JPH09326135A - Optical information recording medium and its recording and reproducing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information recording medium with which good recording characteristics of a high C/N and decreased bit errors are obtainable with a wide power margin in recording and reproducing of information small in the ratio of a recording bit length to a spot diameter. SOLUTION: This optical information recording medium has a recording thin film consisting of a material which exhibits a change to a state of different optical characteristics by at least irradiation with a light beam on a transparent substrate. This recording thin film consists of the recording thin film which consists essentially of Te, O and Pd and in which the ratio of the Te atoms incorporated into the recording thin film is within 20 to 70atom%, the ratio of the O atoms 25 to 45atom% and that of the Pd atoms 5 to 35atom%. The region enclosed by A, B, C, D in Fig. or the region enclosed by E, F, G, H is the compsn. range of the recording thin film of the optical information recording medium.

Description

Detailed Description of the Invention

[0001]

The present invention relates to an optical system capable of recording / reproducing an information signal having high signal quality by irradiating a phase change material thin film formed on a substrate with a high energy beam such as a laser beam. Information recording medium and its recording / reproducing method.

[0002]

2. Description of the Related Art A technique for recording / reproducing high density information by using a laser beam is well known. As a recording medium used for such recording and reproduction, Te and T on a substrate are used.
It has been proposed that a material thin film containing TeO _x (0 <x <2), which is a mixture of eO ₂ , as a main component is provided (Japanese Patent Laid-Open No. 50-46317 and US Pat. No. 3,971,874). In such a recording medium, it is possible to obtain a large change in transmittance upon irradiation with a reproduction light beam.

However, there is a limit to the output of the laser light source that can be used for downsizing and simplification of the recording / reproducing apparatus, and recording / reproducing is performed by using a small semiconductor laser emitting device having an output of 20 mW or less. Conventional TeO _x
A recording medium having a thin film containing (0 <x <2) as a main component has insufficient sensitivity. Moreover, even if the recorded information is reproduced, a sufficient change in the amount of reflected light cannot be obtained.

Further, in TeO _x , it takes some time until the signal is saturated after recording, that is, until the crystallization of the laser light irradiation portion in the recording thin film is sufficiently advanced. This is unsuitable as a recording medium that requires high-speed response, such as a computer data file in which data is recorded on a disk and the data is verified after one rotation.

Therefore, a method has been proposed in which TeO _x is added with, for example, Pd as a third element in order to make up for the above-mentioned drawbacks (Japanese Patent Laid-Open No. 61-68296). Pd is Te
It is considered that the O _x thin film acts like a crystal nucleus that promotes the crystal growth of Te when irradiated with laser light, and thereby Te crystal grains with more advanced crystallinity are generated at high speed. . As a result, a larger reflectance change of the reproduction light, that is, a higher C / N ratio can be obtained. Further, TeO _x increases the light absorption efficiency by adding Pd, and therefore the sensitivity is also improved. Further, Pd does not impair the excellent moisture resistance of the TeO _x thin film due to its high oxidation resistance.

However, with the recent increase in the capacity of information, further improvement in the recording density is required, and a recording medium that can be used for high density recording using an optical system with a short wavelength and a high NA is required. Development is needed.

[0007]

When recording / reproducing at a higher density using the same optical system, sufficient recording characteristics cannot be obtained unless the thermal conductivity of the recording thin film is within an appropriate range. Conceivable. That is, if the thermal conductivity of the recording thin film is too low, the heat is less likely to spread from the portion heated by the laser light, and the recording mark does not increase even if the recording power is increased, so the sensitivity is poor and the C / N ratio is also low. Tend to end up. On the contrary, if the thermal conductivity of the recording thin film is too high, heat easily spreads from the portion heated by the laser beam, and if the recording power is increased a little, the recording mark becomes large, so that the sensitivity is good and the C / N ratio becomes high. Tend. However, the edges of the recording marks are easily blurred, and if the recording power of the laser light is raised even more than the optimum power, adjacent marks will start to connect and the C / N ratio will decrease.
The power margin is narrow and there is a practical problem. This is considered to be more remarkable as the mark spacing becomes narrower and the density becomes higher even in recording / reproducing with the same optical system.

Even if a high C / N ratio is obtained, the number of bit errors is not always small. For example, when the thermal conductivity of the recording thin film is high, thermal interference is likely to occur between the recording marks, and as a result, the position of the detected recording mark fluctuates, causing a change in reflectance or C / N. It is possible that there are many bit errors even if the ratio is high. Therefore, as an evaluation method of signal quality that does not appear in the C / N ratio, that is, as one index of the number of bit errors, there is an evaluation item called verify. Verify is to verify whether or not there are fewer bit errors than the specified value when the recorded data is played back, and whether error correction is possible within the error correction area provided in advance by the error correction code. If it is possible, it is said that "verification is possible".

In particular, when the thermal conductivity of the recording thin film is too high, the mark position varies due to the thermal interference between the marks, so that even if the reflectance change or the C / N ratio is high, there are many bit errors and the verification is impossible. Could be.

The recording conditions of the conventional example (Japanese Patent Laid-Open No. 61-68296) in which Pd is added to TeO _x are as follows: laser wavelength 830 nm, wavelength limit 0.8 μm, rotation speed 1800.
rpm, recording position (radius) 75 mm, recording frequency 5 MH
It is written as z. Since this is considered to be a PPM record from the technical background at the time of the invention of 1986, the linear velocity calculated from the above radial position and rotation speed was 14.
Under the condition of 1 m / s, the shortest mark interval is 2.83μ.
m and bit length b correspond to 1.89 μm. The wavelength limit of 0.8 μm is approximated to a Gaussian distribution of the beam intensity of laser light, and the diameter at which the beam intensity is 1/2 of the spot center is defined as the wavelength limit.
Is considered to be calculated as 0.5. This is approximated to the Gaussian distribution of the beam intensity of the laser light, and the diameter at which the beam intensity is 1 / e of the spot center is the spot diameter d.
In that case, the spot diameter d is 1.01 μm. From the above, the ratio b / d of the bit length b to the spot diameter d is 1.87.

In the above conventional example (Japanese Patent Laid-Open No. 61-68296), 50 dB under the condition of b / d = 1.87.
As described above, depending on the composition, a high C / N ratio of about 60 dB is obtained. However, in recent years, a recording medium has a capacity of 650.
There is a demand for recording capacity that is equal to that of MB CD-ROMs, etc., and this capacity has been technically matured such that the CD size area has a wavelength of 780 nm and NA 0.5.
When recording using an appropriate optical system in terms of manufacturing cost,
b / d = 0.92. This is because b / d is remarkably smaller than that of the above-mentioned conventional example, and it is difficult for the recording medium of the above-mentioned conventional example to obtain a sufficient contrast between the recording marks. Not necessarily. Therefore, in order to obtain good recording characteristics with a high C / N ratio and a small bit error in a wide power margin in high-density recording / reproducing with a small b / d, it is necessary to review the composition range of the recording thin film suitable for this. It is thought that there is.

In order to solve the above-mentioned conventional problems, the present invention has a high C / N ratio in recording / reproducing information having a small ratio b / d of the recording bit length b to the spot diameter d, and has a good bit error. It is an object of the present invention to provide an optical information recording medium having a wide recording power and a wide power margin, and a recording / reproducing method thereof.

[0013]

In order to achieve the above-mentioned object, the optical information recording medium of the present invention comprises a transparent substrate made of a material exhibiting a change in optical characteristics to at least a different state upon irradiation with a light beam. The recording thin film is mainly composed of Te, O and Pd, and the proportion of Te atoms contained in the recording thin film is 20 to 70 atom%, O.
It is characterized in that the proportion of atoms is in the range of 25 to 45 atom% and the proportion of Pd atoms is in the range of 5 to 35 atom%.

In the above optical information recording medium, the proportion of Te atoms contained in the recording thin film is 30 to 65 at.
It is more preferable that the composition ratios of om% and O atom are 30 to 40 atom%, and Pd atom ratio is 5 to 30 atom%.

In the above optical information recording medium, it is preferable that the film thickness of the recording thin film is in the range of 20 to 200 nm. Further, in the above optical information recording medium, it is preferable that a protective layer made of a dielectric material is provided on either or both of the substrate side and the opposite side of the recording thin film.

The optical information recording medium preferably has a reflective layer on the side of the recording thin film opposite to the substrate. Further, in order to solve the above-mentioned problems, a recording / reproducing method of an optical information recording medium of the present invention is a recording made of a material exhibiting a change in optical characteristics to a different state at least on irradiation with a light beam on a transparent substrate. Has a thin film,
The recording thin film contains Te, O and Pd as main components, and the proportion of the O atoms contained in the recording thin film is 25 to 45 at.
om% and an information signal to an optical information recording medium in which the proportion of Pd atoms is in the range of composition proportion of 5 to 35 atom%,
When it is approximated that the beam intensity is Gaussian distributed when the light beam is applied to the optical information recording medium through the objective lens, the diameter at which the beam intensity becomes 1 / e of the spot center, that is, the spot diameter is d and the recording bit length is Where b is the ratio of the bit length b to the spot diameter d, b /
Recording and reproduction are performed under the condition that d is 1.0 or less.

In the recording / reproducing method of the optical information recording medium, the proportion of the O atom contained in the recording thin film is 30 to 40 atom%, and the proportion of the Pd atom is 5 to 5.
Within the composition ratio range of 30 atom%, the bit length b
It is more preferable that the ratio b / d to the spot diameter d is 0.8 or less.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a composition diagram of a Te—O—Pd ternary system. In FIG. 1, the region surrounded by A, B, C, D or the region surrounded by E, F, G, H is the present invention. 2 shows the composition range of the recording thin film of the optical information recording medium. FIG. 2 is a sectional view showing the configuration of the optical information recording medium according to the present invention. In FIG. 2, 1 is a transparent disk substrate, 2 is a recording thin film, an alloy material containing Te-O-Pd as a main component, 3
Is an overcoat layer.

As the material of the transparent substrate 1, polycarbonate resin, polymethylmethacrylate resin, polyolefin resin, glass or the like can be used. Transparent substrate 1
The thickness is not particularly limited, but a thickness of about 0.1 to 1.5 mm can be used.

The recording thin film 2 is formed by vacuum vapor deposition, sputtering, ion plating, CVD (Chemical Vapor).
Deposition) method, MBE (Molecukar Beam Epitaxy)
It can be formed by a method or the like.

The optical information recording medium of the present invention is shown in FIG.
It can be used as a double-sided disc by overcoating with a UV-curable resin as shown in Fig. 3 to form a single disk, or by laminating it with a UV-curable resin or a hot-melt type adhesive 4 as shown in Fig. 3.

Further, the optical information recording medium of the present invention has, for example, ZnS-Si as shown in FIG. 4 for the purpose of suppressing the increase of noise due to thermal damage of the recording film and as necessary.
The dielectric protective layer 5 such as an O ₂ mixed material may be provided on either the substrate side or the opposite side of the recording thin film, or both.

Further, the optical information recording medium of the present invention, as shown in FIG. 5, is made of, for example, Au or Al as necessary for the purpose of improving the absorptance, improving the reflectance, reducing the thermal load on the recording thin film, and the like.
The reflective layer 6 made of a metal such as -Cr or an alloy material may be provided on the opposite side of the recording thin film from the substrate.

FIG. 6 is a schematic view of an apparatus for recording / reproducing an optical information recording medium according to the present invention. When recording is performed, the output of the semiconductor laser 9 is modulated between two values of the peak power and the bias power weaker than that according to the input signal (arrow 18). The laser beam 10 emitted from the semiconductor laser is condensed by the collimator lens 10 to be a parallel light beam, and is passed through the beam splitter 12, the λ / 4 wavelength plate 13 and the objective lens 7 onto the optical disk 17, and the objective lens is moved up and down by the voice coil 16. Focused by moving. The optical disk is fixed on the turntable 14 and rotated by the motor 8 to record an information signal. When reproducing this information signal, continuous light of a constant power, which weakens the output of the semiconductor laser as compared with that during recording, is applied to the optical disk in the same manner as during recording, and the reflected light is made incident on the detector 15, and The change in the amount of reflected light is detected as a reproduction signal (reproduction output: arrow 19).

(Embodiment 1) A recording thin film made of Te, O, and Pd is formed on a transparent substrate made of polycarbonate resin having a thickness of 1.2 mm and a groove pitch of 1.2 μm and provided with laser guide grooves. Using a single material target of Pd and Pd, a stack of about 130 nm was formed by a sputtering method in an atmosphere of sputtering gas Ar and O ₂ . UV-curable resin on the surface (brand name "Dicure Clear SD-1"
01 ", manufactured by Dainippon Ink and Chemicals, Inc.) was used to make single-plate discs Nos. 1 to 20. These discs had different compositions in order to examine the dependence of the recording characteristics on the recording thin film composition. The results of elemental analysis of the recording thin film of each disk by Auger electron spectroscopy (hereinafter abbreviated as AES) are shown in Table 1. The composition of each disk is shown in FIG.

[0026]

[Table 1]

With respect to the above disc, a wavelength of 780 nm, N
Using an A0.5 optical system, PPM recording with a bit length of 0.95 μm was performed at a linear velocity of 5.3 m / s (rotation speed 2700 rpm). Under this condition, it is approximated that the beam intensity of the laser light is Gaussian distributed, and the beam intensity is 1
When the diameter of / e is defined as the spot diameter d, the spot diameter d = 0.95 μm, and the ratio of the bit length b to the spot diameter d is b / d = 1.0.

Under this condition, the recording power (peak power) in the range of 2.0 to 20.0 mW (in increments of 0.5 mW) is 3
A single signal with a T period and a 2-7 RLL random signal were recorded once on an unrecorded track to evaluate the C / N ratio and the verify, respectively. The bias power was 1 mW like the reproducing power. The C / N ratio is usually measured several minutes after recording, but depending on the composition of the recording thin film, crystallization of the laser light irradiation part in the recording thin film is sufficient until the signal is saturated after recording. Since it may take some time to proceed, the data was recorded on the disk, and the C / N ratio was also measured after one rotation (after 22 ms).

Table 1 shows each disc No. The evaluation results of 1 to 20 show the maximum value of the C / N ratio and the width of the verifyable recording power margin after 22 ms and several minutes after recording. According to Table 1, O atoms in the recording thin film are 25 atom%
In the following region, the thermal conductivity of the recording thin film is too high, so C
Although the / N ratio is high, the verifyable recording power margin is very narrow or absent, which poses a practical problem. On the other hand, in the region where the number of O atoms in the recording thin film is 25 atom% or more, the thermal conductivity of the recording thin film is low, so that the C / N ratio is relatively low and the sensitivity is a little poor, but the verifyable recording power margin is wide. Become. It can be said that this is more suitable as a practical recording medium that must cope with a certain degree of power fluctuation. Since the thermal conductivity of the recording thin film becomes too low in the region where the number of O atoms in the recording thin film is 45 atom% or more,
The recording mark cannot be written sufficiently large, the C / N ratio is considerably low, and the sensitivity becomes insufficient, which is not suitable for practical use.

In a region where the Pd atoms in the recording thin film are 5 atom% or less, crystallization of the recording thin film, that is, saturation of the recording signal takes time due to insufficient Pd, and the C / N ratio immediately after recording becomes low. This can be solved by increasing the Pd content, but conversely, if the Pd content is increased too much, the reflectance change due to crystallization will be an optically small composition, resulting in a low C / N ratio. The limit is about 35 atom%.

Therefore, considering all of the C / N ratio (including immediately after recording), sensitivity, verify, etc.,
Depending on the linear velocity, O atoms in the recording thin film are 25 to 45 atoms.
%, And the composition range of 5 to 35 atom% of Pd atoms is said to be suitable for this recording condition. This range is A in FIG.
It is shown as a region surrounded by B, C, and D.

Further, when only the recording density is changed to 0.76 μm in bit length under exactly the same conditions, that is, the ratio b / d = 0.8 of the bit length b to the spot diameter d, the disc No. Table 2 shows the results of recording and reproducing 1 to 20.
Shown in

[0033]

[Table 2]

As is clear from Table 2, the composition range suitable for this recording condition was the same as when b / d = 1.0, with the lower limit of the Pd content being about 5 atom%, but the upper limit was 30.
The atom% and O content were widened to about 30 atom% to 40 atom%. This range is shown in FIG. 1 as a region surrounded by E, F, G, and H.

From these results, it is understood that when the ratio b / d of the bit length b to the spot diameter d becomes small, the composition range of the recording thin film where sufficient recording characteristics can be obtained becomes narrow. Therefore, under the condition of b / d = 1.0, O in the recording thin film
25-45 atom% of atoms and 5-35 atom of Pd atoms
%, B / d = 0.8, the number of O atoms in the recording thin film was 3
It is necessary that the composition range is 0 to 40 atom% and Pd atoms is 5 to 30 atom%.

However, in the present invention, the recording condition b / d
Although the lower limit of is not particularly shown, the recording medium of the present embodiment is suitable for a condition of b / d = 0.8 to 1.0, and a condition that b / d is smaller, for example, b / d. d
Does not always yield good recording characteristics even under conditions of 0.6 or less, and it is considered necessary to study recording thin films suitable for such conditions with different composition ranges. .

In the above description, the linear velocity is 5.3 m / s.
Although only the result in the case of is shown, only the linear velocity is 11.9 m /
No. under the same conditions other than the above. Disks 1 to 20 were evaluated. Under the conditions of b / d = 1.0 and 0.8, almost the same results as in Table 1 and Table 2 were obtained. From this, it was found that the recording medium having the above composition range had good recording characteristics even at a high linear velocity of 10 m / s or more.

Further, in the above description, T is used as the recording thin film.
Although an example using a material consisting of only three elements of e, O, and Pd has been described, it is necessary for the purpose of fine adjustment of each characteristic such as thermal conductivity and optical constant, or improvement of heat resistance and environmental reliability. Accordingly, Au, Pt, Ag, Cu, Bi, Si, Se, S,
At least one element selected from metals, semimetals, semiconductors and non-metal elements such as N, F and C can be added as a sub-component within a composition ratio within 5 atom% of the entire recording thin film.

[0039]

As described above, according to the present invention,
At least a recording thin film made of a material exhibiting changes in optical characteristics upon irradiation with a light beam on a transparent substrate, wherein the recording thin film contains Te, O and Pd as main components and is contained in the recording thin film. The ratio of the O atom is 25 to 45 atom%, and the ratio of the Pd atom is 5 to 35 atom%.
A material within the composition ratio of atom% is used. As a result, in recording / reproducing information having a small ratio b / d of the recording bit length b to the spot diameter d, an optical information recording medium having a high C / N ratio and good recording characteristics with few bit errors and a wide power margin can be obtained. Can be provided.

[Brief description of drawings]

FIG. 1 is a recording thin film composition range diagram according to an embodiment of the present invention.

FIG. 2 is a sectional view showing the configuration of a disc according to an embodiment of the present invention.

FIG. 3 is a sectional view showing the configuration of a disc according to an embodiment of the present invention.

FIG. 4 is a sectional view showing the configuration of a disc according to an embodiment of the present invention.

FIG. 5 is a sectional view showing the configuration of a disc according to an embodiment of the present invention.

FIG. 6 is an apparatus diagram for recording / reproducing according to an embodiment of the present invention.

[Explanation of symbols]

 1 Transparent Substrate 2 Recording Thin Film 3 Overcoat Layer 4 Adhesive Layer 5 Dielectric Layer 6 Reflective Layer 7 Objective Lens 8 Motor 9 Semiconductor Laser 10 Collimating Lens 11 Laser Beam 12 Beam Splitter 13 λ / 4 Wave Plate 14 Turntable 15 Detector 16 Voice coil 17 Optical disc 18 Input signal 19 Playback output

Claims (7)

[Claims] 1. An optical information recording medium having a recording thin film on a transparent substrate, the recording thin film being made of a material exhibiting a change in optical characteristics to different states upon irradiation with a light beam, wherein the recording thin film is Te, O. And Pd as a main component, and the ratio of the Te atoms contained in the recording thin film is 20 to 20.
An optical information recording medium, wherein the composition ratio is 70 atom%, the O atom ratio is 25 to 45 atom%, and the Pd atom ratio is 5 to 35 atom%. 2. The ratio of Te atoms contained in the recording thin film is 30 to 65 atom%, and the ratio of O atoms is 30 to 40 atom.
%, And the proportion of Pd atoms is within the range of composition ratio of 5 to 30 atom%. 3. The optical information recording medium according to claim 1, wherein the thickness of the recording thin film is in the range of 20 to 200 nm. 4. The optical information recording medium according to claim 1, wherein a protective layer made of a dielectric material is provided on at least one of the substrate side and the side opposite to the substrate of the recording thin film. 5. The optical information recording medium according to claim 1, further comprising a reflective layer on the side of the recording thin film opposite to the substrate. 6. A recording thin film made of a material exhibiting a change in optical characteristics to a different state upon irradiation of a light beam on a transparent substrate, the recording thin film containing Te, O and Pd as main components, The O contained in the recording thin film
A method for recording / reproducing an information signal to / from an optical information recording medium in which the atomic ratio is 25 to 45 atom% and the Pd atomic ratio is in the range of 5 to 35 atom%.
When the light intensity is approximated to a Gaussian distribution when the light beam is applied to the optical information recording medium through the objective lens, the diameter (that is, the spot diameter) at which the beam intensity is 1 / e of the spot center is d, Recording bit length is b
The recording / reproducing method is characterized in that recording / reproducing is performed under the condition that the ratio b / d of the bit length b to the spot diameter d is 1.0 or less. 7. The ratio of the O atom contained in the recording thin film is 30 to 40 atom%, and the ratio of Pd atom is 5 to 30.
The optical information recording medium according to claim 6, wherein the composition ratio is in the range of atom% and the ratio b / d of the bit length b to the spot diameter d is 0.8 or less.