JP2557407B2 - Information recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to an optical disc for recording and erasing information by causing a phase change in a recording layer by irradiating a light beam such as a laser beam. And other information recording media.

(Prior Art) Conventionally, a phase change type optical disc has been known as an erasable optical disc. In this phase change type optical disc, by irradiating the recording layer with a laser beam,
Information is recorded and erased by utilizing the reversible phase change of the recording layer between, for example, crystalline and amorphous.

Examples of such phase change materials include Te, Ge,
There are semiconductors such as TeGe, InSe, SbSe, SbTe, semiconductor compounds or intermetallic compounds. These selectively take two states, a crystalline phase and an amorphous phase, depending on the temperature, and the complex refractive index represented by N = n-ik is different in each state. Information is recorded and erased by reversibly changing these two states (SROvshinsky
Metallurgical Trasactions 2 641 1971).

On the other hand, unlike the above-described method, there is also a technique of recording and erasing information by reversibly changing the phase between different crystalline materials by irradiation with a laser beam. An In-Sb alloy is known as a material that undergoes such a phase change.

The In-Sb alloy thin film has a relatively long pulse width, and becomes a fine crystal grain when irradiated with a weak laser beam.The pulse width is short, and the fine crystal grain is generated in a short time when irradiated with a laser beam having a large output. Grow into relatively large crystals.
These two crystal structures have different complex refractive indexes, and when reproducing by irradiating a laser beam, for example, the crystal states are distinguished as a difference in the amount of reflected light.

(Problems to be Solved by the Invention) However, all of the above-mentioned materials used in the technique of recording and erasing information by changing the phase between crystalline and amorphous, have a low crystallization rate, and initialization and information It takes a long time to erase. In addition, in the case of this technique, the recording mark portion of the recording layer is usually amorphous, but in general, amorphous has low stability, and for example, if it is used in a high temperature environment for a long time, it will crystallize. However, there is a drawback that it becomes impossible to distinguish between the recorded portion and the non-recorded portion.

On the other hand, in the case of an optical disk of the type in which the recording layer is formed of In-Sb and the phase changes between different crystalline materials, the recorded mark is crystalline, and thus the recorded information is stable. In addition, the composition near the In ₅₀ Sb ₅₀ intermetallic compound has an advantage that the crystallization rate is extremely fast, but in this case, since segregation of Sb as described later does not occur, information is substantially recorded. There is a problem that it is difficult. On the other hand, it has also been attempted to form the recording layer from an alloy having a composition in which Sb is slightly in excess of In ₅₀ Sb ₅₀ . In this case, by irradiating the recording layer with a laser beam, the recording layer becomes a mixed phase of In ₅₀ Sb ₅₀ crystal grains and Sb crystal grains, and the size of the Sb crystal grain changes depending on the laser beam irradiation conditions. Therefore, the recording level can be maintained by this.
However, since Sb has a low crystallization speed, the processing and erasing speeds are low, and it is not possible to increase the processing speed, and there is a risk that initialization failure and unerased residue may occur.
Also, when recording, if the optical disk rotates at a high speed, there is a possibility that the crystal growth will not be sufficient and the recording will be insufficient.

As described above, when a material that undergoes phase change between crystals and between crystals and amorphous is used for the recording layer, there are advantages and disadvantages, and none of them have sufficient characteristics.

The present invention has been made in view of the above circumstances, and is capable of performing initialization and erasing at high speed, suppressing occurrence of defective initialization and erasure residue, and recording information with good recording characteristics. The purpose is to provide a medium.

[Structure of the Invention] (Means for Solving Problems) An information recording medium according to the present invention comprises a substrate, a crystalline phase by irradiation with a light beam, and a mixed phase in which crystals are mixed in an amorphous state. And a recording layer on which information is recorded and erased by reversibly changing the phase.

(Operation) In the present invention, a material that can cause a phase change between the crystalline phase and the mixed phase in which crystals are mixed in the amorphous phase is used as the recording layer. In such a composition, the crystallization speed is high, and the rate of change of phase change between the fine crystals and the mixed phase in which the fine crystals are mixed in the amorphous phase is high. It can speed up. Further, by making the recording mark portion a mixed phase in which crystals are mixed in an amorphous state, information can be stably recorded,
The recording level can be increased.

(Example) Hereinafter, the Example of this invention is described concretely.

When the phase change at the time of recording and erasing the information in the light beam irradiation portion of the recording layer occurs between the crystalline phase and the mixed phase in which crystals are mixed in the amorphous, the conventional crystal / amorphous or Inconveniences such as those between crystals / crystals can be avoided. That is, when information is recorded and erased by causing such a phase change, the crystallization and phase change speeds are high, so that the initialization and erase speeds can be increased.
In addition, since the recording mark portion can be made into a mixed phase of amorphous and crystalline, the crystal existing in the recording mark portion can maintain the stability of the crystal, and the amorphous state in the recording mark portion makes it possible to maintain a certain degree of stability. The recording level can be maintained. For example, the recording layer is formed of an alloy having a composition represented by the general formula (In _100-x Sb _x ) _100-y Te _y , and x and y are 48 ≦ x ≦ 52 and 0.05 ≦, respectively.
In the case of y ≦ 5, when the recording layer is irradiated with a light beam, a phase in which fine crystals of InSb intermetallic compound and InTe or SbTe are mixed and In
A phase change occurs between the amorphous phase of Te or SbTe and a mixed phase in which fine crystals of InSb are mixed. Then, at the time of initialization and erasing of information, it becomes a phase in which a fine crystal of InSb intermetallic compound and a fine crystal of InTe or SbTe are mixed, and when recording information, InTe or
It becomes a mixed phase in which fine crystals of InSb are mixed in the amorphous of SbTe. The composition range in which such a phase change occurs will be described in detail. As described above, the In—Sb alloy forms an intermetallic compound when both In and Sb are 50 atomic%, and the crystallization rate becomes maximum at this composition. However, with this composition,
As described above, since Sb segregation does not occur, it is difficult to record information. Therefore, it is considered effective to add the third element to the RnSb intermetallic compound in order to record information and increase the initialization speed and the erasing speed. However, since the composition is only one point and there is no composition width, it is extremely difficult to manufacture and the retention during mass production is reduced, so that the basic In-Sb alloy requires a certain composition width. On the other hand, as described above, when the composition deviates from the InSb intermetallic compound and Sb becomes excessive (for example, In ₄₅ Sb
₅₅ ), Sb segregation reduces the crystallization rate,
Although the initialization and the erasing speed of information become small, the experiment by the inventor of the present application revealed that the crystallization speed does not decrease if the deviation of Sb is within ± 2 atomic% from the InSb intermetallic compound. ing. From this, the composition of the basic InSb alloy is in the above range where the crystallization rate does not decrease, that is, In
_{In 100-x} Sb _x , the range is 48 ≦ x ≦ 52.

Further, as the third component, an element that facilitates recording of information, that is, an element that can increase the reproduction signal level is required. Te is such an element. Te is a material that is extremely likely to become amorphous, and the aforementioned In _100-x Sb _x (48
When Te is added to ≦ x ≦ 52), the proportion of amorphous in the recording mark portion increases in proportion to the amount of Te added during recording. That is, as the amount of Te added increases, the amorphous portion of InTe or SbTe becomes larger than the fine crystal of InSb in the recording mark portion, so that the reproduction signal from the recording mark portion increases. However, since the amorphous phase of InTe and SbTe has a relatively low crystallization rate, the initialization and erasing rates decrease as Te increases, and when the optical disc is rotated at a high speed, initialization failure and erasing residual Will become bigger. That is, although the crystallization rate of Te itself is as high as several tens of nanoseconds, if the ratio of InTe or SbTe alloy is increased, the crystallization rate of the whole is decreased. In this case, if the content of Te exceeds 5 atomic%, the crystallization speed becomes too slow,
The initialization speed and erase speed will be insufficient. On the other hand, the In _100-x Sb _x (48 ≦ x ≦ 52) alloy described above has little segregation of Sb, and thus the recording signal is small. In this case, Te is required to be 0.05 atomic% or more to effectively record information. Therefore, as described above, the range of 0.05 ≦ y ≦ 5 is suitable.

The state in which crystals are mixed in amorphous can be clearly distinguished from crystals and amorphous by electron beam diffraction. That is, in the case of amorphous, only the halo appears by electron beam diffraction, and in the case of crystal, only the ring appears, but when the crystal is mixed in the amorphous, the diffraction point is present at the position of the ring. Dotted things and halos appear.

The information recording medium according to this embodiment is configured, for example, as shown in FIG. Substrate 11 is made of a material that is transparent and does not easily change with time, for example, a material such as glass or polycarbonate resin, and a group is formed on substrate 11. On the substrate 11, a protective layer 12, a recording layer 13, a protective layer 14, and a protective layer 15 are formed in this order. The protective layers 12 and 14 are made of SiO ₂ and prevent the recording layer 13 from melting. The protective layer 15 is made of an ultraviolet curable resin and has a function of preventing scratches or the like from being generated on the surface in handling the disc. Recording layer 13
Is formed of a material that undergoes a phase change between a fine crystal and a mixed phase in which a fine crystal is mixed in an amorphous material due to the difference in laser beam irradiation conditions. For example, (In _100-x Sb _x ) _100-y Te _y (however, 48 ≦ x ≦ 52, 0.05 ≦
It is formed of an alloy having a composition represented by y ≦ 5).

Such an optical disc is manufactured as follows. First, the substrate was placed 11 into the sputtering apparatus, and sputtering in an argon atmosphere using a SiO ₂ target, SiO ₂
A protective layer 12 made of a material is formed. Then, while maintaining the same atmosphere, the recording layer 13 is formed by ternary simultaneous sputtering with a target made of each constituent element of the recording layer or sputtering with a target whose composition of the recording layer is to be obtained in advance. . Then, the SiO ₂ target is sputtered again to form the SiO ₂ protective layer 14, and then the substrate is removed from the sputtering apparatus and the protective layer 14 is formed by spin coating.
An ultraviolet curable resin is applied on the above and is irradiated with ultraviolet rays to form a protective layer 15.

Next, the operation of such an optical disc will be described.

Initialization The recording layer 13 is amorphous immediately after it is formed.
Continuously irradiating a laser beam having a relatively weak output and a long pulse width to 13 to melt and slowly cool the recording layer 13 to solidify, for example, fine crystal grains of InSb intermetallic compound and fine crystal grains of InTe or SbTe. The phase is changed to the crystalline phase formed by.

On the recording layer 13 that has been initialized for recording, a laser beam 18 with a relatively strong output and a short pulse width is irradiated to melt and then rapidly cool to form a recording mark 19 composed of a mixed phase in which crystals are mixed in an amorphous phase. . When the recording layer has the above-mentioned composition, for example, the recording mark 19 is formed by a mixed phase of fine crystals of InSb intermetallic compound and InTe or SbTe amorphous.

Irradiate the recording layer 13 with a laser beam of relatively weak output,
Information is read by detecting the intensity of the reflected light of the recording layer.

The erasing laser beam is irradiated to the recording mark 19 basically in the same condition as the condition for initialization. As in the case of initialization, the recording mark 19 is melted and gradually cooled and solidified into a crystalline state, and the information is erased. In the case where the recording layer has the above composition, the recording marks 19 are In ₅₀ Sb ₅₀ fine crystals and InSe.
Or, the phase changes to a mixed state with SbTe fine crystals and the information is erased.

Next, a test example in which the information recording medium according to this example is manufactured and the characteristics are tested will be described.

Test Example 1 An argon sputter was used to form a 1000 Å SiO ₂ layer on a grooved polycarbonate substrate, and then a ternary alloy of (In ₄₈ Sb ₅₂ ) ₉₈ Te ₂ was sputtered on it to 800 Å. A film was formed to form a recording layer, and an SiO ₂ layer was further formed on the recording layer in an amount of 1000Å. Thereafter, an ultraviolet curable resin layer was formed on the SiO ₂ layer to a thickness of 10 μm to manufacture an optical disc, which was designated as Sample A. In this case, the (In ₄₈ Sb ₅₂ ) ₉₈ Te ₂ ternary alloy target for forming the recording layer 13 has a direct influence on the composition of the recording layer, and therefore the composition accuracy was particularly strictly adjusted. Further, an optical disc manufactured in the same manner as Sample A was used as Sample B, except that the recording layer was In ₄₃ Sb ₅₇ . The dynamic characteristics of these samples were evaluated by a dynamic characteristics evaluation device. A semiconductor laser with a wavelength of 830 nm is used.In initialization, continuous irradiation with an output of 7 mW is performed.In recording, a laser beam with an output of 12 mW, a pulse width of 100 nsec, and a duty ratio of 50% is pulsed for erasing. Was continuously illuminated with the same output as the initialization. Table 1 shows the results.

Here, the rotation speed of the disk is 400,800,1200 and 1800rp.
It was m. In the table, the number of times of initialization indicates the number of times of rotation of the disk required to crystallize one track at the time of initialization, and the reproduction signal of the recording mark is a direct current component in reproduction of the recording portion. Shows the amplitude of the AC signal for. In addition, “erasure remaining” means the remaining amount of the AC signal after the recording mark is irradiated with the laser beam during the erasing.

As a result, it can be seen that sample A requires a smaller number of initializations and less erasure residue than sample B, and this tendency becomes more remarkable as the rotation speed of the disk increases. Especially, the rotation speed of the disk is 1800 rpm
In the case of, the sample B could not be initialized at all, but the sample A could be initialized with two initializations. Further, it can be seen that Sample A is also superior in recording characteristics. That is, the sample A shows a small decrease in the reproduction signal even if the disc rotation speed increases, whereas the sample B shows a remarkable decrease in the reproduction signal as the disc rotation speed increases. That is, in the case of sample B, the recording marks are InSb fine crystals and Sb.
In the mixed state with the coarse crystals, the Sb crystal growth due to laser beam irradiation becomes insufficient when the disk rotates at a high speed, but in the case of sample A, this does not occur, and the disk rotation speed is Even if it is high, the recording level will be sufficient.

Test Example 2 A recording layer was formed of (In ₄₈ Sb ₅₂ ) _100-y Te _y , the value of y was changed, and an optical disk sample having the same layer structure as in Test Example 1 was prepared and the dynamic characteristics were evaluated. .

FIG. 2 is a graph showing the relationship between the values of y on the horizontal axis and the reproduction signal of the recording mark on the vertical axis, for the case where the disk linear velocity is 5.0 m / sec. It is shown. From this graph, it can be seen that the reproduction signal level rises as the amount of Te added increases. That is, the recording characteristics become better as the amount of Te increases.
However, when Te was added in an amount of more than 5 atomic%, the unerased signal increased when the information was erased, and the erase characteristics deteriorated. This is because the amorphous content of InTe or SbTe, which has a low crystallization rate, increased in the recording mark portion as the content of Te increased.

Test Example 3 It has the same layer structure as Test Examples 1 and 2, and the recording layers are each made of In ₄₈ S.
b _52, In ₄₅ Sb _55, to prepare three samples with _{(In 48 Sb 52) 98 Te} 2, ( each sample C, D, and E), were conducted static characterization. In this test, the amorphous recording layer immediately after film formation was irradiated with a pulsed laser beam with an output of 9 mW, and the pulse width for crystallization of the beam irradiation portion was obtained. In this case, since the minimum value of the laser pulse width of the measuring device is 100 nsec, the pulse width smaller than this value was extrapolated from the graph showing the relationship between the pulse width and the reflectance change. As a result, sample C has a pulse width for crystallization of 20 nsec and sample E of 85 nsec, both of which show extremely high crystallization rate of less than 100 nsec, but sample D has a low crystallization rate of 2 to 3 μsec. Was confirmed. Regarding recording characteristics, Sample C
Recording could not be practically performed because the segregation of Sb was extremely small, but Samples D and E were able to obtain good recording characteristics. From these results, it was confirmed that the sample E within the scope of the present invention has excellent initialization, erasing and recording characteristics.

In this embodiment, the recording layer is (In _100-x Sb _x ).
_The case of forming the alloy with the composition shown by _100-y Te _y has been specifically shown, but the invention is not limited to this, and a phase change between a crystalline phase and a mixed phase in which crystals are mixed in an amorphous phase is possible. Any material can be applied to the recording layer.

[Effect of the Invention] According to the present invention, the crystallization and phase change of the recording layer can be accelerated, so that the initialization and the recording / erasing can be accelerated. Moreover, since information is recorded by changing the phase between the crystalline phase and the liquid phase in which the crystalline is mixed with the amorphous, the recording is stable and the recording level is high. For this reason,
It is possible to suppress the initialization failure and the unerased residue and improve the recording characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an information recording medium according to an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the amount of Te added and the reproduction signal level of a recording mark. . 11 ... Substrate, 12,14,15 ... Protective layer, 13 ... Recording layer, 18 ...
… Laser beam, 19… Record mark.

Claims (4)

(57) [Claims] 1. A recording layer comprising: a substrate; and a recording layer that reversibly undergoes a phase change between a crystalline phase and a mixed phase in which crystals are mixed in an amorphous material when irradiated with a light beam. Information recording medium. 2. The recording layer comprises (In _100-x Sb _x ) _100-y Te
The information recording medium according to claim 1, characterized by being represented by _y (where 48≤x≤52, 0.05≤y≤5). 3. The information recording medium according to claim 2, further comprising a protective layer provided between the substrate and the recording layer to prevent the recording layer from melting. 4. The information recording medium according to claim 3, further comprising a second protective layer provided on the recording layer to prevent the recording layer from melting.