JP2003145943A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To develop a recording film having high reflectivity and sensitivity and to inexpensively provide an optical recording medium excellent in C/N of a playback signal and in weather resistance. SOLUTION: The optical recording medium has at least a light-transmitting metal thin film and a low-melting thin film on the surface of a translucent base and the light-transmitting metal thin film is constituted mainly of at least one kind of element selected from a IB group of an elemental periodic table, while the low-melting thin film is constituted mainly of at least one element selected from IIIB, IVB, VB and VIB groups (1). The optical recording medium satisfies any of the conditions that the film thickness of the light-transmitting metal thin film is set so that the transmittance of the thin film is 20% or above by the film itself, that the melting point of this film is made higher than that of the low-melting thin film, that an organic protective film is provided on the low-melting thin film, that (the film thickness of the light-transmitting metal thin film)/(the film thickness of the low-melting thin film) is in the range of 0.06-1.0, that the film thickness of the light-transmitting metal thin film is 30-200 Åor that the film thickness of the low-melting thin film is 200-500 Å (2).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to recording / recording by causing an optical change in a recording layer by irradiation with an energy beam.
The present invention relates to an optical recording medium for reproduction.

[0002]

2. Description of the Related Art Write-once optical recording media such as CD-R and DVD-R are examples of optical recording media that can be recorded by laser beam irradiation. These optical recording media have reproduction compatibility with CD-ROMs or DVD-ROMs, and are used as small-scale distribution media and storage media. But the CD
Since -R and DVD-R are coated with an organic dye, there is a problem that the manufacturing cost is significantly higher than that in the ROM process. Therefore, CD-write once (hereinafter abbreviated as WO) and DVD-WO media have been developed. There are hole type, phase change type, and alloy type in WO media depending on the recording method. From the viewpoint of cost, the hole type recording method is promising, but the hole type recording has a low C / N. There was a problem of being lost. This was because the melted film remained in the pit like a polka dot and swelled up in the peripheral part in the pit part where the hole was formed. In addition, since the layer structure of the punching type recording system is one layer, the recording film that has been normally used cannot support the high reflectance of the ROM and is a nonstandard product. In order to realize a high reflectance for ROM with a single recording film layer, it is conceivable to use a material with a high reflectance such as Al, Ag, and Cu, but the reflectance is too high and a very normal laser irradiation is required. Then the hole didn't open.

As the perforation type recording material, there are disclosed in JP-A-60-179953 and JP-A-60-179952.
Japanese Unexamined Patent Publications and the like disclose compounds composed of Te and Au or Ag, but the boiling points of these materials were 1000 ° C. or higher, and the sensitivity was extremely low. Also, JP-A-57-1
Japanese Patent Laid-Open No. 57790 discloses an invention in which a corrosion resistant metal layer is formed on a first layer which releases a volatile component at a temperature of 400 ° C. or lower to improve recording sensitivity. Is not intended to be ROM compatible. Further, although Au, Ag, etc. are used as the corrosion resistant metal, these have extremely high thermal conductivity and the heated energy escapes due to diffusion, so that the effect is low as a result, and it is not suitable for high linear velocity recording. It was inappropriate. Also,
When recording, the phase change type only needs to raise the temperature to the melting point, whereas the perforated type requires a large amount of heat to raise the temperature above the boiling point, and requires a larger laser power than the phase change type, Since the power of the semiconductor laser is insufficient for high linear velocity recording, a recording film with higher sensitivity is required.

As an alloying type recording system, Japanese Patent Laid-Open No. 4-226784 discloses a layer made of any element of Ge, Si and Sn and an element of Au, Ag, Al and Cu. A method of recording by irradiating a laser on a laminated recording layer with the layers and alloying the two layers is disclosed, but it is low to high recording and is not ROM compatible. I didn't get it. Also,
Japanese Unexamined Patent Publication No. 1-162247 discloses an invention of forming a phase change type recording layer by using an alloy of In and Te, and In: Te = 2: 1 to 1: 1 or 2 :. 3-
It is an object of the present invention to provide a phase change type optical recording medium by setting the ratio to 2: 5. However, in the present invention, since the state at the time of film formation is amorphous and the reflectance is low, initialization processing is required. Therefore, the number of processes is increased and the cost is increased.

Further, in Japanese Patent No. 2948899, Ag
-Zn first layer (phase change alloy thin film), Te,
Disclosed is a recording medium in which the constituent elements of the second layer (low melting point thin film) containing Se or S as a main component are mutually diffused. The thickness of the layer is 300 to 700Å and the thickness of the second layer is 500 to 1500Å, which is disadvantageous in terms of tact during production and cost. Further, although the reflectance is greatly increased by increasing the film thickness, in the investigation by the present inventors, the reflectance is high and the absorptance is too small, so that heat absorption on the recording film hardly occurs. , I found that the sensitivity was very poor. Therefore, it cannot be used in a medium such as a DVD which requires a high linear velocity. Inorganic W has various problems as described above.
This has been a major obstacle to the popularization of O recording media.

[0006]

Under the above circumstances, the present invention has developed a recording film having high reflectance and sensitivity, and has an excellent C / N of reproduced signal and excellent weather resistance. It is an object to provide a recording medium at low cost.

[0007]

[Means for Solving the Problems] The above problems are solved in the following 1) to
This is solved by the invention 7) (hereinafter referred to as the present inventions 1 to 7). 1) At least a light-transmissive metal thin film and a low-melting-point thin film are formed on the surface of a light-transmissive substrate, and the light-transmissive metal thin film contains at least one element selected from Group IB of the Periodic Table of Elements as a main component, An optical recording medium, wherein the low melting point thin film contains at least one element selected from the group IIIB, IVB, VB and VIB as a main component. 2) The transmittance of the light-transmissive metal thin film is 20% when the thin film alone is used.
The film thickness is set to the above value 1)
The optical recording medium described. 3) The optical recording medium according to 1) or 2), wherein the melting point of the light-transmissive metal thin film is higher than that of the low melting point thin film. 4) The optical recording medium according to any one of 1) to 3), which has an organic protective film on the low melting point thin film. 5) The light according to any one of 1) to 4), wherein (thickness of light-transmissive metal thin film) / (thickness of low melting point thin film) is in a range of 0.06 to 1.0. recoding media. 6) The optical recording medium according to any one of 1) to 5), wherein the light-transmissive metal thin film has a thickness of 30 to 200Å. 7) The optical recording medium according to any one of 1) to 6), wherein the low melting point thin film has a thickness of 200 to 500 Å.

The present invention will be described in detail below. As a result of diligent studies, the inventors of the present invention have at least a light-transmissive metal thin film and a low-melting-point thin film on the surface of a light-transmissive substrate as in the first invention, and the light-transmissive metal thin film has a periodic table IB
Based on at least one element selected from the group,
By using at least one element selected from the group IIIB, IVB, VB and VIB as the main component, the low melting point thin film has succeeded in obtaining an optical recording medium having high reflectance and sensitivity. Here, the main component means that these elements are 5
It means 0% or more. Although the mechanism of this recording has not been elucidated accurately, one idea is that the electrons generated by the Sb-Te semiconductor forming the low melting point thin film absorbing light are trapped in the impurity level or the like to generate a negative electric field. It is also considered that this is created and attracts an element selected from the IB group that has become a positive ion to cause diffusion. Furthermore, it is considered that the heat generated by the absorption of light also enhances the diffusion effect.

Further, as in the second aspect of the present invention, by setting the film thickness such that the transmittance of the light-transmissive metal thin film is 20% or more by itself, the metal thin film as in the prior art is used as a reflective film. When used, the transmittance was low and there was almost no absorptance, so that the defect that the sensitivity was very poor was eliminated, and both reflectance and sensitivity could be made compatible. Further, since the transmittance is too high, that is, the reflectance is lowered, the transmittance of the light transmissive metal thin film is preferably 80% or less.
Further, it has been found that by making the melting point of the light-transmissive metal thin film higher than the melting point of the low melting point thin film as in the present invention 3, mutual diffusion of the constituent elements of both thin films becomes faster and the sensitivity is improved. . Further, as in the case of the present invention 4, by stacking the organic protective film on the low melting point thin film, the stability of the film was enhanced, and the storage reliability was remarkably improved. Moreover, in the conventional two-layer recording layer, the strength of the film is weak and the holes may be opened by laser irradiation. However, by laminating the organic protective film, the physical strength of the film is improved and the holes are opened. It is no longer lost. As a material for the organic protective film, a conventionally known material may be used, but an ultraviolet curable resin is preferable.

Further, by setting the ratio of (thickness of light-transmissive metal thin film) / (thickness of low melting point thin film) in the range of 0.1 to 1.0 as in the present invention 5, reflectance is high and sensitivity is high. High 2
We succeeded in achieving both characteristics. Furthermore, the present invention 6
As described above, by setting the thickness of the light-transmissive metal thin film to 30 to 200Å, the reflectance is too high and the absorption rate is too low to absorb light as in the invention of Japanese Patent No. 2948899, and the sensitivity is poor. It has become possible to obtain an optical recording medium having a high reflectance and a high sensitivity by overcoming the drawbacks of the prior art. Further, as in the case of the present invention 7, the low melting point thin film has a thickness of 200
By setting the thickness to 500 Å, it is possible to achieve the reflectance that enables ROM compatibility even though the recording film is a medium composed of only two layers of a light-transmissive metal thin film and a low melting point thin film. Regarding this effect, the simulation and the actual reflectance agree well. In addition, the two-layer structure enables high-to-low recording, resulting in a significant cost reduction.

FIG. 1 shows an example of a layer structure in which the present invention is applied to a DVD, but the application target of the present invention is not limited to the DVD. In the example of FIG. 1, a recording layer composed of a light-transmissive metal thin film and a low melting point thin film and an ultraviolet curable resin layer are sequentially laminated on an information substrate, and a cover substrate is bonded onto the recording layer via an adhesive layer. ing. When this medium is irradiated with a recording laser beam from the information substrate side, the light-transmissive metal thin film and the low melting point thin film are heated. By this heating, the constituent elements of both layers mutually diffuse, an alloy or compound of the constituent elements of both layers is produced, and the light reflectance of the laser light irradiation portion is significantly reduced. Since this change in reflectance is irreversible, it can be used as a write-once type optical recording medium. The recording layer of the present invention can be formed by various vapor phase growth methods such as a vacuum vapor deposition method, a sputtering method and an electron beam method.

As a material for the substrate of the present invention, glass, ceramics or resin is usually used, but a resin substrate is preferable in terms of moldability and cost. Typical examples include polycarbonate, polymethylmethacrylate, acrylic resin, epoxy resin, polystyrene, polypropylene, silicon resin, fluororesin, ABS resin, urethane resin, etc., but polycarbonate resin is preferable from the viewpoint of processability and optical characteristics. . The substrate may have any shape such as a disk shape, a card shape, and a sheet shape. The bonding method of the cover substrate may be any of a radical UV method, a cation method, a heat seal method, and a double-sided adhesive sheet method. However, in the structure without the ultraviolet curable resin layer, oxygen and moisture are removed as in the radical UV method. A method that does not penetrate is desirable.

[0013]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Examples 1 to 8 DVD media having the layer structure shown in FIG. 1 were prepared. On a polycarbonate resin information board having a pitch of 0.74 μm and a depth of 400 Å and having a thickness of 0.6 mm and a diameter of Φ120 mm, the materials shown in the columns of Examples 1 to 8 in Table 1 below were used. A light-transmissive metal thin film having a film thickness of 100 Å and a low melting point thin film having a film thickness of 400 Å were sequentially formed by a sputtering method, and further an ultraviolet curable resin was spin-coated and irradiated with ultraviolet rays to form an organic protective film. The bonding of the cover substrate with the adhesive layer was performed by radical UV method. The recording / reproducing characteristics are evaluated under the following conditions: recording linear velocity 3.5 m / s (1 × speed), linear density = 0.267 μm / bit, recording frequency = 26.2 M.
Hz, recording laser wavelength 635 nm, NA = 0.6, and the reflectance and C / N of Examples 1 to 8 with different low melting point thin film materials are 55 dB or more (resolution: measured at 1 kHz).
Table 1 shows the laser powers at which the 1 × speed and the 2 × speed are compared.

Comparative Examples 1 to 4 As materials for the light transmissive metal thin film and the low melting point thin film, those described in Comparative Examples 1 to 4 in Table 1 are used. A DVD medium was prepared in the same manner as in Examples 1 to 8 except that the film thickness was 400 Å and the film thickness of the low melting point thin film was 800 Å, and was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0016]

[Table 1] From the results in Table 1, it is clear that the examples are superior to the comparative examples.

Example 9 FIGS. 2 and 3 show a light-transmissive metal thin film of Ag (film thickness 30Å,
100 Å, 200 Å) and a low melting point thin film of In ₈ Sn ₄
As Sb ₅₆ Te ₃₂ , the recording (laser) power showing the reflectance change and the signal intensity of 55 dB or more at 1 × speed is shown for the medium in which the film thickness of the low melting point thin film is changed. The recording here is a 3T rectangular wave recording. It can be seen from FIG. 2 that the reflectance is low when the thickness of the low melting point thin film is thin, and from FIG. 3 that the sensitivity is poor when the film is too thick. Further, from FIG. 2, in the case of the light-transmissive metal thin film 200Å, when the low melting point thin film becomes thinner than 200Å (that is, when the ratio of both layers exceeds 1.0), the reflectance becomes 40% or less. The light-transmissive metal thin film 3 can be seen from FIG.
It can be seen that when the low melting point thin film is thicker than 450 liters in the case of 0 liters (that is, when the ratio of both layers is less than 0.6), the recording power exceeds 10 mW. Therefore, the reflectance and sensitivity are simultaneously satisfied when the ratio of both layers is in the range of 0.6 to 1.0 (Invention 5). Further, it can be seen from FIGS. 2 and 3 that the reflectance and the sensitivity are simultaneously satisfied when the film thickness of the low melting point thin film is in the range of 200 to 500 Å (Invention 7). Furthermore, FIG.
The result of the optical simulation regarding the relationship between the film thickness of Ag and the reflectance and the transmittance is shown in FIG. As you can see from Figure 4,
Ag has a transmittance of more than 20% at about 200 Å (20 nm) or less. Further, the transmittance is 20 in the range of Ag, that is, the film thickness of the light-transmissive metal thin film is 30 to 200Å (3 to 20 nm).
It turns out that it becomes -80% (invention 6). Note that almost the same results were obtained even when Au or Cu was used instead of Ag.

[0018]

According to the present invention 1, an optical recording medium having high reflectance and sensitivity can be obtained. According to the present invention 2, when a metal thin film as in the prior art is used as a reflective film, the transmittance is low and there is almost no absorptance, so that the disadvantage of very poor sensitivity is eliminated, and both reflectance and sensitivity are compatible. Can be made. According to the third aspect of the present invention, the mutual diffusion of the constituent elements of the light transmissive metal thin film and the low melting point thin film is accelerated, and the sensitivity can be further improved. According to the present invention 4, the stability of the film can be increased and the storage reliability can be improved significantly. Further, in the conventional recording layer having a two-layer structure, the strength of the film is weak and the holes may be opened by laser irradiation, but in the present invention 4, the physical strength of the film is improved by laminating the organic protective film. , No more opening holes. Invention 5
According to this, it is possible to achieve both of the two characteristics of high reflectance and high sensitivity. According to the sixth aspect of the present invention, for example, the invention of Japanese Patent No. 2948899 overcomes the drawback of the prior art that the reflectance is too high and the absorption rate is too low to absorb light so that the sensitivity is poor. It is possible to obtain an optical recording medium having high sensitivity. According to the seventh aspect of the present invention, it is possible to achieve a reflectance that is ROM compatible even though the medium has only two recording films. Also,
High-to-low recording is possible with a two-layer structure, resulting in a significant cost reduction.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a layer structure in which the present invention is applied to a DVD.

FIG. 2 shows a light-transmissive metal thin film made of Ag (film thickness 30Å, 100
Å, 200Å) and the low melting point thin film is made of In ₈ Sn ₄ Sb.
As ₅₆ Te _32, shows the change in reflectance of the medium waved film thickness of the low melting point film.

FIG. 3 shows a light-transmissive metal thin film made of Ag (film thickness 30Å, 100
Å, 200Å) and the low melting point thin film is made of In ₈ Sn ₄ Sb.
As ₅₆ Te _32, shows a recording (laser) power showing a signal strength of at least 55dB at 1 × speed for medium waved film thickness of the low melting point film.

FIG. 4 is a diagram showing a result of an optical simulation regarding a relationship between a film thickness of Ag, reflectance, and transmittance.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaaki Umehara             1-3-3 Nakamagome, Ota-ku, Tokyo Stocks             Company Ricoh F-term (reference) 2H111 EA03 EA12 EA21 EA43 FA02                       FA14 FA30 FB04 FB08 FB12                       FB15 FB17 FB20 FB25 FB27                 5D029 JA01 JB28 JB35 JC04 JC20

Claims (7)

[Claims] 1. A light transmissive substrate having at least a light transmissive metal thin film and a low melting point thin film on a surface thereof, the light transmissive metal thin film containing at least one element selected from Group IB of the periodic table as a main component. And the low melting point thin film is IIIB, IVB, VB, VI
An optical recording medium comprising, as a main component, at least one element selected from Group B. 2. The optical recording medium according to claim 1, wherein the thickness of the light-transmissive metal thin film is set to 20% or more for the thin film alone. 3. The optical recording medium according to claim 1, wherein the light transmissive metal thin film has a melting point higher than that of the low melting point thin film. 4. The optical recording medium according to claim 1, further comprising an organic protective film on the low melting point thin film. 5. The method according to claim 1, wherein (thickness of light transmitting metal thin film) / (thickness of low melting point thin film) is in a range of 0.06 to 1.0. The optical recording medium described. 6. The film thickness of the light-transmissive metal thin film is 30 to 200.
The optical recording medium according to claim 1, wherein the optical recording medium is Å. 7. The optical recording medium according to claim 1, wherein the low melting point thin film has a thickness of 200 to 500 Å.