JPH01303643A - Laser recording medium - Google Patents

Abstract

PURPOSE:To obtain the rewriting type medium of high performance which satisfies long-term stability (stability in an amorphous state at room temp.) and high-speed erasing property by using a specific Sb-Te alloy film as a recording medium. CONSTITUTION:The alloy film consisting of the compsn. expressed by the formula (Sb1-xTex)1-yMy is used as the recording layer. In the formula, x is in a 0.1<=x<=0.3 range; y is in a 0<y<=0.2 range; M is at least one kind of the elements selected from the group consisting of Ag, Al, As, Au, Bi, Cu, Ga, Ge, In, Pb, Pd, Pt, Se, Si, Sn, and Zn. The rewriting type laser recording medium which allows the easy high-speed erasing, has the high stability of the recording state and allows many times of repetitive writing, reproducing and erasing is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a laser recording medium that records information using the thermal effect of light such as a laser beam or the photon effect.

More specifically, it is possible to record and erase information by reversibly causing amorphization and crystallization of a thin film, and it also improves recording/erasing sensitivity, long-term storage of recorded information, and recording/erasing.
A rewritable laser recording medium with excellent erasing repeatability, and information recording using crystallization of an amorphous material or crystallization of a crystal, and a long-term recording sensitivity and long-term recording of recorded information. The present invention relates to a write-once laser recording medium with excellent storage stability.

[Conventional technology]

Recently, with the development of compact and high-performance lasers, research on technologies using laser light, 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 wI film medium on a substrate with a focused laser beam to cause structural changes such as perforation or amorphous-crystalline transition in the thin film, is a method of high-density and large-scale recording. It is attracting attention as a new technology that enables capacity recording.

The method of recording by perforating a thin film is called a write-once optical recording medium because it is characterized by the fact that once information is written, it is not erased and can permanently retain information. It is. On the other hand, the recording method based on the amorphous-crystalline transition is capable of writing and erasing multiple times by reversibly transitioning between two states, so it is possible to use rewritable optical recording media. It is called. Rewritable laser 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 laser recording medium usually uses Te-based chalcogenide glass or Se-based chalcogenide glass.
Alternatively, a metal film such as sb or an alloy film thereof may be used. These rewritable laser recording media are written on by rapidly heating a thin film to below its melting point with a laser beam and rapidly cooling it to make it amorphous, and then heating it to a temperature above its crystallization temperature with a laser beam and slowly cooling it. to crystallize and erase.

If such a laser recording medium is set to a mode in which the initial state is amorphous and crystallized writing is performed, or the initial state is crystalline and amorphous writing is performed, recorded information is not erased separately. As a permanent information recording method, it can of course be used as a write-once laser recording medium as well as perforation recording.

(Problems to be Solved by the Invention) When an optical recording system based on such a principle is used in a practical optical disc, there are the following problems.

(a) Laser light irradiation conditions for writing and erasing are severe.

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

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

Nowadays, with the remarkable development of semiconductor lasers and optical heads incorporating them, the restrictions on the laser beam irradiation conditions in (a) are being eased, but it is still difficult to write (amorphous) when recording at high speeds such as on optical discs. In this case, the laser light output is 20mW or less, the pulse width is 100nsec or less,
In the case of erasing (crystallization), it is required to satisfy the condition that the pulse width is approximately 1 μsec or less. Furthermore, as optical-related technology progresses in the future, it is inevitable that even higher speeds will be desired due to the large capacity of a single optical disk, and in that case, the erasing speed will be required to be 1 oonsec or less. Become so.

In addition, regarding the issue of long-term stability, it is necessary to maintain the amorphous state that is the writing state of the recording medium sufficiently at around room temperature.
Long-term stability of more than 20 years is required.

Furthermore, oxidative deterioration of the medium may be a problem in terms of long-term stability depending on the media structure that includes an overcoat layer and an undercoat layer, so it is important that the recording layer itself has sufficient oxidation resistance. is desirable. That is, it is required that the reflectance of the recording medium at room temperature remains stable for 10 years or more without any change due to oxidation.

Furthermore, in order to obtain stable repeatability of writing and erasing, the medium is subjected to laser beam heating many times, so it is necessary to prevent irreversible changes such as deformation and perforation of the medium due to heat cycles, phase separation in the alloy film, etc. Must be suppressed. The required number of repetitions varies depending on the purpose of optical recording, but 103 to 10' repetitions are often 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, as the former requires that the medium be easily crystallized when heated with laser light, and the latter that the medium is difficult to crystallize when kept at room temperature.

This problem will be explained by taking a Te-based alloy film as an example.

Pure Te R film is heated to above the melting point of Te (450°C) by short pulse laser light irradiation and then rapidly cooled.
Easily becomes amorphous. In addition, in Te-based alloy films, there is a large difference in optical constants such as refractive index and absorption coefficient between the amorphous and crystalline states, and the difference in reflectance between the two states is also large, so sufficient contrast cannot be obtained. can get. However, the glass transition temperature of pure Te is as low as room temperature (~20°C), and the amorphous portion obtained by laser beam irradiation crystallizes again in a short period of several seconds or less, resulting in poor long-term stability. It's completely useless.

For this purpose, Ge, Sb, As%Bi
Attempts have been made to stabilize the amorphous state by adding such substances as impurities. In previous research, impurity elements were
It has been found that in Te alloy films added to an amount of 0 to 20 at.%, the glass transition temperature rises to several tens of degrees to over 100 degrees Celsius, and therefore an amorphous life of more than 10 years can be obtained at room temperature. There is.

However, stabilizing the amorphous state is equivalent to making it difficult to crystallize the amorphous part by irradiation with laser pulse light, and therefore it is expected that high-speed erasing will be difficult. Ru. In fact, in the above Te alloy system, 1
For those with long-term stability of 0 years or more, erasing the written state takes more than 10 μsec, usually 10 to several 100 μs.
It has been shown that irradiation with laser pulse light having a pulse width of ec is required.

As described above, there is still no 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 beam 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. Aiming to improve the performance of media, active research is currently being carried out at research institutions in Japan and abroad.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to overcome the above-mentioned drawbacks of the prior art, to facilitate writing, reproducing, and erasing information, especially high-speed erasing, and to provide high stability of the recording state.
An object of the present invention is to provide a rewritable laser recording medium that can be reproduced and erased many times.

Apart from these problems, laser recording media also have a large reflectance difference between the recorded state and the erased state.
It is required that a sufficient signal can be obtained. In particular, when used as a write-once medium, it is desired that there be a reflectance difference of 20% or more between the two states, even in crystal-amorphous phase change recording, since it is in a position to compete with perforated recording. In terms of disc characteristics, at 18 Gorpm rotation, 55d
C/N ratio of i1 or more (Carrier-noise r
atio) is required. Such high-speed rotation, ie, high-speed recording, is highly desirable in order to achieve high transfer rates 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 laser recording media, the present inventors have conducted extensive research on laser recording media, and have conducted multi-f! After examining various materials, we succeeded in creating a high-performance laser recording medium that satisfies all of the above requirements by carefully selecting the combination of additive elements and composition ratio for the Te-based alloy film.

In order to achieve the above object, the laser recording medium according to the present invention has a composition represented by (Sb1-xTej r-yMV, where X is in the range of 0.1≦X≦0.3, and y is in the range of 0 and y
The range is ≦0.2, and M is 8g5^1. As%Au
.

Di, Cu, Ga, Ge, In, Pb, Pd
, Pt, Se%Si, Sn and Zn) in the recording layer.

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 laser recording medium has a structure in which two or more of the above alloy thin films are provided, each of the plurality of alloy film layers is sandwiched between dielectric layers, and each of the alloy layers is The film thickness is 30 nm or less.

Here, the dielectric layer is 5in2, SiO, Al2O3, Y2
O3, WO3, Ta205, Cr2O3, CeO2, M
Inorganic oxide materials such as oO2, In2O3, Gem2, Tie, ZrO2, metal fluorides such as MgF2, CeF3, inorganic nitrides such as AIN, BN, Si3N4,
Metal sulfides such as ZnS, inorganic carbides such as SiC, or organic materials exclusively for polyphenylene sulfide, polytetrafluoroethylene, polyimide, plasma polymerized organic films such as propylene hexafluoride, hexamethylene disiloxane, tetramethyltin, norbornadiene, adamantane, etc. At least one type selected from the group consisting of the following may be used.

[For production]

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 80at.%, 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 as follows: Te: 10at% 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
We examined the film structure in detail using X-ray diffraction and found that within this composition range, a structure different from that reported so far was formed. FIG. 1 shows examples of X-ray diffraction peaks. Curve A in FIG. 1 shows an X-ray diffraction peak obtained from a 5b-Te alloy film exhibiting a δ phase, and the alloy composition is 5b5
This is for sTe4s. Both peaks are δ
This applies to the structure of -5b2Te3, and the composition also matches the composition region of the δ phase. Curve B shows the Tfl content of 10 to 3 in the 5b-Te alloy found in the present invention.
It shows a characteristic X-ray diffraction peak in the composition range of 0 at.%.

This is for a sample with an alloy composition of Sb, Te, and a diffraction peak different from that of the δ phase. 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 5b2Tes, which is usually called the δ phase. Some of the diffraction peaks are from the document Abriko
sov et al., Ru5s, J., Inor.
g, (:hem, 4°1153 (1959)), but not all peaks match.Moreover, the composition range 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, by linking the existence of this γ phase to the high performance of optical recording media, we will be able to elucidate the cause of the high performance. Now, if the thin film of the recording medium material has a single-phase crystal structure, it will undergo an amorphous-crystalline phase change and no phase separation will occur, which will improve the characteristics of the medium. In terms of erasing speed and reproducibility of repeated conditions for recording and erasing, significant improvements are seen in compositions that exhibit a single phase than in compositions that are a mixture of multiple crystal phases.5b- of the 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 γ
This is due to the fact that the values of optical constants differ greatly between the crystalline states as phases, resulting in a large difference in reflectance. According to the measurement of the dynamic characteristics of an optical disc, Te is 10at,
In the composition range from % to 30 at.%, the C/N ratio is 55
It reaches more than dB. 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.

Furthermore, the present inventors have found that by adding a small amount of a third element other than sb and Te to the γ phase of the 5b-Te alloy, the optical recording characteristics as listed below can be further improved. I discovered that it is possible.

a) Further increase the crystallization temperature to stabilize the amorphous state.

b) To further speed up crystallization by laser light irradiation and improve high-speed erasability.

Here, regarding a), the effect of adding the third element is
Because the element has chemical bonds with sb and Te, it strengthens the bonds between atoms and suppresses the movement and rearrangement of atoms.
Since the crystallization temperature is effectively raised, the stability of the amorphous state is increased.

Regarding b), since the third element is mixed into the matrix of sb and Te as a different atom, it acts as a crystal nucleus for crystallization when heated with laser light. In this case, if the crystal nuclei are microscopically uniformly dispersed, many microcrystals will be generated at the same time during laser beam heating, so there is no need for long-range atomic diffusion during crystallization, and crystallization can be performed at high speed. It has the effect of transforming Furthermore, since individual crystal grains do not grow unnecessarily large, the domains of each crystal grain are sufficiently small, and a -like and homogeneous crystal state can be obtained. Apart from high-speed erasing, this also reduces the noise component of the reproduced signal in optical recording, and
This is also effective in improving the /N ratio.

For the above reasons, the present inventors conducted intensive research and study by adding various elements to an alloy film having a γ phase composition of 5b-Te. %Bi
, Cu, Ga, Ge, In, Pb, Pd,
Pt, Se, Si.

It has been found that by adding at least one selected from Sn and Zn, a recording medium that is even more excellent than the 5b-Te γ phase alone can be obtained.

Here, the most important condition when adding the third element is that even after the addition of the third element, the γ phase of 5b-Te and the third element do not undergo phase separation during crystallization. It means that it is a phase. If phase separation occurs, not only the excellent write-erase repeatability of the γ phase is impaired, but also the high-speed erase performance is degraded, and the addition of the third element becomes counterproductive.

The range of the amount of third element added that satisfies the above conditions is 20at
,% or less, and considering composition deviations during mass production, it is less than 1%.
A suitable range is 5 at.% or less.

Also, regarding the composition range of the γ phase of 5b-Te,
The composition itself where the γ phase appears is Te: 10-30at,
%, but in the composition of Te1Oat, % which is the boundary, the sb part is mixed and becomes a mixed crystal of sb and γ phase, and in the composition of Te30at, % which is the other boundary, the δ phase is mixed. There is a possibility that a mixed crystal of γ phase and δ phase may be formed. If there is a risk of phase separation as described above, this is not desirable in terms of improving the performance of the laser recording medium.

Therefore, in order to increase the yield during mass production, it would be necessary to narrow down the composition range to about 15 to 25 at% Te.

Of course, this range of 15 to 25 at and %Te is also
It is sufficiently spacious for manufacturing purposes, and is convenient in terms of economy and productivity.

When using the alloy film described above, which is a 5b-Te alloy to which a third element is added, as an optical disk medium, it is usually formed using a method such as vacuum evaporation or sputtering using a plastic disk such as acrylic resin or polycarbonate resin as a substrate. to make it a thin film. In this case, in order to prevent irreversible changes such as perforation or deformation of the thin film when the alloy film is heated with laser light, or deformation of the plastic substrate in contact with the alloy film, a uE body layer with excellent heat resistance is placed above and below the alloy film. It is preferable to provide

According to a preferred embodiment of the present invention, the undercoat and overcoat materials for the alloy film include 5in2, SiO, 81203, Y2O3, WO3, Ta205,
Cr2O3, CeO,, TeO2, MoO3, In
Inorganic oxide materials such as 2O3, GeO2, TiO2, Mg
Metal fluorides such as F2, PbF2, CeF3, ^IN
, BN, inorganic nitrides such as Si3N4, metal sulfides such as ZnS, inorganic carbides such as SiC, polymer deposited films such as polyethylene, polyvinylidene fluoride, polyphenylene sulfide, and low molecular deposited films such as Cu phthalocyanine and fluorescein. Further, sputtered films of polytetrafluoroethylene, polyvinylidene fluoride, polyimide, polyphenylene sulfide, etc. can be used as the organic sputtered film.

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 Si-containing compounds such as hexamethyldisiloxane, organometallic compounds such as tetramethyltin, and various organic compounds such as norbornadiene and adamantane can be used.

In addition, when trying to improve the performance of rewritable optical recording media from the viewpoint of these medium configurations, Te
It is effective to laminate thin alloy layers, that is, to provide two or more alloy layers with a thickness of 30 nm or less, each sandwiched between dielectric layers. 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.

Example 1 An attempt was made to add a third element to a 5b-Te alloy as a base. First, a 5b-Te-Ge alloy film was produced by electron beam heating vapor deposition. The board is 50 x 5011I for the test piece.
A heat-resistant glass plate of 11 sides and a thickness of 1.2 mm was used, and a grooved polycarbonate resin disk of 5 inches in diameter and 1.2 mm in thickness was used for disk characteristic evaluation. The degree of vacuum during deposition is 1
x 10-'Torr, and sb, Te, and Ge were contained in three evaporation sources, respectively, and the film was formed by a three-component simultaneous evaporation method. Here, 5b-Te-Ge alloy films having different compositions were fabricated by changing the electron beam output of each evaporation source. The film thickness was 1100n. According to X-ray photoelectron spectroscopy,
The composition of the produced alloy film was as follows. That is, (Sbo, 90TeO-1o) 0.95GeO-0
8% (Sb0.907eO6IO). 90GeO-1
0% (Sbo9oTeo, to). ao [ieo, 2o
, (Sbo, aoTeo-2o). 95Ge0.05
, (Sbo, aoTeo, 2o). 90GeO-10
, (Sl)o, aoTeo, 2o) 11. aoc
eo, 20, (Sbo7oTeo・3o) O, 11s
Geo-05% (sb., 70TeO-30). 90
GeO, I 05 (Sbo, yoTeo-3o) 0
．． It was aOGeo-20. Furthermore, after completely crystallizing samples with these nine compositions by heating them at 300°C, we observed the crystalline state using X-ray diffraction. As a result, no Ge precipitation was observed in any of the compositions, and 5b -Te was a single γ phase. Prior to the fabrication of these alloy films, a 5in2 film with a thickness of 150 nm was undercoated on each substrate by electron beam heating vapor deposition, and after fabrication of the alloy film, a 5in2 film with a thickness of 150 nm was undercoated.
The characteristics were evaluated using a recording medium overcoated with a 50 nm 5in2 film.

Regarding the laser light recording characteristics, an AlGaAs laser diode (oscillation wavelength λ = 8
Writing and erasing were performed by irradiating the recording medium with a laser beam converged to a diameter of 1.4 μm from the substrate side. Changes in the amorphous and crystalline states were determined by irradiating the recording portion of the medium with a reproducing laser beam (continuous wave, output 0.1 mW) and measuring the amount of reflected light. Not only the 5b-Te alloy, but generally the crystalline state has a higher reflectance than the amorphous state. In addition, since the prepared sample is generally in the as-deposited state and is in an intermediate state between amorphous and crystalline, it is irradiated with a continuous wave laser beam with an output of about 6 mW to heat the medium above the crystallization temperature. After that, it was slowly cooled to completely crystallize it, which was taken as the initial state. That is, initial crystallization of the alloy film by heat treatment was performed using laser light. However, in the composition range of the sample prepared here, the as-deposited state is in an intermediate state, but at least optically, this state is very close to amorphous. .

The initial crystallization described here is also considered to be a phenomenon almost equivalent to the transition from amorphous to crystalline.

Writing was performed on these samples with the laser power constant at 15 mW and the pulse width varied, and changes in reflectance were measured. As a result, it was found that in the samples examined here, the reflectance in the crystalline state is about 60% or more, while the reflectance in the amorphous state is about 30% or less, and the difference △R is significantly large. Ta.

FIG. 2 shows the recording/erasing repetition characteristics of a recording medium using a 5b-Te-Ge alloy film as a recording film in comparison with a 5b-Te alloy film to which no Ge is added.

In each case, the overcoat and undercoat are 5in2 sputtered films, and the substrate is a heat-resistant glass substrate. This figure shows how the reflectance changes with repeated recording (amorphization) and erasure (crystallization) after initialization. 5baoTe2o
The recording conditions for the film were 15 mW, +50 nsec, and the erasing conditions were 15 mW, 300 nsec.
The recording condition for the Te2o)9oGe+o film is 15 mW.
, +50nsec, erasure conditions are 8mW, 200n
sec. It can be seen that in both cases, the variation in the reflectance level with respect to repetition is small, and it is stable up to approximately 5 x 103 repetitions without any influence of phase separation. 5 x 1
After 03 times or more, the reflectance level decreases, but this can be recovered by increasing the erasing pulse width to about 1 μs or the like. Therefore, this is considered to be a measurement problem such as a slight positional shift in the beam irradiation position. Also, 5b-
In the Te-Ge alloy film, it is shown that the reflectance level in the amorphous state is 10% lower than that of the 5b-Te alloy film, and ΔR is as high as about 30%. This large change in reflectance increases the recording signal and leads to an improvement in the C/N ratio.

The laser irradiation conditions for such amorphization differ depending on the sample, but for polycarbonate resin substrates, the pulse width was 40 to 80 nsec, and for heat-resistant glass substrates, it was between loo to 2 oon seconds. .

Erasing conditions were subsequently evaluated for this written state. Here, the laser power and pulse width were varied and the one with the shortest pulse width among the laser pulses required to erase the written signal was taken as the erasing speed.

Next, regarding the lifespan in the written state, we examined a device fabricated on a heat-resistant glass substrate.

Here, the written sample was heat-treated 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, the sample having the composition studied here has a crystallization temperature of 150° C. or higher, and is sufficiently stable as an amorphous state at room temperature. If the crystallization temperature exceeds 100'C,
Normally, the lifespan at room temperature is estimated to be 10 years or more. Also,
In this composition range, the erasing rate, that is, the crystallization rate during laser irradiation, is on the contrary very fast, and laser crystallization, that is, erasing, of the amorphous spot is achieved with a short pulse with a pulse width of 100 to 200 ns. I found out what I can do. Therefore, high-speed erasing is possible and the crystallization temperature is high.
The result was that the written state had a long life, and it was found that this medium could overcome the above-mentioned biggest problem of rewritable media.

In addition, in this composition range, the repeatability of writing and erasing is also relatively excellent, for example, Te: 20at, desk Sb:
80at! k and Ge: 10at, %i, i.e. (
SbaoTe2a) 90cal.

For a sample of a heat-resistant glass substrate with a composition of
%150nsec, erase 8mW, 200nsec
Under each condition, as shown in FIG. 2, it was confirmed that writing and erasing could be repeated more than 103 times with good reproducibility. However, when the number of repetitions exceeds 5 x 103 times, complete erasing cannot be achieved with the erasing pulse of 200 nsec, and unerased areas become visible. In this case as well, it has been found that by increasing the erasing pulse width to ~1 μsec or by irradiating pulses several times even with the width of 200 nsec, there is no unerasable residue and complete erasure can be achieved. Also in other compositions, 15≦Te≦25at, %
It was confirmed that similarly good repeatability was exhibited within the range of . Here, in the samples with a Te content of IO and 30 at%, when the number of repetitions exceeded 2 x 10', complete erasure was no longer possible and unerased areas were observed. These two compositions are almost at the boundary of the γ phase region, so Te1
In the case of Oat, %, it contains a small amount of sb in addition to the γ phase, and T
In the case of e 3Qat,%, 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 the phase progresses gradually due to repeated recording and erasing, the recording state and the erasing state are not uniquely determined, and it can therefore be assumed that the repeatability is slightly reduced. This situation is similar to the case of the 5b-Te binary alloy film. It has been found that even for a sample in which the amount of Ge added is roughly 20 at. This is also presumed to be because if the amount of Ge added is too large, Ge will not be solidly dissolved in the 5b-Te-based crystal, but will form another crystal phase, causing phase separation. Therefore, it is not preferable to add more than 20 at% of the third element in order to maintain the repeatability of recording and erasing. The amount of the third element (Ge in this case) added is
It was also confirmed that when the amount was less than 20 at.%, no deterioration in the repeatability of recording and erasing was observed.

Next, we evaluated the rotation system as an optical disk for media of each composition fabricated on a grooved polycarbonate resin disk with a diameter of 5 inches, and in particular, we evaluated the carrier wave-to-noise ratio (generally C
/N ratio) was measured.

Recording and playback experiments were conducted with a laser light output of 15 mW during disk writing, a laser pulse width of 500 nsec, a laser light output of 1.2 mVf during playback, and a disk rotation speed of 1800 rpm. /N ratio was 57 dB or more, which showed rather higher characteristics than before addition of the third element. Subsequently, when the information writing area of the disk was scanned with a laser beam of output mW, it was possible to completely erase the written information on disks of any composition, and writing and erasing could be repeated up to 10' times. An experiment was conducted, and no decrease in the C/N ratio was observed, and complete erasure was possible with no unerasable residue.

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

At a rotational speed of 1800 rpm, the laser first output cuff mW during writing (in this case, laser crystallization) and the output during playback 1.2
When recording and reproducing experiments were conducted at mW, a high C/N ratio of 59 dB was obtained. This is an excellent value for the performance of a write-once medium in perforation mode.

Next, in place of Ge as the third element, A3%AI, As
, ＾u, Bi%(:u%Ga%In, Pb%Pd,
Pt, Se, Si, Sn, and Zn were selected, and similar media were prepared and evaluated.

As a result, the effects of the third element are similar, but based on the laser recording characteristics, the relative differences are classified according to the type of added element: Ag%AI, Au,
Bi%Cu, Ga, In, Pb%Pd, Pt
%Sn.

Zn is particularly effective in improving high-speed erasing properties, and As,
Se and Si were particularly effective in stabilizing the written state, that is, in stabilizing the amorphous state by increasing the crystallization temperature.

Example 2 A medium having the same composition as the medium manufactured in Example 1 was manufactured by RF sputtering. Further, the overcoat and undercoat are also the same as in Example 1. The sputtering gas is Ar with a gas pressure of 5×10” Torr.
The RF specific output was set to 100W. Here, films with different compositions were produced by sputtering with different compositions of the 5b-Te-Ge alloy of the target. Further, the 5in2 films of the overcoat and undercoat were similarly formed by RF sputtering.

No difference was observed between the characteristic evaluation results of the medium fabricated by sputtering shown in the unexamined examples and the results of the medium fabricated by electron beam heating evaporation shown in Example 1, indicating excellent write-erase repeatability. It was found that the composition exhibited good properties similar to those of Example 1 in terms of long-term stability and high-speed erasability while maintaining its properties.

Example 3 In Examples 1 and 2, the 5i02 film was used as the overcoat and undercoat layer of the alloy film, but in this practical example, various inorganic phone material films and organic materials were used to form the recording medium. were fabricated and their properties were evaluated. The recording layer used was an alloy film (thickness: 1100 nm) in which Ge was added to the γ-phase single-phase region of 5b-Te shown in Examples 1 and 2. Above and below this recording layer, the following overcoat was used. A coat and undercoat material was applied to a thickness of 150 nm.

The thin films prototyped as overcoat and undercoat materials include inorganic materials other than 5in2, SiO, 812
03, Y2O3, WO3, Ta205,
Cr2O3, CeO2, MoO2, in, 03, Gem
,, Tie, oxides such as ZrO2 and ZnO, and F2
, fluorides such as CeF3, AIN, BN, Si3N
These are inorganic substances such as nitrides such as No. 4, sulfides such as ZnS, and carbides such as SiC.

Among these materials, those with relatively low melting points such as SiO, PbF2, and TaO2 are processed by resistance heating vapor deposition, Al2O3, and ZrO.
A film having a high melting point such as No. 2 was formed into a thin film by electron beam heating evaporation or RF sputtering, and was deposited on the top and bottom of the 5b-Te-Ge 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 the 5b-Te-Ge film. In addition, olefinic compounds such as ethylene, aromatic compounds such as styrene, fluorinated 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-Ge films. However, when comparing the laser recording characteristics, it was found that writing and erasing conditions and repeatability were considerably superior and inferior 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 sb-D-Ge film, and in extreme cases, even an overcoated medium may become perforated. Even in the case of inorganic thin films, it is necessary to heat the 5b4e-Ge film to a high temperature higher than the melting point of 5b-Te-Ge to make it amorphous, so PbF (melting point 855°C),
Those with relatively low melting points such as TaO2 (melting point 733°C) are
It has been found that problems with repeatability may occur due to the occurrence of irreversible deformation. This is thought to be because the laser beam has a Gaussian profile, so the medium surface may reach a temperature higher than the melting point of the protective film material at the center of the beam.

On the other hand, 5in2, Al2O3, Cr2O3, 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 Examples! and any 5b-Te-G of 2
Writing and erasing of 103 times or more was also achieved on the e-film with good reproducibility.

In addition, when overcoating or undercoating an organic thin film, 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 a medium using an organic film as an overcoat or an undercoat is that the thermal conductivity (h) is much lower than that of inorganic materials such as SiO7, so that less energy is required during laser writing. That is, when the temperature is raised above the melting point of the 5b-Te-Ge layer by laser heating, it is difficult to prevent loss of laser energy due to heat dissipation because the overcoat and undercoat layers that cover the top and bottom surfaces have low thermal conductivity. can.

For example, (SbaoTe2o) 9o and 1. +o is used for the recording film, and when laser writing is performed with a laser power of 15 mW, a pulse width of 30 nsec or more is required for a medium overcoated or undercoated with 5i02, but it is possible to overcoat or undercoat a polyimide sputtered film. It has been found that a pulse width of 20-25 nsec is sufficient for such media.

Although we have discussed the overcoat and undercoat materials above, depending on the use and configuration of the optical recording medium, only the overcoat or only the undercoat can be used with 5b-T.
It is sufficient to deposit it on the e-Ge 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. In addition, if the laser energy (power and pulse width) is precisely controlled, T
without causing irreversible deformation or perforation of the eJ-alloy membrane.
It is possible to induce amorphization or crystallization; in this case,
No overcoat is required, and the plastic substrate and Te
It is sufficient to simply apply an undercoat between the alloy film and the alloy film.

As described above, even when the recording layer is an alloy film based on 5b-Te in the composition range of the present invention with the addition of a third element, the overcoat and undercoat of the above-mentioned dielectric layers protect the recording layer. It was confirmed that the laser recording characteristics differ depending on the material properties.

Example 4 In the recording medium of Example 1, the composition of the alloy film was (Sbao
For Te2o)9oGe+o, a laminated film with a 5in2 film was produced. The substrate-sputtering conditions were the same as in Example 2, and the 5in2 film was sputtered by magnetron sputtering.

The structure of the laminated medium was such that the 5b-Te-Ge alloy layer had a thickness of 2 nm, the number of layers was 5, and two 5-inch layers were deposited in the middle of each layer with a thickness of 20 nm. That is, in sputtering, a Te-5b-Ge alloy target,
Regarding each of the 5in2 (magnetron) targets,
A SiO undercoat layer was applied to a heat-resistant glass substrate by alternating sputtering, first with a layer thickness of 150 r+m, then with a layer thickness of 20 r+m, respectively.
This is done by alternately laminating Te-5b-Ge alloy layers and 5i02 intermediate layers of 150 nm thick, and further laminating a SiO□ overcoat layer of 150 nm thick. It has been verified that a medium in which the recording film is thinned and laminated with dielectric layers sandwiched therebetween is stable as amorphous (Japanese Patent Application Laid-open No. 44692/1982). However, if the thickness of each stacked recording film exceeds 30 nm, the stability as an amorphous state will be impaired, so the film thickness is preferably 30 nm or less.

The same characteristics evaluation as in Example 1 was performed on the medium prepared using the tree-like sample. As a result, the write/erase conditions were almost the same (however, the erase pulse width tended to be slightly longer)
On the other hand, the crystallization temperature rose to 200° 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
At least 105 write and erase cycles were achieved with good reproducibility under the conditions of 0 nsec, 8 mW, and 200 nsec.

In addition, in this example, the layer thickness of the 5b-Te-Ge layer was 10 nm.
, a medium with 10 layers was also studied. In this laminated film, the crystallization temperature was 220° C., which showed a tendency to increase further.

Furthermore, the dielectric thin film as an intermediate layer of the alloy layer is 5i02
In addition, various materials mentioned in Example 3, namely A
Even if an inorganic film such as l2O3 or 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 3.

In the examples, the conditions for writing and erasing the medium were described in detail for media fabricated on a heat-resistant glass substrate, 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,
In particular, the write threshold and erase threshold are significantly improved.

(Effects of the Invention) As explained above, the optical recording medium of the present invention has high signal strength, high performance that satisfies both long-term stability (stability in an amorphous state at room temperature) and high-speed erasability. This is a rewritable medium with excellent repeatability of writing and erasing.The problem with the deterioration of the recording medium due to oxidation deterioration of the di-alloy film is that the overcoat and undercoat are coated with water to block moisture, such as the 5i02 film. The provision of a countermeasure will resolve the issue and will not pose any problem to long-term stability.

In addition, 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 γ phase 11 phase that does not cause phase separation. Since the composition range is based on the γ phase of Te, it has the advantage that no deviation in characteristics occurs even after repeated recording and erasing. In particular, the composition range showing the 5b-Te single phase (γ phase), which is the base of this alloy film, is as wide as 1O~30at% (there is ample room in the composition to satisfy certain writing and erasing conditions. Therefore, it is characterized by a large manufacturing margin and excellent mass production and productivity.As mentioned above, due to phase separation at the boundaries of the γ phase region where Te is around 10 at.% and around 30 at.%, recording, The repeatability of erasing may be slightly reduced.To prevent this, the composition range must be narrowed down to ensure that a single γ phase is obtained, with a Te content ranging from 15at% 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. Also, regarding the addition of a third element, if it is approximately 20 at.% or less (certainly 15 at.% or less), there is no risk of phase separation, and this amount of addition is sufficient to improve the media properties. give. It is also advantageous in terms of productivity and manufacturability, and there are no problems.

Furthermore, a recording medium using an alloy film in the composition range of the present invention as a recording material has a very high signal strength, and in disk evaluation, the C/N ratio is as high as 59 dB, compared to a perforation mode write-once medium. It's comparable. That is, it is also used 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 enormous.

[Brief explanation of the drawing]

Figure 1 shows the X-ray diffraction pattern of a 5b-Te alloy, where curve A is 5b55Te4s and uAB is 5b8oTe2.
Figure 2 shows the recording/erasing repetition characteristics of a recording medium using a 5b-Te-Ge alloy film in comparison with a 5b-Te alloy film without Ge added. It is a characteristic diagram.

Claims (1)

[Claims] 1) General formula: (Sb_1_-_xTe_x)_1_-_
Composition expressed as yM_y (where x is 0.1≦x
≦0.3, y is 0<y≦0.2, and M
is Ag, Al, As, Au, Bi, Cu, Ga, Ge,
In, Pb, Pd, Pt, Se, Si, Sn and Zn
1. A laser recording medium comprising, in a recording layer, an alloy film of at least one element selected from the group consisting of: 2) The laser 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 laser recording medium described in .