JPH10162435A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve both of erasing characteristics and repetition characteristics while maintaining the recording sensitivity and to increase the film forming rate and the productivity by forming a reflection layer of a mixture compsn. of Mg (main component) and a specified additive element. SOLUTION: A reflection layer 5 of an optical information recording medium consists of a thin film containing Mg as the main component and one additive element selected from Li, C, Al, Ca, Ti, Cr, Mn, Cu, Zn, Zr, Ag, Cd, Tl, Bi, Th, La and Ce. The reflection layer is produced by preparing a Mg alloy as a target such as Mg-Al, Mg-Al-Zn, Mg-Zn-Zr and Mg-Ce alloys and sputtering the target. Or, the layer can be formed by separately preparing a target comprising Mg and a target comprising the additive element to be incorporated and then sputtering the targets at one time. The film thickness of the reflection layer is preferably >=50nm and <=300nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium capable of recording, erasing, and reproducing information by irradiating light.
The present invention relates to a phase-change optical disc formed of a material in which a reversible phase change between crystals occurs.

[0002]

2. Description of the Related Art A technique for recording and reproducing information by using light such as a laser beam is well known, and development of a rewritable optical information recording medium is also in progress. One of the rewritable optical information recording media is a phase change optical disk.

A phase-change type optical disk has a recording layer made of a material that undergoes a reversible amorphous-crystal phase change upon irradiation with light. It has an excellent feature that it is easy to record new information while erasing the recorded information (so-called overwriting).

Generally, in a rewritable phase-change optical disk, an amorphous state in a recording layer is a recording state, and a crystalline state is an erasing state. That is, information is recorded by irradiating a laser beam at a recording level to a high temperature equal to or higher than the melting point and then rapidly cooling to form an amorphous recording mark corresponding to a signal indicating information. This is performed by irradiating a laser beam at an erasing level to a crystallization temperature lower than the melting point and then gradually cooling the crystal to crystallize the amorphous recording mark.

In reproducing a recorded signal, a change in the amount of light reflected from a disk is detected by utilizing a difference in reflectance between an amorphous portion and a crystal portion and a difference in phase of reflected light. Done by

[0006] Such a phase-change type optical disk generally has a four-layer structure in which a first protective layer, a recording layer, a second protective layer, and a reflective layer are formed in this order on a substrate. Here, the reflection layer is provided to increase the reflectance of the optical disc and to diffuse heat generated in the recording layer to the outside. The C / N ratio (carrier to noise ratio) of the reproduction light is increased by the high reflectance. ), And high thermal conductivity allows rapid cooling, so that amorphous recording marks can be formed satisfactorily, and erasing characteristics and repetition characteristics are improved.

As a material for forming such a reflective layer, as disclosed in JP-A-4-349242 and JP-B-7-19396, mainly Al and Al alloys (for example, Al-Ti alloys) are disclosed. , Al-Cr alloy, Al-Hf
Alloys, Al-Si alloys, etc.), or Ag or Au, or alloys thereof.

[0008]

However, in a phase-change type optical disk in which the reflective layer is formed of the above-mentioned material, the repetition characteristics can be sufficiently improved unless some measures are taken for layers other than the reflective layer. Could not. Also, Al-based thin films such as Al and Al alloys have a low film forming rate, and there is room for improvement in terms of improving productivity.

The present invention has been made in view of such problems of the prior art. By specifying the material of the reflective layer, it is possible to improve the repetitive recording / erasing characteristics of the optical information recording medium. Another object is to improve productivity.

[0010]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a transparent substrate and a reversible amorphous-crystal formed on one surface of the substrate and irradiated with light. In an optical information recording medium including at least a recording layer made of a material in which a phase change occurs, and a reflection layer formed on a surface of the recording layer opposite to the substrate, the reflection layer contains Mg as a main component. And Li, C, Al, Ca, Ti, Cr, M
n, Cu, Zn, Zr, Ag, Cd, Tl, Bi, T
Provided is an optical information recording medium comprising a thin film containing at least one additional element selected from h, La, and Ce.

[0011] Mg is a material having high reflectivity and high thermal conductivity, but pure Mg has too high thermal conductivity. If the power of irradiation light is low, heating of the recording layer becomes insufficient, and The sensitivity decreases. However, for this Mg,
Specific additional elements, namely, Li, C, Al, Ca, T
i, Cr, Mn, Cu, Zn, Zr, Ag, Cd, T
By adding at least one element selected from the group consisting of l, Bi, Th, La, and Ce, a high reflectance and a suitable thermal conductivity are compatible, so that the erasing characteristics and the repetition characteristics of the optical information recording medium are obtained. While the recording sensitivity is not reduced.

The content of the additional element in the reflective layer (the total content when two or more elements are contained) varies depending on the type of the additional element, but is preferably 0.1 to 20 wt%. , 0.1 to 10 wt%. That is, if the content of the additive element is too high, the characteristics of Mg having high reflectance and high thermal conductivity are not sufficiently exhibited. Further, the content of the additive element is 0.1 w
If it is less than t%, it becomes close to pure Mg and the thermal conductivity cannot be reduced appropriately, so that the effect of maintaining the recording sensitivity cannot be obtained.

Among the additional elements, more preferable elements are Ti, Zr, Th, and Ce, and more preferable elements are Ce and Th, which correspond to rare earth elements. When these elements are contained, the heat resistance of the reflective film is improved. In addition, since Zr has an effect of making crystal grains fine, Zr
When contained, the mechanical properties of the reflective film are improved. Also, Z
Ca, Cu, Zn, Ag, Cd, Tl, B with r
It is preferable that i and Ce are contained, because the refinement of Zr crystal grains is promoted.

Such a reflective layer is made of, for example, Mg-Al
System, Mg-Al-Zn system, Mg-Zn-Zr system, Mg-
A Mg alloy such as a Ce alloy is prepared as a target and can be formed by a sputtering method. In addition, Mg
And a target made of an additive element to be contained can be separately prepared and formed by a co-sputtering method in which sputtering is performed simultaneously.

The thickness of the reflective layer is preferably 50 nm or more and 300 nm or less. Further, from the viewpoint of recording sensitivity, productivity and the like, it is more preferable that the thickness be 100 nm or more and 200 nm or less.

In the optical information recording medium of the present invention, the layer constitution other than the reflection layer can be a conventionally known constitution. That is, as the transparent substrate, glass, polycarbonate resin, acrylic resin, epoxy resin, or the like can be used. Among them, it is preferable to use a polycarbonate resin in terms of cost, good optical characteristics, high mechanical strength, and excellent dimensional stability.

Further, as a material for forming the recording layer, Sb-
Te-Ge, Sb-Te-Ge-Pd, Sb-Te-G
e-Nb, Sb-Te-Ge-Pt, Sb-Te-I
n, Sb-Te-In-Ag, Sb-In-Ga, or the like can be used.

As a material for forming the protective layer formed above and below the recording layer, ZnS to which SiO ₂ is added,
Oxides such as O ₂ , Ta ₂ O ₅ and ZrO ₂ , carbides such as SiC and C, fluorides such as MgF, ZnS, SmS and Sr
Sulfides such as S can be used.

Examples of the method for forming each layer include a vacuum evaporation method, a sputtering method, an ion plating method, a CVD (chemical vapor deposition) method, and an MBE (molecular beam epitaxy) method. It is preferable to employ a sputtering method which can form a large-area film and can easily control the composition.

Regarding the thickness of each layer, the contrast of the first protective layer periodically changes depending on the thickness thereof, but it is preferably 100 nm or more and 600 nm or less. If the thickness is more than 600 nm, it is not preferable from the viewpoints of deterioration of recording sensitivity, accuracy of a disc, and productivity. If the thickness is less than 100 nm, the heat resistance function is not sufficiently exhibited, and the substrate is deformed. A more preferred range is from 100 nm to 400 nm.

The contrast of the recording layer also changes periodically depending on its thickness, but it is preferably 20 nm or more and 100 nm or less. When the thickness is more than 100 nm, the recording sensitivity is deteriorated, and when the thickness is less than 20 nm, mass transfer of the recording layer is apt to occur, and the repetition characteristics are remarkably deteriorated. A more preferred range is from 20 nm to 50 nm.
It is as follows.

The thickness of the second protective layer is 5 nm or more and 150 n.
m or less. In terms of recording sensitivity, 1
The thickness is more preferably 0 nm or more and 100 nm or less.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to specific examples. Example 1 A phase change type optical disk having the layer structure shown in FIG. 1 was manufactured as follows.

First, an outer diameter of 120 mm and a thickness of 1.2 mm
Then, ZnS and SiO ₂ were formed on a polycarbonate substrate 1 in which grooves having a pitch of 1.2 μm were provided in advance.
(20 mol%) to form a first protective layer 2 of about 150 nm. Next, a recording layer 3 of about 25 nm made of Sb-Te-Ge was formed on the first protective layer 2. On top of that, about 35 of the same composition as the first protective layer 2
The second protective layer 4 of nm was formed. These layers were formed by a RF sputtering method in the same manner as in the related art.

On this second protective layer 4, Mg, Al and Z
n, and 3.3 wt% of Al and 2.6 watts of Zn
The reflection layer 5 having a composition containing t% was formed with a thickness of about 150 nm. That is, Mg—Al (3.3 wt%) — Zn
(2.6 wt%) based alloy as a target and RF
The reflection film 5 was formed by a sputtering method. The film formation rate of this reflective layer was 56.5 nm / min.

Next, a protective coating layer 6 was provided on the reflective layer 5 by applying an ultraviolet-curable resin by spin coating to a thickness of 10 μm and curing by applying ultraviolet rays. After initializing the phase-change optical disk thus obtained, the disk is rotated at a rotation speed of 2000 rpm by a driving device (numerical aperture of an objective lens 0.47, laser wavelength 795 nm), a frequency of 8.8 MHz and a pulse width of 33 nsec. At a recording power of 8 to 17 mW and an erasing power of 4 to 8 m
Overwriting was performed 100 times under each condition of W. Thereafter, reproduction was performed at a reproduction power of 1 mW, and the C / N ratio of the recording signal was measured.

Thereafter, the same track has a frequency of 3.3 MHz.
The signal of z was overwritten once under the same conditions. Then, the erasing characteristics of the previously recorded signal of frequency 8.8 MHz were examined.

[0028] That is, the recording signal having a frequency 8.8 MHz, measured beforehand overwriting previous signal strength I _B, to measure the residual signal intensities I _A after overwriting. Then, the difference between the signal intensities before and after overwriting (I
_B− I _A ) is calculated as the erasure ratio. In addition, the erasing ratio is 2
The difference between the maximum value and the minimum value of the peak power of 0 dB or more was calculated, and this was defined as an erasing margin. The larger the erase margin, the higher the erase characteristics.

The measurement of the C / N ratio and the measurement of the signal intensity for calculating the erasure ratio were performed using a spectrum analyzer. As a result, the lowest peak power (recording sensitivity) at which the C / N ratio became 50 dB or more was 10 mW. The lowest peak power at which the erasure ratio was 20 bdB was 10 mW. The erase margin is 5.5 m
W.

On the other hand, the phase-change optical disk obtained as described above is applied to the driving device and rotated at the same speed as above, and a random pattern is recorded on the same track.
The repetition was performed under the conditions of a recording power of 14.3 mW and an erasing power of 6.8 mW, and the number of repetitions (the number of repetitions) at which the bit error rate (bit error rate) became “0” was measured.

As a result, the repeatable number was 210,000. Example 2 The composition of the reflective layer 5 was changed to Mg, Th, Zr, and Z.
n, and Th is 2.5 wt% and Zr is 0.5 w
t% and 1.7 wt% Zn,
A phase change optical disk was manufactured in the same manner as in Example 1.

That is, the reflective layer 5 is formed by Mg-Th
(2.5 wt%)-Zr (0.5 wt%)-Zn (1.
(7 wt%) based alloy was used as a target. The film formation rate of this reflective layer was 49 nm / min.

The performance of the obtained phase change optical disk was evaluated in the same manner as in Example 1. As a result, the lowest peak power (recording sensitivity) at which the C / N ratio became 50 dB or more was 10 mW. The lowest peak power at which the erasure ratio was 20 bdB was 10 mW. The erase margin was 6.0 mW. The number of repetitions was 260,000. Example 3 The procedure of Example 1 was repeated, except that the composition of the reflective layer 5 was Mg, Ce and Zr, and contained 3.0 wt% of Ce and 0.5 wt% of Zr. A phase change optical disk was manufactured.

That is, the reflective layer 5 is formed by Mg-Ce
The test was performed using a (3.0 wt%)-Zr (0.5 wt%) alloy as a target. The film forming speed of this reflective layer was 51 nm / min.

The performance of the obtained phase change optical disk was evaluated in the same manner as in Example 1. As a result, the lowest peak power (recording sensitivity) at which the C / N ratio became 50 dB or more was 10 mW. The lowest peak power at which the erasure ratio was 20 bdB was 10 mW. The erasing margin was 5.8 mW. The repeatable number was 250,000 times. [Comparative Example 1] The composition of the reflective layer 5 was made of Al and Ti,
A phase change optical disk was manufactured in the same manner as in Example 1 except that Ti was contained at 2.0 wt%.

That is, the reflective layer 5 is formed by Al-Ti
(2.0 wt%) based alloy was used as a target. The film formation rate of this reflective layer was 13 nm / min.

The performance of the obtained phase change optical disk was evaluated in the same manner as in Example 1. As a result, the lowest peak power (recording sensitivity) at which the C / N ratio became 50 dB or more was 10 mW. The lowest peak power at which the erasure ratio was 20 bdB was 10 mW. The erase margin was 4.0 mW. The number of possible repetitions was 130,000.

The results are summarized in Table 1 below.

[0039]

[Table 1] As can be seen from this table, in the phase-change optical discs of Examples 1 to 3, the reflective layer contains Mg as the main component and the additive element (A
1 and Zn, Th and Zr and Zn, or Ce and Zr), a wider erasing margin is obtained and the number of repetitions is 2 compared to Comparative Example 1 in which the reflective layer is an Al alloy system. Nearly doubled. In addition, the deposition rate is 3 to
It was about 5 times faster. The recording sensitivity was almost the same.

Therefore, by making the reflective layer a mixed composition of Mg (main component) and an additive element, it is possible to prevent the recording sensitivity from lowering while improving the erasing characteristics and the repetition characteristics. In addition, since the reflective layer has a high film forming rate, the productivity of the optical disk is improved. Also,
In Examples 2 and 3, Th and Z which are preferable as additional elements are used.
Since it contains r or Ce and Zr, the erasing characteristics and the repetition characteristics are particularly high.

In each of the above embodiments, Al and Zn, Th and Zr and Zn, or Ce and Zr are listed as the elements to be added to Mg. However, the present invention is not limited thereto.
Li, C, Al, Ca, Ti, Cr, Mn, Cu, Z
Similar effects can be obtained with n, Zr, Ag, Cd, Tl, Bi, Th, La, and Ce, or a combination thereof.

In each of the above embodiments, a phase-change type optical disk having a layer structure in which protective layers are provided above and below a recording layer is described. However, the optical information recording medium of the present invention is not limited to this. Even when there is no such protective layer or when there is no both protective layers, the above-mentioned effect can be obtained by forming the reflective layer with a mixed composition of Mg (main component) and an additive element.

[0043]

As described above, according to the optical information recording medium of the present invention, by setting the reflective layer to a mixed composition of Mg (main component) and an additive element, erasing can be performed while maintaining recording sensitivity. Improved characteristics and repetition characteristics are achieved. In addition, there is also an effect that productivity is improved by increasing the deposition rate.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a layer configuration of an optical information recording medium corresponding to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 First protective layer 3 Recording layer 4 Second protective layer 5 Reflective layer 6 Protective coat layer

Claims (1)

[Claims] 1. A transparent substrate, a recording layer formed on one surface of the substrate, and made of a material that undergoes a reversible amorphous-crystal phase change upon irradiation with light, An optical information recording medium comprising at least a reflective layer formed on a surface opposite to a substrate, wherein the reflective layer is composed of Mg as a main component, Li, C, Al,
Ca, Ti, Cr, Mn, Cu, Zn, Zr, Ag, C
An optical information recording medium comprising a thin film containing at least one additional element selected from d, Tl, Bi, Th, La, and Ce.