JPH06171236A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain an optical recording medium having high reliability by utilizing the reflectivity difference due to thermal diffusion between Al or Au and Ge in a write-once optical recording medium recordable only once by providing a recording layer consisting of an Al- or Au-layer and a Ge-layer. CONSTITUTION:A write-once optical recording medium is constituted so as to be recordable only once. For example, a recording layer 3 is laminated on the upper surface of a substrate 1 through a heat-resistance protective layer 2. In this case, the recording layer 3 is formed from an Al- or Au-layer 3-2 and a Ge-layer 3-1. The Ge-layer 3-1 is arranged on the side of the substrate 1 and the Al- or Au-layer 3-2 is arranged on the upper surface of the Ge-layer 3-1. Further, a Ge or Al oxide layer is not allowed to be present between the Ge-layer 3-1 and the A-layer 3-2. At the time of recording, Al or Au and Ge is mutually thermally diffused to generate large reflectivity difference to enable writing.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a writable optical recording medium such as a CD.

[0002]

2. Description of the Related Art At present, as a recordable CD, a CD which uses an organic dye as a recording material is commercially available. However, this material has problems that it is deteriorated by light and that the reflectance changes greatly depending on the wavelength of the reproduction light.

On the other hand, when an inorganic material is used as the recording material, it is necessary to use a metal as the recording material in order to obtain a high reflectance of 70% or more. Since the melting point of this metal material is high, the recording sensitivity is low. is there.

When classifying currently known optical discs, there are a read-only type represented by an audio compact disc, a write-once type capable of recording once, and a rewritable type utilizing a magneto-optical effect and a phase transition. .

Inorganic materials that are single-recording type materials include a pierced type and a phase change type, which are represented by Te series. The perforated type is TeC, TeSe, etc., and the phase change type is typically TeO ₂ .

On the other hand, as organic materials, dyes such as polymethine dyes and cyclic azaannulene dyes are used.

However, Te used for the perforated type of inorganic material has a problem in moisture resistance, and the phase change type TeO ₂ type has a problem that it is not compatible with the conventional CD in terms of reflectance. .

On the other hand, organic materials have insufficient light resistance.

[0009]

SUMMARY OF THE INVENTION The present invention is intended to solve the above problems of the prior art and to provide a highly reliable write-once type optical recording material.

[0010]

The constitution of the present invention for solving the above-mentioned problems is an optical recording medium as set forth in the claims.

That is, a recording layer having a two-layer structure of Al and Ge is irradiated with electromagnetic waves, particularly a semiconductor laser, to cause mutual diffusion between Al and Ge, thereby causing segregation of Al and Ge. It is an optical recording medium that causes a large change in reflectance.

In order to efficiently use the LD light emitted for recording, it is preferable to dispose a Ge layer on the substrate side of the recording medium.

When the reflectance of the recording film thus obtained from the substrate side was 10% in the initial state with respect to the wavelength of 830 nm, the reflectance of Al or A caused by heat increased.
As a result of segregation due to the mutual diffusion of u and Ge, the reflectance increases to 70%.

Therefore, the weather resistance is improved as compared with the Te system because it has the reflectance change close to that of the conventional CD-ROM and is Al system. Therefore, in the material system of the present invention, it becomes possible to provide a write-once recording medium compatible with the conventional CD-ROM. Also, in a recording medium in which Al or Au is arranged on the substrate side and Ge is arranged thereon, this 2
By controlling the layer thickness, it is possible to provide a recording medium with relatively high sensitivity.

As described above, in the substrate of the present invention, the Ge layer and the Al layer or the Au2 layer are recording layers, and at the time of recording, the optical constant can be changed by the diffusion / segregation of Al or Au and Ge between the two layers. is there. This makes it possible to obtain extremely high reflectance. Further, since it is an Al type or an Au type, the weather resistance is better than that of a Te type or an organic type.

The present invention relates to a write-once optical recording material, which is characterized by a Ge layer and an Al layer or Au.
The above two layers are used as a recording layer, and by irradiating an electromagnetic wave, particularly a semiconductor laser, during recording, mutual diffusion of Al or Au and Ge is caused between the Al layer or Au layer and the Ge layer, This utilizes the fact that segregation of Al or Au and Ge occurs to cause a change in optical constant. In order to efficiently use the incident semiconductor laser light at this time, it is preferable to dispose the Ge layer on the substrate side of the recording medium. The Al layer needs to be in direct contact with the Ge layer. That is, if an oxide such as a germanium oxide or aluminum oxide layer is present between the Al layer and the Ge layer, interdiffusion of Al and Ge may be hindered and the recording sensitivity may be lowered.

The function of this recording layer will be specifically described. When the temperature of the spot portion on the recording layer, that is, the Ge layer is increased by laser irradiation, Ge and Al of the Ge layer and the Al layer are thermally diffused mutually, and the spot portion becomes Al-rich as compared with the Ge layer portion before recording. (Depending on the film thicknesses of Ge and Al, the spot portion may be only Ge to Al. It is confirmed from Auger electron spectroscopy that this is due to diffusion rather than evaporation and elimination of Ge. ). Therefore, the reflectance increases. So-called low-to-high recording is realized. Of course, if high-to-low recording is desired, the Al layer and the Ge layer may be exchanged. However, since the Al layer is provided on the laser incident side, the recording sensitivity may decrease.

The substrate 1 of the recording medium of the present invention shown in FIG. 1 is usually glass, ceramics or resin, but a resin substrate is preferable in terms of moldability and cost.
Typical examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polypropylene resin, silicon resin, fluorine resin, ABS resin, urethane resin, and the like, but polycarbonate resin, acrylic resin, acrylic resin, acrylic resin, etc. in terms of processability and optical characteristics. Systems are preferred. Further, the substrate may have a disk shape, a card shape, or a sheet shape.

As the material of the heat resistant protective layer 2, SiO,
_{SiO 2, ZnO, SnO 2,} Al 2 O 3, TiO 2, In 2
Metal oxides such as O ₃ , MgO and ZrO ₂ , Si ₃ N ₄ and Al
N, TiN, BN, nitrides such as ZrN, ZnS, I
sulfides such as n ₂ S ₃ and TaS ₄ , SiC, TaC, B ₄ C,
Examples thereof include carbides such as WC, TiC, ZrC, diamond-like carbon, and mixtures thereof. Moreover, you may contain impurities as needed. Such a heat resistant protective layer can be formed by various vapor phase growth methods such as a vacuum vapor deposition method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method and an electron beam vapor deposition method.

The thickness of the heat resistant protective layer is 200 to 50.
00Å, preferably 500 to 3000Å.
When the thickness is less than 200Å, the function as the heat resistant protective layer is not fulfilled, and when the thickness is more than 5000Å, the sensitivity is lowered and the interfacial peeling is likely to occur. or,
If necessary, the protective layer can be multi-layered.

The Ge layer 3-1 and the Al layer 3-2 as the recording layer 3 can be formed by a vacuum vapor deposition method, a sputtering method or the like. At this time, the thickness of the Ge layer is preferably 50Å to 1000Å, more preferably 150Å to 500Å. Also, the film thickness of Al should be between 50Å and 1500Å,
It is preferably between 100Å and 500Å.

As the electromagnetic waves used for recording and reproduction, several kinds such as laser light, electron beams, X-rays, ultraviolet rays, visible rays, infrared rays and microwaves can be adopted, but when mounted on a drive, they are small and compact. Most suitable semiconductor lasers are suitable.

[0023]

EXAMPLES The present invention will be specifically described below with reference to examples. However, this example does not limit the present invention in any way.

Example 1 Pitch of 1.6 μm, depth of 700 Å with grooves, thickness of 1.2
mm on a polycarbonate substrate with a diameter of 86 mm and rf
ZnS-Si as a heat-resistant protective layer by a sputtering method
O ₂ film 2000 Å, the Ge film as the recording layer 250 Å,
An optical film for evaluation was manufactured by sequentially stacking 300 Å Al films. Also, to measure the reflectance of this disc, 30 mm
A glass substrate having a size of x30 mm x 1 mm was attached.

The spectral reflectance of the glass substrate after film formation was measured, and the spectral reflectance after heat treatment at 300 ° C. for 30 minutes was measured. The values are shown in Table 1. The reflectance was measured from the glass substrate side.

[0026]

[Table 1]

As can be seen from Table 1, the heat treatment of this recording film greatly increases the reflectance. Also, this sample was analyzed by Auger electron spectroscopy in the thickness direction for Al and Ge.
The density profile of the
e, it was found that what was Al on the free surface side was Al rich on the substrate side by heat treatment, and Al and Ge were interdiffused.

Next, at a linear velocity of 1.3 m / s, a wavelength of 830
A 680 KHz signal was recorded using a semiconductor laser of nm. The laser power of the disk surface at this time is 10 m
W.

When this recording signal was evaluated by an evaluation device for audio compact discs, a C / N value of 53 dB was obtained.

Example 2 A recording medium was manufactured by the same procedure as in Example 1. ZnS-SiO ₂ of the heat-resistant protective layer was 2000 Å, and the Ge layer of the recording layer was 250 Å and the Al layer was 150 Å. Moreover, in order to measure the reflectance of the medium at this time, 30 mm x 30 mm
A × 1 mm glass substrate was attached. Then, after film formation, the spectral reflectance of this glass substrate is measured and further 30
The spectral reflectance after heat treatment at 0 ° C. for 30 minutes was also measured.
The results are shown in Table 2.

[0031]

[Table 2]

As can be seen from Table 2, the heat treatment of this recording film significantly increases the reflectance. Next, in the same manner as in Example 1, a wavelength of 830 n was obtained under a linear velocity of 1.3 m / s.
A 680 KHz signal was recorded using a semiconductor laser of m. The laser power at this time is 10 mW on the disk surface.
And The C / N of this recording signal was evaluated by an evaluation device for audio compact discs to be 50 dB.
Got the value of.

Example 3 A recording medium was manufactured by the same procedure as in Examples 1 and 2. The thickness of ZnS and SiO ₂ of the heat resistant protective layer is 2000
Å, the Ge layer of the recording layer was 250 Å, and the Al layer was 500 Å. Also, in order to measure the reflectance of the recording medium at this time, 30
A glass substrate of mm × 30 mm × 1 mm was attached. After film formation, the spectral reflectance of this glass substrate was measured, and the spectral reflectance after heat treatment at 350 ° C. for 30 minutes was also measured. The results are shown in Table 3.

[0034]

[Table 3]

As is clear from Table 3, the reflectance of the recording film according to the present invention is greatly increased by heat treatment.
This increase in reflectance can be obtained by heat treatment of Al and Ge.
It was confirmed from the Auger electron spectroscopy that each of the elements diffused into each other and became Al-rich on the substrate side.

Next, as in Examples 1 and 2, a linear velocity of 1.3 m /
6 using a semiconductor laser with a wavelength of 830 nm under
The 80 KHz signal was recorded. The laser power at that time was 10 mW on the disk surface. When the C / N of this recording signal was evaluated by an evaluation device for audio compact discs, a value of 53 dB was obtained.

Example 4 A recording layer was formed as a Ge layer 250 in the same manner as in Examples 1, 2, and 3.
Å, Au layer 250 Å, SiO ₂ : 20 as heat resistant protective layer
A recording medium provided with 00Å was produced. Table 4 shows the spectral characteristics of this film.

[0038]

[Table 4]

From these results, it can be seen that the recording film of the present invention greatly increases in reflectance by heat treatment. According to Auger electron spectroscopy, Au and G similar to those of Al-Ge system
It was confirmed that mutual diffusion of e occurred. Then, a signal of 680 kHz was recorded using a semiconductor laser having a wavelength of 830 nm under a linear velocity of 1.3 m / s. The power at that time was set to 10 mW, and the C / N was evaluated to be 51 dB.
Got the value of.

As is clear from Examples 1, 2, 3, and 4, the optical recording medium having the recording layer of Ge and Al or Au according to the present invention can be sufficiently used for a writable compact disc. .

[0041]

The optical recording medium of the present invention has an Al recording layer.
Layer or two layers of Au layer and Ge layer, and when Al or Au and Ge mutually thermally diffuse during recording, a large reflectance difference can be caused, and writing can be performed. It is possible to provide a possible compact disk.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of an optical recording medium of the present invention.

[Explanation of symbols]

 1 substrate 2 heat resistant protective layer 3 recording layer 3-1 Ge layer 3-2 Al layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshiyuki Kageyama 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72) Hiroko Iwasaki 1-3-6 Nakamagome, Ota-ku, Tokyo Shares Company Ricoh

Claims (3)

[Claims] 1. An optical recording medium having a recording layer composed of an Al layer or an Au layer and a Ge layer. 2. The optical recording medium according to claim 1, wherein a Ge layer is present on the substrate side, and an Al layer or an Au layer is present on the Ge layer. 3. Ge or Al between the Ge layer and the Al layer
3. The optical recording medium according to claim 1, wherein the oxide layer of 1. is absent.