JPH01201836A - Information recording medium - Google Patents

Abstract

PURPOSE:To obtain an information recording medium having a long life and high recording sensitivity by increasing the content of a protective material in the surface layer part of a recording layer and decreasing the content of the protective material and increasing the content of a material contributing to recording in the central part. CONSTITUTION:The recording layer 2 on a substrate 1 is formed of the material 12 which consists of a metal or semiconductor for recording information and the protective material 11 which consists of carbon and hydrogen. The mixing ratio of the material 12 and the material 11 is changed in the thickness direction of the layer so that the content of the material 11 is increased in the surface layer part than in the central part. Since the content of the material 11 is high in the part which is liable to be oxidized by contact with the atm., the oxidation resistance of the layer 2 increases. Since the central part is hardly oxidized, the degradation in the oxidation resistance is obviated even if the content of the material 11 is high. The oxidation resistance over the entire part of the recording layer is thereby improved and the total content of the material contributing to the recording is increased, by which the information recording medium having the long file and the high recording sensitivity is obtd.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) This invention provides a method for recording a recording layer by irradiating a recording layer with a light beam, which is made of a mixture of a substance involved in recording and a substance protecting this substance. The present invention relates to an information recording medium such as an optical disk that records information by changing the optical properties of a substance involved in recording in an irradiated area.

(Prior Art) Conventionally, as an information recording medium that records and reproduces information using optical changes in a recording layer, for example, a recording layer is irradiated with a light beam and the irradiated portion is melted or evaporated to form bits. There are known devices that detect changes in the optical characteristics of the bit portion, such as changes in reflectance. For the recording layer of such an information recording medium, for example, Te metal is made of carbon-hydrogen (C-H
) Dispersed in a compound, or an organic discharge polymerized film containing Te. In such a recording layer, recording and reproducing information is mainly performed using T, which has a high light reflectance and absorption rate.
It depends on e. On the other hand, since Te has low oxidation resistance,
Oxidation of Te is suppressed by C and H5 or an organic discharge polymer to extend the life of the recording layer.

(Problems to be Solved by the Invention) However, if the proportion of a protective substance such as CH in the recording layer is increased and the proportion of Te is decreased, there is a possibility that the recording sensitivity will decrease. That is, there is a limit to increasing the lifespan of an information recording medium by increasing the proportion of the protective substance, depending on the recording sensitivity.

This invention was made in view of such circumstances, and
An object of the present invention is to provide an information recording medium that can stably maintain a substance involved in recording in a recording layer and has high recording sensitivity.

[Structure of the Invention] (Means for Solving the Problems) An information recording medium according to the present invention has a substrate and a recording layer made of a mixture of a substance involved in recording and a substance protecting this substance. The recording layer is characterized in that a mixing ratio of the substance involved in recording and the protective substance changes in the layer thickness direction.

(Function) In the present invention, as described above, since the mixing ratio of the substance involved in recording and the protective substance can be changed in the thickness direction of the recording layer, the areas where oxidation etc. of the recording layer are likely to occur, For example, by increasing the content of protective substances in the surface layer,
In addition, the content of the protective substance can be reduced in a region where there is little risk of oxidation, for example, in the center of the recording layer.

Therefore, the stability of the areas of the recording layer where oxidation etc. are likely to occur can be increased, making it possible to extend the life of the entire recording layer. By reducing the amount, the amount of the substance involved in recording in the entire recording layer can be increased compared to the case where the mixing ratio is constant, so that the recording sensitivity can be maintained high.

(Embodiments) Hereinafter, embodiments of the present invention will be specifically described with reference to the accompanying drawings.

Figure 1 shows an information recording medium (optical disk) according to this embodiment.
FIG. The substrate 1 is made of a resin such as polycarbonate, polymethyl methacrylate, or epoxy, or a material that does not change easily over time, such as glass. A recording layer 2 is provided on the substrate 1 . This recording layer 2
is made of carbon, hydrogen, and metal or semiconductor, and metal or semiconductor 12 is dispersed in carbon and hydrogen 11. Then, by being irradiated with a light beam such as a laser beam, the irradiated portion is melted or evaporated to form pits and information is recorded.

In this case, those involved in recording information are:
It is mainly made of metal or semiconductor 12, and information is read by detecting its reflectance or transmittance.

As the metal or semiconductor constituting the recording layer 2, a material having a relatively low melting point, easy to form bits, and high reflectance and absorption, such as Te, can be used. On the other hand, carbon and hydrogen 11 in the recording layer 2 act as a protective substance that protects the metal or semiconductor in the recording layer 2 from oxidation and the like.

The recording layer 2 includes a metal or semiconductor 12 and carbon and hydrogen 11.
The mixing ratio of carbon and hydrogen changes in the direction of the layer thickness, and the content of carbon and hydrogen is relatively higher in the surface layer than in the center. In this case, since the surface layer portion, which is easily oxidized by contact with the atmosphere, has a high carbon and hydrogen content, the recording layer has high oxidation resistance and has a long life. In addition, since the center part of the recording layer 2 is less likely to be oxidized than the surface layer part,
As mentioned above, even if the contents of carbon and hydrogen are low, there is little possibility that the oxidation resistance of the recording layer will deteriorate. In this way, by lowering the content of carbon and hydrogen in the center, the content of metal or semiconductor in the entire recording layer can be increased compared to when the content of carbon and hydrogen is constant. The recording sensitivity of the layer can be maintained high.

In the information recording medium shown in FIG. 1, the mixing ratio of metal or semiconductor (eg Te) and carbon and hydrogen can be changed, for example, as shown in FIGS. 3 and 4. In other words, in Figures 3 and 4, the horizontal axis represents the distance in the layer thickness direction, and the vertical axis represents the content of metal or semiconductor, carbon, and hydrogen, and shows changes in the respective contents in the layer thickness direction. The mixing ratio may change continuously in the layer thickness direction as shown in FIG. 3, or may change stepwise as shown in FIG. 4.

FIG. 2 shows a recording layer 3 formed on the same substrate 1 as in FIG. 1 and having the same structure as the recording layer 2 except that the distribution of carbon and hydrogen is different.
1 is a cross-sectional view showing an information recording medium (optical disc) provided with an information recording medium (optical disc). In other words, this recording layer 3 has not only its surface layer but also
The content of carbon and hydrogen is also higher in the boundary portion with the substrate 1 than in the central portion. For example, if resin is used as the substrate 1, there is a risk that moisture or the like will enter the recording layer through gaps in the substrate and oxidize the recording layer.
By increasing the content of carbon and hydrogen in the boundary portion of the recording layer with the substrate in this manner, oxidation of this portion can be suppressed, and the oxidation resistance of the recording layer can be further improved.

In the information recording medium shown in FIG. 2, the mixing ratio of metal or semiconductor to carbon and hydrogen can be changed as shown in FIGS. 5 and 6. These figures 5 and 6 are
Similar to Figures 3 and 4, this shows changes in the mixing ratio in the layer thickness direction, and as shown in these figures, the mixing ratio of metals or semiconductors and carbon and hydrogen changes continuously in the layer thickness direction. It doesn't matter if there is, or it can be done in stages.

Next, an example of a method for manufacturing such an information recording medium (optical disc) will be described. First, a substrate 1 is placed in a vacuum chamber, and a target made of, for example, Te is placed opposite the substrate. Next, the inside of the chamber is evacuated using a cryopump or the like to create a high vacuum of, for example, 5×10″6 Torr or less. Thereafter, a hydrocarbon gas such as methane gas or a mixed gas of hydrocarbon gas and a rare gas such as argon is introduced into the chamber. For example, 5 x 1
The target is maintained at 0-3 Torr, and a predetermined power is supplied to the target to perform sputtering for a predetermined time. As a result, substrate 1
Recording layer 2 or recording layer 3 is deposited thereon. In this case,
The ratio of metal or semiconductor to carbon and hydrogen in the recording layer can be adjusted by changing the gas flow rate, the ratio of each gas, the sputtering power, etc. For example, when the gas flow rate (hydrocarbon gas+rare gas) and sputtering power are constant, the higher the flow rate ratio of hydrocarbons, the higher the carbon and hydrogen contents. Also,
If the gas flow rate and ratio are constant, the lower the sputtering power, the higher the carbon and hydrogen content. Therefore, by changing these conditions continuously or discontinuously during film formation, the mixing ratio of metal or semiconductor and carbon and hydrogen in the recording layer can be changed in the layer thickness direction.

In the above embodiments, the present invention is applied to an information recording medium of a type in which information is recorded by irradiating the recording layer with a light beam and forming pits in the irradiated area.
The present invention is not limited to this, and can also be applied to, for example, magnetic recording type or phase change type information recording media. Furthermore, the material constituting the recording layer is not limited to those described in this example, and in short, the recording layer is a mixture of a recording-related substance that is relatively easily oxidized and a protective substance that protects this substance from oxidation. It can be applied as long as it is made of.

Test Example A test example in which an information recording medium (optical disk) according to the present invention was actually manufactured will be described below.

A circular polycarbonate substrate was placed in a vacuum chamber, and the chamber was evacuated to 5 x 10'6 Torr or less. Argon gas and methane gas were introduced into the chamber, and a Te substrate placed opposite the substrate was evacuated. Sputtering was performed by supplying power to the target. In this case, the flow rate of both argon gas and methane gas was kept constant at 503 CCM from the start of film formation to the end of film formation. Then, for 30 seconds from the start of film formation, the sputtering power was increased from 50 W to 100 W in proportion to time, then for the next 30 seconds, the sputtering power was kept constant at 100 W, and for the next 30 seconds, the sputtering power was increased from 100 W to 5 W.
It decreased in proportion to time until it reached 0W. As a result, an optical disk having a recording layer in which Te was dispersed in carbon and hydrogen was formed, and the profile of the mixing ratio of the recording layer was as shown in FIG. Furthermore, by changing the gas flow rate or gas mixture ratio, the mixture ratio of Te, carbon, and hydrogen in the layer thickness direction could be similarly changed.

[Effects of the Invention] According to this invention, in the recording layer, the mixing ratio of the substance involved in recording and the substance protecting this substance can be changed in the layer thickness direction, so that, for example, it is possible to easily contact the outside air. The content of the protective substance is relatively increased in areas where oxidation etc. are likely to occur, such as the surface layer, and the content of the protective substance is relatively decreased in areas where oxidation etc. are relatively unlikely to occur, such as the central area. can do. This makes it possible to improve the oxidation resistance of the entire recording layer, and also to increase the total amount of substances involved in recording compared to when the mixing ratio is made uniform.

Therefore, an information recording medium with a long life and high recording sensitivity can be obtained.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing an information recording medium according to an embodiment of the present invention, and FIGS. 3 to 6 show changes in the mixing ratio of metal or semiconductor and carbon and hydrogen in the layer thickness direction. It is a graph diagram. 1; Substrate, 2, 3; Recording layer, 11; Carbon and hydrogen (protective substance), 12; Metal or semiconductor (substance involved in recording)
. Applicant's Representative Patent Attorney Takehiko Suzue Figure 2 Of course Figure 3 Figure 4 ω Figure 5L Jun Figure 6

Claims (1)

[Claims] An information recording medium comprising a substrate and a recording layer made of a mixture of a substance involved in recording and a substance protecting this substance, wherein the recording layer has a mixture ratio of the substance involved in recording and the protection substance. An information recording medium characterized in that: changes in the layer thickness direction.