JPH04252442A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To provide the recording medium which allows easy overwriting of information regardless of the previous recording states of a phase change type disk. CONSTITUTION:A diamond-like thin film 5 is used as a reflection layer. The difference in absorptivity is decreased while the difference in the reflectivity between a recorded part and an erased part is held large.

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 that records and erases information by utilizing changes in optical constants caused by phase changes induced by differences in thermal history.

0002

[Prior Art] Optical information recording media that record, erase, and reproduce information by irradiation with laser light include, for example, magneto-optical disks and phase-change disks as described in "Optical Disc" (Ohm Co., Ltd.). type optical discs are known. Among these, phase-change optical disks are heated by laser beam irradiation.
Recording and erasing is performed using phase changes, such as between amorphous and crystalline, induced by differences in the thermal history of cooling. As shown in FIG. 3, a phase change optical disc usually has a four-layer structure in which a base layer 2, a recording layer 3, a protective layer 4, and a metal reflective layer 6 are provided in this order on a substrate 1. Among these, the reflective layer 6 is used from an optical point of view to efficiently use incident light, and to improve the recording/erasing power by increasing the cooling rate to make it easier to make the recording layer amorphous, or by smoothing the temperature distribution of the recording layer. - It was added from two points of view: the thermal point of view, which is to widen the margin. The film thickness of each layer is optically optimized, but if the difference in reflectance between the recorded part and the erased part is 15 (%) or more, and the difference in absorbance is 5 (%) or less, is desirable.

[0003] Metals such as Al and Au are usually used for the reflective layer. However, when a metal with high reflectance is used for the reflective layer, the difference in reflectance between the recorded area and the erased area becomes almost the same as the difference in absorption rate, so the difference in absorption rate is reduced by 5 (%).
) It was difficult to do the following. As an extreme case, if we consider a reflective layer with a reflectance of 100%, the difference in reflectance between the recorded portion and the erased portion directly becomes the difference in absorption rate.

0004

[Problem to be Solved by the Invention] When a metal reflective layer is used as in the past, there is a large difference in absorption rate between recorded areas and erased areas. When overwriting information, the temperature rise is not determined solely by the intensity of the irradiated light, but depends on the previous recording state, resulting in problems such as difficulty in writing new information or difficulty in erasing previous signals. . The present invention has been made in response to such conventional circumstances, and an object of the present invention is to provide an optical information recording medium on which information can be easily overwritten regardless of the previous recording state.

[0005]

[Means for Solving the Problems] The present invention provides, on a substrate, a recording layer whose optical properties change depending on the thermal history of heating and cooling caused by laser beam irradiation, and a reflective layer. The present invention is an optical information recording medium characterized in that the reflective layer is made of a diamond-like thin film.

[0006]

[Operation] The diamond-like thin film has high thermal conductivity, a refractive index of 2.0 to 2.7, and an extinction coefficient of 0.1 or less, so it has an appropriate reflectance, so it can be used as a reflective layer. This makes it possible to reduce the difference in absorbance between the recorded portion and the erased portion while keeping the difference in reflectance large. Therefore, it is possible to easily and reliably overwrite information regardless of the previous recording state.

[0007]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of an optical information recording medium according to the present invention, in which a base layer 2, a recording layer 3, a protective layer 4 are provided on a substrate 1.
, a reflective layer 5 made of a diamond-like thin film is sequentially laminated.

Example 1 Polycarbonate (PC) was used as the substrate 1, Si3N4 with a thickness of 100 (nm) was used as the underlayer 2, Ge19Sb38Te43 was used with a thickness of 40 (nm) as the recording layer 3, and SiO2 with a thickness of 60 (nm) was used as the protective layer 4. A disk was prepared in which diamond-like thin films of 80 (nm) were sequentially stacked as the reflective layer 5 by sputtering. In this configuration, Table 1 shows the reflectance and absorption when the recording layer 3 is in the recording state and erasing state.

[0009]

[Table 1]

As shown in Table 1, it was possible to increase the difference in reflectance to 15 (%) or more while keeping the difference in absorbance to 5 (%) or less. The disk was rotated at a linear velocity of 11.3 (m/s), and a signal with a frequency of 3.7 (MHz) and a duty of 50 (%) was recorded.
3.7 (MHz) by overwriting the signal of 50 (%)
The cancellation rate of the signal was measured. Note that the recording layer 3
Evaluation was performed after crystallization. The results are shown in FIG. Erasing rate is 2 over a wide erasing power range of 6 to 10 (mW)
It has an excellent erasing characteristic of 5 (dB) or more. In addition, the optimum recording power of 3.7 (MHz) and 2.8 (MHz)
) had the same optimal recording power.

Comparative Example 1 As a comparative example, polycarbonate (PC) was used as the substrate, Si3N4 was 100 (nm) thick as the underlayer, and Ge19Sb38Te43 was 100 (nm thick) as the recording layer 3.
A disk was manufactured by sequentially laminating SiO2 with a thickness of 60 (nm) as a protective layer and Au with a thickness of 30 (nm) as a reflective layer by sputtering. Table 2 shows the reflectance and absorption when the recording layer 3 is in the recording state and erasing state in this configuration.

0012

[Table 2]

As shown in Table 2, the difference in reflectance is 15 (%) or more, but the difference in absorbance is as large as 15 (%). The same measurements as in Example 1 were performed on this disk, and the results are shown in FIG. The erasing rate becomes 25 (dB) or more when the erasing power is 8 to 10 (mW), and the margin of the erasing power is narrower than in the first embodiment. Further, there was a problem in that the optimum recording power at 3.7 (MHz) and the optimum recording power at 2.8 (MHz) were different. The reason for this is as follows.

A signal of 3.7 (MHz) is recorded in an unrecorded area where the recording layer is crystallized, whereas a signal of 2.7 (MHz)
．． The 8 (MHz) signal is recorded where the 3.7 (MHz) signal has already been recorded. In this disc, as shown in Table 2, the absorption rate differs greatly between when the recording layer is in the erased state and when it is in the recorded state. This causes a difference in the average absorption rate of the recording layer, and as a result, the optimum recording power changes.

[0015]

Effects of the Invention As explained above, by using a diamond-like thin film as a reflective layer in a phase change optical disc, the difference in absorbance can be reduced while increasing the difference in reflectance between recorded areas and erased areas. As a result, it becomes possible to easily and reliably overwrite information regardless of the previous recording state. Furthermore, since the diamond-like thin film has a very high thermal conductivity, it is easy to make the recording layer amorphous, and high-quality signals can be recorded. Furthermore, since the diamond-like thin film has excellent thermal shock resistance, information can be overwritten many times without suffering thermal or mechanical damage.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an optical information recording medium according to the present invention.

FIG. 2 is an erasing characteristic diagram of a phase change optical disc using a reflective layer made of a diamond-like thin film.

FIG. 3 is a cross-sectional view of a conventional optical information recording medium.

FIG. 4 is an erasing characteristic diagram of a phase change optical disc using Au as a reflective layer.

[Explanation of symbols]

Claims (1)

[Claims] 1. An optical information recording medium comprising a recording layer whose optical properties change due to differences in thermal history of heating and cooling due to laser beam irradiation and a reflective layer on a substrate, in order. An optical information recording medium characterized in that the layer is made of a diamond-like thin film.