JPH02112987A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide stable operation even if recording and erasing are repeated many times and to reduce deterioration in recording characteristic such as a decrease in recording sensitivity by incorporating specific composition of Sb, Te, Ge and Co, Zr and Hf in the recording layer of an optical recording medium. CONSTITUTION:A recording layer formed on a substrate has a recording layer, a heat insulating layer and a cooling layer, and the composition of the layer is represented by a general formula, where x, y and alpha are ratio of number of atoms, Sb, antimony, Te, tellurium, Ge, germanium, M representing at least one or more of Co (cobalt), Zr (zirconium) and Hf (hafnium). The insulating layers are laminated on both side faces of the recording layer, and made of a thin film of ZnS, oxide thin film of metal such as Si, Ge, Ti, Zr and Te, and a film of mixture thereof. The cooling layer is laminated on one side of the insulating layer, and made of metal having higher thermal conductivity than that of the insulating layer and particularly small specific heat and high thermal conductivity, and Au and Sb are desirable. The substrate may be made of plastic, glass, etc. similar to that of the conventional recording medium. The recording, insulating and cooling layers are formed on the substrate by a thin film forming method such as a sputtering method, a resistance heat depositing method, an electron beam heat depositing method and an ion plating method, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to optical information recording media, and more specifically relates to optical recording media such as optical cards and optical disks that record and reproduce information using light. It is something.

[Conventional technology]

Conventionally, a replaceable optical recording medium has always been one that utilizes a reversible change between two optically detectable states, an amorphous state and a crystalline state.

A typical example is Te81G, which has Te as its main component.
e15sb282 film as a recording layer (Unexamined Japanese Patent Publication No. 47-2
6897), Te 80S whose main component is Te
JP-A-61-1 by Chinoku using blO8elO film as recording layer
Publication No. 45737, 5PIE VOl, 5291) 2
), 3b-3e alloy having a composition such as S b 2 Se is used as a recording layer (Japanese Patent Application Laid-open No. 155495/1983,
Appl, Phys, Iett, 48(19), 12
May 1986), one with a recording layer made of Sb2Se3 alloy (Japanese Patent Application Laid-Open No. 185048/1982), and one with a recording layer made of a Te-Ge-3b alloy containing Te as a main component (Japanese Patent Laid-Open No. 209742/1982). Publication No.) etc.

In these optical recording media, during recording, the recording layer in the recorded state is irradiated with light for a short period of time. At this time, the recording layer partially melts, and then rapidly cools and solidifies due to thermal diffusion.
Amorphous marks are formed.

The light reflectance of this amorphous mark is lower than that of the crystalline state, and can be optically detected as a recording signal. When erasing, the amorphous mark is irradiated with light and heated to below its melting point, thereby crystallizing the amorphous mark, returning it to its original state, and erasing it.

[Problems to be Solved by the Invention] However, the above-mentioned conventional technology has the following problems.

That is, Te81Ge15Sb232 film or l'-e8
In the case of using an 0SblO3elO film as a recording layer, the crystallization speed is slow, and it has not been possible to realize a real-time rewritable optical disk that requires high-speed erasing of 1 μsec or less. On the other hand, with the Sb2Te3.5b2Se and Te-Ge-3b films, the crystallization speed is fast and the erasing speed can be set to 1 μsec or less, but the following problems often occur. That is, in the Sb 2 Te 3 film, the crystallization temperature was as low as 70° C. or less, and the thermal stability was low, resulting in poor reliability.

Furthermore, the 5b2Se film has the disadvantage that noise increases with repeated recording and erasing. Furthermore, l'-e-Ge-3
In the b film, if the composition allows high-speed erasing, the recording film is likely to be deformed and open during recording, resulting in poor reliability.

The present invention improves these problems, enables high-speed recording and erasing, has high recording and erasing sensitivity, has good C/N and erasing rate, and is capable of repeating recording and erasing many times. It is an object of the present invention to provide an optical recording medium that is less likely to be degraded by heat treatment and has good thermal stability.

(Means for Solving the Problems) An object of the present invention is to record, erase, and reproduce information by irradiating a recording layer formed on a substrate with light; , an optical recording medium that undergoes a phase change between a crystalline state and an amorphous state, wherein the recording layer comprises at least a recording layer, a heat insulating layer and a cold F
An optical recording medium characterized in that the composition of the recording layer is represented by the following general formula.

(SbxTel-x)1-y-αGeyMα However, 0.55≦x≦0.65 0.01≦y≦0.10 0.001≦α≦0.03 x, y, and α each represent the atomic ratio , Sb is antimony, D is tellurium, Ge is germanium, M is Co
(cobalt), Zr (zirconium), and Hf (hafnium).

The main component of the composition of the recording layer is 5b-T whose main component is sb.
It is an e-alloy. The 5b-Te binary alloy with the composition expressed in parentheses in the above general formula tends to be amorphous and has a lower melting point than Sb and Sb2Te3 compounds, so it is easy to record by amorphization and it is not crystalline. It is also fast to erase, and can be erased by laser light irradiation for approximately 1 μsec or less. In addition, when this 3b-Te alloy is the main component, irreversible phase separation and crystal coarsening that occur with repeated recording and erasing, as seen in the 5b-3 film alloy system, are less likely to occur. Deterioration of recording characteristics such as recording sensitivity and C/N ratio is reduced.

Furthermore, within the composition range represented by the above general formula, Ge contained in the recording layer stabilizes the amorphous state and improves recording stability, and also improves the light reflectance of the amorphous phase and crystalline phase.
This has the effect of increasing the difference in transmittance and improving the contrast of the reproduced signal.

CO, Zr and) represented by M contained in the recording layer
The metal containing at least one element of 1f, within the composition range represented by the above general formula, improves the erasure rate during recording and erasing, reduces noise increase due to repeated recording, and improves the resistance to repeated recording and erasing. This prevents fluctuations in recording and erasing power, fluctuations in reflectance, etc. It also has the effect of improving erasing speed (crystallization speed).

In the general formula of the composition of the recording layer, the atomic ratio of sb
If it exceeds 0.65, the crystallization speed is increased, but the reversibility of recording and erasing repetitions deteriorates, and it becomes difficult to amorphize, making recording difficult. On the other hand, 0.
If it is smaller than 55, the crystallization speed is slow, making it difficult to erase records at high speed.

In the general formula of the composition of the recording layer, the atomic ratio of Te is 1
If -x is larger than 0.35, the crystallization rate is slow and the recording erasing rate is slow, which is not practical. Also 0, 4
If it is smaller than 5, it is difficult to amorphize, making recording difficult and making it difficult to repeat recording and erasing.

In the general formula of the composition of the recording layer, the Ge atomic ratio y
If it is larger than 0.10, it is not practical because the crystallization speed becomes slow and high-speed erasing of records becomes difficult. On the other hand, when it is smaller than 0.01, the crystallization temperature is low, resulting in a decrease in thermal stability of recording. Furthermore, no significant improvement in signal contrast was observed due to the addition of Ge.

In the general formula for the composition of the recording layer, C0 represented by M
If the atomic ratio α of at least one element metal among 1lr and Hf is more than 0.03, amorphization becomes difficult and the erasing rate deteriorates. Further, noise also increases, which is impractical. On the other hand, if it is less than 0.001, the effects of addition, such as improving the erasing rate and reducing the increase in noise caused by repeated recording and erasing, cannot be obtained.

In particular, since it is possible to erase records many times, α is 0.
．． It is preferable that it is 002-0.01.

The thickness of the recording layer of the present invention is 10 nm to 100 nm.
In particular, in order to obtain high sensitivity as an optical disc, it is preferably used in the range of 10 nm or more and 150 nm or less, and even better, the carrier-to-noise ratio of the recording/reproducing signal is 1. It is preferable that

The heat insulating layer of the present invention is laminated on both sides of the recording layer.

This heat insulating layer prevents the substrate from being deformed by the heat of the recording layer during recording and deteriorating the recording/erasing characteristics, and also reduces the diffusion of heat from the recording layer during recording, making it easier to heat adiabaticly. This improves recording sensitivity. As the heat insulating layer, inorganic thin films such as Zns and 5i02,
Especially thin films of ZnS, 31. Thin oxide films of metals such as Ge, Tr, ZR, and Te, and films of mixtures thereof are preferred because of their high heat resistance.

The cooling layer of the present invention is laminated on one side of the heat insulating layer.

This cooling layer facilitates heat diffusion from the heat insulating layer and increases the cooling rate of the melted portion during recording, thereby facilitating the formation of amorphous marks. The thickness of the cooling layer is approximately 100
Required between m and 11000n. As the material for the cooling layer, a metal having a higher thermal conductivity than the heat insulating layer, or a mixture of a metal and a metal oxide, metal nitride, metal carbide, metal chalcogenide, etc. can be used. In particular, Au and sb are preferred because they have low specific heat and high thermal conductivity.

The substrate used in the present invention may be the same as conventional recording media, such as plastic, glass, or aluminum. For the purpose of avoiding the influence of dust by recording from the substrate side using convergent light, it is preferable to use a transparent material as the substrate. The above materials include polyethylene terephthalate, polymethyl methacrylate, polycarbonate, epoxy resin, polyolefin resin,
Polyimide resin, glass, etc. are preferred. More preferably, polycarbonate and epoxy resin are used because they have low birefringence and are easy to form. Although the thickness of the substrate is not particularly limited, it is practically 10 microns or more and 5 mm or less. If it is less than 10 microns, it will be susceptible to dust even when recording with convergent light from the substrate side, and if it exceeds 5 mm,
When recording with convergent light, it becomes impossible to increase the numerical aperture of the objective lens, and the pit size increases, making it difficult to increase the recording density.

The substrate may be flexible or rigid. The flexible substrate can be used in the form of a tape or a sheet. The rigid substrate can be used in the form of a card or a circular disk. Furthermore, if necessary, two substrates may be used to form an air sandwich structure, an air incident structure, a closely bonded structure, or the like.

The light used for recording on the optical recording medium of the present invention is light such as a laser beam or a strobe light. In particular, the use of a semiconductor laser means that the light source is small, consumes low power, and can be easily modulated. preferred.

The recording layer, the heat insulating layer, and the cooling layer can be formed by known thin film forming methods such as sputtering, resistance heating evaporation, electron beam heating evaporation, and ion blating.

Recording can be performed by forming amorphous marks on the crystalline recording layer by irradiating the recording layer with laser light.

Alternatively, crystallization marks can be formed on the recording layer in an amorphous state by laser beam irradiation. Further, erasing can be carried out by irradiating laser light in the same manner as recording to crystallize an amorphous mark or amorphize a crystallized mark.

Recording is performed by forming amorphous marks on a crystalline recording layer by laser beam irradiation, and erasing is performed by crystallizing the amorphous marks by laser beam irradiation, which increases the recording speed and reduces the deformation of the recording layer. This is preferable because it is unlikely to occur.

[Example] Hereinafter, the present invention will be explained based on examples.

The composition of the recording layer in the Examples was confirmed by ICP emission analysis (Model F-Cho S-1100, manufactured by Seiko Electronics Co., Ltd.).

Further, the carrier-to-noise ratio (C/N ratio) of the recording signal was measured using a spectrum analyzer.

Example 1 A recording layer,
A thermal insulation layer and a cooling layer were formed.

First, a 120 nm thick ZnS heat insulating layer was formed on the substrate in an Ar gas atmosphere of 7×10-”Pa, and a Te
, Sb, TeGe, and Co were simultaneously sputtered while monitoring them with a crystal vibrating film thickness meter to form (Sb O, 60 Te O, 4
A recording layer having an elemental composition ratio of 0>0.98 Ge O, 02Go 0.002 and a thickness of 5 Q nm was formed. Further, a 180 nm ZnS heat insulating layer was formed on the recording layer, and a 2Q nm Au cooling layer was formed on this heat insulating layer, thereby constructing an optical recording medium of the present invention.

This optical recording medium was rotated at a linear velocity of 0.5 m/sec, and light was focused at a wavelength of 830 from the substrate side using an objective lens with a numerical aperture of 0.5.
The recording layer was crystallized by scanning the track while continuously irradiating the recording layer with a nm semiconductor laser beam at a film surface intensity of 1.5 mW. At this time, due to crystallization, the reflectance of the recording layer decreases from the initial 2
It has doubled.

Thereafter, using the same optical system as before, recording was performed using a 11 mW semiconductor laser beam modulated to a frequency of 3 MH2 and a duty ratio of 50% under the condition of a linear velocity of 7 m/sec.

When the recorded portion of the recording layer was scanned with the intensity of the semiconductor laser light being 0.7 mW and the recording was reproduced, the reflectance of the recording mark portion decreased due to amorphization, and it was confirmed that recording was being performed. Ta. When the C/N ratio of this reproduced signal was measured under the condition of a bandwidth of 30 kHz, a C/N ratio of 50 dB, which is digitally recordable, was obtained.

Roughly recorded part, 2.8 at a linear velocity of 1.5 m/sec.
When irradiated with mW semiconductor laser light, the recording was erased. Even after repeating recording and erasing 50 times under the above recording and erasing conditions, the laser power required for recording and erasing remained unchanged, the noise level of the reproduced signal increased by 1 dB, and the C/N increased by 49 dB. Almost no deterioration in erasing characteristics was observed.

Also, a good value of -30 dB was obtained for the erasure rate.

Furthermore, the amorphous mark in the recorded portion remained stable even after the optical recording medium was heated to 60° C. for 2 hours in a ventilated oven.

Example 2 The composition of the recording layer of Example 1 was (SbO, 57TeO,
43) An optical recording medium was produced in the same manner as in Example 1, except that the composition was changed to 0.92 Ge O,07Co O,01. When recording and reproducing on this optical recording medium were performed under the same conditions as in Example 1, the C/N ratio of the recorded and reproduced signal was as follows.
It was 47dB. Also, this recorded part was recorded at a linear velocity of 1.5
Erasing was possible under the erasing conditions of m/sec and 3.0 mW. The erasure rate at this time was -29 dB.

Example 3 An optical recording medium was produced in the same manner as in Example 1, except that the substrate in Example 1 was a 32 mm square glass plate with a thickness of 1.2 mm, and the cooling layer was replaced with SB. This recording medium was fixed in a stationary state, and recording and erasing were performed using the same optical system as in Example 1. The recording pulse was 14 mW, 350 nsec,
The erase pulse is 5.5mW and 700nsec. Mata regeneration was performed at 0.6 mW. Recording and erasing was possible even after 100,000 recording and erasing cycles were repeated under these conditions, with almost no change observed in the rate of change of the reflected signal and no deterioration of characteristics.

In addition, the crystallization temperature of this recording layer was measured from the change in DC electrical resistance and the change in light transmittance when the temperature was increased.
The temperature was 140°C under the temperature increasing condition of 10°C/min. Therefore, it can be estimated that the thermal stability at room temperature is good.

Comparative Example 1 In Example 1, the composition of the recording layer was as follows (a) and (b).
Optical recording media were prepared in the same manner as in Example 1 except that the following was changed, and evaluated in the same manner.

(A) (Sb O, 70Te O, 30) 0.
85 Ge O,15Co O,002 (0) (Sb O,50Te 0.50 > 0
．． In the case of the composition of 95 Ge O, 05 Go 0.002 (a), when recording and erasing were repeated under the same recording and erasing conditions as in Example 1, the recording and erasing characteristics were significantly deteriorated after 30 repetitions. .

The erasure rate at this time deteriorated to about -15 dB, and the noise level of the recording/reproduction signal also deteriorated by 10 dB.

In the case of the composition (b), the crystallization rate was slow and real-time crystallization by laser beam irradiation was difficult.

Comparative Example 2 An optical recording medium was prepared in the same manner as in Example 3 except that the composition of the recording layer was changed to (c) below, and recording and erasing were performed in the same manner.

(c) (Sb O,130Te 0.40 > 0
．． In the case of the composition (c) of 94 Ge O,0, the difference in reflectance between the recorded state and the erased state varied with the number of repetitions of recording and erasing and was unstable. Furthermore, after 50,000 times of recording and erasing, the amount of change in reflectance gradually decreased, making recording and erasing difficult.

Example 4 In Example 3, the composition of the recording layer was changed to (SbO
,60TeO,40>0.98GeO,02
Z rO,005, and (Sb 0.60 Te 0
140) 0.98Ge O,02Hf O,00
5 was prepared.

Recording and erasing were performed on these optical recording media in the same manner as in Example 3. The recording pulse was 14 mW.

The erase pulse was 6 mW and 300 ns. Even after repeating the recording/erasing cycle 100,000 times under these conditions, recording and erasing was still possible.

[Effect of the invention] The present invention provides a recording layer of an optical recording medium made of Sb, Te, Ge, and CO.
, Zr and 1-1f,
The following effects were obtained.

(1) The erasing rate is high and there is very little unerased material.

(2) Erasing speed is fast, and erasing can be performed with light beam irradiation for approximately 1 μsec or less.

(3) Operation is stable even after repeated recording and erasing many times, and there is little deterioration in recording characteristics such as a decrease in recording sensitivity, a decrease in reproduction signal strength, and an increase in noise.

(4) High transition temperature and excellent thermal stability.

(5) Recording and erasing is possible with a low-power semiconductor laser, and the sensitivity is high.

Claims (1)

[Claims] 1 Information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light, and information can be recorded and erased between a crystalline state and an amorphous state. What is claimed is: 1. An optical recording medium in which phase change is effected by phase change, wherein the recording layer comprises at least a recording layer, a heat insulating layer, and a cooling layer, and the composition of the recording layer is represented by the following general formula. (Sb_xTe_1_-_x)_1_-_y_-_αG
e_yM_α However, 0.55≦x≦0.65 0.01≦y≦0.10 0.001≦α≦0.03 x, y and α each indicate the atomic ratio, Sb is antimony, Te is tellurium , Ge is germanium, M is Co
(cobalt), Zr (zirconium), and Hf (hafnium).