JP2592800B2 - Optical information recording member - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording member capable of recording, erasing, and retransmitting information at high speed and high density using light, heat, and the like.

2. Description of the Related Art In recent years, an optical disk using a laser beam has attracted attention with an increase in the amount of information, a higher speed of recording and reproduction, and a higher density. Optical discs include write-once optical discs that can be recorded only once, and rewritable optical discs that can erase recorded signals and can be used many times. Some write-once optical disks use a recording signal in a perforated state, and others reproduce information by generating irregularities. As a rewritable material, a Te—Ge-based carbonide thin film utilizing a reversible change between amorphous and crystal is well known (for example, Japanese Patent Publication No. 47-26).
No. 897).

The present inventors have previously proposed a system in which a change in reflectance due to phase transition of a system containing an oxide such as Te—TeO ₂ is used as a signal. Further, as a rewritable optical disc that utilizes a phase transition, adding various additives to the _{Te-TeO 2 (Sn, Ge} , B
i, In, Pb, Tl, Se, etc.) (JP-A-59-185048).
No.). These recording members are characterized by high C / N and excellent moisture resistance.

Problems to be Solved by the Invention A rewritable information recording member made of a conventional chalcogenide generally has a disadvantage that stability against repeated recording and erasing is poor.

The reason for this seems to be that Te, Ge and other additional components cause phase separation in the film by repeating several times, and the components of the film are partially different between the initial stage and after the iteration. .

When phase transition is used in an erasable optical disk, usually, a method is used in which the unrecorded and erased state is made crystalline and the recorded state is made amorphous. In this case, at the time of recording, the film is temporarily melted by using a laser beam and becomes amorphous by rapid cooling. However, since the current semiconductor laser has a power limit, a film having a melting point as low as possible is recorded. It was desirable in terms of high sensitivity. For this reason, the film made of the above-described chalcogenide has a composition having a melting point as low as possible, that is, a film composition containing a large amount of Te in order to improve the recording sensitivity. However, the fact that Te is larger than the other additive components means that phase separation is more likely to occur during repetition. Therefore, how to fix the excess Te added to lower the melting point and make the composition hard to move has a great effect on the repetition characteristics, the CNR and the erasure rate over time.

Recording members containing oxides also have the disadvantages described below. That is, the erasing rate is reduced by the repetition of recording / rewriting.

Generally, a rewritable optical disk performs recording with an initial state being a crystalline state and a recording state being amorphous. The erasure is made crystalline as in the initial state. The phase transition between crystalline and amorphous of the recording member is achieved by changing the condition of slow cooling and rapid cooling of the laser. That is, after heating by the laser beam, it becomes crystalline by slow cooling and becomes amorphous by rapid cooling. Therefore, the film goes through a crystalline or amorphous state many times by repeating recording and erasing. In this case, if an oxide is present in the film, the viscosity of the film is high, so that the migration property of the chalcogenide is reduced and segregation is likely to occur in the film composition. Further, since the presence of the oxide lowers the heat conduction of the film itself, a temperature distribution difference occurs between the film on the side where the laser beam is incident and the opposite side, and segregation of the film composition still occurs. For these reasons, a film containing an oxide has a drawback that its characteristics gradually change due to repetition of recording and erasing.

An object of the present invention is to improve the repetition characteristics of the above-mentioned oxide-containing film, and furthermore, the disadvantages of the conventional composition comprising a chalcogenide (low C / N, insufficient erasing rate, moisture resistance, heat resistance) The present invention provides an optical information recording member which overcomes the problem of poor reproducibility and insufficient repetition characteristics.

Means for Solving the Problems The present invention comprises, on a substrate, a recording thin film layer which exhibits a change in optical characteristics by causing a reversible phase transition between an amorphous phase and a crystalline phase by irradiation with a laser beam, Is composed of at least three elements of Te, Ge and Bi,
In the Ge · Bi triangular diagram, B ₁ : (Te ₅₅ Ge ₅ Bi ₄₀ ), C ₁ : (Te ₄₅ Ge ₁₅ Bi ₄₀ ), D ₁ : (Te ₄₅ Ge ₄₀ Bi ₁₅ ), E ₁ : ( Te ₅₇ Ge ₄₀ Bi ₃ ), E ₂ : (Te ₆₀ Ge ₃₀ Bi ₁₀ ), and B ₂ : (Te ₆₂ Ge ₈ Bi ₃₀ ).

Action A feature of the present invention is that Bi is added to a Te—Ge system to fix excess Te. This Bi combines with Te to form the compound Bi ₂ T
forming a e _3, Te concentration in 50at% or more Te-Ge-Bi-based, its melting point is in the vicinity of 550 ° C..

This temperature is lower than that of eutectic Te-Ge, Te-Sn, etc.
High near 00 ° C. This means that the composition having the above-mentioned composition has a high thermal transition temperature (the temperature at which the composition changes from an amorphous state to a crystalline state by heating) and has high thermal stability. When used as a rewritable memory medium (it is customary to heat and quench the crystal state to make it amorphous and use this as a recording medium)
The recording portion in the amorphous state becomes stable against heating, thereby ensuring long-term stability of recorded information.

On the other hand, the stoichiometric composition Te-Ge, Te-Sn, that is, Te ₅₀ Ge
_The melting point is lower by about 150 ° C. compared to the composition of ₅₀ , Te ₅₀ Sn ₅₀ . This means that the energy required for recording is small in the case where a minute portion of the crystalline memory thin film in a crystalline state is heated and melted, rapidly cooled to become amorphous, and recording is performed.

From the above, it is possible to obtain a rewritable memory medium having excellent thermal stability of a recording signal without significantly lowering the recording sensitivity by a laser beam or the like.

An embodiment of the present invention will be described below with reference to the drawings. The optical information recording member of the present invention includes at least Te-Ge-Bi. In the present invention, Te alone or combined with Ge or Bi is considered to be a component mainly responsible for the change in optical density in the amorphous state and the crystalline state. In the Te-Ge system, the melting point of Te ₅₀ Ge ₅₀ having a stoichiometric composition is about 725 ° C., which is heated and melted, and rapidly cooled to become large energy, for example, a large energy when laser light is used. Requires laser power.

Further, in the Te-Ge-based, such as, for example, Te ₈₅ Ge ₁₅ eutectic composition, its melting point is about 375 ° C., but requires only a laser power less required for printing, the excess of this system as described above The presence of Te tends to cause the separation of Te-TeGe, and when this is repeated amorphization and crystallization, the film composition becomes non-uniform, which becomes a noise component of the optical information recording medium.

In the Te-Ge-Bi system, its melting point is about 550 ° C. to 630 ° C., depending on the composition. Therefore,
It requires less recording laser power than the Te-Ge system.

In addition, the crystallization speed is improved by the combination of Te and Bi. This is because, when free Te is present, when crystallized by slow cooling from the melt, Te in the molten state has three coordinations, which are retained when the crystal is slowly cooled. Conceivable. In other words, since the two-coordinates are stable in the crystalline state, it is necessary to convert the once frozen three-coordinate bonds into the two-coordinates, so that the crystallization speed may be low. However, when solidifying from the melt by adding Bi, the bond of Te-Bi is immediately formed and stabilized. For this reason, the crystallization speed is improved, and a practical rewritable memory medium can be realized.

Since Bi fixes the remaining excess Te bonded to Ge, the required concentration (addition amount) is governed by the amount of Te / Ge.

FIG. 1 shows an appropriate range of a recording member composed mainly of Te-Ge-Bi. In FIG. 1, each point has the following composition.

A ₁ point: (Te ₈₀ Ge ₅ Bi ₁₅ ) B ₁ point: (Te ₄₅ Ge ₅ Bi ₄₀ ) C ₁ point: (Te ₄₅ Ge ₁₅ Bi ₄₀ ) D ₁ point: (Te ₄₅ Ge ₄₀ Bi ₁₅ ) E ₁ Point: (Te ₅₇ Ge ₄₀ Bi ₃ ) As described above, the amount of added Bi differs depending on the composition ratio of the Te—Ge system. For example, in the high Ge concentration region, the crystallization speed of Te-Ge is high, so the Bi concentration is relatively low, and in the region with a small Ge component, the crystallization speed is low,
Requires Bi addition.

When the ratio is outside the above range, for example, Ge-rich Ge—TeGe having a high melting point becomes a base material on the Ge (rich) side, so that a very high power is required for a laser required for recording, which is unsuitable as a memory material.

On the Te (rich) side, the thermal transition temperature from amorphous to crystalline decreases to around 100 ° C., and a memory medium with excellent thermal stability cannot be obtained.

Further, on the Bi (rich) side, it is difficult to obtain the optical contrast of the signal between the recorded portion and the unrecorded portion, so that sufficient recording characteristics cannot be obtained.

For the reasons described above, the points A ₁ -B _1-
It is limited to the range surrounded by C ₁ -D ₁ -E ₁ . That is,
When the composition of Te-Ge-Bi in this range is used, information recording, utilizing the reversibility of crystalline and amorphous in practical use,
An optical information recording medium that can be erased and rewritten can be realized.

Next, we describe a region surrounded by points _{A 2 -B 2 -C 2 -D 2} -E 2 of Figure 1. This region corresponds to the point A ₁ -B _{1 in} FIG.
Than the range surrounded by -C ₁ -D ₁ -E _1, there is shown a more practical composition range. In FIG. 1, the composition of each point of A ₂ , B ₂ , C ₂ , D ₂ and E ₂ is shown below.

A ₂ points: (Te ₇₈ Ge ₈ Bi ₁₄ ) B ₂ points: (Te ₆₂ Ge ₈ Bi ₃₀ ) C ₂ points: (Te ₅₀ Ge ₂₀ Bi ₃₀ ) D ₂ points: (Te ₅₀ Ge ₃₀ Bi ₂₀ ) E ₂ Point: (Te ₆₀ Ge ₃₀ Bi ₁₀ ) The thermal transition temperature from amorphous to crystalline in this region is 13
0 ° C to 200 ° C. The transition temperature of A ₂ is the lowest, B ₂ , C ₂ ,
As the Ge or Bi concentration increases in the directions of D ₂ and E _2, the thermal transition temperature increases. In particular, the dependence on the Ge concentration is large. Therefore, in the area surrounded by the point A ₂ −B ₂ −C ₂ −D ₂ −E ₂ , the relative area is smaller than the area surrounded by the point A ₁ −B ₁ −C ₁ −D ₁ −E _1. It is excellent in both thermal stability and laser beam recording sensitivity.

In FIG. ₁ , for a composition outside the range of A ₂ -B ₂ -C ₂ -D ₂ -E ₂ and within the range of A ₁ -B ₁ -C ₁ -D ₁ -E ₁ , It is necessary to use them properly according to the purpose and purpose.

That is, in the above composition, for example, on the Ge (rich) side such as D ₁ or E ₁ , the melting point and the crystallization temperature are high, so that a somewhat large laser power is required, but the thermal stability is excellent. ing.

Further, for example, Te (rich) side as A _1, the melting point and the crystallization temperature is lowered, thermal stability slightly inferior, but a memory medium of extremely high sensitivity. This trend is the same in A _2.

The effect of adding Bi to the Te—Ge system generally raises the thermal transition temperature, which means the thermal stability of the memory medium, lowers the melting point of the film, and facilitates amorphization. However, as described above, the addition of Bi reduces the excess Te to Bi ₂ T
fixed as e _3, but to 550 ° C. vicinity of the melting point of the Te-Ge-Bi-based, it is necessary to line or more Te component connecting for example a point C ₂ and the point D _2.

For the reasons described above, the optimum composition of Te-Ge-Bi of the present invention is limited.

Next, a method for producing the optical information recording member according to the present invention will be described.

FIG. 2 is a schematic sectional view of an optical disc constituted by using the recording layer of the present invention. In FIG. 2, reference numerals 1 and 5 denote substrates, and the material may be a transparent base material such as polycarbonate, acrylic resin, glass, polyester, or the like. Reference numerals 2 and 4 are for preventing thermal deterioration of the substrate due to repeated recording and erasing of the recording film 3 interposed therebetween, and for protecting the recording film 3 from humidity. Therefore, the material and the film thickness of the protective layers 2 and 4 are determined from the viewpoint described above, and various oxides, sulfides, carbides and the like are appropriately applied.

The recording layer 3 is formed by vapor deposition, sputtering, or the like. In the case of vapor deposition, it is desirable to use a three-source vapor deposition machine that can vapor-deposit each composition independently since a uniform film can be formed.

The thickness of the recording film 3 is set to a value that matches the optical characteristics of the protective layers 2 and 4, that is, the difference in reflectance between the recorded portion and the unrecorded portion is large.

 Hereinafter, the present invention will be described in detail with specific examples.

Example 1 Using an electron beam evaporation machine capable of three-source evaporation, Te, Ge,
Bi was simultaneously deposited on the substrate from each source. The substrate used was a glass plate having a thickness of 0.3 mm × φ8 mm, and the evaporation was performed at a vacuum degree of 1 × 10 ⁻⁵ Torr and a rotation speed of the substrate of 150 rpm.
The film thickness was 1000 mm. In addition, the rate of the number of atoms of Te, Ge, and Bi in the recording film was adjusted by variously changing the deposition rate from each source.

The composition ratio in Table 1 is a value converted from the deposition rate. When a typical composition was measured with an X-ray microanalyzer (XMA), quantitative results almost the same as the charged values were obtained. . Therefore, the charged composition in the table seems to be the same in the film.

The evaluation method of the test piece prepared by the above manufacturing method is described below.

[Transition temperature] The transition temperature refers to the temperature at which an amorphous film immediately after vapor deposition becomes crystalline due to heat.

The measurement was performed using a device capable of measuring the transmittance of the film, and the temperature at which the transmittance started to decrease when the temperature of the test piece was increased at a heating rate of 1 ° C./sec by a heater was measured and evaluated. A high transition temperature means that the film is thermally stable.

[Blackening Whitening Characteristic] The blackening characteristic indicates the transition speed for transformation from amorphous to crystalline, and the whitening characteristic indicates the transition speed from crystalline to amorphous. It is a thing.

The measurement was carried out by using a device in which laser light was condensed on a recording film on a φ8 mm glass piece using a lens and the sample piece could be moved up, down, left and right. However, the laser beam spot is 45 × 0.4μm, pulse width 200ns, power density 10.6mW
/ μm ² and a wavelength of 900 nm.

As for the blackening characteristics, the speed of transformation (from amorphous to crystalline) when the test piece is moved relatively slowly is observed, the speed is sufficiently fast, and the contrast ratio between the unrecorded portion and the recorded portion is sufficiently large. The thing was marked as ◎. × indicates a substance that does not turn black even if moved gently, or a substance with a small contrast ratio. △ and △ are located between ◎ and ×. In this qualitative expression, the practical blackening characteristics are ○ or more.

Next, the whitening characteristics will be described. When observing the whitening characteristics, first, the sample is blackened first, and the test piece is quickly moved thereon to create a quenched state, thereby causing whitening (from crystalline to amorphous). When the whitening state is ◎, the whitening occurs even when the moving speed is relatively slow, and the contrast ratio between the amorphous portion and the crystalline portion is large. X shows what does not whiten at all. ○ and △ are located between ◎ and ×.

According to the above expression, when both the blackening and whitening characteristics are very excellent, ◎ and ◎ are obtained. However, as a practical problem, both cannot be ど ち ら at the same moving speed. , ，, あ る い は or ◎, △, which are somewhat superior in blackening characteristics.

Table 1 shows the results of the transition temperature, blackening and whitening characteristics of the film in the range shown in FIG.

As is clear from the results in Table 1, the Te-Ge-Bi-based recording thin film within the range shown in FIG. 1 can be blackened and whitened, respectively. That is, the recording member within this range, heating conditions, for example, the irradiation intensity of the laser beam to be irradiated,
By properly selecting the irradiation time, it is possible to take both the amorphous state and the crystalline state, in other words,
It is possible to record information optically and erase the recorded information.

As described above, the Te-Ge-Bi-based recording thin film according to the present invention has extremely excellent heat resistance and moisture resistance, and does not break even when recording and erasing are repeated. A recording member is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a composition diagram showing a composition range of an optical information recording member according to the present invention, and FIG. 2 is a cross-sectional view showing a configuration of the optical information recording member according to one embodiment of the present invention. . 1,5 ... substrate, 2,4 ... protective layer, 3 ... recording film.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Susumu Sunai 1006 Kazuma Kadoma, Matsushita Electric Industrial Co., Ltd. (56) References JP-A-61-31291 (JP, A) JP-A-59-68850 (JP) , A) JP-A-58-203096 (JP, A)

Claims (3)

(57) [Claims] 1. A recording thin film layer having a reversible phase transition between an amorphous phase and a crystalline phase upon irradiation with a laser beam to exhibit a change in optical characteristics, wherein the composition of the recording thin film layer is at least Te, Ge. Te and G
In the triangular diagram of e · Bi, B ₁ : (Te ₅₅ Ge ₅ Bi ₄₀ ), C ₁ : (Te ₄₅ Ge ₁₅ Bi ₄₀ ), D ₁ : (Te ₄₅ Ge ₄₀ Bi ₁₅ ), E ₁ : (Te Optical information recording characterized by being within a range surrounded by the composition points of ₅₇ Ge ₄₀ Bi ₃ ), E ₂ : (Te ₆₀ Ge ₃₀ Bi ₁₀ ), and B ₂ : (Te ₆₂ Ge ₈ Bi ₃₀ ). Element. 2. The rewritable optical information recording member according to claim 1, further comprising a protective layer on at least one surface of the recording layer. 3. The optical information recording member according to claim 2, wherein any one selected from oxides, sulfides, and carbides is used as the protective layer.