JPH01112538A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To raise crystallization temp., to increase crystallization speed and to improve recording sensitivity by using a mixed crystal system consisting of three kinds of compds. and AgSbTe2 as an active material whose optical constant varies. CONSTITUTION:A heat resistant protective layer 2, a recording layer 3, a heat resistant protective layer 4, an adhesive layer 5 and a protective substrate 6 are successively formed on a substrate 1 to obtain a medium. Laser light is projected on the medium from the substrate 1 side to carry out recording, reproduction and erasure. In the recording layer 3, a Te-Sb-Ag-Ge alloy is used as an active material whose optical constant varies. The compsn. of the alloy is within a region defined by a point A(Ge7Sb6Te16), B(AgGe7Sb7Te18), C(AgGe3Sb15Te27) and D(Ge3Sb14Te24) in the GeTe-Ag2Te-Sb2Te3 pseudo-ternary constitutional diagram.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to optical information recording media, and in particular to improvements in optically active materials thereof.

2. Description of the Related Art Techniques for recording and reproducing high-density information using laser beams are well known, and are currently being applied to document file systems, still image file systems, and the like. Research and development is also being conducted on rewritable information recording systems, and examples have been reported. The active layer that controls the recording of optical discs mainly contains chalcogens such as Te,
Or its compound (chalcogenide) is the main component. In these substances, an amorphous phase can be obtained relatively easily by heating and cooling, and optical constants change between the crystalline phase and the amorphous phase.

Information is reproduced by detecting this phenomenon.

The amorphous phase can be obtained, for example, by irradiating an intense and short pulsed laser beam, heating the irradiated part to a liquid phase, and then rapidly cooling it. On the other hand, the crystalline phase can be obtained by heating and slowly cooling the amorphous phase by, for example, irradiating it with weak and long pulsed laser light. Changes in optical constants are mainly observed as changes in reflectance.

In the case of a rewritable optical disc device, the amorphous phase corresponds to a recorded signal, and the crystalline phase corresponds to an erased state. In other words, the pattern in which information is recorded is a state in which amorphous islands are floating in a sea of crystals. In this case, compared to the reverse case, it is possible to deal with rapid cooling conditions when recording, which requires high-speed switching.
It's advantageous.

Elemental Te is stable as a crystal at room temperature and does not exist in an amorphous state. Therefore, in order to stably exist the amorphous phase at room temperature, the addition of various elements is being considered, and Ge is widely known as one of the typical additives.

Ge, which has a strong covalent bond and a coordination number of 4, penetrates into the chain-like chain of atoms (coordination number 2) formed by covalent bonds of Te up to a certain concentration (approximately 30 atomic %) and forms a three-dimensional structure. It stabilizes the network structure of glass, so adding an appropriate amount makes the amorphous structure stable even at room temperature.

That is, as Ge is added, the transformation temperature (Tx) between an amorphous state and a crystal shifts toward a higher temperature side. However, although the Tx increases with the addition of Ge, the time required for crystallization (hereinafter referred to as crystallization time) is still too long and insufficient for practical use in an actual optical disk device. Practically speaking, the crystallization time (erasing time) needs to be several microseconds or less.

When the Ge concentration is further increased, the ionic bond becomes stronger (Ge
In Te, the crystal has a structure close to a face-centered cubic structure (rock salt type). With this composition, the crystallization temperature is sufficiently high and the crystallization rate is also sufficiently fast. However, since the melting point of this composition is too high, the laser power required for recording signals (making the recording film amorphous) is too large, and it cannot be considered a practical recording thin film material.

Note that optical recording materials (hereinafter referred to as recording films) based on Te-Ge as a conventional example include, for example, GeT
e5bS etc. (Japanese Patent Publication No. 47-26897).

However, when small amounts of sb and S are added, although they may stabilize the amorphous state due to the nature of the elements, they have little effect on promoting crystallization. (Erase) takes a long time (, also,
Since the contrast ratio of the recorded pattern was also insufficient, it was not practically satisfactory.

On the other hand, the present inventors have developed a T e-G e-Au based alloy (
(Japanese Unexamined Patent Publication No. 61-219692) or T e
-G e -S n -A u-based alloy (JP-A-61-
270190) etc., it was discovered that the aforementioned insufficient characteristics of the Te-Ge binary system were improved when specific amounts of Au and Sn were added. These Au and Sn are thought to play a role in promoting crystallization by partially destroying the strong covalent bond structure, and the crystallization time is shortened to several microseconds or less.

However, considering future high signal transfer rates, it will be necessary to further shorten the crystallization time.

In addition, as a recording thin film material with a high crystallization rate, 5b
Te is known. Although this crystallization speed is faster than that of GeTe, the crystallization temperature is not high enough, so there is a problem in the thermal stability of the recorded signal.

Problems to be Solved by the Invention As mentioned above, Ge're has a high crystallization temperature Tx and a fast crystallization speed, but has low recording sensitivity.

Further, although 5bTe has a high crystallization rate, it has a problem of a low crystallization temperature.

The present invention has been made in view of these points, and it is an object of the present invention to provide a recording thin film that satisfies the crystallization speed, crystallization temperature, and recording sensitivity at the same time.

Means for solving the problem In optical information recording and reproducing media that record, reproduce, and erase information by causing changes in optical constants using means such as light or heat, change in optical constants is used. An alloy consisting of tellurium, antimony, silver and germanium was used as the active material exhibiting
Point A (Ge7SbeTexe) in Figure 1, which is the pseudo-ternary phase diagram of Ag2Te -3b 2 Te s
, 8 points (AgGe7sb7Texs), C point (AgGe
3Sb 115 T e 27 ) and point D (G e
3S b 14 Te24).

Effects According to the present invention, a recording thin film material having a high crystallization temperature (high crystallization rate) and good recording sensitivity can be obtained.

Example As mentioned above (in a rewritable optical disc,
In order to achieve high performance by recording and erasing data at high speed, it is necessary to shorten crystallization, that is, erasing time, which takes more time than recording.

In order to shorten the crystallization time, it is necessary to create an amorphous structure consisting of a network consisting mainly of covalent bonds, which are anisotropic bonds in terms of material, and to create a structure with a considerable portion of isotropic ionic bonds and metallic bonds. As a result of considering the need to form an amorphous network with mixed properties, we decided to use a quaternary alloy system consisting of TTe-8b-Ge-A, or from a different perspective, GeTeGeT.
It was found that the e-8bzTe3-A pseudo-ternary alloy has this possibility.

Figure 2 shows the phase diagram of the Sb2Te3Ag2Te pseudo-binary system. As a ternary compound, A g S b Te 2 (rock salt type crystal structure, melting point is about 570°C) is generally known, but in this phase diagram, from AgSbTe2 to S b
This shows that a solid solution phase (beta phase) exists in the 2 T e 3 bond. (Reference: Rose Marie Monk Marin et al., Journal of Materials Science (J
, Mater, Sci, ) vol, 20(19
83) 730. ).

FIG. 3 shows the phase diagram of the 5b2Tes-GeTeJ element system. This system contains three types of hexagonal compounds (A
:Ge2Sb2Tes5B:GeS b 2 T e
4, and C: GeSb4Te7. Melting point is approximately 600℃
before and after) are known. [References: Mr. Agayev et al., Soviet Physics Gristarographia (Sov
iet Phys, Crystal, ), 11
(1966) 400. , and Petrov et al., Soviet Physics Gristarographia (S.

Viet Phys, Crystal, ), 1
3 (1968) 339. ] The present inventors added AgSbTe2 to the above three ternary compounds (A, B and C).
It was found that the crystallization rate is high in the case of a composition in which . The inventors have previously
It has already been found that the crystallization rate is fast in the seed compound composition and the A g S b T e 2 composition (Japanese Patent Application No. 184530/1982), but this time we newly found that the three compound compositions and the A g S b T e
Even in the mixed crystal system with two compositions, the crystallization rate was faster (and the repeatability of recording and erasing was improved compared to when no mixed crystal system was formed. Moreover, in all of these compositions, the crystallization rate was faster). thick (and the crystallization temperature is also A g S b T
It has been found that by adding e2, there is almost no change and the recording sensitivity is also good.

The recording layer can be formed by a method such as vacuum evaporation or sputtering, but in the following examples, a vacuum evaporation method is used.
It was formed on a transparent substrate. The recording film after formation is amorphous. The structure of the recording medium is shown in FIG. 1 is the board,
2 is a heat-resistant protective layer made of an inorganic substance for protecting the substrate from heat, 3 is a recording layer, 4 is a heat-resistant protective layer similar to 2, and the protective substrate 6 is bonded with the adhesive 5.

Laser light for recording, reproducing, and erasing is input from the substrate side of 1.

The material used for the substrate was glass, quartz, polycarbonate, or polymethyl methacrylate (PMMA).

The thickness of the recording film is approximately 1100 nm, and both sides are protected by heat-resistant protective layers. Zinc sulfide (ZnS) was used as the material for the heat-resistant protective layer. The thickness of the heat-resistant protective layer was determined to be optimal in terms of optical and thermal design.

Specifically, the substrate side is 1100n, and the recording film is 200n.
nm was provided.

The characteristics of the obtained recording layer were investigated by various means.

Among these, what is required in the present invention is the crystallization temperature (Tx), which is a measure of thermal stability, the power and pulse width of the laser light that starts crystallization, and the power and pulse width of the laser light that starts amorphization. be. First, regarding the crystallization temperature, a constant temperature increase rate (1℃/s e
Place the sample prepared on the glass substrate on the stage whose temperature is being raised in step c), measure the transmittance or reflectance while irradiating it with a low-intensity laser beam, and determine the temperature at which the transmittance or reflectance starts to change. It was determined by measuring.

Crystallization time was measured by static and dynamic methods. In static measurements, a heat-resistant protective layer is provided on PMMA and a simulated sample having the same structure as an optical disk is measured with the medium and laser beam stationary. After irradiating a laser pulse with a specific intensity, the presence or absence of a change in reflectance is measured, and the pulse width at which the change starts is determined, and this is used as the crystallization threshold. Moreover, the threshold value of amorphization was similarly measured by irradiating the crystallized sample with a laser again.

For dynamic measurements, we actually created optical discs and measured their recording, playback, and erasing characteristics. The substrate of the optical disc was made of polycarbonate.

Next, the present invention will be explained in detail with reference to more detailed examples.

Example 1 Stoichiometric compounds S b A g T e 2 and GeS
A recording thin film having a mixed crystal composition of b2T e 4' was prepared by vacuum evaporation, and its recording characteristics, erasing characteristics, and crystallization temperature were measured. The thickness of the recording film is 1100n, and the heat-resistant protective layer is Zn.
S was used.

Figure 5 shows an example of crystallization characteristics measured statically.
The results of a recording film having a composition of (GeSb2Te4)90 (SbAgTe2)10 are shown. As shown in the figure, as the irradiation power is increased from 2 mW to 10 mW, the crystallization start pulse width shifts to the shorter pulse side. In this example, crystallization starts in 30 ns with a power of 10 mW. A threshold has been obtained.

The amorphization characteristics are as follows: -1 power 4 mW, pulse width 2
After sufficient crystallization by irradiation with a single microsecond pulse,
Measurements were made by irradiating the same position with a laser beam stronger than that power. As shown in FIG. 6, when the power is 15 mW or more and the pulse width is 100 ns or more, a change in reflectance occurs, which indicates that amorphization is realized.

(GeSb2Te4)Lx・(Ag
SbTe2)
The gSbTe2 concentration (X) dependence is shown in Figure 7 (b) and (c).
) are shown respectively. Here, the crystallization threshold is when the laser power is 10 mW, and the amorphization threshold is when the laser power is 18 mW. Note that FIG. 7(a) shows the composition dependence of the crystallization temperature. What can be seen from Figure 7 is described below.

(1) Even if the amount of A g S b T e 2 added increases, the crystallization temperature hardly changes.

(2) The threshold for starting crystallization is G e
It is almost the same as that of S b 2 T e 4. That is, G e S b 2 in the entire area
It shows high-speed crystallinity equivalent to T e 4.

(3) The threshold for starting amorphization is Ag5bT e
Even if 2 increases, there is almost no change.

From the above, (GeSb2Te4)1-x・(Ag
It can be seen that in the region of SbTe2)x (0,1≦a≦0.6), high crystallization temperature, high crystallization speed, and good recording sensitivity are simultaneously satisfied.

According to this example, the stoichiometric compound G e
S b 2 T e 4 and A g S b T e 2
It was shown that excellent properties as an optical recording thin film can be obtained on the line connecting the .

Example 2 Stoichiometric compound G e 2 S b 2 T e [
5 and Ge S b 4 T e 7 and AgSbTe
A recording thin film having a mixed crystal composition with No. 2 was prepared by vacuum evaporation, and its recording characteristics, erasing characteristics, and crystallization temperature were measured. The thickness of the recording film is 1100n, and the heat-resistant image: l! ZnS was used for the layer.

Figure 8 shows statically measured (Ge2Sb2Tes)I
-X” (AgSbTe2)x (0≦X≦0゜5) composition, and (GeSb4Te7)I-X・(A g S
b T e 2 ) AgS of (b) the threshold of crystallization initiation and (C) the threshold of amorphization initiation of x
bTe2a degree (X) dependence is shown. Here, the crystallization threshold is when the laser power is 10 mW, and the amorphization threshold is when the laser power is 18 mW. In addition,
Figure (a) shows the dependence of crystallization temperature on composition. What can be seen from Figure 8 is described below.

(1) Even if the amount of A g S b T e 2 added increases, the crystallization temperature hardly changes.

(2) The threshold for starting crystallization is G
e 2 S b 2 T e 6 and G e S b
It is almost the same as that of 4T e 7.

(3) The threshold for the start of amorphization is Ag5bT
There is almost no change even if e2 increases.

From the above, (Ge2Sb2Tes)I-X(Ag
It can be seen that in the region of SbTez), (0,1≦a≦0.5), a high crystallization temperature, a large crystallization speed, and good recording sensitivity are simultaneously satisfied.

According to this example, the stoichiometric compound G e
It was shown that excellent properties as an optical recording thin film can be obtained on the line connecting 2S b 2 Te s and GeSb4Te7.

Example 3 Stoichiometric Compound G e 2 S b 2 T e s
, GeSb 2 T e 4, and G e S b
A recording thin film having a mixed crystal composition of 4T e 7 and Ag5bT e 2 and a composition in the vicinity thereof was prepared by a vacuum evaporation method, and the recording characteristics, erasing characteristics, and crystallization temperature were measured. The thickness of the recording film was 1100 nm, and the heat-resistant protective layer was made of ZnS.

Figures 9 and 10 show GeTe, 5b2Tes, and A
g2Te pseudoternary system, mainly GeTe-3b 2 Te
3 shows statically measured threshold values for the initiation of crystallization and threshold values for the initiation of amorphization in compositions 3 and 3. Here, the crystallization threshold is determined by the laser power being 1
In the case of 0 mW, the threshold for amorphization is 18
This is the case of mW.

Further, FIG. 11 shows the crystallization temperature in the same composition range. As can be seen from these three figures, point A (Ge7Sbe
Tete), point B (AgGe7Sb7Te1g), point C (AgGe3SbtsTe27) and point D (Ge3S
It can be seen that the crystallization and amorphization characteristics are good in the region surrounded by bt4Te2a). In particular, this region is defined by the crystallization temperature, and beyond this region, the thermal stability (when Tx is low) and the sensitivity of amorphization after melting (when Tx is high) deteriorate.

Therefore, it can be seen that the range surrounded by A%B%C1 and point D is suitable for an optical information recording medium.

Effects of the Invention The recording thin film made of tellurium, antimony, germanium, and silver according to the present invention has a high crystallization temperature, a high crystallization speed, and can provide an optical disk with good recording sensitivity.

[Brief explanation of the drawing]

Figure 1 shows GeTe-8b2Tes Ag2T of the present invention.
A composition diagram showing the composition range of eq ternary recording medium material,
Figure 2 is the phase diagram of the 5b2Tes Ag2Te system, Figure 3 is the phase diagram of the G e Te -S b 2 Te 3 system, Figure 4 is a cross-sectional diagram showing the structure of the recording medium, and Figure 5 is the static Crystallization characteristic diagram, Figure 6 is static amorphization characteristic diagram, Figure 7 is static crystallization characteristic diagram, Figure 8 is static amorphization characteristic diagram, Figure 9 is GeTeGeTe-8b2Te3-A.
The static crystallization characteristic diagram of the system, FIG. 10 is also an amorphization characteristic diagram, and FIG. 11 is a diagram of the crystallization temperature of the same system. Name of agent: Patent attorney Toshio Nakao and 1 other person ^-Qet
Sb6 T6/6 β-Af Qet 5h7Te ts C, ---Ay Qe3Sbt57e27 3rd Sbt!
JD-1ie3Sbt4Te24(:ttTe ApTe AySbTez 5bz
Tes Figure 2 ID u) J 44 50
6a riD 80 9゜@Figure 3-Figure 4 (e3Sbz Tea)qo (AlSbTet)t
. o, ot o, t t
t. Pulse width (Fig. 6 (rtsbzTe4)qo (AySbTez)10
001 θ/ /
/l) Buffless ↑ (My 7 Lott')
y) Figure 7 Oori / O, / /
10 Figure 8 a, ot o, t
/l. Figure 9Q Self-contained AyzTe AI Sb Tez
5b2Tes 2nd Te sek

Claims (4)

[Claims] (1) In an optical information recording and reproducing medium that records, reproduces, and erases information by causing a change in optical constants using means such as light or heat, an active material that exhibits a change in optical constants is used. It is an alloy consisting of tellurium, antimony, silver and germanium, and the composition of the alloy is a pseudoternary phase diagram of GeTe-Ag_2Te-Sb_2Te_3.
e_1_6), point B (AgGe_7Sb_7Te_1_
8), point C (AgGe_3Sb_1_5Te_2_7)
and point D (Ge_3Sb_1_4Te_2_4). (2) The composition of the alloy serving as the active material is Ge_2Sb_2
The optical information recording medium according to claim 1, which corresponds to a mixed crystal of Te_5 and AgSbTe_2. (3) The composition of the alloy serving as the active material is GeSb_2Ge_
4. The optical information recording medium according to claim 1, wherein the optical information recording medium corresponds to a mixed crystal of 4 and AgSbTe_2. (4) The composition of the alloy serving as the active material is GeSb_4Te_
2. The optical information recording medium according to claim 1, wherein the optical information recording medium corresponds to a mixed crystal of No. 7 and AgSbTe_2.