JPH01191345A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To prolong the life of the recording medium without deteriorating the CNR thereof by forming an optical recording film of a film which consists essentially of a thin film of GeTe added with Ag and in which a part of the Ge is substd. with Pb. CONSTITUTION:This recording medium has the thin film 12 of the GePbTe added with the Ag as the optical information thin film on a substrate 11 and is laminated with a resin protective film 13 for preventing flaws and dust thereon. Since a part of the Ge in the optical recording thin film 12 is substd. with the Pb in this case, the interatomic distance of the Ge(Pb)-Te bond is larger than the interatomic of the Ge-Te bond and the quantity of the Ag atoms. which can intrude into the GePbTe lattices of the crystal phase increased. Precipitation of the Ag does not take place even if the thin film of the GePbTe is crystallized. Only the oxidation corrosion resistance is thus improved without degrading the CNR. The optical information recording medium having the long life and the large CNR is thereby obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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) has high recording sensitivity as an optical recording material, and has a low signal-to-noise ratio (CNR) of the reproduced signal.
) is a suitable material that can increase the

Now, optical information recording media are used for long-term storage of information, for example, 10
Since the recording material may be used for many years or more, it is necessary that the recording material does not change even if it is left in an environment of high temperature and humidity, and that recorded information can be read and written accurately.

Regarding this point, GeTe material has a phenomenon in which its thin film undergoes oxidative corrosion, albeit gradually, in a high temperature and high humidity environment, resulting in changes in reflectance and transmittance computational properties.

This can be attributed to the fact that although the GeTe crystal has a rhombohedral structure, there are gaps through which other atoms with small atomic radii can enter. In other words, the distance between Ge-Te crystal atoms in an amorphous GeTe thin film is not uniform and has a very wide distribution. Oxygen enters this gap, forming Ge-Te and Ge-Ge.

Cut the Te-Te bond, G e Oz + T e'
02 and gradually oxidizes the thin film.

For this reason, in the past, inorganic thin films such as oxides and nitrides were deposited on the GeTe thin film as a protective film to prevent the deterioration of the ceTe2 film in high temperature and high humidity environments, but it took a long time to prepare the above protective film. There are disadvantages in that it takes time, complicates the optical information recording medium manufacturing process, and increases the media manufacturing price.

The present applicant has solved these drawbacks by adding Ag to GeTe material as a recording thin film that can provide an optical information recording medium that can accurately record and reproduce information even when left in a hot and humid environment.
We have discovered a recording thin film made of a material doped with . In this kind of Ag-doped GeTe thin IFJ, the gaps in the Ge-Te lattice are filled in advance by Ag atoms, making it difficult for oxygen to penetrate, so the GeTe thin IFJ is protected from deterioration due to oxygen penetration. be done.

[Problem that the invention seeks to solve]

However, although the lifetime of an optical information recording medium using the above-mentioned Ag-doped GeTe thin film as an optical recording film becomes longer as the amount of Ag added increases, the signal-to-noise ratio (CNR) gradually deteriorates. If the Ag content exceeds 2.2 atomic percent, it is difficult to obtain reliable performance as an optical information recording medium, and if the Ag content is reduced, the service life will not be extended much.

That is, when the GeTe thin film is irradiated with the recording light beam, it changes from an amorphous phase to a crystalline 'I! When transitioning to the GeTe phase, the distribution of GeTe bond interatomic distance becomes uniform, and the Ag atoms change to the crystalline GeTe phase.
-The amount that can enter the Te lattice is limited, and the amorphous phase Ge-
The Ag atoms present in the Te lattice are expelled from the Ge-Te crystal lattice by the crystallization of the G e Te thin film, and Ag is precipitated. In this way, the precipitated Ag changes the reflectance of the reproduction light beam and becomes a noise component, resulting in the above-mentioned < CNR
It is thought that this will reduce the

Therefore, the present invention has been made with the object of providing an optical information recording medium that has a long life and a high CNR.

Means for Solving Problem C] An optical information recording medium according to the present invention includes an optical recording thin film formed on a substrate and a protective film formed on the optical recording thin film. The main component of the optical recording film is a Ge-Te based material to which Ag is added, and a part of the Ge in the optical recording thin film is replaced with Pb.

[Function] As described above, in the optical information recording medium according to the present invention, since a part of Ge is replaced with Pb during optical recording gj film formation, G
e The interatomic distance of the (Pb)-Te bond is larger than the interatomic distance of the Ge-Te bond.

Therefore, the amount of Ag atoms that can enter the crystal phase GePbTe lattice increases, and even if GePbTe1 is crystallized, Ag
No precipitation occurs, CNR does not decrease, and only oxidation corrosion resistance improves.

〔Example〕

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

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

The optical recording thin film 12 is produced by sputtering and vapor deposition.

FIG. 2 is a schematic diagram of a sputtering apparatus used when producing the optical recording thin film. The polycarbonate substrate 11 is attached to the bottom surface of the rotary substrate support table 22 provided at the upper part of the vacuum chamber 21, and the inside of the vacuum chamber 21 is
After evacuation to X10-'Pa, active gas such as Ar is introduced into the vacuum chamber 21 to make the gas pressure about 5X10-'Pa. In this state, when a high frequency current is simultaneously applied to the alloy target 23 consisting of 34 atomic percent Ge, 16 atomic percent Pb, and 50 atomic percent Te and the Ag target 24, the sputtering action causes the Ag
An Ag-GePbTe thin film is formed in which a portion of Ge in the thin film is replaced with Pb. At this time, the amount of Pb in the thin film is GePbTe
It can be arbitrarily adjusted by changing the Pb content in the alloy target 23, and the Ag content can be adjusted as desired by changing the Pb content in the alloy target 23.
It can be arbitrarily adjusted by the high frequency power applied to 4.

Another method for adjusting Pb is to use an alloy containing 50 atomic percent of Ge and 50 atomic percent of Te, and place 50 atomic percent of Pb on the target.
When obtaining a GePbTe thin film in which a portion of Ge is replaced with Pb by placing alloy chips containing 50 atomic percent Te and sputtering, if the number of the PbTe alloy chips is increased or decreased, the Pb in the GePbTe thin film will increase or decrease accordingly. The amount can be increased or decreased.

In addition, in order to change Ag while keeping Ge, Pb, and Te4ii constant, in addition to the above method, by placing an Ag chip on the GePbTe alloy target 23 and sputtering, when obtaining an Ag-added GePbTeFf film, the Ag Ag-doped Ge P bT by increasing or decreasing the number of chips
eThe amount of Ag in the thin film can be increased or decreased.

Similarly, in the vacuum evaporation method, GePbTe alloy and Ag
G e P
An Ag-doped GePbTe thin film is obtained by adjusting the evaporation rate of the bTe alloy and the evaporation rate of Ag.

The resin protective film 13 is formed by applying an ultraviolet curable resin liquid using a spinner, and then irradiating ultraviolet rays to cure the resin and remove the skin.
form a ridge. The resin protective film 13 can be made of not only an ultraviolet curable resin, but also a moisture curable resin, a two-component reactive resin, or a solvent-based resin.

The disc-shaped optical information recording medium produced in this manner was irradiated with a laser beam at a rotational speed of 1800 rpm.

Record the signal with a frequency of IMHz, then JISC502
A 4M-1 temperature and humidity accelerated test was conducted, and the medium life was determined from the rate of increase in the bit error rate. Table 1 shows the optical recording film composition, crystallization temperature of the optical recording film, CNR, and medium life of the optical information recording medium according to this example. For comparison, the optical recording composition, optical recording film crystallization temperature, CNR,
It also shows the media lifespan.

Table 1 As shown, in the optical information recording medium of this example, about 32% of Ge in the GeTe optical recording film is replaced with Pb, so even if the added Agl is increased to 5 atomic percent, The CNR shows a high value of 50 dB, and since a larger amount of Ag is added than in the conventional example, the medium life is extremely long at 12 years.

FIG. 3 shows the amount of Pb, amount of Ag, and the optical information when the amount of Pb and the amount of Ag in the optical recording film of the optical information recording medium of the present invention manufactured in the same manner as in this example were varied. The relationship between CNR of a recording medium and medium life is shown.

In the conventional example, as shown in dotted line 33 (Ag
As Ag is added, the media life improves as shown by the dashed line 34, but the CNR gradually decreases as shown by the dotted line 33, and when the amount of Ag added exceeds 2.2 atomic percent,
The obtained CNR is 45 dB or less, and the performance as an optical information recording medium is insufficient. If the amount of Ag added is less than 2.2 atomic percent, performance as an optical information recording medium can be obtained, but the medium life will be less than 5 years, making it unsuitable for long-term storage of information.

On the other hand, in the optical information recording medium according to the present invention, GeT
Since a portion of Ge in the e-optical recording film is replaced with Pb, even if the amount of Ag added is increased, the decrease in CNR is small, and therefore, the lifetime of the medium can be extended by increasing the amount of Ag added. When Pb-1i1 in the optical recording film is 22 atomic percent, a CNR of 55 dB can be obtained even if the Ag addition amount is 6 atomic percent, and the lifetime is extremely long at 16 years.

〔effect〕

As explained above, in the optical information recording medium according to the present invention, the optical recording film is mainly composed of Ag-doped GeTe, and a part of Ge is replaced with Pb. The amount of Ag added can be increased without deteriorating the CNR of the optical information recording medium, and therefore the life of the optical information recording medium can be extended.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an 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)

[Claims] 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 main component of the optical recording thin film is a Ge-Te-based material doped with Ag, An optical information recording medium characterized in that a part of Ge in the optical recording thin film is replaced with Pb.