JPH05159398A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To decrease the dependency on the linear speed of the laser power necessary for information recording by constituting a reflection layer of metallic polycrystalline thin films having 100 to 3000Angstrom crystal grain sizes. CONSTITUTION:A recording layer consisting of an SiNx layer of 1200Angstrom is formed on a format substrate with spiral grooves made of, for example, a polycarbonate resin. A thin film of TbFeCo having 200Angstrom thickness is then formed by a DC sputtering methodthereon and thereafter, the SiNx layer of 300Angstrom thickness is formed by the reactive sputtering method thereon. Further, the reflection layer essentially consisting of Al is formed on the SiNx layer by RF sputtering. The crystal grain sizes of the SiNx layers of respective samples are controlled by the addition amt. of the Ti to be added as an impurity into the Al of the reflection layer material. The dependency on the linear speed of the laser power necessary for information recording is decreased according to the result of experiment and, therefore, the degradation in the recording sensitivity in the high rotating region is prevented.

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. More specifically, the present invention relates to a novel configuration of an optical information recording medium of a type in which information is written by irradiating laser light and information recorded is read by reflection of laser light.

[0002]

2. Description of the Related Art A great variety of optical information recording media, which are expected to be used as large-capacity and high-density information recording media, have been developed due to differences in their recording systems and shapes. Among them, a so-called magneto-optical disk that performs recording by utilizing reversible magnetization reversal of a recording layer by irradiation with a laser beam is used as a central mass storage device in various information devices instead of a conventional magnetic recording medium. If possible, various improvements are still proposed.

In this type of optical information recording medium of the photothermographic recording system, it is general to provide a reflective layer adjacent to the recording layer in order to efficiently transfer the energy of the laser beam to the recording layer. As a material for such a reflective layer,
Al and its alloy compounds are widely used.

By the way, one of the constant problems in a series of optical information recording media is improvement of recording sensitivity. That is, how to reduce the laser power required to record information of a predetermined signal level not only reduces the power consumption during recording, but also greatly contributes to the improvement of recording speed. ..

[0005]

As one of the methods for improving the recording sensitivity of an optical information recording medium having a reflective layer as described above, JP-A-62-137743 discloses that the Al reflective layer is made amorphous. A method is disclosed. However, in this method, the number of rotations of the recording medium is 2400 rpm or less, that is,
This is an effective method when the relative linear velocity between the recording medium and the laser beam is low, but when the rotational speed of the medium is 3600 rpm or higher and the linear velocity in the recording area is high, the effect may be significantly reduced. Are known.

Therefore, it is an object of the present invention to provide a novel optical information recording medium which solves the above-mentioned problems of the prior art and can maintain a high recording sensitivity even in a high rotation region.

[0007]

According to the present invention, in an optical information recording medium provided with a substrate and a recording layer and a reflective layer sequentially laminated on the substrate, the reflective layer has a crystal grain size.
Provided is an optical information recording medium characterized by being composed of a metal polycrystalline thin film of 100 to 3000 Å.

[0008]

The optical information recording medium according to the present invention effectively reduces the dependence of the laser power required for information recording on the linear velocity by appropriately controlling the crystalline state of the reflective layer. It has major characteristics.

That is, in the optical information recording medium according to the present invention, the reflective layer is formed of a metal polycrystal thin film having a crystal grain size of 100 to 3000Å. Here, when the reflective layer contains a metal crystal having a crystal grain size outside the above range, the linear sensitivity depends on the recording speed due to the influence of the crystal grain boundary and amorphization in the metal thin film, resulting in a high recording sensitivity. A decrease in recording sensitivity occurs in the rotating area.

In other words, the decrease in recording sensitivity due to the crystal grain boundaries and the amorphization becomes more remarkable in response to the increase in the rotation speed of the recording medium. Therefore, the present invention is more effective in the high rotation region. There is.

As a specific method for forming the metal reflection layer, any known film formation method such as a sputtering method or a vacuum deposition method can be applied, and as a method for controlling the crystal grain size in the reflection layer, In addition to the method of appropriately setting the film forming conditions during film formation, there is also a method of adding impurities in an appropriate amount to the vapor deposition source. Examples of the material of the reflective layer include Al and Au.

Examples of the material of the recording layer in the optical information recording medium according to the present invention include TbFeCo and GdFeCo.

Further, as the material of the substrate for mounting the above-mentioned reflection layer and recording layer, it is possible to use glass other than transparent resin materials such as polycarbonate, polymethylmethacrylate and amorphous polyolefin. The present invention can be applied not only to the most widely used disk shape but also to a card shape or a drum shape.

Hereinafter, the present invention will be specifically described with reference to examples, but the following disclosure is merely one example of the present invention and does not limit the technical scope of the present invention.

[0015]

Example A recording layer was formed on a spiral grooved format substrate made of a polycarbonate resin having a diameter of 130 mm. Specifically, a 1200 Å-thick SiN _X layer was formed on the substrate by a reactive sputtering method using a Si target and a mixed gas of Ar and N ₂ using an in-line type sputtering device. Next, the thickness is 200Å by DC sputtering method.
After the TbFeCo thin film of No. 3 was formed, a SiN _x layer having a thickness of 300 Å was formed by reactive sputtering with a mixed gas of Ar and N ₂ . Furthermore, by RF sputtering, SiN _x
A reflective layer containing Al as a main component was formed on the layer. The crystal grain size of the reflective layer of each sample was controlled by the amount of Ti added as an impurity in Al of the reflective layer material. For comparison,
Multiple samples (a) to (d) with different crystal grain sizes in the reflective layer
Was produced.

The crystal grain size of each sample is as shown in Table 1 below. In addition, FIG. 2 shows each sample (a), (b),
It is an electron micrograph which image | photographed the crystal state of the reflection layer of (c) and (d) with TEM (transmission electron microscope).

[0017]

[Table 1]

The thickness of the reflective layer in each sample is 830
Frequency using semiconductor laser of nm 3.7MHz, duty22%
The repetitive signal of was set to a thickness such that the recording sensitivity when writing at a position 30 mm from the center of rotation on a medium having a rotation speed of 1800 rpm was equal. Incidentally, the recording sensitivity mentioned here means a laser power such that the C / N ratio of written information becomes 10 dB or more.

FIG. 1 is a graph showing the linear velocity dependence of the recording sensitivity when the linear velocity was changed while the pit length was kept constant at 0.76 μm for each of the samples prepared as described above.

As shown in the same figure, in the samples (a), (b) and (c) having the reflective layer having a crystal grain size of 100 Å or more, the laser power of the laser power necessary for writing the information is high even in the high linear velocity region. The rise is small. On the other hand, it can be seen that the sample (d) having the amorphous reflective layer having a crystal grain size of 100 Å or less requires remarkably large laser power for writing information in the high linear velocity region. As described above, in the optical information recording medium according to the present invention, the dependence of the writing laser power on the change of the linear velocity of the medium is small.

[0021]

As described above, by appropriately controlling the crystal grain size of the reflective layer according to the present invention, the optical information whose recording / reproducing characteristics do not depend on the linear velocity of the recording medium in the range up to the high linear velocity region. A recording medium is provided.

[Brief description of drawings]

FIG. 1 is a graph showing the linear velocity dependence of recording sensitivity for each sample.

FIG. 2 shows the state of crystal grains in the reflection layer of each sample as TE.
It is an electron microscope photograph taken by M (transmission electron microscope).

Claims (1)

[Claims] 1. An optical information recording medium comprising a substrate, and a recording layer and a reflective layer which are sequentially laminated on the substrate, wherein the reflective layer is composed of a metal polycrystalline thin film having a crystal grain size of 100 to 3000Å. An optical information recording medium characterized in that.