JPH05225603A - Phase transition optical disk medium for short wavelength - Google Patents

Abstract

PURPOSE:To enable high-density recording and reproducing by laminating and forming an under coat layer, a recording layer, an over coat layer and a metallic reflection layer successively from below in the order on a transparent substrate and setting the thicknesses of the respective layers at combinations of a specific range. CONSTITUTION:The under coat layer 2 consisting of a transparent dielectric film having 1.9 to 2.2 refractive index, the recording layer 3 consisting of a GeSbTe alloy film, the over coat layer 4 consisting of the transparent dielectric film like wise having 1.9 to 2.2 refractive index and the metallic reflection layer 5 are successively laminated and formed from below on the transparent substrate 1. The thicknesses of the respective layers mentioned above are limited to the properly selected and combined thicknesses, i.e., the thickness of the under coat layer 2 is 160 to 220nm and the thickness of the recording layer is 15 to 30nm, more preferably 200 to 280nm. The short wavelength phase transition optical disk medium relating to the structure can make recording and reproducing at 450 to 670nm wavelength. The high-=density recording and reproducing are thus attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short wavelength phase change optical disk medium for high density recording / reproducing by using a laser beam having a short wavelength.

[0002]

2. Description of the Related Art Recently, optical recording media such as optical disks and optical cards have been developed as large-capacity recording media. The optical recording media record and reproduce by condensing laser light to near the wavelength limit. Therefore, the recording density limit is determined by the wavelength of the laser light.

More specifically, in the conventional optical disc, by irradiating the recording film with a semiconductor laser beam having a wavelength of about 830 nm through the transparent substrate, the recording film is perforated (drilling type) or the refractive index is changed. A mark is recorded by causing (phase change type) or exciting a magnetic change (magneto-optical type). In any of the above types,
The light narrowed down by the lens is irradiated to the recording film and is converted into heat to change the recording film. Therefore, the power of the recording laser light is made smaller than the normal value to record a smaller mark. Is possible.

[0004]

However, a signal obtained from such a small mark as described above causes a decrease in signal intensity due to interference between adjacent marks as long as a laser beam having the same wavelength as that at the time of recording is used during reproduction. cause. That is, in the conventional optical disc, the recording density is determined by the wavelength limit because the semiconductor laser having a wavelength near 830 nm is used for both recording and reproduction, and it is impossible to increase the recording density beyond that.

On the other hand, a short wavelength laser light source has a wavelength of 6
A 70 nm semiconductor laser is in the development stage. Further, as a light source with a shorter wavelength, there is a light source with a wavelength of about 530 nm using the second harmonic of a YAG laser, an Ar laser light source with a wavelength of 488 nm or 458 nm, and the like.

However, the conventional optical disc is 830 nm.
It is designed so that marks can be recorded most efficiently and a contrast can be obtained at wavelengths in the vicinity, and it is impossible to perform recording and reproduction using the light source of the short wavelength. In view of the above conventional problems, the present invention has a wavelength of 450 nm.
It is intended to provide a short-wavelength phase change optical disk medium capable of recording and reproducing by using a light source of nm to 670 nm.

[0007]

The above-mentioned problems can be solved by the present invention by adopting the following novel characteristic construction means. That is, the feature of the present invention is that an undercoat layer, a recording layer, an overcoat layer, a
A metal reflective layer is laminated in this order, and Ge is formed in the recording layer.
In an optical disc medium using an SbTe alloy film and a transparent dielectric film having a refractive index of 1.9 to 2.2 for the undercoat layer and the overcoat layer, the recording layer has a thickness of 15 to 30 nm. Either 30-45 nm or 70-110 nm and the thickness of the undercoat layer is 160-22.
0 nm and the thickness of the overcoat layer is 80 to 160 n
It is a phase-change optical disk medium for short wavelengths, which is layered by a range combination of m or 200 to 280 nm.

[0008]

Since the present invention has taken the above-mentioned means, it is composed of a GeSbTe alloy film and an undercoat layer made of a transparent dielectric film having a refractive index of 1.9 to 2.2 from below on a transparent substrate. Like the recording layer, the undercoat layer, an overcoat layer made of a transparent dielectric film having a refractive index of 1.9 to 2.2 and a metal reflective layer are laminated in this order.

The thickness of each layer is 160 to 220 nm for the undercoat layer and 15 for the recording layer.
~ 30 nm, 30-45 nm or 70-110 n
m, the thickness of the overcoat layer is set to 80 to 160 nm or 200 to 280 nm, and the layer is limited to a layer formed by a proper selective combination. The short-wavelength phase change optical disk medium having the above structure can record and reproduce at a wavelength of 450 to 670 nm, and realizes high density recording and reproduction.

[0010]

Embodiments of the present invention will be described in detail with reference to the drawings. Figure 1
Is a tomographic view of the short-wavelength phase change optical disk medium of the present embodiment,
FIG. 2 is a principle diagram of optical calculation applied to the short wavelength phase change optical disk medium of the present embodiment. In the figure, A1, A2, A3
Is a short wavelength phase change optical disk medium, 1 is a transparent substrate, 2 is an undercoat layer, 3 is a recording layer, 4 is an overcoat layer, 5 is a metal reflection layer, 6 is a sealing layer, 7 is an optical interference layer,
L is a laser beam.

As shown in FIG. 1, the constitution of the short wavelength phase change optical disk media A1, A2 and A3 of this embodiment is such that an undercoat layer 2, a recording layer 3 and an overcoat are formed on a transparent substrate 1 such as glass or polycarbonate. The layer 4, the metal reflection layer 5, and the sealing layer 6 are laminated in this order. The undercoat layer 2, the recording layer 3, and the overcoat layer 4 form an optical interference layer 7, and the optical characteristics such as reflectance change greatly depending on the selection of the combination of these film thicknesses.

In the short wavelength phase change optical disk media A1, A2 and A3 of the present embodiment, since recording / reproducing is performed at a wavelength of 450 to 670 nm, the absorption rate of the laser light L in this wavelength range is large, And the difference in reflectance between the crystalline state and the amorphous state,
That is, the condition that the contrast is high is necessary.

Therefore, the combination of the film thicknesses of the layers satisfying the above conditions was obtained by optical calculation. This optical calculation is based on the theory of optical multi-layer (for example, GEORGE HAS
S: "Physics of thin films", Vol.1, ACADEMIC PRESS (19
63), p69-). The reflectance and the absorptance (1-reflectance-transmittance) are obtained by substituting the refractive index n _j and the film thickness d _j of each layer shown in FIG. 2, which is the principle diagram of the optical calculation, into the following equations. Be done.

[0014]

[Equation 1] In the formula, λ is the wavelength of light.

As an example, GeSbT in the recording layer 3
e of amorphous refractive index n _a = 4.8-j1.1, crystalline refractive index n _c = 6.0-j3.1, undercoat layer 2 and overcoat layer 4 refractive index n = 2 0.0, transparent substrate 1
And the refractive index of the metal reflective layer 5 (Au) is 0.17-j5.3, and the film thickness of the metal reflective layer 5 is 40n.
m, the thickness of the recording layer 3 is set to 26, 40, and 80 nm, and the thickness of the undercoat layer 2 and the overcoat layer 4 is changed to obtain a wavelength of 450 to 670 nm.
Has a contrast of 10% or more and an absorption rate of 6
The range of 0% or more was determined.

As a result, it was found that the above conditions can be satisfied by the combinations shown in the following table.

[Table 1]

The specification of the present embodiment is such a concrete embodiment, and next, the short-wavelength phase change optical disk media A1, A2, A produced respectively based on the calculation results.
It will be explained in detail for each item 3. (Production Example 1) First, a short wavelength phase change optical disc medium A1
Will be explained. In the configuration of FIG. 1, a polycarbonate substrate is used as the transparent substrate 1 and Ge ₂ Sb ₂ Te is used as the recording layer 3.
₅ Alloy film, undercoat layer 2 and overcoat layer 4
A mixed film of ZnS and SiO ₂ was used as the above, and an Au film was used as the metal reflection layer 5.

The undercoat layer 2 has a thickness of 1
The thickness was 90 nm, the recording layer 3 was 26 nm, and the overcoat layer 4 was 120 nm, all of which were formed by the RF sputtering method. Further, a UV curable resin was formed on the sealing layer 6 by a spin coating method and ultraviolet irradiation.

The thus manufactured short-wavelength phase-change optical disk medium A1 was mounted on a recording / reproducing apparatus using an argon laser as a light source, and the recording / reproducing erasing characteristics were measured. As a result, the recording power and the erasing power at 457.9 nm were 12 mW and 6 mW, respectively, and C / N 55 dB and an erasing rate of -26 dB were obtained.

Next, the signal contrast was measured by changing the mark pitch. As a result, it was found that the limit of the recording density (value that becomes half the saturation value) was 0.7 μm. Incidentally, the limit of the recording density by the same measurement at the wavelength of 830 nm of the conventional optical disk medium was 1.3 μm.

Further, in the short wavelength phase change optical disk medium A1 of this manufacturing example, the recording / reproducing erasing characteristics were measured with the wavelength of the light source set to 488 nm. As a result, C / N 56 dB,
An erasing rate of -28 dB was obtained. YAG with wavelength 530nm
It was mounted on a recording / reproducing apparatus using a second harmonic light source and a semiconductor laser light source with a wavelength of 670 nm, and as a result of recording / reproducing / erasing characteristics, a C / N of 55 dB or more and an erasing rate of -25 dB or less were observed at any wavelength. Obtained.

(Production Example 2) Next, the short wavelength phase change optical disk medium A2 will be described. The short wavelength phase change optical disc medium A2 is the short wavelength phase change optical disc medium A1.
The recording layer 3 has a thickness of 40 nm and is otherwise the same. The thus-produced short wavelength phase change optical disk medium A2 is used as the short wavelength phase change optical disk medium A1.
The recording / reproducing apparatus was mounted on the same recording / reproducing apparatus as the above, and the recording / reproducing erasing characteristics were measured.
C / N of 55 dB or more and an erasing rate of -25 dB or less were obtained at both nm and 670 nm.

(Manufacturing Example 3) Next, a short wavelength phase change optical disk medium A3 will be described. The short wavelength phase change optical disc medium A3 is the short wavelength phase change optical disc medium A1.
The undercoat layer 2 has a thickness of 200 nm, the recording layer 3 has a thickness of 80 nm, and the overcoat layer 4 has a thickness of 240 n.
m is the same as the others.

The short-wavelength phase change optical disc medium A3 thus manufactured was mounted on the same recording / reproducing apparatus as the short-wavelength phase change optical disc medium A1 and the recording / reproducing characteristics were measured. As a result, the wavelengths were 457.9 nm, 488 nm and 530n.
m / 670nm, C / N 55dB or more,
An erasing rate of -25 dB or less was obtained.

[0025]

As described above, according to the present invention, in a conventional optical disk using a semiconductor laser having a wavelength of around 830 nm for both recording and reproduction, the recording density cannot be increased beyond the present stage because of the wavelength limit. What was impossible was 4
There is an advantage that a high density recording / reproducing can be performed by utilizing a short wavelength of 50 to 670 nm and a good recording / reproducing / erasing characteristic can be obtained even in the short wavelength.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a configuration of a short wavelength phase change optical disk medium according to an embodiment of the present invention.

FIG. 2 is a principle diagram of an optical calculation applied to the above.

[Explanation of symbols]

 A1, A2, A3 ... Phase change optical disk medium for short wavelength 1 ... Transparent substrate 2 ... Undercoat layer 3 ... Recording layer 4 ... Overcoat layer 5 ... Metal reflective layer 6 ... Sealing layer 7 ... Optical interference layer L ... Laser light

Claims (1)

[Claims] 1. An undercoat layer, a recording layer, an overcoat layer, and a metal reflection layer are sequentially laminated from the bottom on a transparent substrate, and a GeSbTe alloy film is formed on the recording layer, and the undercoat layer and the overcoat layer are formed. Has a refractive index of 1.9.
In the optical disk medium using the transparent dielectric film of 2.2 to 2.2, the thickness of the recording layer is 15 to 30 nm or 30.
To 45 nm or 70 to 110 nm, the thickness of the undercoat layer is 160 to 220 nm, and the thickness of the overcoat layer is 80 to 160 nm or 200 to 280 n.
a phase-change optical disc medium for short wavelength, which is layered by a range combination with any of m