JP2576959B2 - Optical information recording medium - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium on which information is recorded and reproduced using a light beam.

[Conventional technology]

Germanium telluride (GeTe) is a suitable material as an optical recording material that has high recording sensitivity and can increase the signal-to-noise ratio (CNR) of a reproduced signal.

By the way, the optical information recording medium has a long-term storage of information, for example, 10
It may be used for more than one year, and it is necessary that the recording material does not change even if left in an environment of high temperature and high humidity, and that the recorded information can be read and written accurately.

In view of this point, the GeTe material has a phenomenon that its thin film is gradually oxidized and corroded in a high-temperature and high-humidity environment to change optical properties such as reflectance and transmittance.

The reason for this is that the GeTe crystal has a rhombohedral structure, but there is a gap capable of penetrating other atoms having a small atomic radius. That is, the Ge-Te crystal atomic distance in the amorphous phase GeTe thin film is not uniform and has a very wide distribution. Oxygen penetrates this gap to break Ge-Te, Ge-Ge, Te-te bonds,
O ₂ and TeO _{2 are formed} and the thin film is gradually oxidized.

For this reason, conventionally, an inorganic thin film such as an oxide or a nitride is applied to a GeTe thin film to form a protective film, which is used in a high-temperature, high-humidity environment.
Although the deterioration of the GeTe thin film was prevented, there were disadvantages that it took a long time to produce the above protective film, complicated the optical information recording medium production process, and increased the medium production price.

The present applicant has solved such a drawback, and a material obtained by adding Ag to a GeTe material as a recording thin film capable of providing an optical information recording medium capable of accurately recording and reproducing information even when left in a high temperature and high humidity environment. Was found. In such a GeTe thin film to which Ag is added, Ge atoms are
The GeTe thin film is protected from degradation due to oxygen intrusion because oxygen is less likely to penetrate because the gaps in the Te lattice are filled.

[Problems to be solved by the invention]

However, the optical information recording medium using the above-mentioned Ag-doped GeTe thin film as an optical recording film has a longer life as the amount of added Ag increases, but the signal-to-noise ratio (CNR) gradually deteriorates. At 2.2 atomic percent or more, there is a problem that it is difficult to obtain a reliable performance as an optical information recording medium, and there is a problem that if the Ag content is reduced, the life is not extended much.

That is, when the GeTe thin film undergoes a recording light beam irradiation and changes from an amorphous phase to a crystalline phase, the distribution of the distance between GeTe bonding atoms becomes uniform, and Ag atoms enter the crystalline phase Ge-Te lattice. The amount to be obtained is limited, and Ag atoms in the amorphous phase Ge-Te lattice are rejected out of the Ge-Te crystal lattice by crystallization of the GeTe thin film, and Ag is precipitated. Thus, the deposited Ag changes the reflectance of the reproduction light beam to become a noise component, and as described above, the CN
It seems to lower R.

Accordingly, an object of the present invention is to provide an optical information recording medium having a long life and a large CNR.

[Means for solving the problem]

An optical information recording medium according to the present invention is an optical information recording medium comprising an optical recording thin film formed on a substrate and a protective film formed on the optical recording thin film, wherein Ag is added as a main component of the optical recording thin film. Ge-Te-based material, wherein part of Ge in the optical recording thin film is replaced by Pb.

[Operation] As described above, in the optical information recording medium according to the present invention, since Ge in the optical recording thin film is partially replaced by Pb, Ge (P
b) The inter-atomic distance of the -Te bond is larger than the inter-atomic distance of the Ge-Te bond. Therefore, Ag that can enter the crystalline phase GePbTe lattice
Ag deposition does not occur even if the amount of atoms increases and the GePbTe thin film crystallizes, the CNR does not decrease, and only the oxidation corrosion resistance improves.

〔Example〕

FIG. 1 shows an embodiment of the optical information recording medium according to the present invention. That is, 11 is a polycarbonate substrate on which GePbTe with Ag added as an optical information thin film
It has a thin film 12. Further, a resin protective film 13 for preventing scratches and dust was laminated on the recording thin film.

Here, the substrate 11 is not limited to polycarbonate, and a conventionally known transparent resin plate or glass plate of PMMA, polyolefin, epoxy or the like can be used.

The optical recording thin film 12 is produced by a stuttering method and a vapor deposition method.

FIG. 2 is a schematic view of a sputtering apparatus used for producing the optical recording thin film. The polycarbonate substrate 11 is mounted on the lower surface of the rotary substrate support table 22 provided on the upper part in the vacuum chamber 21 and the inside of the vacuum chamber 21 is about 5 × 10 ⁻⁴ Pa
After the evacuation, an active gas such as Ar is introduced into the vacuum chamber 21 to make the gas pressure about 5 × 10 ^-1 Pa. In this state, when a high-frequency current is simultaneously applied to the alloy target 23 and the Ag target 24 consisting of 34 atomic percent of Ge, 16 atomic percent of Pb, and 50 atomic percent of Te, Ag is deposited on the substrate 11 by sputtering.
Is a GeTe thin film to which Ge is added, and a part of Ge in the thin film is
Ag-GePbTe substituted with Pb is formed. At this time, the Pb content in the thin film can be arbitrarily adjusted by changing the Pb content in the GePbTe alloy target 23, and the Ag content is Ag.
It can be arbitrarily adjusted by the high-frequency power applied to the target 24.

Another way to adjust Pb is to target
A GePbTe thin film in which part of Ge is replaced with Pb is obtained by mounting an alloy chip of 50 atomic percent of Pb and 50 atomic percent of Pb on the target using an alloy of 50 atomic percent of Ge and 50 atomic percent of Te, and sputtering. When the number of PbTe alloy chips is increased or decreased, the amount of Pb in the GePbTe thin film can be increased or decreased accordingly.

To change Ag while keeping the amount of Ge, Pb, and Te constant,
In addition to the above method, by placing an Ag chip on the GePbTe alloy target 23 and sputtering, to obtain an Ag-added GePbTe thin film, Ag was added by increasing or decreasing the number of Ag chips.
The amount of Ag in the GePbTe thin film can be increased or decreased.

Similarly, in the vacuum evaporation method, an Ag-added GePbTe thin film is obtained by adjusting the evaporation rate of the GePbTe alloy and the evaporation rate of Ag by a two-source simultaneous evaporation method using two evaporation sources of a GePbTe alloy and Ag.

The resin protective film 13 is formed by applying an ultraviolet-curable resin liquid with a spinner and then irradiating with ultraviolet light to cure the resin and form a film. As the resin protective film 13, not only an ultraviolet curable resin but also a moisture curable resin, a two-component reactive resin, or a solvent resin can be used.

The disc-shaped optical information recording medium thus manufactured is irradiated with laser light to record a signal having a rotation speed of 1800 rpm and a frequency of 1 MHz. Thereafter, a temperature / humidity acceleration test of JISC5024M-1 is performed, and an increase rate of a bit error rate is measured. Determined the media life.
Table 1 shows the composition of the optical recording film of the optical information recording medium according to the present embodiment, the crystallization temperature of the optical recording film, the CNR, and the medium life. For comparison, the optical recording composition, optical recording film crystallization temperature, CNR, and medium life of a conventional optical information recording medium using a GeTe thin film doped with Ag as an optical recording film are also shown.

As described above, in the optical information recording medium according to the present embodiment, since about 32% of Ge in the GeTe optical recording film is substituted with Pb, the CNR is maintained even if the added Ag amount is increased to 5 atomic percent. 50d
B shows a high value, and the medium life is extremely long at 12 years since Ag is added in a larger amount than in the conventional example.

FIG. 3 shows the amounts of Pb and Ag when the Pb amount and Ag amount in the optical recording film of the optical information recording medium according to the present invention manufactured in the same manner as in the present embodiment were variously changed. CNR of recording medium,
The relation of the medium life is shown.

In the conventional example, as Ag is added to the GeTe thin film as indicated by the dotted line 33, the medium life is improved as indicated by the dashed line 34, but the CNR gradually decreases as indicated by the dotted line 33, and the amount of Ag added is 2.2 atomic percent or more. , The resulting CNR is 45dB
Below, the performance as an optical information recording medium is insufficient. When the amount of Ag added is less than 2.2 atomic percent, the performance as an optical information recording medium can be obtained, but the medium life is less than 5 years, which makes it unsuitable for long-term storage of information.

On the other hand, in the optical information recording medium according to the present invention, GeTe
Because part of Ge in the optical recording film was replaced by Pb, Ag
Even if the addition amount is increased, the decrease in CNR is small, and therefore the medium life can be prolonged by increasing the Ag addition amount.
When the amount of Pb in the optical recording film is 22 atomic percent, even if the amount of Ag added is 6 atomic percent, a CNR of 55 dB can be obtained, and the lifetime is as long as 16 years.

〔effect〕

As described above, in the optical information recording medium according to the present invention, the optical recording film is mainly composed of a GeTe thin film to which Ag is added, and a part of Ge is replaced by Pb. The amount of Ag added can be increased without deteriorating the CNR, so that the life of the optical information recording medium can be extended.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the optical information recording medium according to the present invention, FIG. 2 is a schematic diagram of a sputtering apparatus applicable to the present invention, and FIG. 3 is a diagram for explaining its characteristics. . 11 Substrate 12 Optical recording thin film 13 Resin protective film 21 Vacuum chamber 22 Substrate support table 23 GePbTe target 24 Ag target

Claims (1)

(57) [Claims] An optical information recording medium comprising an optical recording thin film formed on a base and a protective film formed on the optical recording thin film, wherein the main component of the optical recording thin film is Ge-doped with Ag added.
An optical information recording medium comprising a Te-based material, wherein part of Ge in the optical recording thin film is replaced by Pb.