JP2903616B2 - Write-once optical recording medium - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a so-called DRAW (Direct Read After Writ) in which a user can record information only once.
e) The present invention relates to a write-once optical recording medium referred to as a type, and more particularly to a write-once optical recording medium for recording information by utilizing a change in reflectance due to alloying.

[Summary of the Invention]

The present invention relates to a write-once optical recording medium in which the SbSe layer and the BiTe layer are alloyed by laser light irradiation, and the information is recorded by changing the conditions of multiple repetitive reflections and changing the substantial reflectance. By adding the third element, the number of times of reproduction is greatly increased.

[Conventional technology]

2. Description of the Related Art Conventionally, write-once optical recording media include those that perform recording by melting or evaporating the recording layer by local heating with a laser beam and change the shape, and that the optical characteristics (eg, reflectance) of the recording layer change. Various systems, such as a system that performs recording by causing the system to perform recording, have been proposed.

However, these conventional write-once optical recording media have advantages and disadvantages in terms of recording power, resolution, stability, and the like.
Japanese Patent Application Laid-Open No. 60-28045 proposed a write-once optical recording medium in which a recording layer is composed of an SbSe layer and a BiTe layer, and information is recorded by alloying these layers.

Briefly describing the configuration and the recording principle of the write-once optical recording medium, this write-once optical recording medium has a recording layer provided on a substrate, and focuses a laser beam whose intensity is modulated in accordance with recording information on the recording layer. Irradiating to record information, wherein the recording layer is a SbSe layer and a BiTe layer sequentially deposited on a substrate.
And a light transmission layer and a reflection layer.

Here, the SbSe layer has a high transmittance for the used laser light, while the BiTe layer shows a high absorption for the used laser light and easily forms an alloy with the SbSe layer.

In addition, the thickness of the SbSe layer is selected so that its reflectance is low with respect to laser light incident from the substrate side by utilizing an interference effect due to multiple repetitive reflection, and the thickness of the light transmission layer is It is selected to reduce the amount of light transmitted through the interface with the BiTe layer.

When a write-once optical recording medium having such a configuration is irradiated with laser light according to information, the laser light is efficiently absorbed by the BiTe layer and converted into heat, and the heat causes the SbeS layer and the BiTe layer to be converted. Alloyed. As a result, the condition of the multiple repetitive reflection by the SbSe layer changes, and the optical characteristics, that is, the reflectivity greatly changes, and information is recorded.

[Problems to be solved by the invention]

By the way, in a write-once optical recording medium, the reliability over a long period of time is a major factor in determining the commercial value, and it is necessary to increase the number of times of stable reproduction without changing the C / N as much as possible.

In a write-once optical recording medium utilizing the change in reflectivity due to alloying described above, for example, when a digital signal is recorded, 10 ⁶
In this case, the number of times of reproduction is higher than that of the conventional write-once optical recording medium.

However, considering the field in which the write-once optical recording medium will be used in the future, the above-mentioned number of times of reproduction is not sufficient. The recordable optical recording medium of Example If video recording (for analog signal recording), about 10 ⁹ times is required.

In order to increase the number of times of reproduction, it is conceivable to take measures on the reproduction apparatus side, such as lowering the laser output at the time of reproduction, but in this case, S / N is sacrificed.

Therefore, it is basically preferable to increase the number of times of reproduction corresponding to the medium side.

Accordingly, the present invention has been proposed in view of such a conventional situation, and provides a write-once optical recording medium which has excellent long-term reliability and can greatly increase the number of times of stable reproduction. The purpose is to do.

[Means for solving the problem]

The present inventors have conducted intensive research over a long period of time to achieve the above object, and as a result, the addition of a third element to the SbSe layer is effective for stabilization, and alloying is hindered and even during long-term regeneration. It has been found that the unrecorded part is kept unrecorded.

The present invention has been completed on the basis of such knowledge, and an SbSe layer and a BiTe layer are formed on a substrate by lamination, and the SbSe layer is at least one selected from Ge, Mn, Cu, Ag, and Zn. One type is characterized by containing 0.1 to 3.0 atomic%.

In the write-once optical recording medium of the present invention, first, SbSe is formed on a substrate.

The substrate is made of a material having a high transmittance with respect to recording and reading laser beams. Therefore, an acrylic resin such as polymethyl methacrylate or a polycarbonate resin is used as the substrate material. Groups (guide grooves), pits and the like may be formed on this substrate.

On the other hand, the SbSe layer is sufficiently transparent to a laser beam to be used and is made of a material that easily alloys with the BiTe layer, and its basic composition is represented by SbSe _x (0.5 <x <2). . Usually, a composition close to Sb ₂ Se ₃ is selected.

Here, in the present invention, in addition to the above basic composition, Sb
At least one of Ge, Mn, Cu, Ag, and Zn is added to the Se layer to stabilize the amorphous SbSe layer.

According to experiments performed by the present inventors, it has been confirmed that the addition of these third elements increases the crystallization temperature of the SbSe layer, suppresses alloying, and leads to an increase in the number of times of reproduction.

At this time, the amount of Ge, Mn, Cu, Ag or Zn added was SbS
It is preferably set to 0.1 to 3.0 atomic% with respect to e _x. If the addition amount is less than 0.1 atomic%, the effect of improving the number of repetitions can hardly be expected. Conversely, if the amount exceeds 3.0 atomic%, stability during reproduction is improved, but a large laser output is required for recording. Therefore, when considering the reduction of the laser output, it becomes difficult to perform sufficient recording,
Inconveniences such as deterioration of C / N occur.

The thickness of the above-described SbSe layer is substantially reduced when laser light is irradiated from the substrate side as a result of interference of repeated multiple reflections occurring between the interface with the substrate and the interface with the BiTe layer, and the BiTe The layer is set so that the recording laser light is efficiently absorbed. In order to increase the absorption efficiency of the recording laser light in the BiTe layer, it is advantageous that the reflectance is as low as possible, but for the stable operation of the laser beam auto-focusing mechanism or auto-tracking mechanism in the recording / reproducing apparatus. It is necessary that the amount of reflected light is large to some extent. In this sense, the reflectance in an unrecorded state is 10 to
It is desirable to set to about 20%.

A BiTe layer is formed adjacently on the SbSe layer. The BiTe layer is made of a metal having a low melting point (Bi, Te in this case) that sufficiently absorbs laser light, and is a metal layer that is alloyed with the SbSe layer to change the optical properties of the SbSe layer. The basic composition of this BiTe layer is represented by BiTe _y (0.1 <y <3),
Usually, a composition close to Bi ₂ Te ₃ is selected. The thickness of the BiTe layer is preferably selected in the range of 100 to 500 °.

In the write-once optical recording medium of the present invention, the aforementioned SbSe
In addition to the layer and the BiTe layer, a light transmitting layer and a reflecting layer may be provided.

The light-transmitting layer is to make a part of the laser light that has also passed through the BiTe layer reflected on the reflective layer described later and return to the BiTe layer again, and is formed of a chalcogenide glass having a low thermal conductivity. The same material as the SbSe layer such as SbSe ₃ is used.

The light transmitting layer is formed on the BiTe layer, and is disposed on the back side of the BiTe layer when viewed from the substrate side. The thickness of the light transmitting layer is set so as to reduce the amount of laser light transmitted through the interface with the BiTe layer, and to increase the efficiency of laser light absorption in the BiTe layer. Therefore, the thickness of the light transmitting layer is selected to be about 1200 to 1500 °.

The reflection layer is provided on the back side of the BiTe layer or the light transmission layer, and is formed of a metal or alloy material such as Al, Sn, Ag, and Au so that the reflectance with respect to a used laser beam is increased. Is done. Alternatively, a high melting point metal such as NiCr, W, Mo, Ti or the like may be used to prevent the BiTe layer from scattering or evaporating to the periphery due to heating by laser beam irradiation. In any case, the thickness of the reflective layer is selected in a range where the amount of laser light leaking to the outside is sufficiently small and can be neglected. It is set to about 200 mm or less, for example, about 60 mm.

The above is the description of the single-sided type optical recording medium. However, it is also possible to form a double-sided type by bonding together those having the same configuration via an adhesive layer.

[Action]

When any one of Ge, Mn, Cu, Ag, and Zn is added to the SbSe layer as a third element, the crystallization temperature becomes higher than in the case of SbSe alone.

This increase in the crystallization temperature leads to stabilization of the SbSe layer in an amorphous state, and suppresses alloying with the BiTe layer.

Therefore, even if the reproduction light is irradiated, the state of the unrecorded portion can be kept good, and the number of reproducible times increases.

〔Example〕

Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.

As shown in FIG. 1, a write-once optical recording medium according to the present embodiment has an SbSe layer (2), a BiTe layer (3), a Sb ₂ S layer on a substrate (1).
e light transmission layer of ₃ (4), the reflective layer made of Al-Ti alloy (5) and the protective layer (6) is made of are sequentially laminated.

The thickness of the SbSe layer (2) is 300 °, the thickness of the BiTe layer (3) is 150
Å, the light transmitting layer (4) is 1300 （, and the reflecting layer (5) is 1000Å. The SbSe layer (2) and the light transmitting layer (4) were formed by RF sputtering, and the BiTe layer (3) and the reflecting layer (5) were formed by DC sputtering.

On the premise of such a configuration, first, Ge or Mn was added to the single film of the SbSe layer (2), and how the crystallization temperature of the SbSe layer (2) changes depending on the addition amount was examined.

The results are shown in FIG. Here, in the measurement by DSC, the peak temperature of the heat generation curve when the heating rate was 3 deg / min was defined as the crystallization temperature Tc.

As a result, it was confirmed that the crystal temperature Tc increased with the addition amount in both cases of adding Ge (line i in the figure) and adding Mn (line ii in the figure). This indicates that the addition of Ge or Mn has stabilized the amorphous phase of the SbSe layer.

Therefore, next, a sample in which 2.0 atomic% of Ge was added to the SbSe layer (2) (the structure is as shown in FIG. 1; the same applies hereinafter), Mn
Was prepared in which 1.1 atomic% was added and a sample in which the third element was not added (corresponding to a comparative example), and the relationship between the crystallization temperature Tc of the SbSe layer and the number of reproducible times was examined for each sample. The output of the laser diode when reproducing a digital signal in a write-once optical recording medium is usually set to about 1.9 mW.
The reproduction output was set to 2.5 mW for the acceleration test. Also,
Each sample was rotated at a linear speed of 13.2 m / sec with respect to the optical pickup.

The results are shown in FIG. The point a in the figure corresponds to the sample to which the third element is not added, the point b corresponds to the sample to which Mn is added at 1.1 atomic%, and the point c corresponds to the sample to which Ge is added at 2.0 atomic%.

As can be seen from FIG. 3, the number of reproducible times increases as the crystallization temperature Tc of the SbSe layer increases. It can be seen that the number of reproducible times is increased by one digit or more.

As described above, the experimental results in the case where Ge and Mn are added have been described. However, the same effect was observed in the case where Cu, Ag, and Zn were added.

〔The invention's effect〕

As is clear from the above description, in the present invention, the third element is added to the SbSe layer of the write-once optical recording medium that records information by using a change in reflectance due to alloying of SbSe and BiTe. Therefore, the crystallization temperature of the SbSe layer can be increased and stabilized, and the unrecorded portion can be kept in an unrecorded state even when the reproduction light is irradiated for a long time.

Therefore, the number of reproducible times and the possible still time can be increased, and a write-once magneto-optical recording medium excellent in long-term reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a main part showing a configuration example of a write-once optical recording medium to which the present invention is applied. FIG. 2 is a characteristic diagram showing the relationship between the amounts of Ge and Mn added and the crystallization temperature of the SbSe layer. FIG. 3 is a characteristic diagram plotting the relationship between the crystallization temperature of the SbSe layer and the number of reproducible times for the sample to which Ge or Mn is added and the sample to which no third element is added. 1 ... substrate 2 ... SbSe layer 3 ... BiTe layer

Claims (1)

(57) [Claims] An SbSe layer and a BiTe layer are laminated on a substrate, wherein the SbSe layer is at least one selected from Ge, Mn, Cu, Ag, and Zn.
A write-once optical recording medium comprising 0.1 to 3.0 atomic% of a seed.