JP2868849B2 - Information recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an information recording medium, in particular, a phase change type information recording medium, which irradiates a light beam to cause a phase change in a recording layer material, and The present invention relates to an information recording medium capable of recording, reproducing, and rewriting information, and is applied to an optical memory related device.

[Prior art] Recording and recording of information by irradiation of electromagnetic waves, especially laser beams
As one of the rewritable and erasable optical memory media, utilizing a transition between a crystal and an amorphous phase or between a crystal and a crystal phase,
So-called phase change recording media are well known. In particular, overwriting with a single beam, which is difficult with a magneto-optical memory, is possible, and the drive-side optical system is simpler. Typical examples of the material include Ge-Te, Ge-Te-Sb-S, Ge-Te-S, and Ge-Se as disclosed in US Pat. No. 3,530,441.
-S, Ge-Se-Sb, Ge-As-Se, In-Te, Se-Te, Se-
So-called chalcogen-based alloy materials such as As. For the purpose of improving stability, high-speed crystallization, etc., Au (Japanese Patent Application Laid-Open
61-219692), Sn and Au (Japanese Patent Application Laid-Open No. 61-270190), Pd (Japanese Patent Application Laid-Open No. 62-19490), etc., and Ge-Te- There has been proposed a material (JP-A-62-73438) in which the composition ratio of Se-Sb is specified. However, none of them can satisfy all of the characteristics required for a phase-change rewritable optical memory medium.

Japanese Patent Application Laid-Open No. 63-251290 proposes an optical recording medium having a recording layer composed of a single phase of a multi-component compound having a crystalline state of substantially three or more. Here, a ternary or higher ternary compound single phase is defined as a compound having a ternary or higher stoichiometric composition (eg, In ₃ SbTe ₂ ) in a recording layer of 90 atomic% or more.

By using such a recording layer, high-speed recording and high-speed erasing can be performed.

However, the laser power required for recording and erasing is not yet sufficient. Low erasure ratio (large erasure remaining)
And the like.

Further, in JP-A-1-277338, (Sb _X Te _1-X ) _1-Y M
_Y (where 0.4 ≦ x <0.7, y ≦ 0.2, M is Ag, Al, As, A
optical recording medium having a recording layer composed of an alloy having a composition represented by at least one selected from the group consisting of u, Bi, Cu, Ga, Ge, In, Pb, Pt, Se, Si, Sn and Zn) Has been proposed.

The basis of this system is Sb ₂ Te ₃ , and when Sb is excessive, high-speed erasing and repetition characteristics are improved, and addition of M promotes high-speed erasing. It also states that the erasing rate by DC light is large.

However, the erasing rate at the time of overwriting is not shown (results of study by the present inventors have left unerased data), and the recording sensitivity is also insufficient.

Similarly, in JP-A-60-177446, (In _1-X Sb _X ) _1-Y M
_Y (0.55 ≦ x ≦ 0.80, 0 ≦ Y ≦ 0.20)
Are used respectively Sho _{63-228433 GeTe-Sb 2 Te 3 -Sb} ( excessive) in the recording layer becomes an alloy, the sensitivity, does not satisfy the characteristics such as erase ratio.

JP-A-63-173241 proposes a recording layer in which a recording material is dispersed in a thermally stable matrix.

However, all of the matrix materials are high-melting materials having high light-transmitting properties, and a sufficient light absorptance and reflectivity cannot be obtained for the entire recording layer, resulting in a decrease in sensitivity, contrast, and the like. Also, the one-beam overwrite performance is not sufficient.

In particular, improvement of recording sensitivity and erasing sensitivity, prevention of a decrease in erasing ratio due to unerased portion at the time of overwriting, and extension of life of a recorded portion and an unrecorded portion are the most important issues to be solved.

In particular, as for the laser writing power on the medium surface under the condition that the laser irradiation time is 100 nsec or less, all of the reported examples up to now require a power of about 15 mW or more, which is a major barrier to improving the transfer speed. ing. Also, due to the heat generated when recording / erasing is repeated,
Since the recording layer, the heat-resistant protective layer, and the like are damaged and the characteristics are deteriorated, it is a great obstacle to the improvement of the repetition performance.

[Problems to be Solved by the Invention] An object of the present invention is to provide an information recording medium in which the following points are improved as compared with the above-mentioned conventional technology.

(1) Improvement of laser writing (recording) sensitivity, (2) Improvement of erasing sensitivity, (3) Improvement of repetition performance of recording and erasing, (4) Improvement of erasing ratio [Means for solving the problems] To solve the problem, it has been found that it is extremely effective to use the following substances as the recording layer material of the phase change type information recording medium.

A phase (M phase) in which the main component of the recording layer provided on the substrate undergoes a crystal-to-amorphous or crystal-to-crystal phase transition during recording / erasing, and a phase (L-phase) in which no phase transition occurs during recording / erasing.
Phase), wherein the M phase and the L phase satisfy the following conditions.

L _1−a + M _a (0.30 ≦ a ≦ 0.92) M melting point ≦ 700 ° C. L melting point> M melting point M phase, L for electromagnetic wave of wavelength used for recording / erasing
Phase each of the optical absorption coefficient α _M, α _L is α _M ≧ 10 ³ cm ^-1, the α _L ≧ 10 ² cm ^-1 where _{α I = I O (1-} R) 2 exp -α1 I O: incident Light intensity I: transmitted light intensity 1: film thickness R: reflectance α _M is preferably 5 × 10 ³ cm ⁻¹ or more, and most preferably 1 × 10 ⁴ cm ⁻¹
As described above, α _L is preferably 1 × 10 ³ cm ⁻¹ or more, and most preferably 5 × 10 ³ cm ^−1.
3 cm ^-1 or more.

Further, L is preferably a compound composition of two or more components or a composition in the vicinity thereof in order to improve the repetition performance. The M phase and the L phase need to be in a mixed phase, but it is desirable that the M phases, which are phase transition phases, are completely separated by the L phase. In this case, the average size of the exfoliated M phase (hereinafter, referred to as fine particle diameter) is 30 to 500 °, preferably 50 to 300 °.
Å, optimally 80-200Å. The content a of M is 0.30
≦ a ≦ 0.92, preferably 0.50 ≦ a ≦ 0.90, optimally 0.60 ≦
a ≦ 0.90.

Further, the melting point of M is 700 ° C. or less, preferably 650 ° C. or less, and most preferably 600 ° C. or less.

The attached drawings schematically show the recording layer in a simplified manner.

The phase transition phase (M phase) 1 forms a mixed phase in a state of being dispersed in the non-phase transition phase (L phase) 2 forming a matrix. Examples of the M phase include Sb (mp 630 ° C.), L
AgInTe ₂ (mp680 ° C.) as phase.

With such a configuration, the recording layer has the following characteristics.

(1) Both the phase transition phase (M phase) and the non-phase transition phase (L phase)
Due to its light absorbing ability, electromagnetic waves (eg LD
Light) efficiency is increased. As a result, the sensitivity is improved.

(2) Since the M phase exists in a fine particle state, the melting point is lower than that in the bulk state. Therefore, it is possible to reduce the energy required at the time of amorphous recording (usually melting / quenching). That is, recording sensitivity and response speed are improved.

In addition, sensitivity and response speed are improved during recrystallization (erasing).

Among them, it has been found that an extremely large improvement can be achieved by using a material represented by the following general formula as a main component, particularly as a recording layer material.

The structure is as follows: (1) The main component of the recording layer provided on the substrate is represented by the following general formula, and the presence state in the recording layer is a mixed phase of XYZ _two phase and M phase. Information recording medium.

Formula _{(XYZ 2) 1-a M} a XYZ 2 is a periodic table Ib-IIIb-VIb ₂ or IIb-IVb-Vb
Chalcopyrite type compound represented by ₂ , M is one or more elements selected from Sb, Bi, S, Se and Te, or AgSbTe ₂ .

0.30 ≦ a ≦ 0.92.

(2) The information recording medium according to the above (1), wherein XYZ ₂ is AgInTe ₂ and M is Sb or Bi.

If a is less than 0.3 or more than 0.92, there is no effect on improving the sensitivity, the erasing ratio, and the contrast.

Further, the recording layer may contain trace amounts (1% or less) of other impurities and the like.

Furthermore, the present invention includes the following items as its embodiments.

a) An information recording medium in which the L phase is a binary compound or more.

b) An information recording medium in which a main component of a recording layer provided on a substrate is represented by the following general formula, and an existing state in the recording layer is a mixed phase of XYZ _two- phase and M-phase.

Formula _{(XYZ 2) 1-a M} a XYZ 2 is a periodic table Ib-IIIb-VIb ₂ or IIb-IVb-Vb
Alcopyrite-type compound represented by ₂ , M is one or more elements selected from Sb, Bi, S, Se, and Te, or AgSbTe ₂ .

0.30 ≦ a ≦ 0.92 c) The information recording medium according to the above item b), wherein XYZ ₂ is AgInTe ₂ and M is Sb or Bi.

d) b) above, or c) the general formula in claim (XYZ ₂₎ results material represented by _1-a Ma is contained traces of oxygen, the general formula (XYZ ₂₎ instead _1-a M _a {(XYZ ₂ ) _1-a M _{a ｂ 1-b} O _b (where 0.01 ≦ b ≦ 0.30, and other symbols are the same as item b)). .

Specific examples of XYZ ₂ include: Ib-IIIb-VIb ₂ ; AgInTe ₂ , AgInSe ₂ , AgGaSe ₂ , AgIn
S ₂ , CuInTe ₂ , CuInSe ₂ IIb-IVb-Vb ₂ ; ZnSnSb ₂ , ZnSnAs ₂ , ZnSnP ₂ , ZnGeAs ₂ ,
CdSnP ₂ and CdSnAs ₂ are exemplified.

XYZ ₂ preferably has a stoichiometric composition, but each may have a slight composition deviation.

Specifically, when irradiating a laser beam to the recording layer of the X _o Y _p Z when the _{q 0.2 ≦ o ≦ 0.3 0.2 ≦} p ≦ 0.3 0.4 ≦ q ≦ 0.6 o + p + q = 1.0 [ Operation] The present invention, by irradiation conditions It is considered that the following phase transition occurs.

For simplicity, take AgInTe ₂ as XYZ ₂ and
Sb will be described as an example.

In the amorphous and / or Chalcopyrite-type structure and / or Zincblende-type structure of AgInTe ₂ , M (in this case, Sb) crystal-crystal and / or crystal-amorphous, and / or microcrystal-coarse crystal Transition (AgInTe ₂ facilitates and stabilizes the transition).

The information currently available alone cannot clearly identify the mechanism of the phase transition, but in any case AgInTe ₂ and S
The following points were found to be particularly excellent as compared with the case where b exists alone.

(1) The light absorptance is increased, and the recording / erasing sensitivity is improved.

(2) The optical contrast before and after the transition is increased, and the C / N is improved.

(3) The erasing ratio during overwriting is dramatically improved.

In particular, as for the erasing characteristics, surprisingly, almost complete erasing was possible not only in simple erasing with DC light but also in one-beam overwrite mode.

This is a performance not found at all in any material known to date.

Now it will be described as an example the case of the AgSbTe ₂ system phase with the M phase, the recording layer according to the present invention AgSbTe ₂ system phase (M
Phase) and the L-based phase exist in a mixed phase. There are several methods for obtaining such a mixed phase. For example, it can be obtained by forming a thin film containing Ag, Sb, and Te on a substrate by a film forming method such as sputtering and heat-treating the thin film to separate AgSbTe ₂ and L phase. Examples of the heat treatment method include a method using a laser beam and a method using a heater. The use of a laser beam is preferable because the heat treatment conditions can be arbitrarily selected by controlling the laser beam intensity and the number of rotations by rotating the disk.

By the way, when a laser beam of recording power (Pw) is irradiated, the AgSbTe ₂ phase undergoes a phase transition from a crystal to an amorphous phase, and the other L phase of the mixed phase (the crystal-
The phase that is made of a material that does not cause a phase transition between amorphous states always maintains the amorphous state.

When a laser beam having an erasing power (P _E ) is applied, the AgSbTe-based phase undergoes a phase transition from amorphous to crystalline, and the L phase maintains an amorphous state without causing a phase transition.

In this example, the L phase is amorphous, but the L phase may be crystalline. In this example, the AgSbTe ₂ phase has an amorphous state as a recording state, but may have a crystalline state as a recording state.

In any case, the AgSbTe ₂ phase and the L phase are in a so-called mixed phase.

As the L phase, those having a light absorption coefficient of 10 ² cm ⁻² or more are preferable, and specific examples thereof include In-Sb-based, In-Sb-Te-based,
Sb-Te system, In-Te system, Ge-Sb system, Ge-Te system, Ge-Sb-Te
And the like.

In the present invention, as described above, the phase change does not occur in any case of the L phase, and the reflectivity of the disk changes due to the phase transition between the crystal and amorphous phase of the AgSbTe ₂ phase. And an extremely high erase ratio can be obtained.

The mechanism by which a high erase ratio is obtained is not always clear, but can be considered as follows. AgSbTe ₂
Since is originally a substance that easily crystallizes, it is expected that the effect of facilitating recording (amorphization) by covering this with the non-phase transition phase L. The mechanism is considered as follows.

AgSbTe ₂ of the ordering for AgSbTe ₂ the Oh you L-phase is less likely to occur.

By controlling the thermal conductivity of the recording layer in the L phase while maintaining the characteristics of AgSbTe ₂ to some extent, the quenching condition is satisfied during recording. In this case, it is desirable that the L phase has a higher thermal conductivity than AgSbTe ₂ .

Further, by covering the AgSbTe ₂ phase with the L phase, the particle size of AgSbTe ₂ can be kept constant, and the repetition reliability can be improved.

As can be seen from the general formula, in the recording layer of the present invention, the amount of the AgSbTe ₂ phase is considerably larger than the amount of the L phase. That is, the amount of the former AgSbTe ₂ phase accounts for 30 to 92% of the whole mixed phase. In the above general formula, if the value of a is less than 30% or more than 92%, the effect of improving the erase ratio cannot be recognized. The recording layer may contain a small amount (1% by weight or less) of another impurity (for example, oxygen or the like).

That is, the fact that a high erasing ratio can be obtained means that, when an erasing operation is performed on a recording portion, crystallization or amorphization proceeds in a form that completely covers the recording portion. Therefore, a large amount of AgSbTe ₂ uniform nucleation and growth first proceed in the amorphous or crystalline recording part,
It is considered that a process in which the heterogeneous nucleation and growth of AgSbTe ₂ proceed from the surface of the amorphous L phase in parallel with this.

Further, according to the recording layer of the present invention, (1) the light absorptance is increased, and the recording / erasing sensitivity is improved.

(2) The optical contrast before and after the transition increases and C / N
Is improved.

(3) The erasure ratio during overwriting was dramatically improved.

The optical information recording medium of the present invention basically comprises such a recording layer formed on a substrate with a thickness of 200 to 10,000 mm, preferably 500 to 3000 mm, more preferably 700 to 2000 mm.

The information recording medium of the present invention may be provided with auxiliary layers such as a heat-resistant protective layer, a surface protective layer, a reflective layer, a heat dissipation layer, and an adhesive layer, if necessary.

The substrate used in the present invention is usually glass, ceramic or resin, and a resin substrate is suitable in terms of moldability, cost, and the like. Representative examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin, fluorine resin, ABS resin, urethane resin and the like. Polycarbonate resin in terms of workability, optical properties, etc.,
Acrylic resins are preferred. The shape of the substrate may be a disk shape, a card shape or a sheet shape.

Materials for the heat-resistant protective layer include SiO, SiO ₂ , ZnO, and Sn.
Metal oxides such as O ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ , S
_{i 3 N 4, AlN, TiN} , BN, nitrides such as _{ZrN, ZnS, In 2 S 3} , TaS 4
Sulfides _{etc., SiC, TaC, B 4 C} , WC, TiC, a mixture of carbide and diamond-like carbon, or their like ZrC and the like. Further, it may contain impurities as needed.
Such a heat-resistant protective layer can be formed by various vapor deposition methods, for example, a vacuum evaporation method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method, an electron beam evaporation method and the like.

The thickness of the heat-resistant protective layer is 200 to 5000 mm, preferably 5
It is good to be 00-3000Å. When the thickness is less than 200 mm, the layer does not function as a heat-resistant protective layer. On the other hand, when the thickness is more than 5000 mm, the sensitivity is lowered and the interface is apt to be peeled off. Further, if necessary, the protective layer can be multi-layered.

A thin film (about 200 to 2000 mm thick) of Al, Au, or the like is used as a material that functions as both the reflection layer and the heat radiation layer.

The phase-change material is not limited to a single layer, but may be a multilayer film or an ultra-fine particle in which the phase-change material according to claim 1 is dispersed in a heat-resistant matrix.

As a method of producing the recording film as the latter, a wet process such as a sol-gel method can be applied in addition to the vapor phase film formation.

Among the vapor deposition methods, a high frequency (rf) sputtering method is a preferable method in terms of film characteristics, ease of film formation, and the like.

Typical recording layer preparation conditions for the rf sputtering method include: target: XYZ ₂ + M (eg, AgInTe ₂ + Sb); pressure during sputtering (reaction): 0.5 to 20 Pa; rf power: 20 W to 1 kW; sputter gas: Ar + ( (O ₂ : when controlling the amount of oxygen in the film) Sputtering time: 10 seconds to 20 minutes, but the production method and conditions are not limited at all.

The thickness of the recording layer is 200 to 10,000Å, preferably 500 to
3000Å, optimally 700-2000Å.

Various types of electromagnetic waves such as laser light, electron beam, X-ray, ultraviolet ray, visible light, infrared ray, and microwave can be used for recording, reproduction, and erasing, but when mounted on a drive, a small and compact semiconductor is used. The laser beam is optimal.

[Examples] Hereinafter, the present invention will be specifically described with reference to Examples. However, these examples do not limit the present invention at all.

Example I-1 Pitch: 1.6 μm, groove with 700 mm depth, thickness: 1.2 mm, 86 mmφ
A heat-resistant protective layer, a recording layer, a heat-resistant protective layer, and a reflective layer are sequentially laminated on a polycarbonate substrate by rf sputtering,
An optical disk for evaluation was produced.

 The materials and film thicknesses used for each layer are shown in Table I-1 below.

The evaluation of the optical disk uses a 830 nm semiconductor laser beam with NA 0.
This was performed by narrowing down the spot diameter of 1 μmφ on the medium surface through the lens No. 5 and irradiating from the substrate side.

Although the recording film after the film formation was amorphous, at the time of measurement, the entire surface of the disk was first sufficiently crystallized with 4 to 10 mW DC light on the medium surface, and was brought into an initial (unrecorded) state.

 The linear velocity of the disk was 7 m / s.

The recording conditions were such that the linear velocity was 7 m / s and the frequency was constant at 3.7 MHz, and the laser power (Pw) was varied from 7 to 14 mW.

The reading power (P _R ) was 1.0 mW. Table I-1 shows the laser power (P _W ) and the optimum erasing power (P _E ) when the C / N (carrier-to-noise ratio) value is saturated or maximum, and the obtained C / N value and erasing ratio. Shown in

Further, for a disc having a C / N value of 45 dB or more and an erasing ratio of 35 dB or more, two writing frequencies (f ₁ = 3.7 MHz,
f ₂ = 4.5 MHz), and an overwrite test was performed alternately.

The optimum values of the write power (P _W ) and the erase power (P _E ) during overwriting were selected depending on the disc.

Linear velocity, P _R or the like, the other conditions were the same as when writing test.

 The results of the overwrite performance are shown in Table I-2 below.

From Tables I-1 and I-2, it is confirmed that the phase-change type optical recording medium according to the present invention has excellent performance, and particularly high recording sensitivity has been achieved.

Example I-2 The write performance was tested under the same conditions as in Example I-1, except that the layer configuration was changed. The results are shown in Table I-3 below.

The overwrite performance was tested under the same conditions as in Example I-1. The results are shown in Table I-4 below.

Example I-3 As in Example I-2, the write performance was tested under the same conditions as Example I-1, except that the layer configuration of Example I-1 was changed. The results are shown in Table I-5 below.

The overwrite performance was tested under the same conditions as in Example I-1. The results are shown in Table I-6 below.

Example II-1 Pitch: 1.6 μm, groove with a depth of 700 mm, thickness: 1.2 mm, 86 mmφ
A heat-resistant protective layer, a recording layer, a heat-resistant protective layer, and a reflective layer are sequentially laminated on a polycarbonate substrate by rf sputtering,
An optical disk for evaluation was produced. The recording layer during the production of Example II- (1, 2, 3), the oxygen concentration in the sputtering gas and O ₂ gas
Control was performed by changing the flow ratio of Ar gas (O ₂ / Ar) to obtain recording layers having different oxygen concentrations.

 The materials and film thicknesses used for each layer are shown in Table II-1 below.

The evaluation of the optical disk uses a 830 nm semiconductor laser beam with NA 0.
This was performed by narrowing down the spot diameter of 1 μmφ on the medium surface through the lens No. 5 and irradiating from the substrate side.

Although the recording film after the film formation was amorphous, at the time of measurement, the entire surface of the disk was first sufficiently crystallized with 4 to 10 mW DC light on the medium surface, and was brought into an initial (unrecorded) state.

 The linear velocity of the disk was 7 m / s.

The recording conditions were such that the linear velocity was 7 m / s, the frequency was constant at 3.7 MHz, and the laser power (P _W ) was varied from 7 to 14 mW.

The reading power (P _R ) was 1.0 mW. Table II-1 shows the laser power (P _W ) and the optimum erasing power (P _E ) when the C / N (carrier-to-noise ratio) value is saturated or maximum, and the obtained C / N value and erasing ratio. Shown in

Further, for a disc having a C / N value of 45 dB or more and an erasing ratio of 35 dB or more, two writing frequencies (f ₁ = 3.7 MHz,
f ₂ = 4.5 MHz), and an overwrite test was performed alternately.

The optimum values of the write power (P _W ) and the erase power (P _E ) during overwriting were selected depending on the disc.

Linear velocity, P _R or the like, the other conditions were the same as when writing test.

 The results of overwrite performance are shown in Table II-2 below.

From Tables II-1 and II, it is confirmed that the phase-change type optical recording medium according to the present invention has excellent performance, and particularly high recording sensitivity has been achieved.

Example II-2 The write performance was tested under the same conditions as in Example II-1, except that the layer configuration was changed. The results are shown in Table II-3 below.

The overwrite performance was tested under the same conditions as in Example II-1. The results are shown in Table II-4 below.

Example II-3 As in Example II-2, the write performance was tested under the same conditions as in Example II-1, except that the layer configuration of Example II-1 was changed. The results are shown in Table II-5 below.

The overwrite performance was tested under the same conditions as in Example II-1. The results are shown in Table II-6 below.

Example III-1, Comparative Examples III-1 and III-2 A groove having a pitch of about 1.6 μm and a depth of about 700 mm and a thickness of 1.2 mm
A lower (substrate side) heat-resistant protective layer, a recording layer, an upper heat-resistant protective layer, and a reflective layer were sequentially laminated on a 6 mmφ polycarbonate substrate by rf sputtering to produce three types of optical disks for evaluation.

The materials and film thicknesses used for each layer are shown in Table III-1 below. In addition, in common, Si ₃ N ₄ (about 2
000 mm thick) and Si ₃ N ₄ (approx.
Thickness) and Al (about 500 mm thick) as the reflective layer.

The evaluation of the optical disk uses a 830 nm semiconductor laser beam with NA 0.
This was performed by narrowing down the spot diameter of about 1 μmφ on the recording layer surface through the lens No. 5 and irradiating it from the substrate side.

Although the recording layer after the film formation was amorphous, at the time of measurement, the entire surface of the disk was first sufficiently crystallized with DC light of 4 to 10 mW on the recording layer surface to bring it to an initial (unrecorded) state. The linear velocity of the disk was 7 m / s.

The recording conditions were such that the linear velocity was 7 m / s, the frequency was constant at 3.7 MHz, and the laser power (P _W ) was varied from 7 to 14 mW.

The reading power (P _R ) was 1.0 mW. The table also shows the laser power (P _W ) and the optimum erasing power (P _E ) when the C / N (carrier-to-noise ratio) value is saturated or maximum, and the obtained C / N value and erasing ratio. It is shown in III-1.

Subsequently, the overwrite characteristics were evaluated. Method 2
Overwriting was alternately performed at two writing frequencies f ₁ = 3.7 MHz and f ₂ = 4.5 MHz. Further, the optimum values of the writing power (P _W ) and the erasing power (P _E ) during overwriting were selected depending on the disc. Other conditions were the same as in the writing test. Table III-2 shows the results.

When electron beam diffraction was performed on each of the recording portion and the erasing portion of the overwritten recording layer, a broad ring pattern unique to amorphous was observed in the recording portion. On the other hand, in the erased portion, in addition to the same ring pattern as the recording portion, a clear Bragg reflection point was observed, and it was confirmed that the crystal was AgSbTe ₂ from the plane spacing.

[Effects of the Invention] As described above, the effects of the present invention are summarized as follows.

(1) The heating temperature required for recording / erasing is low. or,
Since the material of the present invention has a high light absorptivity, the recording layer heating efficiency at the time of absorbing laser light is also high. For the above reasons, the required laser power can be reduced.

 That is, the recording / erasing sensitivity is greatly improved.

(2) Since the required laser power can be reduced, a commercially available inexpensive and stable semiconductor laser can be used.

(3) Since the temperature of the laser irradiation part can be kept low, deterioration of characteristics due to thermal damage can be reduced.

(4) The erasing ratio during overwriting can be dramatically increased.

[Brief description of the drawings]

The drawing is a schematic view of the multi-phase recording layer of the information recording medium of the present invention. 1 ... phase transition phase, 2 ... non-phase transition phase.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroko Iwasaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-62-73438 (JP, A) (58) Surveyed field (Int.Cl. ⁶ , DB name) G11B 7/24 511 G11B 7/24 522

Claims (1)

(57) [Claims] A main component of a recording layer provided on a substrate is a phase (M phase) which causes a phase transition between crystal and amorphous or between crystal and crystal during recording / erasing, and a phase transition during recording / erasing. An information recording medium, which is present in a mixed state with a phase (L phase) that does not cause turbidity, wherein both the M phase and the L phase have a light absorbing ability with respect to an electromagnetic wave having a wavelength used for recording / erasing.