JPS6329334A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide high stability of recorded information to long-term preservation by specifying the compsn. of an optical recording medium of an optical disk which permits the recording, reproduction and erasure of the information to make use of the reversible phase transformation of an optical recording material to be generated by projection of laser light. CONSTITUTION:The average compsn. in the film thickness direction of the optical recording medium material is expressed by InxTeySezMalpha, where M is at least one of As and Ge, and the values of x, y, z, and alpha are respectively in 1<=x<=30, 40<=y<=95, 2<=z<=59, 0<alpha<=5 ranges, and x+y+z+alpha=100. As or Ge is added in order to obtain the stability of the long-term preservation of the information. The chalcogenide material of Te-Se has usually a chain molecular structure and the As or Ge added thereto crosslinks these molecular chains to each other to increase the viscosity and further to increase the amorphous-crystalline transition temp. The effect is remarkably high if the compsn. ratio alpha of As or Ge is particularly in a 2-3 with In-Te-Se. The recording medium having the high stability to the long-term preservation of the recorded information is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an optical recording medium of a rewritable optical disk having high sensitivity to laser light.

[Technical field to which the invention pertains]

In recent years, there has been an increasing demand for higher density and larger capacity information storage, and research and development in this field has been actively conducted both domestically and internationally.
In particular, optical disks that use a laser as a light source have a recording density of about 10 to tOU times that of conventional magnetic recording media, and are capable of recording.

Since information can be recorded and reproduced without contact between the recording medium and the recording medium during reproduction, it has a long lifespan and is therefore being developed as a high-density, large-capacity recording method.

These optical discs can be roughly divided into three types depending on their purpose: read-only type, write-once type, and rewritable type. A read-only type is a read-only disk from which information can only be read, and a write-once type allows information to be recorded and reproduced as needed, but recorded information cannot be erased. On the other hand, the rewritable type is capable of recording and reproducing information, as well as erasing and rewriting the recorded information, so it is desired to be used as a data file for computers, and is the most anticipated type. It is.

Two recording methods, magneto-optical recording and phase change recording, are being developed for rewritable disks, but both still have room for improvement in terms of recording materials, writing mechanisms, etc. Among these, phase transformation recording is a recording method that utilizes phase transformation of the recording material to create a rewritable optical disc. Generally, laser light is focused on the recording surface and heated, and the pulse output and duration of the laser light are controlled. Information is recorded based on the difference in reflectance between the phases before and after the phase transformation of the recording material, which is caused by this.

An example of the structure of this phase change type optical disk is shown in the cross-sectional schematic diagram of FIG. ) is also shown in Fig. 4, many tracking grooves 2 are provided in advance on one side of a substrate 1 made of polycarbonate, for example, and the substrate 1 having these grooves 2 is
A SiO2 film 3 is formed on the surface of the substrate by sputtering or the like, and a recording material, that is, a medium film 4 is formed thereon.

Further, the 8102 film 5 and the organic substance protection W16 are deposited in this order on top of the 8102 film 5. In this way, the media film 4
is sandwiched between the SiO2 films 3.5.The reason why the medium film 4 becomes high temperature due to optical heating when writing or erasing signals is that the medium film 4 may react with the substrate 1 at that time. This is to prevent evaporation, scattering, and deterioration of the medium film 4.

The laser beam enters from the surface of the substrate l opposite to the side on which the medium film 4 is provided at -g7.

In order to actually write information on such optical recording media, the medium must be sufficiently crystallized by light irradiation with a mass, lassi, lamp, etc. to ensure a writable initial state, and then a high-power, short-pulse laser is used. Light is irradiated onto the surface of the medium in a spot-like manner to melt the medium, and then the medium is rapidly cooled. As a result, the spot area on the medium surface transforms from crystalline to amorphous, and writing is performed. On the other hand, when information is to be erased, an amorphous medium is irradiated with a relatively low-power laser beam to raise the temperature of the medium to a crystallization temperature and anneal it to make it crystalline. The laser beam irradiation time at this time is determined by the crystallization speed of the medium.

This phase change recording type rewritable optical recording material is
Several methods have been proposed in the past, but the one currently considered to be the most practical is one that takes advantage of the change in reflectance caused by the crystalline-amorphous transition of 'l' e-based materials. be. Many inventions related to this type of material have been filed,
Recent examples include the Sn-'re-8eO system disclosed in JP-A No. 60-42095 and the JP-A No. 60-42095.
're -Ge disclosed in -107744 publication
-8nO series, etc.

For example, Sn-Te-8eO-based media materials contain Sn as an essential component because Sn increases the stability of the amorphous state and provides a medium that can stably record information for a long time. This is because, according to the findings of the present inventors, Sn is an element that increases the crystallization rate of the medium and shortens the erasing time.

Figure 5 is a typical diagram showing the relationship between laser output and laser irradiation time when using a 5n-Te-8eO media material.The writing area and erasing area are clearly shown between each curve. be. However, for example, the laser irradiation conditions during writing are about 10 mW and 0.2 μsec when the laser beam spot is 1 μmφ.
From Figure 5, the laser irradiation conditions for erasing are 3 mW, 2
It can be seen that the irradiation time is about μsec, which is about an order of magnitude longer during erasing than during writing. Therefore, in actual optical desks using this media material, countermeasures are taken such as expanding the spot of the erasing laser beam into an elliptical shape to lengthen the time the medium passes through the laser spot, but the power density of the laser beam is kept constant. If so, there is a limit to the spot size determined by the total output of the laser beam.

Therefore, in practice, it is better to suppress the number of rotations of the disk to increase the time it takes the disk to pass the laser spot, but this is a major factor that limits the data transfer speed.

On the other hand, the present inventor used In instead of Sn as a medium material with a high crystallization rate that can shorten the crystallization time of the medium, and expressed it with the general formula In, Te, Se□, x, y,
The z(7) values are 1<, r<30.40<, and y<9, respectively.
We have discovered an optical recording material in the range of 5°2 x 59, where r+y+z=tou, and are currently applying for a patent for this.

For example, if the erasing conditions are determined according to FIG. 5 for a medium material whose average composition is IO Te5s 5e3s, the diagram in FIG. 6 is obtained. As is clear from the comparison between Fig. 5 and Fig. 6, the In-Te-8e-based media material, in which In is used instead of Sn to give an appropriate composition ratio, has a 0.5M formula when the laser output is 5mW. Can be erased repeatedly
≦, and the laser irradiation time shifts to the shorter side, which indicates the effect of adding In.

-10,000Sn-Te-8eO media materials are still insufficient in terms of stability of the amorphous state when information is written and stored for a long time, and stability when information is repeatedly inserted and erased. For example, while the storage life of recorded information in magneto-optical recording is said to be about 10 years, the storage life of the above-mentioned media materials is 2 to 3 years, which is one of the problems with phase change recording.

From the above, ↓The optical recording medium material that can be beaten is In
In order to further improve the stability of recorded information for long-term storage while maintaining the excellent feature of shortening the erasing time of -'re-8e-based materials, we hope to have the effect of adding a fourth element. It seems effective to accurately determine the content of each constituent element in the medium.

[Purpose of the invention]

The present invention has been made in view of the above points, and its purpose is to provide an optical recording medium that is stable for long-term storage of Nikoroku information without impairing its high-speed erasing characteristics by laser beam irradiation. Our goal is to provide the following.

[Key points of the invention]

The present invention is an optical recording medium material having an average composition in the film thickness direction of InzTey Sez M (represented by 1, where 1M is As).
, Ge, "+ y, z+
The 11 proofs of α are i, r, 30, 40, y, 9, respectively.
5, 2 Kuzku59. O(a in the range of 5, x+y-
1−z+α”1OIl.

[Embodiments of the invention]

First, the reasons for selecting the constituent elements of the medium of the present invention and their composition ratios will be described. Te is an essential constituent element in order to cause the crystalline-amorphous transition as an optical recording medium.
It is necessary to contain 40-95%. Se is a constituent element for maintaining high resistance (violet and oxidation resistance) when using the medium, and for this purpose, the composition ratio of Se is 2.
% or more, it is effective, but if there is too much light wavelength 780 ~
The optical absorption number of the medium at 830r+m decreases, and the laser sensitivity decreases. Upper limit jj 1'e, In
It is determined by the amount of 59%, but the objective can be achieved within this range.

Furthermore, as a result of various studies, the present inventors have found that the medium material easily promotes crystallization from an amorphous state, and plays an effective role in shortening the erasing time of recorded information, which is the objective of the present invention. It was discovered that the element was In, and the following studies were conducted in order to use In as a constituent element of the medium. This point will be explained with reference to the Te-In binary alloy phase diagram shown in FIG. The medium of the present invention is InTe5eAs ((3
Since it is a quaternary alloy (e), it should originally be considered using a quaternary alloy phase diagram, but an accurate equilibrium phase diagram has not yet been obtained for this quaternary alloy.

As mentioned above, when information is imprinted, the medium is locally melted by the laser beam, but according to the phase diagram in Figure 1, for example, a material with a composition of 35% In containing t, indicated by point %A, is in a molten state. Upon coagulation from the liquid, a compound called 1n3Tes is preferentially crystallized due to a certain distribution coefficient. During the laser irradiation time, there is a temperature difference between the center and the periphery of the spot, and the solidification of the medium in the area corresponding to the spot starts from the periphery, so when the solidification is finished, the result is In3
Te5 gathers around the solidified region, and the central region has a high I'e content. If information is written and erased many times, this phenomenon will be repeated.
Since the medium composition at the spot position deviates from its initial state, the medium characteristics become unstable and reproducibility deteriorates over long periods of use.

To avoid this, Te-In alloys should have a composition near the eutectic point of 11% In as indicated by the dotted line B in Figure 1, since the melting point is low and solidification occurs uniformly, making it suitable as a medium material. is desirable. This eutectic point is actually Se,
The addition of As or Ge causes a compositional shift, but as mentioned above, the quaternary alloy phase diagram is unknown. However, it is certain that a range centered around 11% In maintains the stability of repeated writing and erasing, and considering that In is an element that promotes crystallization, the addition of In must be at least 1%. Therefore, the upper limit is preferably set at I%, where the influence of the above-mentioned partial non-uniformity of the composition ratio is small.

The composition ratios up to this point are the same as those currently developed and under development by the present inventors as In-T'e-8e media materials for shortening the erasing time mentioned above.

Furthermore, in the present invention, As or Ge is added in order to obtain stability for long-term information storage. The added As or Ge crosslinks these molecular chains, increases the viscosity, and further increases the amorphous-crystalline transition temperature.

The main reason for the deterioration of the reliability of recorded data after long-term storage is that data points that have become amorphous due to data aggregation often transition to crystalline data due to thermal energy at room temperature. .

The increase in the transition temperature due to the addition of As or (-ie) has the effect of suppressing this amorphous-crystalline transition at room temperature. This is particularly noticeable when the composition ratio α is in the range of 2 to 3. However, when α becomes larger than 5, although the stability of the amorphous state increases, the erasing speed of recorded data decreases, and the performance of the rewritable optical storage medium decreases. Therefore, the composition ratio of As or Ge is lower than that of In-Te.
When adding to -8e series alloys, it is appropriate to set it within this range. Furthermore, As and Ge may be added in combination, in which case the total amount may be in the same composition ratio as when they are added alone.

From the above, the media material of the present invention is In-process 1. , Se
,! x, y, z, a of Mα are each 1 < x (,3
8,40<x ri95°2kuZku59. O<α≦5, x+y−1−z+α=100, M is at least one of As and Ge, and these constituent elements are mixed in a well-balanced manner.

Next, a Y-car body containing a medium in this composition range was exploded, and the amorphous-crystalline transition temperature of the medium was determined.

First, the average composition is In+oTes2Sezs Ag3 and I
Two lumps of nto Te5o 5ezs AS5 were each vacuum-deposited onto a quartz glass substrate to a thickness of 0.1μ.
4 was deposited as a thin film of 4 m, and then a film of SI02 of SI02:I4.i of approximately However, they can be transitioned to crystalline state by heating them on a hot plate.If the heating rate is set to 10℃/-, the change in the main light reflection is monitored, and the transition temperature is measured, xnlo" 662”e25AS
The temperature of the medium film in No. 3 is 70°C.Int.

'I"e so Se 25 As s media film is 85
It was ℃. The transition temperature when the above-mentioned I n +o ``'ess Se 35, which does not contain As, obtained for comparison is used as a medium is 50 °C, and the medium composition of the present invention is amorphous-crystalline. This increases the transition temperature, which is useful in revealing the shelf life of recorded data. Similar results can be obtained by using (je instead of As).

Next, laser irradiation conditions were determined using the thus formed laminate. Therefore, the laser beam incident from the substrate surface on the opposite side of the fi pancreas of these laminates has a wavelength of 33Q.
Using a nm semiconductor laser, it is focused to a spot of approximately 1 pmφ on the medium using a 1x lens. From the relationship diagram of the laser output versus the laser irradiation time ζ, we can see that the laser irradiation condition where the medium becomes amorphous and internal due to laser irradiation, that is, the valley region, and the laser irradiation condition where the medium becomes crystalline due to laser irradiation. In other words, the erased area could be clarified. The results are shown in FIGS. 2 and 3. Figure 2 shows the medium as In1OTe6
2Se25AS3, and the erasing conditions are that the laser output is 4.3 mW, the shortest laser irradiation time is 1.7 μm, and repeated erasing is possible. Similarly, the third
The figure shows the case where the medium is In 1OTe605e25AS5, and the laser output is 5.3 mW, and the minimum time is 2μ, and it is possible to perform sickle-back erasing. 2nd Zo, Figure 3 as the medium mentioned earlier I n +o T6 ss Se :s
Comparing with FIG. 6 when S is used, the erasing conditions for the medium according to the present invention doped with As are such that the laser output increases slightly as the amorphous-crystalline transition temperature rises, and the erasing time decreases. The conventional 5n in Figure 5, although it shifts to the haze and time side.
-Te-8e (has properties equal to or better than J-type steel body, As
The addition of has no negative effect on the erasure time. That is, the recording medium of the present invention achieves both shortening of erasing time by adding In and stability of the amorphous state by adding As. Also in this case, instead of As, (j
Since the same effect can be obtained even if Ge is used, the illustration of Ge addition is omitted, and the same applies to the case of composite addition.

Now, since the structure of the optical disc using the recording medium of the present invention is the same as that shown in FIG. 4 above, the case of the present invention will be described with reference to FIG. 4 again. The polycarbonate substrate 1 has a disk shape, and a tracking plate 2 is previously provided on the negative side. A SiO2 film 3 is formed on this surface by a sparing method or the like, and a film of, for example, In+ is formed thereon.
Optical recording medium film 4 having a composition of oTeszSe2sAs3
is formed to a thickness of 0.1 μm. To form the medium film 4, a multi-component vacuum evaporation method was used in which each of the constituent elements was evaporated from a separate evaporation chamber. Further, on the medium film 4, S
The iOz film 5 and the organic protection material 6 are transferred thereon.

Optical recording is performed on the thus exploded disk according to the following procedure, but the illustration of the apparatus for light irradiation is omitted. First, light irradiation is applied using a flood lamp to sufficiently crystallize the recording medium film 4 of IH1gTc62SezsA33 to bring it into a writable initial state.Then, the disk is rotated at 1200 rpm and a wavelength of 830 rpm is applied.
A semiconductor laser of nm wavelength is irradiated onto the surface of the medium film 4 in a spot-like manner. At this time, the light intensity of the semiconductor laser is first kept at a level that does not cause embedding. After the laser beam is controlled to be correctly focused between the tiger and king grooves 2 by an automatic focusing mechanism with the groove 2, writing is performed by increasing the light intensity of the semiconductor laser according to the information signal. As a result of this writing, the medium film 4 changes from crystalline to amorphous, and a decrease in reflectance due to this transformation is observed.

Erasing of the recording is performed by irradiating laser light in the same manner as in writing, in order to transition the indentation point of the optical recording medium film 4 from amorphous to crystalline. However, when erasing, the intensity of the laser beam is lower than when writing, and it is necessary to lengthen the irradiation time. It is effective to make it larger than usual.

To read the recording, the light intensity of the semiconductor laser is kept at a level that does not lead in, and the intensity of the reflected light from the recording medium 4 is detected while automatic focusing is performed on the tracking groove 2 as in the case of writing described above. Do it by doing this.

As a result of writing and reproducing information using a disk equipped with the optical recording medium of the present invention that exploded as described above, an error rate of approximately 1×10 2 was obtained immediately after writing. Furthermore, the error rate was 1.2 x 10-' for a one-year life test in an environment of ℃ ℃ and humidity %.
Although the error rate increased slightly, this increase in error rate can be ignored in practical terms. This is As or Ge
The above-mentioned In 10 Te 55 Se without the addition of
The error rate obtained when a similar life test was conducted on a disk using Sn-1'e-8e LJ for comparison was 5 x 10, while the error rate obtained for the conventional Sn-1'e-8e LJ system was 5 x 1.
0-', this shows that the recording medium having the composition ratio of the present invention is superior in terms of long-term stability.

As explained above, the optical recording medium having the composition according to the present invention is based on the results shown in FIGS. 2 and 3 and the above-mentioned life test results, and is based on the In-Te-8e based media material invented by the present inventor. By adding As and Ge either singly or in combination and by appropriately setting the composition of each constituent element, it was possible to improve the stability of long-term storage of information without impairing the excellent erasure time characteristics. .

〔Effect of the invention〕

The Sn-Te-3eO system, which is conventionally known as a media material that utilizes the change in reflectance due to the crystalline-amorphous transition of optical discs on which information can be rewritten, has excellent stability when storing recorded information for long periods of time. While the erasing time of recorded information was still unsatisfactory, in the present invention, as described in the embodiment, Sn is replaced with In and As and Ge are added singly or in combination to take advantage of the characteristics of each constituent element. , by setting a well-balanced composition ratio, while retaining the advantage of shortening the erasing time of recorded information due to In content,
As.

A recording medium with high stability for long-term storage of recorded information based on the effect of Ge addition could be obtained.

[Brief explanation of drawings]

Fig. 1 is a phase diagram of a binary alloy of 'L'e-In system, and Fig. 2 is a phase diagram of a binary alloy. Fig. 3 is a diagram showing the relationship between laser irradiation time and laser output for a medium having the composition ratio of the present invention, Fig. 4 is a schematic cross-sectional view showing the structure of an optical disk, and Fig. 5 is a graph showing the relationship between laser irradiation time and laser output for a conventional medium. The relationship diagram with the laser output, Figure 6 is Into Te5S-8e35, which is the invention 1 of the present inventor.
FIG. 2 is a relationship diagram between laser irradiation time of a medium and laser output. 1... Board, 2... Tracking groove, 3, 5...
- SiO2 film, 4... medium film, 6... organic substance protective film. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1) An optical recording medium of an optical disk capable of recording, reproducing and erasing information using reversible phase transformation of an optical recording material caused by laser beam irradiation, the composition of which is of the general formula In
It is represented by _xTe_ySe_zM_α, where M is As, G
at least one of e, and the values of x, y, z, and α are 1≦x≦30, 40≦y≦95, and 2≦z≦5, respectively.
9, in the range of 0<α≦5, and x+y+z+α=1
00. An optical recording medium characterized in that: