JPH01277338A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide the recording medium which has the long-period preservable property of recording and high-speed erasing property of recording in combination by providing a recording layer consisting of an alloy having a specific compsn. to said medium. CONSTITUTION:The recording layer consisting of the alloy having the compsn. expressed by the formula (SbxTe1-x)1-yMy is provided. In the formula x is 0.4<=x<0.7 number; y is <=0.2 number; M is one kind of the element selected from the group consisting of Ag, Al, As, Au, and Zn, etc. The long-period stability of the writing state and the high-speed erasing property are not obtainable in combination if the (x) indicating the ratio of Sb to Te is below 0.4. The crystallization temp. of the alloy film is increased and the stability in the amorphous state is improved by the addition of the element M but the stable repetitiveness of writing and erasing is lost if the (y) indicating the ratio of the element M exceeds 0.2. The recording medium provided with the requirements such as long-period preservable property of the writing state, the high-speed erasing property and the repetitiveness of the writing-erasing with good balance is thereby obtd.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical recording medium, and in particular to a rewritable laser that has improved long-term stability of recorded information, high-speed erasing performance, and writing-erasing repeatability. The present invention relates to an optical recording medium suitable as an optical recording medium.

[Conventional technology]

In recent years, with the advancement of compact and high-performance lasers, recording media that record information on a thin metal film provided on a substrate by irradiating focused laser light have enabled high-density, large-capacity recording. It is expected as such. Among these, rewritable laser beam recording media, which perform recording based on the amorphous-crystalline transition of a thin metal film, write information by heating the thin metal film with laser light to above its melting point and then rapidly cooling it to become amorphous. In addition, the information is erased by heating the thin metal film with a laser beam to a temperature above its melting point and then slowly cooling it to crystallize it.The writing and erasing of information can be repeated many times. It is attracting particular attention because of its advantages.

In such a rewritable laser optical recording medium, (a) Even when high-speed recording is required such as on an optical disk, the laser beam output during writing is 2 hW or less and the pulse width is 1
(b) have stable repeatability of writing and erasing (in practical terms,
3 times or more) and (C) high long-term stability in the written state near room temperature (practically, it is said to be 10 years or more).

However, a recording medium that combines these required characteristics in a well-balanced manner has not yet been developed.

For example, pure Te has a glass transition temperature around room temperature (approximately 20°
C), and even if it is made amorphous, it easily becomes crystalline in a short period of time, so it cannot be used as a recording layer.
A Te alloy film whose glass transition temperature is increased to 100° C. or higher by adding impurity elements such as s and Bi has been proposed as a recording layer.

(Problems to be Solved by the Invention) According to the above Te alloy film, it is possible to obtain long-term stability of the written state for more than 10 years, but in that case, it takes more than 10 B sec to erase the written state. , usually 10 to several 1
Since it is necessary to irradiate the laser beam with a pulse width of 0.00 and czsec, high-speed erasing performance is lost.

As described above, conventional rewritable laser optical recording media have a problem in that they do not sufficiently meet the above-mentioned required characteristics.

Therefore, an object of the present invention is to provide a rewritable laser optical recording medium that has the above-mentioned required characteristics in a well-balanced manner. Particularly, it is an object of the present invention to provide a rewritable laser beam recording medium that has both long-term storage properties and high-speed erasability of records.

[Means to solve the problem]

As described above, conventionally, when an impurity element is added to Te and the amount thereof is increased, the long-term stability of the amorphous state is improved, but the crystallization rate is lowered and the high-speed erasing property is lowered. In addition, it was thought that repeated writing and erasing would cause irreversible changes such as phase separation, resulting in a decrease in reusability. However, the present inventors have surprisingly found that by forming a recording layer with a Te alloy thin film in which sb is added to Te at a much higher concentration than before, a recording medium that can achieve the above object can be obtained. I found it.

That is, the present invention provides formula (I): (Sbz ding e+-x) ty? Iy
(1) [Here, X is a number of 0.4≦x<0.7, y is a number of y≦0.2, and h is Ag+A
L As, Au+Bi+ Cu+ Ga, Ge,
In+ Pb+ Pt+ Se, Si, Sn and Z
At least one element selected from the group consisting of n. ] An optical recording medium having a recording layer made of an alloy having a composition represented by the following is provided.

The Te alloy constituting the recording layer of the recording medium of the present invention has the above-mentioned composition in formula (1) where X is 0.4 or more and 0.4 or more.
is a number less than 7, preferably from 0.45 to 0.65, and y
is a number of 0.2 or less, preferably 0.05 to 0.15. If X, which indicates the ratio of sb to Te, is less than 0.4, it is impossible to obtain a recording layer that has both long-term stability of the written state and high-speed erasing performance. In addition, by adding element H,
As the crystallization temperature of the alloy film increases and the stability of the amorphous state improves, As+Ge+Se and Si are particularly effective.
Among them, As and Ge are preferable), and even faster crystallization and erasure by laser beam irradiation can be achieved (especially Ag, AI, ^u, and Bi).

Cu, Ga, In, Ge+ pb, pt, S
n and Zn are effective, and among them Ge and In are preferable), but if y, which indicates the proportion of this element H, exceeds 0.2, stable repeatability of writing and erasing will be impaired.

In the recording medium of the present invention, the recording layer is usually formed on the substrate. The method for forming the recording layer is not particularly limited, and for example, a vacuum evaporation method, a sputtering method, etc. can be used. The thickness of the recording layer typically ranges from 200 to 1000 thick.

Examples of the substrate used include synthetic resins such as acrylic resin, polycarbonate resin, and polyimide resin, and glass such as Pyrex glass. The thickness of the substrate typically ranges from 1.2 to 1.5 m.

In the recording medium of the present invention, at least one of the upper surface and the lower surface of the recording layer, usually both surfaces, may be perforated or deformed during heating with laser light, or irreversible deformation of the synthetic resin substrate. It is desirable to provide a protective layer (overcoat layer, undercoat layer) in order to prevent this from occurring and to prevent oxidation of the recording layer. Examples of the material for the protective layer include Sing, SiO+ A1z03.
YzOs+ WOs+↑atO5+Cr2O3,Ce
0z+ MoOs+ In! 03+ Ge0z+ Tt
Inorganic oxides such as Oz+ Zr0z, AIN, BN,
Examples include inorganic nitrides such as SizNm, metal fluorides such as MgFz and CeF3, metal sulfides such as ZnS, and organic polymer substances such as polyphenylene sulfide, polytetrafluoroethylene, and polyimide. The protective layer made of these inorganic materials can be formed by, for example, a vapor deposition method such as electron beam heating vapor deposition, or a method such as sputtering. Further, the protective layer made of an organic polymer substance can be formed by a method such as vapor deposition or sputtering, and a plasma polymerized film of tetramethyltin or the like can also be used. The thickness of the protective layer usually ranges from 200 to 1500.

In general, inorganic protective layers have excellent heat resistance and are therefore difficult to cause irreversible deformation (and are particularly suitable for obtaining recording media with high write-erase reversibility.Organic protective layers are Since the thermal conductivity is low, there is less energy loss due to thermal diffusion when the temperature of the alloy film of the recording layer is raised above the melting point using laser light, and this has the advantage that writing and erasing can be performed using laser light with a shorter pulse width. There is.

When manufacturing the recording medium of the present invention, if a heat-resistant plastic such as highly heat-resistant polyimide or heat-resistant glass such as Pyrex is used as the substrate, there is no risk of deformation of the substrate when heated by laser light. , a protective undercoat layer is not required, which is advantageous in improving repeatability of writing and erasing.

Further, the form of the recording medium of the present invention is not particularly limited, and examples thereof include a disk shape, a card shape, and the like.

[Effect]

Although it is not necessarily clear why the excellent balanced properties of the recording medium of the present invention are achieved, the present inventors have found that a Te-Sb alloy with a composition of 40 to 70 atomic % Sb is
bzT6s has been found to be a single phase, which makes it possible to repeat writing and erasing in the single phase state, and combined with the moderate melting point and crystallization temperature, it can be used for various purposes described above. It is presumed that this improves the contradictory required characteristics of

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 (1) As a substrate, dimensions 50 mm square, thickness 1.2 r
Three types of glass plates were used: a Pyrex glass plate with a diameter of 130 mm and a thickness of 1.2 m, a polycarbonate resin plate with the same dimensions, and a polycarbonate resin disk with a diameter of 130 mm and a thickness of 1.2 m. First, a Si0 film with a thickness of 150 ma was deposited on one side of these substrates by electron beam evaporation.
g film was formed. Next, an Sb-Te-Ge alloy film having a thickness of 1000 and having the following 12 types of compositions was formed thereon by electron beam heating vapor deposition.

(Sbo, toTea, zo) o, qsGeo
, 65 (Sbo, toTea, 3g1) 0. qsGe
o, I.

(Sbo, toT13o, 311) +1.5oG
eo, g.

(Sbo, 1oTea, 46) 11. qsGe
o, as(Sbo, 1oTea, no) o,
qsGeo, I.

(Sbo, boTea, no) o, aoGeo
, z.

(Sba, 5oTeo, so) o, qsGec
+, 05(Sbo, 5oTeo, io) o,
Q@ce11. I.

(Sbo, 5oTelo, so) o, It)c
e@, t.

(Sbo, m5Tea, 60) 6.9Sce(1
,115 (Sbo, noTea, 6o) @* 9
@cet1. I.

(Sbo, noTe6.&@) t1.5lice@, t
.

The deposition was carried out under a vacuum of I
The contents of sb and element H in the produced alloy film were adjusted by changing the electron beam output for the three evaporation sources of , Te, and Ge. The above composition was confirmed by X-ray photoelectron spectroscopy. Next, a film with a thickness of 15 mm was deposited on the resulting recording layer, an Sb-Te alloy film, by electron beam evaporation.
A Si0g film of 00 people was formed. The performance of the recording medium thus produced was evaluated as follows.

(2) A recording medium made of a rectangular polycarbonate plate and a Pyrex glass plate as a substrate was used as a sample.

Writing and erasing were performed by using an AlGaAs laser diode (oscillation wavelength: 8300 nm) as a light source, and irradiating laser light converged to a diameter of 1.4 μm from the substrate side of the recording medium.

The change in the amorphous-crystalline state of the recording layer is achieved by using the fact that the crystalline state generally has a lower light reflectance than the amorphous state. The amount of reflected light when irradiated with oscillation, laser light output 0.1o + W) was measured, and the relative change in reflectance ΔR/R (R: reflectance in crystalline state, ΔR: reflection in amorphous state and crystalline state) was measured. (difference in rate) was determined and used as an index. Note that since the alloy film of the recording medium as produced above is in an intermediate state between amorphous and crystalline, the alloy film is first irradiated with continuous wave laser light to heat it above its melting point and then slowly cooled. It was used after complete crystallization.

The output of the included laser beam was kept constant at 15 mW, and laser beams of various pulse widths were irradiated to investigate the conditions under which writing was possible under which the relative change in reflectance was 30%. As a result, in the samples of Examples, the recording medium whose substrate was a rectangular polycarbonate plate had a speed of 30 to 7 Qnsec, and the recording medium whose substrate was a Pyrex glass plate had a speed of 60 to 90 nsec.

Attempts were made to erase the written signal by changing the output and pulse width of the irradiated laser beam, and the shortest erasable pulse width was evaluated as the erasing speed. In all cases, high-speed erasing with a pulse width of 100 nsec or less was possible for the samples of the examples. In the comparative sample that does not contain Ge, 200
It was nsec.

A sample whose substrate is a Pyrex glass plate with writing written on it is heat treated at various temperatures from room temperature to 250°C, and the temperature at which the written signal is halved after 100 seconds of heat treatment is determined. was determined and this temperature was taken as the crystallization temperature. As a result, the crystallization temperature of the samples of Examples was 150°C or higher in all cases. This means that the amorphous state is stable for more than 10 years at room temperature.

Writing was carried out on a sample using a Pyrex glass plate as a substrate for the laser beam with an output of 15 II W and a pulse width of 90 ns.
Erasing was performed at a laser beam output of 6IIIW and a pulse width of 200 nsec, and writing and erasing were repeated.

As a result, all of the samples of Examples had good reproducibility <1.
It was possible to repeat writing and erasing more than 03 times. When the number of repetitions exceeds 5X10' times, the sb content is 40
% and 70% samples could no longer be completely erased, but the samples of other examples still had good reproducibility.

(3) Optical Edoku Toyotomi The above-mentioned recording medium with a polycarbonate disk as a substrate was used as a sample, and the carrier wave-to-noise ratio (C
/N ratio) was evaluated as follows.

Laser light output during writing: 15 ImW, pulse width: 100
nsec, and the laser light output during reproduction is 1.2 mW.

When recording and reproducing experiments were conducted at a disk rotation speed of 180 rpm, the C/N ratio was 55 dB or more in all cases for the samples of the examples.

Subsequently, when the information writing section of the disk was scanned with a laser beam of output 61, it was possible to completely erase the written information on the disk of the example in all cases.

The above writing-erasing process was repeated 103 times, but no decrease in the C/N ratio was observed, and no unerased portions were left, indicating that complete erasing was possible.

Example 2 As element H in formula (1), Ag + instead of Ge
All As, Au+ Bt+ Cu, Ga+
In, Pb+ PtI Se.

Recording media were manufactured and evaluated in the same manner as in Example 1, except that St, Sn, or Zn was used. Performance equivalent to that of Example 1 was confirmed. Among them, AL All Au.

Bi, Cu, Ga, In+ Pb, Pt, S
n and Zn are particularly effective in improving high-speed erasing properties, and As
, Se and Si were found to be particularly effective in improving the stability of the written state.

Example 3 A recording medium was manufactured in the same manner as in Example 1 except that the recording layer and the upper and lower protective layers were formed by RF sputtering. Sputtering for forming the recording layer uses Ar as a sputtering gas, and the gas pressure is 5 x 10-'' Torr, R
The recording layer was 5b-Te-Ge.
The composition of the alloy film was adjusted by changing the composition of the target 5b-Te-Ge alloy.

The obtained recording medium was evaluated in the same manner as in Example 1, and results were found to be equivalent to those in Example 1 in all respects: long-term stability of writing conditions, high-speed erasing performance, and repeatability of writing and erasing. Obtained.

〔Effect of the invention〕

The optical recording medium of the present invention has well-balanced characteristics such as long-term storage of written state, high-speed erasing performance, and repeatability of writing and erasing, which could not be improved at the same time in the past, and is rewritable. It is excellent as a laser beam recording medium.

Claims (2)

[Claims] (1) Formula: (Sb_xTe_1_-_x)_t_-_y
M_y [here, x is a number of 0.4≦x<0.7, y is a number of y≦0.2, and M is Ag, Al, As
, Au, Bi, Cu, Ga, Ge, In, Pb, Pt,
At least one element selected from the group consisting of Be, Si, Sn, and Zn. ] An optical recording medium having a recording layer made of an alloy having a composition represented by: (2) The optical recording medium according to claim 1, wherein at least one of the upper surface and the lower surface of the recording layer contains an inorganic oxide, an inorganic nitride, a metal fluoride, a metal sulfide, and an organic polymer. An optical recording medium provided with a protective layer made of at least one substance selected from substances.