JPS61292239A - Information recording medium - Google Patents

Abstract

PURPOSE:To permit recording in an optimum state with specified recording power by forming a thin inorg. film to at least one side of thin recording films having the property to change with the phase by the effect of heat energy and forming said film in such a manner that the film is thicker nearer the center of rotation of a disk in the radial direction than in the part further therefrom. CONSTITUTION:The thin recording film 13 is formed on a disk substrate 12 made of polycarbonate having guide grooves 11 for tracking and the thin inorg. film 14 is formed at such a film thickness distribution in which the film is thick on the inside circumference and is thin on the outside circumference. This film thickness is so distributed that the sum of the heat capacity of the film 13 and the film 14 is proportional to the inverse number of the square root of the linear speed when the disk is rotated. A protective substrate 16 made of polycarbonate is further tightly adhered thereto via an adhesive agent 15, by which the disk is completed. The recording sensitivity is thereby improved from the inside circumference toward the outside circumference and the recording at the specified recording power is made possible while the highest C/N value is maintained regardless of the inside and outside circumferences.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an information recording medium that records bits of information using a high energy density light beam.

BACKGROUND OF THE INVENTION In recent years, optical memory disks have been used as information recording media that can be recorded and reproduced in real time, and are highly anticipated as large-capacity, high-density memories. In this method, for example, a laser beam is irradiated onto a disk that rotates at high speed to record bits on an information recording layer, and the bits are read using reproduction light. Since recording and reproduction are performed without contact, it has the advantage of not damaging the pick-up or disc, and that information can be accessed at high speed.

As a recording film that makes such an optical memory disk possible, there is a TeO (<!<2) thin film. This TeO material is a mixture of TeO2 and To. This thin film undergoes a phase change due to heat generated by laser beam irradiation, and recording pits are formed by increasing the reflectance and decreasing the transmittance. It is also shown in the specification of Japanese Patent Application No. 59-192003 that by incorporating additives such as Pd into this too-processed thin film, the film can be made even more resistant to temperature and humidity. It can be said that this is an extremely suitable recording film for the required optical memory disks.

Problems to be Solved by the Invention Figure 4 shows that in an optical memory disk with an outer diameter of 120M,
Recording power and C when the disc rotation speed is 120Orpm
/N relationship was determined for the inner circumference and the outer circumference. The disk structure in this case is as shown in FIG. 6, on a polycarbonate disk substrate 62 having a tracking guide groove 61. A recording thin film 63 whose main component is
Too engineer! The value is 1.1, and Pd is 10 for the whole.
It contains 0% of at Omi. FIG. 4d shows the case of the inner circumference with a diameter of eomm, and the highest C/N (55 dB) is obtained with a recording power of 4 mW.

On the other hand, Figure 4 shows the case of an outer circumference with a diameter of 110M, and the highest C/N value (s
sdB), and the optimum recording power at which the C/N value is highest is different between the inner and outer circumferences. This is because the linear velocity on the outer circumference is faster than on the inner circumference, and in order to optimize the recording power, it is necessary to continuously increase the recording power from the inner circumference to the outer circumference. . However, this requires the addition of a mechanism for changing the recording power depending on the positional relationship of the pickup, which poses the problem of increased costs. Another possibility is to change the rotational speed so that the linear velocity is constant regardless of the inner or outer circumference, but this requires adding a mechanism to change the rotational speed depending on the position of the pickup, which is also expensive. Become.

It is also conceivable to make the optimum recording power on the inner and outer circumferences the same by increasing the sensitivity on the outer circumference by increasing the thickness of the recording thin film on the inner circumference and thinner on the outer circumference. However, in this case, a problem arises in that the reflectance varies in the radial direction as the thickness of the recording thin film changes.

Therefore, even if the rotational speed is constant, the present invention provides the highest C/
It is an object of the present invention to provide an information recording medium that can record while maintaining the N value and has the same reflectance in the radial direction.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention forms an inorganic thin film on at least one side of a recording thin film that has the property of changing its phase with thermal energy, and adjusts the thickness of the film to the center of rotation of the disk. The thickness is set to be thicker in areas closer to the area than in areas further away in the radial direction.

Function This configuration, in which the thickness of the inorganic thin film is thicker in areas near the center of rotation and thinner in areas farther from the center of rotation, increases the thermal conductivity of the inner periphery compared to the outer periphery, making the recording sensitivity of the outer periphery higher than that of the inner periphery. can do. That is, the increase in linear velocity toward the outer periphery is compensated for by the improvement in recording sensitivity, and it is possible to maintain an optimal state with a constant recording power regardless of the inner or outer periphery.

EXAMPLE Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 shows a disk structure according to the present invention. A recording thin film 13 with a thickness of 140 nm is formed on a polycarbonate disk substrate 12 having a tracking guide groove 11. The composition of the recording thin film 13 is TeOx (x = 1
．． 1) contains 10 atomic% of Pd based on the total content. Furthermore, an inorganic thin film 14 is formed on the recording thin film 13 with a thickness distribution such that it is thicker at the inner periphery and thinner at the outer periphery, as shown in FIG. Here, the inorganic thin film is Sio2. This film thickness distribution is calculated so that the sum of the heat capacities of the recording thin film 13 and the inorganic thin film 14 is proportional to the reciprocal of the square root of the linear velocity when the disk is rotated. Furthermore, a polycarbonate protective substrate 16 is closely attached to the inorganic thin film 14 via an adhesive layer 15 to form a completed disk. The optical memory disk formed in this manner was rotated at 120 Q rpm, and the relationship between recording power and C/N was determined, and FIG. 3 shows the results. Figure 3 a shows the case of an inner circumference with a diameter of 60111111, 7
The highest C/N value was obtained with a recording power of mW.

On the other hand, Figure 3 shows the case of the outer circumference with a diameter of 110fflffl, and as with the case of the inner circumference in Figure 3, the highest C/N value is obtained at a recording power of 7 mW. Regardless of the circumference, middle circumference, or outer circumference, it is possible to record while maintaining the highest C/N value with constant recording power. We also measured the reflectance from the inner circumference to the outer circumference, and confirmed that almost the same values were obtained.

In this embodiment, the inorganic thin film 14 is
Although it is formed on the disk substrate 12 side, the same effect can be obtained even if it is formed on the disk substrate 12 side. In addition, the inorganic thin film 14 is attached to the recording thin film 1.
It is also effective to form it on both sides.

Furthermore, here the inorganic thin film is 3102, but S
iC, S i3 N4 + T e 02 + A I
203 + Z n S e , Zn○.

Similar effects can be obtained by using ZnS, which is effective.

Effects of the Invention The present invention forms an inorganic thin film on at least one side of a recording thin film that has the property of undergoing a phase change due to thermal energy, and the thickness of the inorganic thin film is varied in a region nearer to the center of rotation of the disk than in a region farthest from the center of rotation in the radial direction. The recording sensitivity is set to increase from the inner circumference to the outer circumference, and at a constant rotation speed, the recording sensitivity increases from the inner circumference to the outer circumference.

Highest C at constant recording power regardless of middle or outer circumference
/N value can be maintained and recorded. Also, the reflectance does not have a gradient in the radial direction. As described above, there is no need to add complicated functions to the recording/reproducing device, and its industrial value is extremely high.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an information recording medium according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the radial thickness distribution of an inorganic thin film according to an embodiment of the present invention, and FIG. 3 is a cross-sectional view of an information recording medium according to an embodiment of the present invention. FIG. 4 is a characteristic diagram showing the relationship between the C/N of the inner and outer circumferences and recording power of the obtained information recording medium, and FIG. FIG. 5 is a cross-sectional view of a conventional information recording medium. 12.52... Disk board, 13, 53.
... Recording thin film, 14... Inorganic thin film. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 16, Protection board Figure 2 (WLW) Figure 3 (a) Recording puff (WLW) (b) Recording buff (yxyl Figure 4 (a)) Recording puff (WLW) <b) Record buff (WLW) Figure 5

Claims (5)

[Claims] (1) An inorganic thin film is formed on at least one side of the recording thin film, and the thickness of this inorganic thin film is set such that the thickness of the inorganic thin film is adjusted relative to a portion radially far from the center of rotation of the disk on which the recording thin film is provided.
The information recording medium is configured to be thicker at a portion near the center of rotation. (2) The information recording medium according to claim 1, wherein the recording thin film has a property of changing its phase by thermal energy. (3) Claim 1 or 2, characterized in that the recording thin film has TeO_x (0<x<2) as a main component.
Information recording medium described in section. (4) Inorganic thin film is SiO_2, SiC, Si_3N
_4, TeO_2, Al_2O_3, ZnSe, ZnO
, ZnS. (5) A patent characterized in that the thickness of the inorganic thin film is distributed in the radial direction so that the sum of the heat capacities of the recording thin film and the inorganic thin film is proportional to the reciprocal of the square root of the linear velocity when the disk is rotated. An information recording medium according to claim 1.