JPH09248965A - Phase change type photo-recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lesson the leftover from erasion by overlighting and improve the erasing percentage of the signal by a method wherein the activation energy for changing a recording layer from an amorphous phase to a crystal phase is set to be not more than a specified value. SOLUTION: On a board made of glass, polycarbonate or the like, a dielectric layer consisting of either one of ZnS, SiO2 , AlN, Ta2 O5 or the like or their mixture as a first protective layer 2. Or the first protective layer 2, a recording layer 3 made of a thin Ge-Sb-Te film, a thin In-Sb-Te film or the like is formed. Further, on the recording layer 3, a dielectric layer consisting of either one of ZnS, SiO2 , AlN, Ta2 O5 or the like or their mixture as a second protective layer 4. Further, the activation energy for changing a recording layer 3 from amorphous phase to crystal phase is set to be not more than 3.5eV. Thus, the leftover of signal from erasion by direct overlighting become smaller, resulting in improving the erasing percentage of the signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical information recording medium in which a phase change is caused in a recording layer by a laser beam or the like to record, reproduce and erase information. Regarding

[0002]

2. Description of the Related Art A phase change type optical recording medium is a kind of rewritable optical recording medium and records information by reversible phase change (mostly between crystal and amorphous) of a recording layer. Optical modulation overwriting is possible with a single-layer recording film by a single head, and a signal is read by a change in reflectance due to a phase change, so high compatibility with existing optical recording media such as a CD-ROM is high. Since it has features such as
As a rewritable optical recording medium, research and development have been actively conducted in recent years.

Generally, a phase change type optical recording medium performs recording by forming recording marks of an amorphous phase by a laser beam on the crystalline phase (erased state) of a recording layer, and the reflectance between the crystalline phase and the amorphous phase. A reproduced signal is obtained by sensing the difference between the two. Moreover, by modulating the intensity of the laser beam during signal recording between the intensity of amorphization (peak power) and the intensity of crystallization (bias power) (see FIG. 1), a single beam, a single layer Optical modulation overwrite (direct overwrite) is possible by combining recording films, and a recording medium having a large capacity and a high transfer rate can be obtained.

[0004]

In the phase change type optical recording medium, direct overwriting is possible as described above, but the second signal is newly overwritten on the already recorded first signal. In this case, the first signal does not completely disappear due to overwriting, and so-called unerased residue occurs (that is, the erasing rate is not sufficiently high), and the recording / recording of the signal
There was a problem of poor reliability in reproduction.

It is an object of the present invention to provide a phase change type optical recording medium in which the unerased residue after overwriting is reduced and the erasing rate is improved.

[0006]

The inventors of the present invention have made earnest studies in view of the above-mentioned situation, and as a result, the activation energy when the recording layer undergoes a phase change from an amorphous phase to a crystalline phase is 3.5 eV or less. It was found that by doing so, the unerased residue after overwriting was reduced and the erasing rate was improved, and the present invention was completed.

That is, the phase change type optical recording medium of the present invention is a phase change type optical recording medium for recording information by utilizing reversible phase change between the crystalline phase and the amorphous phase of the recording layer. The activation energy when the recording layer undergoes a phase change from an amorphous phase to a crystalline phase is 3.5 eV or less.

A phase change type optical recording medium to which the present invention is applied records and erases information by utilizing reversible phase change between a crystalline phase and an amorphous phase of a recording layer,
The recorded information is reproduced by detecting the difference in reflectance between the crystalline phase and the amorphous phase. Structurally, it is sufficient if a multilayer film including a recording layer is formed on a transparent substrate. For example, those having a laminated structure in which a first protective layer / a recording layer / a second protective layer are laminated in this order on a transparent substrate are exemplified.

FIG. 2 is a partial sectional view showing the structure of an embodiment of a phase change type optical recording medium to which the present invention is applied. Substrate 1
Is not particularly limited as long as it is sufficiently transparent in the wavelength range of the laser used and satisfies the properties as a medium substrate such as mechanical properties, and glass, polycarbonate, amorphous polyolefin, etc. can be used. As the first protective layer 2 on the substrate 1, for example, Zn
A dielectric film made of any one of S, SiO ₂ , AlN, Ta ₂ O _{5 and the} like or a mixture thereof is formed. On the first protective layer, for example, a Ge-Sb-Te-based thin film, I
The recording layer 3 made of an n-Sb-Te based thin film or the like is formed.
Further, as a second protective layer 4 on the recording layer, for example, Z
A dielectric film made of any one of nS, SiO ₂ , AlN, Ta ₂ O _{5 and the} like or a mixture thereof is formed. These first protective layer and the second protective layer, in addition to the role of protecting the recording layer, to increase the light absorption efficiency to the recording layer, and also to increase the amount of change in reflected light before and after recording, These thicknesses are designed to be optimum in consideration of the laser wavelength to be used and the film thickness of the recording layer.

If necessary, the upper surface of the recording layer and / or
Alternatively, an interface layer made of a metal, an inorganic substance, or a mixture thereof may be formed on the lower surface.

Further, a metal reflective film made of aluminum or the like may be laminated as a reflective layer on the second protective layer.

The first protective layer, the second protective layer, the recording layer, the interface layer, the reflective layer and the like can be formed by a usual vacuum film forming technique such as a DC sputtering method, an RF sputtering method and a vacuum evaporation method. .

Furthermore, after forming these layers by a vacuum film forming technique, a protective coat layer made of synthetic resin or the like may be further formed thereon, if necessary.

The activation energy when the recording layer undergoes a phase change from an amorphous phase to a crystalline phase can be changed by changing the material of the recording layer, the film forming conditions, the material of the layer in contact with the recording layer, and the like.

[0015]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples.

(Examples and Comparative Examples) A phase change type optical disk having a structure as shown in FIG. 3 was manufactured as follows. A first protective layer 12 (film thickness: 100 nm) made of ZnS-20 mol% SiO ₂ was formed on a polycarbonate disk-shaped substrate 11 by RF sputtering of a ZnS-20 mol% SiO ₂ target. Further, as the first interface layer 13, a mixed film of SiO ₂ and Ta (film thickness: 5 n
m) Simultaneous RF of SiO ₂ target and Ta target
The film was formed by the sputtering method. On top of this, Ge ₁ Sb ₂ T
The recording layer 14 (film thickness: 25 nm) made of e ₄ was formed into Ge ₁ S
The film was formed by DC sputtering of a b ₂ Te ₄ alloy target. On this, a mixed film of SiO ₂ and Ta (film thickness: 5 nm) was formed as the second interface layer 15 by the simultaneous RF sputtering method of the SiO ₂ target and the Ta target.
Further, a second protective layer 16 made of ZnS-20 mol% SiO ₂
(Film thickness: 20 nm) was formed by RF sputtering of a ZnS-20 mol% SiO ₂ target. Thereafter, an Al-1.5 wt% Cr alloy film (film thickness: 200 n
m) was formed by DC sputtering of an Al-1.5 wt% Cr alloy target.

With the above structure, when the first interface layer and the second interface layer are formed, the input powers of the targets of SiO ₂ and Ta are changed to change the SiO ₂ and Ta of the first interface layer and the second interface layer. Sample disks with various mixing ratios were prepared. However, the first interface layer and the second interface layer had the same mixing ratio.

In each of the above sample disks, a film was formed on a glass substrate under the same conditions to obtain a sample for measuring crystallization temperature. The crystallization temperature (Tx) of the recording layer of the obtained glass substrate sample was measured using a differential scanning calorimeter (DSC) under various heating rates (α). Using this measurement result, the following Kissinger equation (Journal of Non-Crystalline Solid 38 & 39
(1980, p.741), the activation energy (Ea) during crystallization was calculated.

Ln (α / (Tx) ² ) =-Ea / (β ·
Tx) + Const. Here, α is the temperature rising rate, β is the Boltzmann constant, Tx is the crystallization temperature, and Ea is the activation energy.

The sample disk produced as described above was set in a recording / reproducing apparatus, and the linear velocity was 10.1 m / s.
While rotating at ec, the recording layer was crystallized by irradiation with a laser beam having a wavelength of 680 nm at an intensity of 6 mW.
Next, using the same apparatus on the track in the area where the recording layer was crystallized, the linear velocity was set to 3.59 M at a linear velocity of 10.1 m / sec.
Hz modulated signal (pulse width = 35 ns) is recorded, and a 9.57 MHz modulated signal (pulse width = 35 ns) is recorded thereon.
Was overwritten. At the time of this recording, a laser modulation pattern with an off pulse added as shown in FIG. 4 was used, the peak power (Pp) was 12.0 mW, the reproduction power (Pr) was 1.0 mW, and the off pulse power (Poff)
Was set to 1.0 mW. The width of the off pulse is 25 ns.
And

When the above overwrite recording is performed, the carrier level of the 9.57 MHz signal and 3.59 MH after the 9.57 MHz signal is overwritten.
The difference in carrier level (unerased portion) of the z signal was defined as the erase rate (OW erase rate), and the bias power (Pb) dependence of this erase rate was measured. The measurement results of the sample disk in which the interface layer is only SiO ₂ are shown in FIG. From such measurement, the maximum value of the OW erasing rate of each sample disk was obtained.

FIG. 6 shows the relationship between the activation energy measured as described above and the maximum value of the OW erasing rate. From this graph, if the activation energy is 3.5 eV or less, OW
It can be seen that the erasing rate is 20 dB or more, which is a practical range.

[0023]

According to the phase change type optical recording medium of the present invention,
By setting the activation energy when the recording layer undergoes the phase change from the amorphous phase to the crystalline phase to 3.5 eV or less,
A high erasing rate can be obtained because the amount of unerased signal due to direct overwrite is reduced. This makes it possible to obtain a more reliable phase change type optical recording medium.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between laser powers of a recording / reproducing apparatus.

FIG. 2 is a partial cross-sectional view showing an example of the structure of a phase-change optical recording medium to which the present invention can be applied.

FIG. 3 is a partial cross-sectional view showing a structure of a phase change type optical recording medium of Examples and Comparative Examples of the present invention.

FIG. 4 is a diagram showing a relationship between laser powers used for measurement in Examples and Comparative Examples.

FIG. 5 is a diagram showing the relationship between the OW erasing rate and the bias power of a sample disk in which the interface layer of the example is SiO ₂ .

FIG. 6 is a diagram showing the relationship between the activation energy and the maximum value of the OW erasing rate of the sample disks of Examples and Comparative Examples.

[Explanation of symbols]

 1: Substrate 2: First protective layer 3: Recording layer 4: Second protective layer 11: Substrate 12: First protective layer 13: First interface layer 14: Recording layer 15: Second interface layer 16: Second protective layer 17: reflective layer

Claims (1)

[Claims] 1. A phase-change optical recording medium for recording information by utilizing reversible phase change between a crystalline phase and an amorphous phase of a recording layer, wherein the recording layer changes from an amorphous phase to a crystalline phase. The activation energy when changing is 3.5e
A phase change type optical recording medium characterized by being V or less.