JPH01303644A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain the rewritable medium of high performance which satisfies long-term stability (stability in an amorphous state at room temp.) and high- speed erasing property by using an Sb-Te alloy film and specifying the compsn. range thereof. CONSTITUTION:The alloy film consisting of the compsn. which is expressed by the formula (Sb1-xTex) and in which (x) is 0.1<=x<=0.3 is used as the recording layer. A dielectric layer is deposited as a protective film on the front and/or rear surface of the recording layer. Further, the optical recording medium is constituted by providing >=2 layers of such thin alloy films and forming these plural thin alloy films between the respective dielectric layers; in addition, the respective film thicknesses of the alloy layers are confined to <=30nm. The rewriting type optical recording medium which allows the easy high-speed erasing, has the high stability of the recording state and allows many times of writing, reproducing and erasing is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium in which information is recorded by the thermal action or photon effect of light such as a laser beam.

More specifically, there are optical recording media that can record information using the crystallization of an amorphous thin film, and optical recording media that can record information using the reversible amorphization and crystallization of the thin film. The present invention relates to an optical recording medium that is erasable and has excellent recording/erasing sensitivity, long-term preservation of recorded information, and recording/erasing repeatability.

[Conventional technology]

Recently, with the development of compact and high-performance lasers, research on technologies using laser beams, that is, so-called optical-related technologies such as optical communication and optical recording, has progressed rapidly, and some of them have been put into practical use. . Among them, optical recording, in which information is recorded by irradiating a thin film-like medium on a substrate with a focused laser beam to cause structural changes in the thin film, such as perforation or amorphous-crystalline expansion, is a high-density, It is attracting attention as a new technology that enables large-capacity recording.

The method of recording by perforating a thin film is called a write-once optical recording medium because it is not erased after the star information is written and can permanently retain the information. ing. On the other hand, recording methods based on amorphous-crystalline transitions are called rewritable optical media because they can be written and erased many times by reversibly transitioning between two states. It is. Rewritable optical recording media are expected to become important in the future because of their high versatility in that different information can be rewritten any number of times.

This rewritable optical recording medium is usually made of Te-based chalcogenide glass or Se-based chalcogenide glass. Alternatively, a metal film such as Bi or sb, or an alloy film thereof may be used. These rewritable optical recording media
The disordered state of atoms in the film is quenched by rapid heating and cooling of the thin film by a laser beam, and the amorphous state is made into an amorphous state for writing, and the amorphous state is made by removing heat and slow cooling by a laser beam. Crystallize and erase.

In such an optical recording medium, if the initial state is amorphous and crystallization writing is performed, or the initial state is crystalline and amorphous writing is performed, the recorded information is not erased separately. As a permanent information recording method, it can of course be used as a write-once recording medium as well as perforated recording.

[Problem to be solved by the invention]

When an optical recording system based on such a principle is used in a practical optical disc, the following problems arise.

(a) The laser irradiation conditions for writing and erasing are severe.

(b) It is difficult to obtain stable repeatability of writing and erasing.

(C) It is difficult to obtain long-term stability of the written state.

Nowadays, with the remarkable development of semiconductor lasers and optical heads incorporating them, the restrictions on the laser irradiation conditions in (a) are being loosened. case,
It is required that the laser power is 20 mW or less, the pulse width is 100 nsec or less, and in the case of erasing (crystallization), the pulse width is about 1 μsec or less.

In addition, regarding the issue of long-term stability, it is sufficient that the amorphous state, which is the writing state of the recording medium, is sufficiently maintained at around room temperature, and one standard for practical use as an optical recording medium is
Long-term stability of more than 20 years is required.

Furthermore, oxidative deterioration of the medium may also be a problem in terms of long-term stability depending on the medium structure that includes overcoat layers and undercoat layers, and the oxidation resistance of the recording film itself is also sufficiently excellent. is desirable. That is, it is required that the reflectance of the recording medium at room temperature remains stable for more than 10 years without any change due to oxidation.

Furthermore, in order to obtain stable repeatability of writing and erasing, the medium is subjected to laser heating many times, so it is necessary to suppress irreversible changes such as deformation and perforation of the medium due to heat cycles, phase separation in the alloy film, etc. It won't happen. The required number of repetitions varies depending on the use of optical recording, but it ranges from 103 times to 1
There are many cases where a 06-time engari-kaeshi is required.

Among the various requirements mentioned above, one problem that is considered difficult to achieve is to simultaneously achieve high-speed erasure (laser pulse width of 1 μsec or less) and long-term stability of the amorphous state. These two conditions are contradictory because the former requires that the medium be easily crystallized when heated by a laser, and the latter that it is difficult to crystallize when the medium is kept at room temperature. It is.

This problem will be explained by taking a Te-based alloy film as an example. Pure T
The thin film of Te is heated to the melting point of Te (4
It easily becomes amorphous by heating to 50° C. or higher and rapidly cooling it. In addition, there is a large difference in optical constants such as refractive index and absorption rate between amorphous and crystalline Te-based alloy films.
Since the difference in reflectance between the two states is also large, sufficient contrast can be obtained. However, the glass transition temperature of pure Te is as low as room temperature (~20°C), and the amorphous portion obtained by laser irradiation crystallizes again in a short period of several seconds or less, resulting in no long-term stability. There is no use.

For this reason, attempts have been made to stabilize the amorphous state by adding impurities such as Ge, Sb, and As to Te. In previous research, impurity elements have been adjusted to lθ~20
In a Te alloy film added to an amount of about at.
It is known that the crystallization temperature of the amorphous portion is in a temperature range far higher than room temperature, and that an amorphous life of 10 years or more can be obtained at room temperature.

However, stabilizing the amorphous state is equivalent to making it difficult to crystallize the amorphous portion by a laser pulse, and therefore it is expected that high-speed erasing will become difficult. In fact, it has been shown that the above Te alloy system with long-term stability of 10 years or more requires laser pulse irradiation with a pulse width of 10 μsec or more, usually tens to hundreds of μsec, to erase the written state. has been done.

As described above, there is still no sufficient material that satisfies both long-term stability and high-speed erasability, and this is currently the focus of research in material development.

In addition to the above-mentioned problems, the occurrence of phase separation in the alloy system due to repeated laser heating is also an important problem that impairs the repeatability of writing and erasing. Until now, various recording media have been proposed and studied, but the aim is to realize a material that satisfies all the three requirements mentioned above.
Currently, research institutions in Japan and abroad are actively conducting research aimed at improving the high-speed performance of rewritable optical recording media that utilize crystalline transitions.

Therefore, an object of the present invention is to overcome the drawbacks of the above-mentioned prior art, to facilitate writing, reproducing, and erasing of information, especially high-speed erasing, and to provide a highly stable recording state, while also providing a method for writing, reproducing, and erasing information. The object of the present invention is to provide a rewritable optical recording medium that can be repeated many times.

In addition to these problems, optical recording media have a large difference in reflectance between the recorded state and the erased state, and are required to be able to obtain a sufficient signal when recording. In particular, when used as a write-once medium, it is in a position to compete with perforated recording, so even in crystal-amorphous phase change recording, it is desirable to have a reflectance difference of 20% or more between the two states. . Regarding disc characteristics, the C/N ratio (Carrier-noise ratio) is 55 dB or more at 18 Q Orpm rotation.
o) is required. Such high-speed rotation, ie, high-speed recording, is highly desirable in order to achieve a high transfer rate in large-capacity storage using optical disks.

[Means to solve the problem]

In view of the above-mentioned current state of conventional rewritable or write-once optical recording media, the present inventors have repeatedly researched optical recording media and examined a wide variety of materials. By carefully selecting the amount and composition ratio, we succeeded in creating a high-performance optical recording medium that satisfies all of the above-mentioned requirements.

The optical recording medium of the present invention for achieving the above object is T
It is an e-based alloy film, and the alloying element to be added to Te is sb.
It is.

That is, the optical recording medium according to the present invention has the general formula=(Sbl
The recording layer is characterized by having an alloy film represented by -xTe+c+, where X satisfies 0.1≦x≦0.3.

Furthermore, according to a preferred embodiment of the present invention, a dielectric layer is deposited as a protective film on the upper surface and/or lower surface of the recording layer.

Furthermore, according to a preferred embodiment of the present invention, the optical recording medium has a structure in which two or more layers of the above alloy thin films are provided, each of the plurality of alloy thin films is sandwiched between dielectric layers, and the thickness of each of the alloy layers is 30r++++ or less.

The dielectric layer is 5in2, SiO, Al2O3% Y
2O3, WO3, Ta205, Cr2O3, CeO2
, TeO2, Mob, , In2O3, Gem2, TiO
2. Inorganic oxide materials such as ZrO2, MgF2, PbF2
, CeF, etc., metal fluorides, AIN, ON.

Inorganic nitrides such as 5j3Na, metal sulfides such as ZnS, S
Inorganic carbides such as iC, organic materials such as polyethylene, polyvinylidene fluoride, polyphenylene sulfite, polytetrafluoroethylene, polyimide, etc., plasma polymerized organic films such as hexafluoropropylene, hexamethyldisiloxane, tetramethyltin, norbornadiene, adamantane, etc. At least one type selected from the group consisting of the following may be used.

[Effect]

First, the properties of the 5b-Te alloy film will be explained. The present inventors conducted a detailed analysis of a Te-based alloy film as an optical recording medium, prepared a large number of samples with different composition ratios of Te and sb in the film, and evaluated various media characteristics.

As a result, when Te is contained in the range of 10at.% to 60at.%, high-performance optical recording media can be obtained, such as a long amorphous life, improved erasing speed, and excellent rewritability. I found out first that it can be done.

The present inventors then conducted a more detailed study of the 5b-Te alloy film, and found that within the above composition range, it may have even more characteristic properties and improve media characteristics. It has been made clear. That is, 5b-T
The composition range of the e-alloy film is from 1 oat% Te to
It has been found that when the range is 30 at.%, the difference in optical reflectance between the two states of amorphous and crystalline becomes significantly large, and as a result, the value of the recorded signal can be sufficiently large.

Other properties such as amorphous life, erasing speed, and repeatability do not particularly deteriorate within this composition range.

It is not yet clear why the performance improves in the range of Te: 10 to 30 at%. However, the inventors
After examining the membrane structure in detail using X-ray diffraction, they found that within this composition range, a lid structure different from those previously reported can be formed. did. FIG. 1 shows examples of X-ray diffraction peaks.

Curve A in FIG. 1 shows the X-ray diffraction peak obtained from a 5b-Te alloy film exhibiting a δ layer, and the alloy composition is 5b-Te alloy.
This is for 5sTe+s. Both peaks are
This applies to the structure of δ-5b2Te, and the composition also matches the composition range of the δ phase. Curve B shows the Te content of 10 to 3 in the 5b-Te alloy found in the present invention.
This is an X-ray diffraction peak specific to the composition range of 0 at.%.

This is for a sample with an alloy composition of 5b6oTe2o, and a diffraction peak different from that of the δ phase is observed. Looking at the diffraction peaks observed in X-ray diffraction, the 5b-Te film at this composition has some kind of single-phase crystal structure, which is different from the structure of Sb2Te, which is usually called the δ phase. Some of the diffraction peaks are from the document Abriko
sov gtal,, Ru5s, J, Inor
g, [:hem, 4°1163 (1959)], but not all peaks match. Moreover, it deviates considerably from the composition range shown in the literature. However, for convenience, the inventors will refer to this crystalline phase as the γ phase. Therefore, it is expected that by linking the presence of this γ phase to the high performance of optical recording media, it will be possible to elucidate the cause of the high performance. Now, if the thin film of the recording medium material has a single phase crystal structure, no phase separation will occur during the amorphous-crystalline phase change, so that the medium characteristics can be improved. In terms of erasing speed, reproducibility of repeated conditions for recording and erasing, etc., a remarkable improvement is seen in the composition region showing a single phase than in a composition that is a mixture of multiple crystal phases. 5b of γ phase
From this point of view as well, it is reasonable that a recording medium made of a -Te alloy film has high performance. Also, the fact that the signal strength can be increased is due to the amorphous state and
This is because the values of optical constants differ greatly between the crystal states as the γ phase, and therefore the difference in reflectance becomes large. According to the measurement of the dynamic characteristics of an optical disc, Te is 10at.
,% to 30at,%, the C7N ratio is 5
It reaches more than 5dB. This value is comparable to that of write-once optical recording media in perforation mode, and considering that the amorphous life at room temperature is sufficiently long, there is no problem in terms of recording life, and it is suitable for use not only in rewritable type but also in rewritable type. It can also be used as a write-once type. In addition, it can also be used as a write-once medium that performs recording by crystallization, taking advantage of the fact that the recording film is in an amorphous state as it is, and that the crystallization speed is fast when heated by laser. can.

When these 5b-Te alloy films are used for optical disk media, they are usually thinned by vacuum evaporation, INF sputtering, etc. using a plastic disk such as acrylic resin or polycarbonate resin as a substrate.

In this case, in order to prevent irreversible changes such as perforation or deformation of the thin film when the alloy film is heated by laser, or deformation of the plastic substrate in contact with the alloy film, a dielectric layer with excellent heat resistance is placed above and below the alloy film. It is preferable to provide one.

According to a preferred embodiment of the present invention, 5in2, SiO, A
l2O3, Y2O3, WO3, Ta205, Cr2
O3, CeO2, TeO2, M2O3, In2O3, G
Inorganic oxide materials such as eO2, TiO2, MgF2, Pb
Metal fluorides such as F2, CeF3, AIN, BN,
Inorganic nitrides such as Si, 84, metal sulfides such as ZnS,
Inorganic carbides such as SiC, polymer vapor deposited films such as polyethylene, polyvinylidene fluoride, polyphenylene sulfite, low molecular vapor deposited films such as Cu phthalocyanine and fluorescein, and organic sputtered films such as polytetrafluoroethylene, polyvinylidene fluoride, polyimide, A sputtered film of polyphenylene sulfide or the like can be used.

Furthermore, as this dielectric layer, a plasma polymerized film can also be used, and may be made of an olefinic compound such as ethylene, an aromatic compound such as styrene, a fluorine-containing compound such as hexafluoropropylene, a nitrogen-containing compound such as acrylonitrile, Polymerized films obtained from St-containing compounds such as hexamethyldisiloxane, organometallic compounds such as tetramethyltin, and various organic compounds such as norbornadiene and adamantane can be used.

In addition, in order to improve the performance of a rewritable optical recording medium from the viewpoint of these medium configurations, it is possible to stack thin Te alloy layers, that is, alloy layers with a layer thickness of 30 nm or less, as described in JP-A No. 61-44692. A structure in which two or more layers are provided and each layer is sandwiched between dielectric layers is effective. Such a laminated structure is considered to be equivalent to a structure in which fine particles are dispersed in the dielectric of the Te alloy part, and as a result, the amorphous state of the Te alloy part is stabilized and the crystal grains become irreversibly enlarged during crystallization. In addition to improving repeatability based on the suppression of , it is also possible to improve signal contrast by optimizing the combination of layer thicknesses.

(Example) Hereinafter, the present invention will be explained in detail by way of examples.

A 5b-Te alloy film was prepared by RF sputtering. The board is 50 x 50 mm square and 1 thick for the test piece.
, zl heat-resistant glass plates and polycarbonate resin plates, and 5-inch diameter, 1.2-thickness plates for disk characterization.
A +++m polycarbonate resin disc was used. The sputtering gas has a gas pressure of 5×10”T.

rr Ar was used, and the RF power was 100W.

Here, sputtering was performed while changing the composition of the 5b-Te alloy of the target, and several types of 5b-Te alloy films with different compositions were produced. The film thickness was 1100n. According to photoelectron spectroscopy, the Te content in the film is 5.10.1, respectively.
5.20.25.30.35at,%. Prior to the fabrication of these alloy films, a 5i02 film with a thickness of 150 r+m was undercoated on the substrate by magnetron sputtering, and after fabrication of the alloy film, a 5i02 film with a thickness of 150 r+m was undercoated.
The characteristics were evaluated using a recording medium overcoated with a nm SiO□ film.

In evaluating the laser recording characteristics, an AlGaAs laser diode (oscillation wavelength λ = 83
Writing and erasing were performed by irradiating a beam converged to a diameter of 1.4 μm from the substrate side of the recording medium. Changes in the amorphous and crystalline states can be detected by applying a reproducing laser beam (continuous wave, laser power 0.1 mW) to the recording section of the medium.
) and measured the amount of reflected light. Generally, the refractive index of a thin film in a crystalline state is higher than that in an amorphous state, so a film with a higher reflectance corresponds to a crystal, and a film with a lower reflectance corresponds to an amorphous state.

In addition, since the prepared sample is generally in an intermediate state between amorphous and crystalline in the as-deposited state, after irradiating it with a continuous wave laser beam and heating the medium above the crystallization temperature,
The initial state was one that was completely crystallized by slow cooling. That is, initial crystallization of the alloy film by heat treatment was performed using a laser beam. However, 5b-T in the above composition range
e-alloy film, especially when the Te content is from 10at% to 30a
For materials between t and %, the as-deposited state can be said to be in an amorphous state rather than an intermediate state, at least from an optical point of view, as described here. Initial crystallization is also considered to be a phenomenon almost equivalent to the transition from amorphous to crystalline.

With the laser power constant at 15 mW, writing was performed while changing the pulse width, and changes in reflectance were measured. As a result, for samples with a Te content in the range of 10 at.% to 30 at. It has been found that the difference ΔR becomes significantly large. The laser irradiation conditions for such amorphization varied depending on the sample, but the pulse width was 40 to 80 ns for polycarbonate resin substrates, and 100 to 200 ns for heat-resistant glass substrates. . Erasing conditions were subsequently evaluated for this written state.

Here, among the laser pulses required to erase the written signal by changing the laser power and pulse width, the one with the shortest pulse width was taken as the erasing speed.

Next, we investigated the lifetime of the written state using a device fabricated on a heat-resistant glass substrate.

Here, we heat-treated the sample to which each write was performed at a temperature from room temperature to 250°C, and the write signal was
The crystallization temperature was defined as the temperature at which the crystallization temperature decreased by half.

As a result, in the composition range of lO≦Te≦30at, %,
The crystallization temperature is 110° C. or higher, and it is sufficiently stable as an amorphous state at room temperature. When the crystallization temperature exceeds 100° C., the lifetime at room temperature is usually estimated to be 10 years or more.

In addition, in this composition range, the erasing rate, that is, the crystallization rate during laser irradiation, is conversely very fast, and a short pulse with a pulse width of 200 to 300 ns can laser crystallize the amorphous spot, that is, erase it. found that it can be achieved. Therefore, it was found that high-speed erasing is possible, the crystallization temperature is high, and the written state has a long life, and it has been found that this medium can overcome the above-mentioned biggest problems of rewritable media.

In addition, in this composition range, the repeatability of writing and erasing is also relatively excellent, for example, Te: 20at, %, sb:
For a sample of a heat-resistant glass substrate with a composition of 80at%, writing was 15mW, 150nsec, erasing was 8mW,
It was confirmed that writing and erasing could be repeated at least 103 times with good reproducibility under each condition of 300 nsec. However, if the number of repetitions exceeds 5 x 103 times,
Complete erasing was no longer possible with an erasing pulse of 300 nsec, and unerased portions became visible. In this case, the erase pulse width should also be increased to ~1μsec or 300n
It has been found that by irradiating pulses several times even at sec, there is no unerasable residue and complete erasure can be achieved. It was confirmed that other compositions also exhibited good repeatability in the range of 15≦Te≦25at%. Here, in the samples with Te contents of 10 and 30 at%, when the number of repetitions exceeded 2 x 103, complete erasure was no longer possible and unerased residues were observed. These two compositions are almost at the boundary of the γ phase region, so Te1Oa
In the case of t,%, it contains a small amount of sb in addition to the γ phase, and Te
In the case of 30 at.%, it is considered that it is not completely single phase because it contains a small amount of δ phase in addition to γ phase.

Therefore, as phase separation progresses gradually due to repeated recording and erasing, the recorded state and erased state are not uniquely determined.
Therefore, it can be inferred that repeatability is slightly reduced.

Furthermore, we evaluated the rotation system of an optical disk for a medium fabricated on a grooved polycarbonate resin disk with a diameter of 5 inches, and in particular evaluated the carrier wave-to-noise ratio (often referred to as the C/N ratio). It was measured.

After initial crystallization, the optical output of the laser during disk writing was 15 mVl, and the output during playback was 1.2 mW.

When a recording/reproduction experiment was conducted at a rotational speed of 1.800 rpm, the C/N ratio was 55 dB.

Subsequently, when the information writing section of the disk was scanned with a semiconductor laser beam with an output of 6 mW, the written information could be completely erased. Although the writing and erasing operations on this disk were repeated up to 102 times, no decrease in the C/N ratio was observed, and complete erasing was possible without any remaining data being erased.

Next, we evaluated the rotation system in a recording mode using laser crystallization on the medium in the as-deposited state.

At a rotation speed of 1.800 rpm, the laser light output during writing (in this case, laser crystallization) is 6 mVl, and the output during playback is 1.
．． When we conducted a recording/playback experiment at 2 mW, the result was 58 d.
A high C/N ratio of B was obtained. This is an excellent value compared to the performance of write-once media in perforation mode.

Example 2 In Example 1, a SiO□ film was used as the overcoat and undercoat layer of the alloy film, but in this example, various inorganic phone material films and organic material films were used to form a recording medium. We fabricated it and evaluated its properties.

In addition to the 5in2 film, the thin films prototyped as overcoat and undercoat materials include SiO, Al2O8, and Y2O.
3, W 03 , Ta 205, Cr 203%
Ce02, TeO2, MOO3, Tn203, Ge
m2, Tie, z"02, oxides such as ZnO, MgF
2. Fluorides such as PbF2 and CeF3, AIN, 8N
, Si, inorganic nitrides such as 84, sulfides such as ZnS, Si
It is an inorganic substance such as carbide such as carbon.

Among these materials, those with relatively low melting points such as SiO, PbF2, and TeO2 are used by resistance heating vapor deposition, Al2O3, Zr(
For high melting point materials such as h, electron beam heating evaporation or R1'
It was made into a thin film by sputtering and deposited on the top and bottom of the 5b-Te film to a thickness of ~150 nm.

Furthermore, regarding organic substances, vacuum evaporation is used to make thin films of polymeric materials such as polyethylene, polyvinylidene fluoride, and polyphenylene sulfide, and low-molecular materials such as Cu phthalocyanine and fluorescein, and polytetrafluoroethylene and polyvinylidene fluoride are made into thin films by RF sputtering. , polyimide, polyphenylene sulfide, etc., were made into thin films and used as overcoat and undercoat materials for 5b-TeN. In addition, olefin compounds such as ethylene, aromatic compounds such as styrene, fluorine-containing compounds such as hexafluorinated propylene, nitrogen-containing compounds such as acrylonitrile, Si-containing compounds such as hexamethyldisiloxane, which can be produced by plasma polymerization, The suitability of polymer films obtained from organometallic compounds such as tetramethyltin and various organic compounds such as norbornadiene and adamantane as overcoat and undercoat materials was also investigated.

As a result, it was confirmed that all of these materials can be used as overcoat and undercoat materials for 5b-Te films. However, when comparing the laser recording characteristics, writing,
It was found that the erasing conditions and repeatability were quite different depending on the material.

In other words, since organic thin films generally have poor heat resistance, they cannot be used for writing or writing.
Repeated erasing tends to cause irreversible deformation at the portion in contact with the 5b-Te film, and in extreme cases, even an overcoated medium may become perforated. Even in the case of inorganic thin films, when making a 5b-Te film amorphous, 5b
- Since it is necessary to heat to a high temperature higher than the melting point of Te, PbF2 (melting point 855°C), Tent (melting point 7
It has been found that materials with relatively low melting points such as 33° C.) may cause problems in edge reversibility due to irreversible deformation.

This is thought to be because the laser beam has a Gaussian profile, so the temperature of the medium surface at the center of the beam may reach the melting point of the protective film material or higher.

On the other hand, Sin, , Al2O3, cr2o8, T
A medium using a high-melting point inorganic thin film such as iO2 or MgF2 as an overcoat or undercoat material has excellent repeatability, and writing and erasing of any of the 5b-Te films in Example 1 was possible over 103 times. This was achieved with good reproducibility.

In addition, organic thin films can be overcoated or undercoated with polytetrafluoroethylene, polyimide,
For materials with relatively excellent heat resistance, such as polyphenylene sulfide and tetramethyltin plasma polymerized films, by carefully selecting recording and erasing conditions, irreversible deformation can be suppressed and writing and erasing can be repeated more than 103 times. succeeded in achieving.

Furthermore, an advantage of media using organic films for overcoat and undercoat is that the thermal conductivity is much lower than that of inorganic materials such as 5i02, so that less energy is required during laser writing. That is, when the temperature is raised above the melting point of the 5b-Te film by laser heating, the loss of laser energy due to heat dissipation can be prevented because the overcoat and undercoat layers covering the top and bottom surfaces have low thermal conductivity.

For example, if 5b6oTe2° is used for the recording film, 1
When laser writing is performed with a laser power of 5mW, 5i
For media overcoated and undercoated with 02,
Although a pulse width of 30 nsec or more is required, it has been found that a pulse width of 20 to 25 nsec is sufficient for a medium overcoated or undercoated with a sputtered polyimide film.

Above, we have discussed the overcoat and undercoat materials, but depending on the use and configuration of the optical recording medium, only the overcoat or only the undercoat may be used.
It is sufficient to coat the Te film. That is, if a plastic with excellent heat resistance such as polyimide or heat-resistant glass is used as the substrate, there is no need for an undercoat to prevent the substrate from deforming during laser heating, and only an overcoat is required. Also, laser energy (power and pulse width)
If controlled precisely, it is possible to induce amorphization or crystallization without causing irreversible deformation or perforation of the Te-based alloy film even without an overcoat; in this case, an overcoat is not required. Therefore, it is sufficient to simply apply an undercoat between the plastic substrate and the Te-based alloy film.

As described above, even when a 5b-Te film having a composition within the range of the present invention is used as a recording layer, the overcoat and undercoat made of the dielectric layer described above play the role of protecting the recording layer, and depending on the material properties, It was confirmed that there were differences in laser recording characteristics.

In the recording medium of Example 1 of Fire Group ■U, the composition of the alloy film was Sb8°T.
For e2o, a laminated film with 5i02 film was produced. The substrate-sputtering conditions are the same as in Example 2.
The sputtering of the i02 film was performed by magnetron sputtering.

The structure of the laminated medium is that the 5b-Te alloy layer has a thickness of 20 mm;
The number of layers is 5, with a 5i02 layer in the middle of each layer and a layer thickness of 20n.
A structure was adopted in which the material was coated with m. That is, in sputtering, a 5b-Te alloy target and a 5io2 (magnetron) target were alternately sputtered to form a SiO undercoat layer of 150 nm on a heat-resistant glass substrate, and then a 20 nm thick Te-based alloy layer was applied to each of the heat-resistant glass substrates. The layers, Sin, and intermediate layers are laminated alternately, and further 15
This is done by laminating a 5i02 overcoat layer with a layer thickness of 0 nm. It has been verified that a medium in which the recording film is thinned and stacked between dielectric layers is stable as amorphous (Japanese Patent Laid-Open No. 44692/1983).
. However, if the thickness of each stacked recording film exceeds 30 nm, the stability as an amorphous substance will be impaired, so the film thickness should be 30 nm.
A value of nm or less is preferable.

The same characteristics evaluation as in Example 1 was performed on the medium produced in this example. As a result, the write/erase conditions are almost the same (
However, there was a tendency for the erase pulse width to become slightly longer. )
On the other hand, the crystallization temperature increased to 180° C., and the repeatability was also good.

For example, in the case of a heat-resistant glass substrate, the writing power is 15 mW, 15
Writing and erasing cycles of 10 times or more were achieved with good reproducibility under the conditions of 0 nsec, 6 mW of erase, and 300 nsec.

Further, in this example, a medium in which the 5b-Te layer had a layer thickness of 10 nm and the number of layers was lO was also studied. In this laminated film,
The crystallization temperature reached 200°C, and a tendency to increase was observed.

Furthermore, the telephone thin film as an intermediate layer of the alloy layer is 5in2
In addition, various materials mentioned in Example 2, namely 81203. Even if an inorganic film such as ZrO2, an organic film such as polyimide or tetrafluoroethylene, or a plasma polymerized film such as tetramethyltin is used, the effect of the laminated medium is equivalent, and any material can be used.

However, the repeatability is poor due to the problem of heat resistance of organic materials, which is the same as the situation described in Example 2.

In the examples of the present invention, RF sputtering is mainly explained as a medium production technique, but it goes without saying that other thin film production methods such as vacuum evaporation can also give the same results in terms of wood quality. . Furthermore, the writing and erasing conditions in the examples are described in detail for media fabricated on heat-resistant glass substrates, but as mentioned in the examples, if acrylic resin or polycarbonate resin, which is commonly used in optical disks, is used for the substrate, Recording conditions, especially write threshold and erase threshold, are significantly improved.

〔Effect of the invention〕

As explained above, the optical recording medium of the present invention is a high-performance rewritable medium that has high signal strength, satisfies both long-term stability (stability in an amorphous state at room temperature) and high-speed erasability. It also has excellent edge reversibility during writing and erasing.

The problem of deterioration of recording media due to oxidative deterioration of the 5b-Te film can be solved by providing a layer that blocks moisture, such as the 5i02 film, in the overcoat and undercoat, without causing any problems in long-term stability. It won't bring anything.

In addition, 5b-Te alloy films generally have the disadvantage of lacking reproducibility in laser recording and erasing characteristics due to compositional deviation, but the medium of the present invention crystallizes as a single γ phase that does not cause phase separation. Because it covers the compositional region that
It has the advantage of not causing any deviation in characteristics even if erased repeatedly. In particular, the composition range showing this single phase (γ phase) is wide, ranging from 10 to 30 at%, and there is plenty of composition to satisfy certain writing and erasing conditions. It has the characteristic of being excellent in sex. As mentioned above, due to phase separation at the boundaries of the γ phase region where Te is around 10at.% and around 30at.%,
The repeatability of recording and erasing may be slightly reduced. To prevent this, the composition range must be narrowed down so that the Te content ranges from 15 at% to 2
It is sufficient to take a value between 5at and %. This 15-25at,%
The composition margin in the range of is also sufficiently large for manufacturing purposes and does not impair the advantage of mass production.

Furthermore, in the composition region (γ phase) where the Te content is between 10at.% and 30at.%, the signal intensity is extremely large, and in disk evaluation, the C/N ratio is up to 58
dB, which is comparable to write-once media in perforation mode. That is, it is also suitable as a write once type phase change optical recording medium.

Therefore, the rewritable laser recording medium of the present invention can be used as a recording medium such as an optical disk as a carrier for high-capacity, high-density recording or an optical card, which is expected to grow in the credit era, and as a medium with high performance rewritability. The medium has optimal performance and its impact on the optoelectronics industry is significant.

[Brief explanation of the drawing]

Figure 1 shows the X-ray diffraction peak of the 5b-Te alloy film,
Curve A is 5b5sTe4s 1Curve B is 5baoTe2
It is an X-ray diffraction pattern of o.

Claims (1)

[Claims] 1) Represented by Sb_1_-_xTe_x, where x is 0.1
An optical recording medium characterized in that the recording layer includes an alloy film having a composition of ≦x≦0.3. 2) The optical recording medium according to claim 1, characterized in that a dielectric layer is deposited as a protective film on the upper surface and/or lower surface of the recording layer. 3) Claim 1 characterized in that two or more layers of the alloy film are provided, each of the plurality of alloy film layers is sandwiched between dielectric layers, and each of the alloy layers has a thickness of 30 nm or less. The optical recording medium described in .