JPH11265522A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase change type optical record medium in which deformation in mark edges due to overwriting is prevented and high density recording is possible. SOLUTION: This phase change type optical record medium is produced by successively forming a first dielectric layer 2, recording layer 3, second dielectric layer 4, semitransmitting reflection layer 5, third dielectric layer 6 and UV-curing resin layer 7 on a transparent substrate 1. The reflectance Rc of the crystal phase part in the recording layer 3, the reflectance Ra of an amorphous phase recording mark recorded in the recording layer 3, the absorptivity Ac of the crystal phase part and the absorptivity Aa of the amorphous phase recording mark are specified to satisfy Rc>Ra and Ac>Aa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable method for recording and reproducing information by condensing and irradiating a laser beam onto an optical recording medium to cause a reversible phase change between a crystalline phase and an amorphous phase in a recording layer material. It relates to a possible phase change optical recording medium.

[0002]

2. Description of the Related Art In a conventional phase-change type optical recording medium, an optical disk in which the reflectance of an amorphous phase is smaller than the reflectance of a crystalline phase is used for reproduction using a difference in the amount of reflected light. Was lower than that of the amorphous phase. When mark edge recording is performed on a disc having such characteristics by overwriting, distortion of the mark edge occurs due to a difference in absorptance, which will be described later, and prevents high-density recording.

In order to solve this problem, a phase-change type optical disk having absorptance control applied thereto is a transparent substrate / first protective layer (first dielectric layer) / recording layer / second protective layer (second protective layer). In the layer structure of (dielectric layer) / reflection layer, when the reflectance Ra of the amorphous phase recording mark, the reflectance of the crystalline phase is Rc, the absorptance of the amorphous phase recording mark is Aa, and the absorptance of the crystalline phase is Ac, A phase change optical disk satisfying Rc> Ra and Ac> Aa is disclosed in JP-A-8-63781. According to this optical disk, it is described that mark edge distortion at the time of overwriting is improved, jitter is reduced, and high density recording is possible.
However, in this optical disk, the reflectance Ra of the amorphous phase is actually larger than the reflectance Rc of the crystalline phase (Rc
<Ra), there is a practical problem. This will be described with reference to FIG.

FIG. 3 shows a phase-change optical recording medium in which a first dielectric layer, a recording layer, a second dielectric layer, a reflective layer, and an ultraviolet curable resin layer (protective layer) are sequentially laminated on a transparent substrate. According to the prior art, the film thickness of each layer is set so that the amorphous phase reflectance Ra of the recording layer is smaller than the crystalline phase reflectance Rc (Rc> Ra). However, in this optical recording medium, while a good reproduction signal can be obtained due to the change in reflectance, most of the light is reflected by the reflective layer. Has a defect that the crystal phase is smaller in absorption rate than the amorphous phase (Ac <Aa).
For this reason, the thermal conductivity of the crystalline phase is generally higher than that of the amorphous phase, and the latent heat required for melting is also larger. Occurs. In addition, it is necessary to accurately form an edge shape in order to give information to a mark edge. In a recording film with insufficient absorptance control, an overwrite signal is modulated by a signal component before overwriting, and edge shape distortion occurs near a mark edge. FIG. 5 shows this state.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a phase-change type optical recording medium which does not exhibit the above-mentioned disadvantageous phenomena (such as generation of edge shape distortion) and can repeatedly perform good recording. It is to be.

[0006]

According to the present invention, first, a first dielectric layer, a recording layer, a second dielectric layer, a semi-transmissive reflective layer, a third dielectric layer, This is a phase-change optical recording medium in which an ultraviolet-curing resin layer is sequentially laminated, and the recording layer is irradiated with a laser beam to cause a reversible phase change between an amorphous phase and a crystalline phase to record or erase information. The reflectance of the amorphous phase recording mark recorded on the recording layer is Ra, the reflectance of the crystalline phase portion of the recording layer is Rc,
When the absorptance of the amorphous phase recording mark is Aa and the absorptivity of the crystalline phase portion is Ac,

[Formula 1] An optical recording medium is provided, wherein Rc> Ra and Ac ≧ Aa.

Second, the first optical recording medium is provided, wherein the semi-transmissive reflection layer is a metal film or a semiconductor film. Third, when the translucency of the translucent reflective layer in a single film is T,

The first or second optical recording medium is provided, wherein 20% ≦ T ≦ 70% is satisfied. Fourthly, the first, second or third optical recording medium is provided, wherein the semi-transmissive reflection layer is a semiconductor film of Si or Ge. Fifth, the optical recording medium according to any one of the first to fourth aspects, wherein the refractive index of the third dielectric layer is larger than the refractive index of the ultraviolet curable resin layer. Sixth, ZnS—SiO ₂ is used as the first dielectric layer, the second dielectric layer, and the third dielectric layer, AgInSbTe is used as the recording layer, and Si is used as the semi-transmissive reflective layer. An optical recording medium according to any one of the first to fifth aspects is provided. Seventh, the thickness of the recording layer is 10 to 25 nm, the thickness of the first dielectric layer is 250 to 800 nm, and the thickness of the second dielectric layer is 10 to 25 nm.
The optical recording medium according to any one of the first to sixth aspects, wherein the thickness is 30 nm, the thickness of the third dielectric layer is 20 to 200 nm, and the thickness of the transflective layer is 10 to 200 nm. You.

In the optical recording medium of the present invention, in order to control the absorptance of the recording layer, a semi-transmissive reflective layer is formed instead of the reflective layer of FIG. 3, and a third dielectric layer is formed on the reflective layer. A five-layer configuration is used to perform reproduction based on the difference in the amount of reflected light between the amorphous phase recording mark and the crystalline phase to prevent mark edge distortion and realize high density recording.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. FIG. 1 shows an embodiment according to the present invention, and is a diagram showing a reflectance characteristic and an absorptivity characteristic of a phase change type optical recording medium. In FIG. 1, the reflectance from the crystalline phase is Rc, the reflectance from the amorphous phase recording mark is Ra, the crystalline phase absorptance of the recording film is Ac, and the absorptivity of the amorphous phase recording mark is Aa. Then, the reflectivity Rc of the crystalline phase is set to be larger than the reflectivity Ra of the amorphous phase recording mark, and at the same time, the absorptance of the crystalline phase is set to be larger than the absorptance Aa of the amorphous phase recording mark.

FIG. 2 is a diagram showing a layer structure of a phase change type optical recording medium of the present invention. A first dielectric layer 2, a recording layer 3, a second dielectric layer 4, a semi-transparent layer are provided on a transparent substrate 1. The reflective layer 5 and the third dielectric layer 6 are sequentially formed by sputtering. An ultraviolet curing resin layer 7 is spin-coated on the third dielectric layer as a protective layer.

As the transparent substrate, a plastic substrate such as acrylic or polycarbonate (PC) or a glass substrate is used. The material of the first dielectric layer, the second dielectric layer, and the third dielectric layer is ZnS—SiO ₂ , ZnS, SiO ₂ , TiO.
₂ , AlN, Si ₃ N _{4 and the} like are used.

The recording layer is made of AgInSbTe,
eSbTe system, InSbTe system, InSe system, InTe
System, AsTeGe system, TeOx-GeSn system, TeSe
Chalcogenide-based materials such as Sn-based, SbSeBi-based, and BiSeGe-based can be used.

The semi-transmissive reflective layer is preferably made of a material having a high thermal conductivity, is a very thin metal film, and is made of a material such as an Al-Ti alloy, Al, Au, Cu, Ag or the like.
Alternatively, a material such as Si or Ge is used as the semiconductor film.

It is important to set the material and the thickness of the semi-transmissive reflective layer so that the transmittance of the layer itself (in a single film) is in the range of 20% ≦ T ≦ 70%. It is. This is because if the transmittance T is smaller than 20%, the amount of reflected light increases, and the absorption rate control, which is the original purpose, cannot be performed. This is because although the light decreases and the absorptance can be controlled, the reproduction signal light becomes small and impractical.

Another function of the semi-transmissive reflective layer is a cooling function, which rapidly cools a melted recording mark to make it amorphous. For this reason, the large thermal conductivity and large heat capacity make the thermal characteristics of the optical recording medium better. A metal material (eg, Au, Ag, Cu, etc.) or a semiconductor material is used as a material having good thermal characteristics while observing the above optical characteristics. In particular, the latter semiconductor material is preferably used.
i, Ge. The thermal conductivity of Si is larger than Ge and has a value of 168 W · m ⁻¹ · k ⁻¹ , which is preferable in terms of thermal characteristics.

The heat capacity of the semiconductor thin film can be increased by increasing the film thickness. When an ultra-thin metal film is used, in order for the film thickness to achieve a desired transmittance,
Since it is necessary to be 10 nm or less, there is a limit to increasing the heat capacity. On the other hand, when a Si semiconductor thin film is used, even if the film thickness is 10 nm to 200 nm, there is no problem in optical characteristics such as transmittance and the heat capacity can be sufficiently increased.

FIG. 1 shows an example of optical characteristics when Si is used as the semi-transmissive reflective layer in the optical recording medium of FIG. Specifically, FIG. 1 uses a PC board as a board,
Zn as the first dielectric layer, the second dielectric layer, and the third dielectric layer
The S-SiO _2, a AgInSbTe recording layer, respectively using Si as a semi-transmissive reflection layer, when changing the thickness of the third dielectric layer, the reflectivity and absorption of the crystalline and amorphous phases of the optical recording medium It is a figure showing a rate. As an example, for example, the thickness of the AgInSbTe layer is 17 nm, the thickness of the first dielectric is 200 nm, and the thickness of the second dielectric is 18 n.
m, when the thickness of the semi-transmissive reflective layer Si is 40 nm, desired conditions are realized when the thickness of the third dielectric layer is in the range of 20 nm to 200 nm. According to FIG. 1, the value of Ac / Aa (Ac> Aa) can be changed by changing the thickness of the third dielectric layer. Such an optical effect
This is realized when an extremely thin metal film or a semi-transmissive material having a high refractive index is used as the semi-transmissive reflective layer.

As a protective film on the third dielectric layer, an ultraviolet curable resin layer having a refractive index of about 1.5 is preferably used, and the above-mentioned optical effect with the third dielectric layer is enhanced. Therefore, the refractive index of the third derivative layer needs to be higher than the refractive index of the ultraviolet curable resin layer of 1.5. As a dielectric material in which the refractive index η of the third derivative layer is larger than 1.5, Zn
S-SiO ₂ (η = 2.1), Al ₂ O ₃ (= 1.7),
AlN (η = 2.0) and TiO ₂ (η = 2.8) can be used.

[0019]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

Example 1 On a clean polycarbonate substrate provided with a guide groove,
The first dielectric layer made of ZnS-SiO ₂ of nm, AgInSbTe recording layer having a thickness of 17 nm, a second dielectric layer made of ZnS-SiO ₂ having a thickness of 18 nm, a thickness of 40nm
Semi-transmissive reflective layer made of Si, Zn having a thickness of 160 nm
Formed by the third dielectric layer sequentially sputtering consisting S-SiO _2, and then the reflective layer surface was spin-coated with an ultraviolet curable resin to prepare a phase-change optical recording medium by performing an initialization process. The optical disk thus created was rotated at a linear velocity of 8 m / s, and a 40 MHz signal was overwritten on the track. The optical system at this time has a wavelength λ = 63.
The laser power was set to 6 mW for the erasing power and 12 mW for the recording power with 5 nm, the objective lens NA = 0.6. FIG. 4 shows the recording waveform at that time. As the value of the reproduction signal jitter at the time of overwriting, a value almost equal to the initial jitter value was obtained, and good overwrite jitter characteristics were realized.

[0021]

(1) According to the first aspect of the present invention, using the semi-transmissive reflective layer and the third dielectric layer, the absorptance Ac of the crystal phase is obtained.
Is larger than the absorptance Aa of the amorphous phase record mark, and the reflectivity Rc of the crystalline phase is the reflectivity Ra of the record mark.
As a result, the distortion of the mark shape during overwriting can be suppressed, the jitter of the reproduced signal can be reduced, and high-density recording can be realized. (2) According to the second, third and fourth aspects of the present invention, since the thermal and optical characteristics are improved by using a metal film or a semiconductor film for the semi-transmissive reflection layer, the absorption rate can be more effectively controlled. This realizes high-density recording. (3) According to the invention of claim 5, since the refractive index of the third dielectric layer is made larger than the refractive index of the ultraviolet curable resin layer, the optical effect is increased, and Ac / Aa (Ac> A)
a) can be efficiently variably controlled. (4) According to the sixth and seventh aspects of the present invention, AgIn
Since SbTe is used, the erasing characteristics are excellent, and the layer configuration and the film thickness are set so that the absorptance can be effectively controlled. Recording can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing the reflectance and absorptance characteristics of a phase-change optical recording medium according to the present invention.

FIG. 2 is a diagram showing a layer configuration of an example of a phase change type optical recording medium of the present invention.

FIG. 3 is a diagram illustrating a layer configuration of an example of a conventional phase-change optical recording medium.

FIG. 4 is a diagram showing signals during overwriting.

FIG. 5 is a diagram illustrating that edge shape distortion occurs near a mark edge.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 transparent substrate 2 first dielectric layer 3 recording layer 4 second dielectric layer 5 semi-transmissive reflective layer 6 third dielectric layer 7 ultraviolet curable resin layer

Claims (7)

[Claims] 1. A first dielectric layer, a recording layer, a second dielectric layer, a semi-transmissive reflective layer, a third dielectric layer, and an ultraviolet curing resin layer are sequentially laminated on a transparent substrate, and the recording layer is formed by a laser. A phase change type optical recording medium in which recording or erasing of information is performed by causing a reversible phase change between an amorphous phase and a crystalline phase under irradiation of light, wherein an amorphous phase recording mark recorded on the recording layer is formed. The reflectance is Ra, the reflectance of the crystalline phase portion of the recording layer is Rc, the absorptance of the amorphous phase recording mark is Aa,
An optical recording medium wherein Rc> Ra and Ac ≧ Aa, where Ac is the absorptance of the crystal phase portion. 2. The optical recording medium according to claim 1, wherein said semi-transmissive reflection layer is a metal film or a semiconductor film. 3. The semi-transmissive reflective layer according to claim 1 or 2, wherein, when the transmittance of a single film of the semi-transmissive reflective layer is T, the following expression is satisfied: 20% ≦ T ≦ 70%. Optical recording medium. 4. The method according to claim 1, wherein the semi-transmissive reflective layer is made of Si or Ge.
4. The semiconductor film according to claim 1, 2 or 3.
The optical recording medium according to the above. 5. The method according to claim 1, wherein the refractive index of the third dielectric layer is larger than the refractive index of the ultraviolet curable resin layer.
5. The optical recording medium according to any one of items 1 to 4, 6. The first dielectric layer, the second dielectric layer and the third dielectric layer are made of ZnS—SiO ₂ , the recording layer is made of AgInSbTe, and the semi-transmissive reflective layer is made of SnS—Te.
The optical recording medium according to claim 1, wherein i is used. 7. The thickness of the recording layer is 10 to 25 nm, the thickness of the first dielectric layer is 250 to 800 nm, and the thickness of the second dielectric layer is 250 to 800 nm.
The thickness of the dielectric layer is 10 to 30 nm, the thickness of the third dielectric layer is 20 to 200 nm, and the thickness of the semi-transmissive reflective layer is 10 to 200 nm.
The optical recording medium according to any one of the above.