JPH02167790A - Information recording medium - Google Patents

Abstract

PURPOSE:To enhance the stability of a recording mark of an amorphous state of a nonequilibrium phase and perform initializing, recording and erasing at a high speed by forming a recording layer of alloy of composition represented by a specific general formula. CONSTITUTION:A protective layer 3, a recording layer 2, a protective layer 4 and a protective layer 5 are sequentially formed in this order on a substrate 1 in an information recording medium. The recording layer 2 is formed of alloy of composition represented by a general formula (InxSbyTez)100-alphaMalpha (where x, y, z, alpha are atomic %, x+y+z=100, 40<=x<=60, 2<=y<=27, 23<=z<=47, 0<=alpha<=20, and M is at least one type of element selected from a group consisting of Cr, Co, Mn and Mg). The elements are added to improve antioxidative characteris tic, and its reliability is improved. Further, since the material of the above composition is easily made amorphous and its crystallizing velocity is high, initializing, recording and erasing can be performed at a high speed.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) This invention provides information by irradiating a recording layer with a light beam such as a laser beam and inducing a phase change in the irradiated area depending on the irradiation conditions. The present invention relates to an information recording medium that reproduces information by recording and erasing information and detecting changes in optical properties such as reflectance and transmittance accompanying this phase change. Examples of such information recording media include optical discs and optical cards.

(Prior Art and Problems to be Solved by the Invention) Phase change type media have been widely known as information recording media from which information can be erased, such as so-called erasable optical discs. This phase change type information recording medium includes, for example, a substrate made of glass or plastic (polycarbonate resin, polymethyl methacrylate resin, etc.) and a recording layer formed on the substrate. Chalcogenide alloys such as GeTe are known as materials for forming this recording layer, and these alloys can be used for light beams under different conditions (
By irradiating it with a laser beam (for example, a laser beam), the phase changes reversibly between crystal and amorphous, so this phase change is used to record and erase information, and the reflectance associated with these phase changes is Alternatively, information can be read using changes in optical characteristics such as transmittance.

As such a recording layer, a material having a eutectic composition or a material forming an intermetallic compound that easily undergoes a phase change depending on the irradiation conditions of the light beam is suitable.

However, although alloys such as GeTe that have been conventionally used as the recording layer of phase change information recording media satisfy the above conditions, it cannot be said that they still have sufficient properties as information recording media. . In particular, it is desired to speed up initialization, recording, and erasing. Also, crystal-
When recording or erasing information through a phase change between amorphous states, the recorded portion usually becomes amorphous, but since amorphous states generally have relatively low stability, it is necessary to make the amorphous state more stable. It is also required to do so. Furthermore, it is also required to further improve reliability.

This invention was made in view of such circumstances, and
It is an object of the present invention to provide an information recording medium that can speed up initialization, recording, and erasing, has stable recorded information, and has high reliability.

[Structure of the Invention] (Means for Solving the Problems) An information recording medium according to the present invention includes a substrate, a recording layer whose irradiated portion changes phase between an equilibrium phase and a non-equilibrium phase when irradiated with a light beam. An information recording medium having a general formula (1nxSbyTez)too-11M, wherein the recording layer has a general formula (1nxSbyTez)too-11M,
(However, X.

y, z, and a are atomic %, x+y 100, and are within the range of 40≦x≦6012≦y≦27.23≦2≦47.0, α≦20, and M is Cr.

It is characterized by being formed of an alloy having a composition represented by at least one element selected from the group consisting of Co, Mn, and Mg.

(Action) In the In-8b-Te system, In35bTe2, In5b3Te7 and In
An intermetallic compound having a composition of 45bTe3 has the advantage of being easily amorphous, so an alloy with the above-mentioned composition in which M is added to this composition or a composition close to this composition can be used for phase change recording as described above. It is a material that satisfies the conditions for a recording layer of a medium. In addition, by containing the element represented by M in a range lower than 20 at%, In-8b
Since the crystallization temperature of the -Te alloy is raised, the stability of the amorphous state is improved. Furthermore, by adding these elements, oxidation resistance is improved and reliability is improved. Furthermore, since the material having the above-mentioned composition not only easily becomes amorphous but also has a high crystallization speed, it is possible to achieve high-speed initialization, recording, and erasing.

(Example) Hereinafter, the present invention will be specifically described with reference to the accompanying drawings. FIG. 1 is a sectional view showing an information recording medium according to an embodiment of the invention. The substrate 1 is made of plastic such as polyolefin, epoxy, polycarbonate (PC), polymethyl methacrylate (PMMA), or glass.
It is made of materials commonly used in this technical field.

On this substrate 1, a protective layer 3, a recording layer 2, a protective layer 4, and a protective layer 5 are formed in this order.

The protective layer 3 and the protective layer 4 are disposed to sandwich the recording layer 2 and are made of an organic polymer material, such as a thermoplastic resin such as PMMA or polystyrene, or an ultraviolet curing resin (so-called 2
P resin), or S f02, A1203, AIN,
It is formed of a dielectric material such as ZnS or ZrO2. These protective layers 3 and 4 serve to prevent the recording layer 2 from being affected by moisture in the air, and to prevent the irradiated portion of the recording layer 2 from being scattered by a light beam such as a laser beam during recording or erasing. It has the effect of preventing the formation of holes. These protective layers 3 and 4 can be suitably formed by a spin coating method, a vapor deposition method, a sputtering method, or the like. Note that the thickness of these protective layers 3.4 is preferably 10 μm to several tens of μm.

The protective layer 5 is provided to prevent scratches, dust, etc. on the surface when handling the information recording medium, and is coated with an ultraviolet curing resin using a spin code method or the like, and then cured by irradiating it with ultraviolet light. It is formed by such things as This protective layer 5
The layer thickness is preferably 100 μm to several tens of μm.

Although it is preferable to provide the protective layers 3.4 and 5, they do not necessarily have to be provided.

The recording layer 2 is (InxSbyTez)too-gM*(
However, X+ y, zr α is atomic %, x y + z-
100, respectively 40≦x≦60.2≦y≦27.2
3≦2≦47.0 and α≦20, M is Cr
, Co, Mn, and Mg), and can be suitably formed by a vapor deposition method, a sputtering method, or the like. Note that when performing vapor deposition or sputtering using an alloy target, it is necessary to take into account that there is a difference between the target composition and the composition of the film actually formed. Further, the film can also be formed by multi-source simultaneous vapor deposition, multi-source simultaneous sputtering, or the like. The thickness of the recording layer 2 is preferably 100 to 3000λ.

(InxSbyTez) Zoo-a Mm constituting the recording layer 2 can be divided into an equilibrium phase and a non-equilibrium phase (
In, Sb, and Te are intermetallic compounds that can easily become amorphous.

Since the composition is close to In[sb, Te7 and In45bTe3, the stability of the amorphous state as a non-equilibrium phase is excellent. Further, since the crystallization speed is high and the crystallization is easily made amorphous, the initialization, recording and erasing speeds are high.

Furthermore, Cr, Co, Mn.

Or, due to the presence of Mg, oxidation resistance is high.

Next, an example of a method for forming the recording layer of the information recording medium according to this embodiment will be explained with reference to FIGS. 2 and 3. FIG. 2 is a longitudinal cross-sectional view showing a schematic configuration of a sputtering apparatus used to form the recording layer of this embodiment, and FIG. 3 is a cross-sectional view thereof. In the figure, numeral 10 indicates a vacuum container, and this vacuum container 10 has a gas introduction boat 1 on its bottom surface.
1 and a gas discharge boat 12. The gas exhaust boat 12 is connected to an exhaust device 13, and the inside of the vacuum container 10 is evacuated by the exhaust device 13 via the exhaust boat 12. Further, the gas introduction boat 11 is connected to an argon gas cylinder 14, and argon gas as a sputtering gas is introduced from the cylinder 14 into the vacuum container 10 through the gas introduction port 11. Vacuum container 10
A disk-shaped rotating base 15 for supporting the substrate is arranged with its surface horizontally at the upper part of the inside, and the substrate 1 is supported on the lower surface thereof and is rotated by a motor (not shown). ing. In addition, near the bottom of the vacuum chamber 10, sputtering rings [21, 22, 23 each made of a predetermined element constituting the recording layer are disposed so as to face the base 15, and each sputtering source is A high frequency power source (not shown) is connected to. These sputtering sources 21
The information of ゜22.23, respectively, includes the monitor devices 24゜25.
26, these monitoring devices monitor the amount of sputtering from each sputtering source, and adjust the amount of power input to each sputtering source so that the recording layer has a predetermined composition.

In such a sputtering apparatus, first, the inside of the vacuum container 10 is evacuated to, for example, 10-6 Torr using an exhaust device. Next, while introducing argon gas into the container 10 via the gas introduction boat 11, the exhaust amount of the exhaust device 13 is adjusted to maintain the inside of the vacuum container 10 in an argon gas atmosphere at a predetermined pressure. In this state, while rotating the substrate 1, a predetermined power is applied to the sputtering sources 21, 22, and 23 for a predetermined time. As a result, a recording layer having a predetermined composition is formed on the substrate 1. In addition, when forming a protective layer,
Prior to the formation of the recording layer 2, the protective layer 3 is formed on the substrate 1 by sputtering as described above using a sputtering source adjusted to the composition of the protective layer, and then the recording layer 2 is formed, and then the protective layer 3 is formed on the substrate 1. The protective layer 4 can be formed on the recording layer 2 under the same conditions as when forming the layer 3.

Next, initialization, recording, erasing, and reproduction of information in the information recording medium of the present invention will be explained.

The initialization recording layer 2 is normally amorphous immediately after film formation, but it needs to be crystalline in order to record information, so the recording layer 2 is heated and slowed by irradiating the entire surface of the recording layer 2 with a light beam such as a laser beam. Cool and crystallize the recording layer 2.

A light beam with high recording power and short pulse width is irradiated onto the recording layer 2,
The irradiated area is heated and rapidly cooled to change its phase to an amorphous state, thereby forming a recording mark.

A light beam having a lower output and a longer pulse width than that used during recording is irradiated onto the recording mark portion formed on the erasing recording layer 2 to change the phase of the recording mark portion into a crystal, thereby erasing information.

A relatively weak light beam is irradiated onto the recording layer 2 on which reproduced information has been recorded, and the information is read by detecting the difference in optical characteristics, such as reflectance, between the recorded mark portion and the non-recorded portion.

In addition, since the information recording medium according to the present invention has a high crystallization speed, overriding is possible. Overriding is erasing by power modulating a light beam such as a laser beam emitted from a single light source between two power levels PE (erasing) and Pw (recording) as shown in Figure 4. This involves superimposing a pulse at a recording power level on a light beam at a high power level, and overwriting new information while erasing already recorded information.

Next, test examples of the present invention will be explained.

Test Example 1 I n x S b of various compositions were deposited onto a heat-resistant glass substrate using the sputtering apparatus shown in FIGS. 2 and 3.
yTez alloy thin films were formed, and the structures of these thin films were confirmed by X-ray diffraction. The range indicated by diagonal lines in the ternary composition diagram in Figure 5, that is, 40≦x≦6012≦y≦
As a result of confirmation in the composition range of 27.23≦2≦47, all of them were amorphous immediately after film formation. In this composition range, In3SbTe is an intermetallic compound that easily becomes amorphous.
2゜In匍5b3Te7 and In4SbTe3 are known, but as mentioned above, these intermetallic compounds can be in an amorphous state even in nearby compositions, and recording can be achieved by selecting the laser beam irradiation conditions.・It was confirmed that it can be used as a phase change type recording layer for erasing.

Test Example 2 In x S by T e in the composition range of Test Example 1
Samples were prepared in which each of Cr, Co, Mn, and Mg was added to z. As a result, all samples showed an increase in crystallization temperature.

Among these additive elements, Cr, Co, and Mn are all materials with high melting points, with Cr at 1863°C and Co at 1
494°C, Mn is 1246°C.

It is known that the crystallization temperature is usually 1/2 to 2/3 of the absolute melting point of an amorphous alloy, so the addition of these elements increases the melting point of the alloy. It is considered that the crystallization temperature increased accordingly.

Furthermore, although Mg has a low melting point of 649°C, it is an active element, so it easily forms bonds with In, Sb, and Te.
It is considered that the addition of g increased the crystallization temperature.

Therefore, Cr, Co, Mn, and Mg are I n x S
It was confirmed that there is an effect of stabilizing the amorphous state of b y T e t.

Test Example 3 The sample prepared in Test Example 2 was irradiated with a laser beam from the substrate side while changing the irradiation conditions, and the crystallization rate was examined. Figure 6 shows 5% Cr, 10%, 20%, and 30% Cr, respectively.
The results for the added samples are shown below. FIG. 6 is a graph showing the relationship between these, with the horizontal axis representing the pulse width of the irradiated laser beam and the vertical axis representing the amount of change in reflectance.

In this graph, changes in reflectance correspond to phase changes between amorphous and crystalline. Note that FIG. 6 shows a case where the power of the irradiated laser beam is 7 mW. As shown in FIG. 6, compared to the case where no Cr was added, the crystallization rate increased at 5% Cr, and decreased at 10% and 20%.

Furthermore, with 30% Cr, the crystallization speed was 1 μm sec or more, and the amount of change in reflectance was also significantly reduced. This is Cr
This is thought to be due to the addition of , which increases the melting point and the energy required for phase change.

Considering practicality, it is desirable that the crystallization rate is 1 μm sec or less, and therefore the amount of Cr added is suitably 20 at % or less.

Similar tests were conducted on samples formed into alloys in which Co, Mn, and Mg were added in place of Cr, and similar results were obtained, indicating that it is appropriate for the amount of addition of these to be 20% or less in practice. It was confirmed that there is.

Moreover, the same effect can be obtained even if some of these elements are added in combination. In this case as well, if the total amount added exceeds 20%, the recording sensitivity will decrease, and for practical purposes, 20% or less is appropriate.

Test example 4 Among the samples prepared in Test Example 2, Cr.

Co, Mn, and Mg added at 5 atomic % each;
Samples without these elements added at 75°C.

The sample was maintained under the condition of 80% RH, and the change in surface oxidation rate over time was measured. Figure 7 shows the results. FIG. 7 is a graph showing changes in reflectance over time for each sample. As shown in FIG. 7, I
It can be seen that the n x S by T e z alloy shows a gradual decrease in reflectance over time. On the other hand, Cr, Co, and Mn, respectively.

Although the sample to which 5 atomic % of Mg was added had a slight decrease in reflectance immediately after the start of the test, the reflectance hardly changed until 1000 hours passed thereafter. This is I
This shows that by adding these elements such as Cr to the nxSbyTez alloy, the oxidation resistance was improved and the reliability of the recording layer was improved.

From the above results, it is possible to use (InxSbyTez)too-a Mz gold alloy phase change type recording layer in the above range, and that such a recording layer changes to an amorphous state with the addition of M element. It was confirmed that the stability of the compound increased, the crystallization rate was as high as 1 μm sec or less, and the oxidation resistance was improved due to the presence of the M element.

In this embodiment, a flat plate-shaped substrate is used as the substrate, but the substrate is not limited to this, and various forms such as a tape-shaped or a drum-shaped substrate can be used.

[Effects of the Invention] According to the present invention, the recording layer is made of the amorphous intermetallic compound 1 n35bTe2 Iny) S b 3 Te 7 and In4Sb.
Based on the composition of Te3 and its vicinity, with the addition of M element that improves the crystallization temperature, it has excellent stability of recording marks in the amorphous state, which is a non-equilibrium phase, and is also effective at first light, recording, and erasing. can be carried out at high speed. Furthermore, the addition of the M element improves the oxidation resistance of the recording layer, making it possible to significantly increase reliability.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an information recording medium according to an embodiment of the present invention, and FIG. 2 is a schematic diagram of an apparatus for forming a recording layer.
3 is a cross-sectional view thereof, FIG. 4 is a diagram showing the power of the laser beam during override, and FIG. 5 is the basic recording layer of the information recording medium according to the present invention. Composition diagram showing the composition range of In-8b-Te ternary alloy,
FIG. 6 is a graph showing the relationship between the pulse width of the irradiated laser beam and the amount of change in reflectance, and FIG. 7 is a graph showing the change in reflectance over time during an environmental test of a sample according to a test example of the present invention. It is a diagram. 1; Substrate, 2; Recording layer, 3, 4, 5. protective layer. Applicant's agent Takehiko Suzue, patent attorney

Claims (1)

[Claims] An information recording medium comprising a substrate and a recording layer whose irradiated portion changes phase between an equilibrium phase and a non-equilibrium phase by irradiation with a light beam, the recording layer having the general formula (In_xSb_y
Te_z)_1_0_0_−_αM_α(However, x,
y, z, α are atomic %, x+y+z=100, respectively 40≦x≦60, 2≦y≦27, 23≦z≦47, 0<
α≦20, and M is at least one element selected from the group consisting of Cr, Co, Mn, and Mg. information recording medium.