JP2571556B2 - 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 of a reproduced signal.

Optical information recording media are sometimes used for long-term storage of data, and it is necessary that there is no change in the recording material even when left in a high-temperature, high-humidity environment, and that the recorded data can be read and written accurately. is there.

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, and the optical properties such as reflectance and transmittance change.

The cause of this is that the GeTe crystal has a rhombohedral structure, but there is a gap into which other atoms having a small atomic radius can penetrate. That is, the distance between Ge-Te bond atoms in the amorphous phase GeTe thin film is not uniform, and has a very wide distribution.Therefore, when the GeTe thin film is placed in an environment of high temperature and high humidity, the atomic radius is small. Oxygen penetrates into 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, Ag atoms are used in advance.
Since the gaps in the Ge-Te lattice are buried, oxygen hardly penetrates, and the slightly penetrated oxygen combines with Ag to form Ag.
Since it becomes O and becomes stable, the GeTe thin film is protected from deterioration due to intrusion of oxygen.

[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 long life, but as the Ag content increases, the signal-to-noise ratio (CNR) gradually deteriorates, and the Ag content exceeds 3 atomic percent. However, there is a problem that it is difficult to obtain a reliable performance as an optical information recording medium, and the life is not extended much if the Ag content is reduced.

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. Therefore, it is considered that the deposited Ag changes the reflectivity of the reproduction light beam, becomes a noise component, and lowers the CNR.

[Means for solving the problem]

The present invention, in order to solve the above problems, the recording thin film, a thin film containing Ge as a main component to which Ag is added, the Ag content in the optical recording thin film on the substrate side from the average Ag content It was also made smaller than the average Ag content on the protective film side.

[Action]

In 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, the thickness of the protective film is 1/100 to 1/10 of the thickness of the substrate. Therefore, the oxidative corrosion of the optical recording thin film in a high-temperature and high-humidity environment starts from the protective film side and gradually spreads to the substrate side. Therefore, as in the present invention, the Ag content in the optical recording thin film is smaller than the average Ag content on the substrate side and larger than the average Ag content on the protective film side, so that the optical recording thin film traveling from the protective film side Oxidative corrosion can be strongly prevented. In general, information recording and reproduction are performed by irradiating a light beam from the substrate side, so that the recording and reproduction characteristics of the optical information recording medium strongly depend on the properties of the optical recording thin film on the substrate side.
Therefore, when the Ag content on the substrate side of the optical recording thin film is smaller than the average Ag content as in the present invention, the amount of precipitated Ag that is a noise component on the substrate side is small, and as a result, the recording / reproducing characteristics are good. Can be kept.

〔Example〕

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

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

The optical recording thin film 12 is produced by a sputter rig method and a vapor deposition method. A method for making the Ag content of the Ag-added GeTe thin film smaller than the average Ag content on the substrate side and larger than the average Ag content on the protective film side will be described below.

FIG. 2 is a schematic diagram of a sputter rig 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 at the upper part in the vacuum chamber 21. After evacuation of the vacuum chamber 21 to about 5 × 10 ⁻⁴ Pa, The gas pressure is adjusted to 5 × 10 ^-1 Pa by introducing an active gas. In this state, GeTe target 23
When high-frequency power is applied to the Ag target 24 at the same time, a GeTe thin film to which Ag is added is formed on the substrate 11 by the sputtering effect. At this time, as shown in FIG. 3, the high-frequency power applied to the GeTe target 23 is kept constant, and the power applied to the Ag target 24 is reduced at the beginning of the sputter rig and increased near the end of the sputtering. In the GeTe thin film, the Ag content is the average Ag on the substrate side.
It is smaller than the content, and is larger than the average Ag content on the protective film side.

Similarly, in the vacuum deposition method, by simultaneously depositing GeTe and Ag from two kinds of evaporation sources, keeping the evaporation rate of GeTe constant, and decreasing the evaporation rate of Ag at the beginning of the deposition start and increasing it near the end of the deposition, The Ag content is smaller than the average Ag content on the substrate side, and larger than the average Ag content on the protective film side.

The resin protective film 13 is formed by applying an ultraviolet-curable resin liquid with a spinner and then irradiating the resin 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.

During the preparation of the Ag-doped GeTe optical recording thin film, the power applied to the Ag target was kept constant while the power applied to the Ag target was varied as shown in FIG. 3 during the sputtering rig. Table 1 shows the life of the optical information recording medium and the signal-to-noise ratio CNR of the reproduced signal of the optical information recording medium according to one embodiment of the present invention in comparison with Table 1.

Here, the medium life was measured by irradiating a disk-shaped optical information recording medium with laser light, recording a signal at a rotation speed of 1800 rpm and a frequency of 1 MHz, performing a temperature / humidity acceleration test of JISc5024M-1, and measuring the bit error rate before the test. It was inferred from the test time until it became three times the value.

As shown in Table 1, according to the above embodiment, in the optical information recording medium, the Ag content in the optical recording thin film was smaller than the average Ag content on the substrate side, and the average Ag content on the protective film side.
Since the content is larger than the content, the medium life is long and the reproduction signal CNR keeps a good value.

〔effect〕

According to the present invention, since the Ag content in the optical recording thin film is larger than the average Ag content on the protective film side, oxidative corrosion of the optical recording thin film starting from the protective film side is prevented, An optical information recording medium capable of accurately recording and reproducing information for a long time even when left in a wet environment is obtained. Also, on the substrate side of the optical recording thin film, the Ag content is an average Ag.
Since it is smaller than the content, deterioration of the recording / reproducing characteristics due to the addition of Ag is small, and an optical information recording medium having good recording / reproducing characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an embodiment of an optical information recording medium according to the present invention, FIG. 2 is a schematic diagram of a sputter rig applicable to the present invention, and FIG. 3 is a diagram for explaining the operation thereof. 11 ... substrate 12 ... optical recording thin film 13 ... resin protective film 21 ... vacuum chamber 22 ... substrate support table 23 ... GeTe target 24 ... Ag target

Claims (1)

(57) [Claims] An optical information medium comprising an optical recording thin film formed on a substrate and a protective film formed on the optical recording thin film, wherein the main component of the optical recording thin film is GeTe to which Ag is added, An optical information recording medium, wherein the Ag content in the optical recording thin film is smaller than the average Ag content on the substrate side.