment of the present invention, and FIG. 2 shows an In-3b-Te composition diagram showing the composition range of the recording layer of the information recording medium shown in FIG. Figure 3 is an explanatory diagram of the beam power pattern obtained by alternately switching the erasing laser beam and the recording laser beam, Figure 4 (A> to Figure 4 (F)) are the C/N values of the disk samples created. and a characteristic diagram showing the degree of erasure, Fig. 5 (A)
and Fig. 5(B) is a reproduced signal display diagram for explaining the degree of erasure, and Fig. 6 is an explanatory diagram of characteristic evaluation regarding the C/N value when the composition range shown in Fig. 2 is expanded and overriding is repeated. It is. ■...Substrate 3...Recording layer 6...Resin layer 8...Crystal phase 2.4...Protective layer 5/Reflection layer 7...Amorphous phase

Claims (1)

[Claims] Information recording comprising a substrate and a recording layer provided on the substrate that reversibly changes phase between a crystalline phase and an amorphous phase depending on the irradiation energy conditions when irradiated with a light beam. In the medium, the recording layer includes Sb_2Te_3 and In_5_0_-_X_/_2Sb_5_0_-_X_
/_2Te_X (in the formula, X is 20≦X≦45) alloy {(InSb)_(_1_0_0_−_Y_)_/
_2_0_0Te_Y_/_1_0_0}_1_0_0
＿−＿Z(Sb_2Te_3)_Z(in the formula, Y and Z are 20
An information recording medium comprising a ternary alloy having the same composition as ≦Y≦45 and 0≦Z≦60, and 25≦Y≦35 and 60<Z≦80.