JPH0863784A - Optical recording medium and method for using same - Google Patents

Abstract

PURPOSE: To obtain a disk having high recording sensitivity and excellent in characteristics at the time of repeating recording and erasure and to provide a recording method by successively forming a 1st dielectric layer, a recording thin film layer, a 2nd dielectric layer and a reflecting layer on one side of a disk substrate 1 and specifying the thickness of each of the four layers from the viewpoint of optical and thermal properties. CONSTITUTION: A 2nd dielectric layer 4 is made thinner than a 1st dielectric layer 2, the thickness of the 2nd dielectric layer 4 is regulated to 35-70nm and that of a reflecting layer 5 is regulated to 70-120nm to enhance the recording sensitivity of the objective optical recording medium. The total thickness is regulated to 250-430nm. Compressive stress in the thin films is compensated by a protective layer 6 of an overcoating resin producing tensile stress. Tilting is suppressed, recording is performed while shifting a recording start position and the cycle characteristics of overwriting are improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention uses a laser beam or the like to
The present invention relates to the structure and recording method of an optical recording medium (hereinafter simply referred to as a disk) capable of recording / reproducing and erasing information with high density and large capacity.

[0002]

2. Description of the Related Art Conventionally, a recording medium layer is formed on one surface of a disk substrate made of a disk-shaped transparent substrate, and a laser beam is irradiated from the disk substrate side to reversibly change the optical density of a recording thin film layer. A rewritable disc that can be repeatedly recorded and erased by changing to, has been put into practical use. This rewritable disc has a thin film crystallized in advance,
The thin film is heated by melting the disk by rotating the disk, and irradiating it with laser light focused to about 1 μm with intensity modulation corresponding to the recorded information to make it amorphous. Information is recorded by erasing, and the amorphous state is heated to a temperature not lower than the crystallization temperature and not higher than the melting point and gradually cooled to be crystallized and erased.

In such a rewritable disc, when a resin substrate is used as the disc substrate to directly form a recording thin film, the temperature becomes high although it is a minute region of about 1 μm. The disk substrate is deformed and the repetitive characteristics of recording and erasing are limited. Therefore, generally, a dielectric layer is formed as a heat insulating layer for preventing thermal deformation between the disk substrate and the recording thin film or between the recording thin film and the protective layer for protecting the recording thin film. Therefore, the temperature rise, rapid cooling / slow cooling characteristics of the recording thin film change depending on the heat conduction characteristics of the protective layer, so that the recording / erasing characteristics can be improved by selecting the material and layer structure. Further, a four-layer disk structure is generally known in which a reflective layer is provided on the protective layer-side dielectric layer to improve the recording / erasing sensitivity by utilizing the multiple interference of laser light. There is.

With this four-layer disc structure, the thickness of the dielectric layer (hereinafter referred to as the second dielectric layer) between the recording thin film and the reflection layer is made thin so as to be close to the reflection layer and heat during recording / erasing is reduced. A quenching disk structure has been proposed in which it quickly escapes to the reflective layer. This quenching disk structure has an advantage that the heat of the recording film is diffused over a wide range to raise the temperature of the dielectric layers on both sides of the recording film, thereby improving the erasing rate and erasing power margin. or,
The recording thin film is rapidly cooled, which is advantageous in making it amorphous. Japanese Unexamined Patent Publication No. 2-56746 has been proposed as a technique for this quenching disk structure. In this application, a dielectric layer (hereinafter referred to as the first
The thickness of the second dielectric layer is smaller than that of the second dielectric layer), and the thickness thereof is 30 nm or less.

[0005]

However, when the film thickness of the second dielectric layer is 30 nm or less, the recording / erasing sensitivity becomes low, and there is a problem that an expensive high power semiconductor laser must be used. It was Further, the first and second dielectric layers are subjected to thermal stress due to expansion and contraction due to rapid heating and cooling at 400 ° C. or higher accompanying repeated recording / erasing and cooling. The thermal load of the second dielectric is relatively smaller than that of the first dielectric, but thermal stress is repeatedly applied, and an appropriate film thickness is required. Further, since the film thickness of the second dielectric layer also affects the optical characteristics, it is necessary to select the film thickness in consideration of the optical characteristics as well as the heat conduction.

In order to solve the above-mentioned conventional problems, it is an object of the present invention to provide an optical recording medium having a high recording sensitivity and excellent recording / erasing repetition characteristics, and a recording method therefor.

[0007]

In order to achieve the above object, the optical recording medium of the present invention comprises a first dielectric layer formed on one surface of a transparent substrate and a first dielectric layer. Recording that is formed on the upper surface and has the property of absorbing its energy by irradiation of laser light, raising the temperature, melting, and rapidly cooling to become amorphous, and the property of crystallizing by raising the temperature of the amorphous state. An optical recording medium having a thin film layer, a second dielectric layer formed on the upper surface of the recording thin film layer, and a reflective layer formed on the upper surface of the second dielectric layer, the optical recording medium comprising: The thickness of the second dielectric layer is thinner than that of the second dielectric layer, the thickness of the second dielectric layer is in the range of 35 nm to 70 nm, and the thickness of the reflective layer is in the range of 70 nm to 120 nm. It is characterized by having done.

In the above structure, it is preferable that the thickness of the recording thin film layer is in the range of 18 nm to 30 nm. In the above structure, the thickness of the first dielectric layer is 140 n
It is preferably in the range of m to 210 nm.

Further, in the above structure, the first and second dielectric layers are a mixture of ZnS and SiO ₂ , and SiO ₂
Abundance of 5 to 40 mol%, ZnS abundance of 60 to 9
It is preferably 5 mol%.

Further, in the above-mentioned structure, the reflection layer is formed by adding Ti, Ni, Cr, Cu, Ag, Au, P to the main component Al.
It is preferable to contain at least one metal selected from t, Mg, Si and Mo.

In the above structure, the recording thin film layer is
It is preferable to contain Te, Ge and Sb. In the above structure, it is preferable that the recording thin film layer further contains nitrogen.

In the above structure, the recording thin film layer is
It preferably comprises GeTe, Sb ₂ Te ₃ , Sb and nitrogen. Further, in the above-mentioned structure, when the composition of the recording thin film layer is Sb / Sb ₂ Te ₃ molar ratio is b,
It is preferable that 0.2 ≦ b ≦ 0.5.

Further, in the above structure, it is preferable that an overcoat resin protective layer having a film thickness in the range of 3 to 15 μm that generates tensile stress is further provided on the upper surface of the reflective layer. Further, in the above-mentioned structure, it is preferable to perform annealing treatment for stress relaxation after forming the overcoat resin protective layer.

In the above structure, the total thickness of the first dielectric layer, the recording thin film layer, the second dielectric layer, and the reflective layer is set in the range of 250 to 430 nm, and the four thin films are compressed. The stress is preferably 0.5 × 10 ⁹ dyn / cm ² or less. The compressive stress of the four thin films is 0.1 × 10 ⁹ d
yn / cm ² or more is preferable.

Further, in the above structure, information is recorded on one surface of the optical recording medium, and the circumferential portion of the optical recording medium has a convex shape on the side on which the information is recorded with respect to the horizontal reference surface. The angle between the tangent line of and the horizontal reference plane is 1-2mr.
It is preferably ad.

Further, in the above structure, the transparent substrate has a single plate structure, information is recorded on one surface of the transparent substrate, and a surface on which information is recorded is convex with respect to a horizontal reference surface of the substrate. The angle between the tangent line of the circumference and the horizontal reference plane is 1 to 2 mrad, and the first dielectric layer, the recording thin film layer, and the second dielectric layer are formed on the surface of the transparent substrate on which information is recorded. ,
It is preferable that the reflective layer and the reflective layer are sequentially formed.

Next, the method of using the optical recording medium of the present invention is the MCAV for recording by changing the recording frequency according to the linear velocity.
(Modified Constant Angular Velocity) recording method is used to form a first dielectric layer formed on one surface of a transparent substrate and an upper surface of the first dielectric layer. Formed on the upper surface of the recording thin film layer, which has a property of absorbing, heating, melting, and rapidly cooling to become amorphous, and a property of crystallizing by heating the amorphous state. The formed second dielectric layer, a reflective layer formed on the upper surface of the second dielectric layer, and the second dielectric layer having a thickness smaller than that of the first dielectric layer, and The film thickness of the second dielectric layer is 35 n
The thickness of the reflective layer is 70 nm to 70 nm.
A method of recording on an optical recording medium in the range of 120 nm, wherein the linear velocity is set to 5 m / s to 12 m / s, the recording pulse width is selected as inner circumference> outer circumference, and the pulse width ratio of the inner circumference and the outer circumference is 1. .2 or more. Here, the usage of the optical recording medium refers to recording, reproduction, erasing and the like.

In the above arrangement, it is preferable that the recording pulse width is 40 to 60 ns in the region of linear velocity 5 m / s and 30 to 40 ns in the region of linear velocity 12 m / s.

Further, in the above structure, the recording start point is changed by a maximum of 7.75 μm in the range of the linear velocity of 5 m / s to 12 m / s of the MCAV recording system in which the recording frequency is changed according to the linear velocity. It is preferable to record it.

In the above structure, it is preferable that the thickness of the recording thin film layer is in the range of 18 nm to 30 nm.
Further, in the above structure, the thickness of the first dielectric layer is set to 14
The range of 0 nm to 210 nm is preferable.

Further, in the above structure, the first and second dielectric layers are a mixture of ZnS and SiO ₂ , and SiO ₂
Abundance of 5 to 40 mol%, ZnS abundance of 60 to 9
It is preferably 5 mol%.

Further, in the above-mentioned structure, the reflection layer is formed by adding Ti, Ni, Cr, Cu, Ag, Au, P to the main component Al.
It is preferable to contain at least one metal selected from t, Mg, Si and Mo.

In the above structure, the recording thin film layer is
It is preferable to contain Te, Ge and Sb. In the above structure, it is preferable that the recording thin film layer further contains nitrogen.

In the above structure, the recording thin film layer is
It preferably comprises GeTe, Sb ₂ Te ₃ , Sb and nitrogen. Further, in the above-mentioned structure, when the composition of the recording thin film layer is Sb / Sb ₂ Te ₃ molar ratio is b,
It is preferable that 0.2 ≦ b ≦ 0.5.

Further, in the above-mentioned constitution, it is preferable that an overcoat resin protective layer having a film thickness in the range of 3 to 15 μm for generating tensile stress is further provided on the upper surface of the reflective layer.

[0026]

According to the above-mentioned structure of the present invention, the first dielectric layer formed on one surface of the transparent substrate and the upper surface of the first dielectric layer are formed by irradiating the laser beam. A recording thin film layer having a property of absorbing energy to raise the temperature, melting, and rapidly cooling to become amorphous, and a property of crystallizing by raising the temperature of the amorphous state, and the upper surface of the recording thin film layer. An optical recording medium having a formed second dielectric layer and a reflective layer formed on the upper surface of the second dielectric layer, wherein the second dielectric is formed from the first dielectric layer. The thickness of the second dielectric layer is reduced to 35 nm to 70 n.
The thickness of the reflective layer is 70 nm to 120 nm in the range of m.
By setting the above range, an optical recording medium having high recording sensitivity and excellent recording / erasing repetition characteristics can be realized.

Further, the first and second dielectric layers are made of a material having a relatively small thermal conductivity, which is made of a mixture of ZnS and SiO ₂ and has excellent heat resistance. Thick 35
Approximately 70 nm to provide optical strength as well as mechanical strength, increase the distance between the recording film and the reflective layer, and gradually cool the film to slow the heat conduction from the recording film, that is, the cooling rate. Thus, the recording sensitivity can be improved.

Further, the reflective layer is to improve the recording sensitivity by reducing the film thickness and heat capacity while maintaining the mechanical strength and the optical characteristics. In this way, the thermal characteristics, that is, the recording sensitivity can be adjusted by optimally selecting the respective film thicknesses. Further, since the reflective layer utilizes multiple interference of laser light, Al
Ti, Ni, Cr, Cu, Ag, Au, Pt, Mg,
By adding at least one element of Si and Mo, deterioration can be prevented without crystal growth in a high temperature and high humidity environment.

Further, Te, Ge, Sb or GeTe, Sb ₂ Te ₃ , Sb is used as the recording film, or a material containing nitrogen therein is used, and the molar ratio of Sb / Sb ₂ Te ₃ is b, and .2 ≦ b ≦ 0.5, the thermal conductivity can be reduced by including nitrogen in the recording film, and the crystallization speed can be reduced by increasing the Sb amount. The sensitivity can be improved.

Next, according to the recording method of the present invention, in the MCAV recording system in which recording is performed by changing the recording frequency according to the linear velocity, the linear velocity of 5 m /
Select the recording pulse width from s to 12 m / s: inner circumference> outer circumference,
The temperatures reached at the inner and outer circumferences during recording are made substantially equal. For this reason, marks having substantially the same size are formed, and the mass transfer of the recording film due to the overlapping marks at the time of overwriting can be suppressed, and the cycle characteristics of overwriting can be improved.

The sum of the four layers of thin film is 250 to 430.
The tilt of the disk can be almost eliminated by forming the overcoat resin layer having a thickness of 3 to 15 μm in the range of nm and generating a tensile stress on the reflective layer. Here, the tilt means an angle formed by the horizontal reference plane of the disk substrate and a tangent line at each point on the substrate. Further, by tilting the signal surface side of the disk substrate in advance to form a four-layer film, the tilt of the disk can be further reduced.

Further, when the overcoat resin protective layer is annealed for stress relaxation, it becomes stable against heat, does not change over time, and does not warp the entire substrate. Further, in the above structure, the linear velocity of the MCAV recording system is 5 m / which changes the recording frequency according to the linear velocity for recording.
The maximum recording start point is 7.75μ in the range of s to 12 m / s.
According to the preferable example in which the recording is performed by changing m, the mass transfer of the recording film is made uniform, and the overwrite cycle characteristics can be improved.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the optical recording medium of the present embodiment has a first dielectric layer 2, a recording thin film layer 3, a second dielectric layer 4, a reflective layer 5 and an overcoat on the upper surface of a transparent disc substrate 1. The protective film layer 6 is sequentially formed. Then, the film thickness of the second dielectric layer is made smaller than that of the first dielectric layer, the film thickness of the second dielectric layer is 35 to 70 nm, and the film thickness of the reflective layer is 70 to 120 n.
By selecting m, the recording sensitivity is increased and the overwrite characteristic is improved. The recording thin film layer is 18 to 30 nm.
By making it thin, the heat capacity can be reduced,
It is possible to record with a small power. In FIG. 1, the disk substrate 1 is made of a transparent resin substrate such as polycarbonate or a glass substrate. A first dielectric layer 2 is formed on the disk substrate 1. The first dielectric layer 2 is made of, for example, a mixture of ZnS and SiO ₂ having excellent heat resistance, and has a film thickness of 140 to 210 nm. A recording thin film layer 3 is formed on the upper surface of the first dielectric layer 2. The recording thin film 3 is made of, for example, a material in which a mixed composition of GeTe, Sb ₂ Te ₃ and Sb contains nitrogen, and the film thickness is 18
nm to 30 nm. The recording film layer 3 is Sb / Sb.
The molar ratio of ₂ Te ₃ is b, and the range is 0.2 ≦ b ≦ 0.5. Sb is related to the crystallization rate, and if b exceeds 0.5, the crystallization rate becomes slow and the erasing rate decreases, which is not preferable. When b is less than 0.2, the recording amplitude decreases on the inner peripheral surface having a low linear velocity, which is not preferable. A second dielectric layer 4 is formed on the upper surface of the recording thin film layer 3. The second dielectric layer 4 is made of the same material as the first dielectric layer 2 and has a film thickness of 35 nm to 70 nm. A reflective layer 5 is formed on the upper surface of the second dielectric layer 4. The reflective layer 5 is a reflective layer for utilizing multiple interference of laser light, is made of a material containing Al as a main component, and has a film thickness of 70 nm to 120 nm.
Is. When only Al is used as the material for the reflective layer, the crystal grain size grows in an environment of high temperature and high humidity, causing intergranular corrosion and deterioration. Therefore, Al, Ti, Ni, Cr, Cu, Ag,
By adding at least one element selected from Au, Pt, Mg, Si and Mo, it is possible to prevent deterioration without crystal growth in an environment of high temperature and high humidity. An overcoat resin protective layer 6 is formed on the upper surface of the reflective layer 5. The overcoat resin protective layer 6 is a layer that shrinks upon curing to generate tensile stress, and is made of an ultraviolet curable resin,
It is formed by a spin coating method to a film thickness of 3 to 15 μm. For forming the first dielectric layer 2, the second dielectric layer 4, the recording thin film layer 3 and the reflective layer 5, a vacuum deposition method or a sputtering method is used.

When recording on a phase change optical disc using a semiconductor laser of 35 mW, if the transmission efficiency of the optical pickup is 40%, the output on the disc is 14 at maximum.
It becomes mW. Considering the variation of the optical pickup, it is necessary for the disc to be able to record at 12 mW or less. In order to increase the recording sensitivity of the disc and extend the rewritable property repeatedly, it is necessary to consider the thermal property and mechanical strength in addition to the optical property.

The reason for limiting the film thickness range of each layer will be described below. (1) The film thickness of the first dielectric layer 2 will be described. When the film thickness of the recording thin film layer 2, the second dielectric layer 4, and the reflective layer 5 is fixed and the film thickness of the first dielectric layer 2 is changed, the optical absorption Ad of the crystal and the amorphous Absorption of quality Aw, reflectance difference ΔR between crystal and amorphous showing signal magnitude is 140 nm to 21
Almost the same in the range of 0 nm. The recording power (C / N ratio> 50 dB) was also the same. Outside the film thickness, ΔR was small, that is, the signal amplitude was small, which was not preferable. (2) Next, the film thickness of the recording thin film layer 3 will be described. Figure 2
In (a), the first dielectric layer 2, the second dielectric layer 4, and the reflective layer 5 are fixed at 170 nm, 40 nm, and 70 nm, respectively,
The graph of the recording power when the film thickness of the recording film is changed is shown. From this graph, the amplitude ± at recording power of 12 mW or less
The film thickness within 2 dB is 18 to 30 nm. When the thickness is 30 nm or more, the heat capacity becomes large and the sensitivity decreases, and when it is less than 18 nm, the amplitude is small, which is not preferable. (3) Next, the film thickness of the second dielectric layer 4 will be described.
The film thickness of the second dielectric layer 4 needs to be determined in consideration of the optical characteristics and the thermal cooling rate. In FIG. 2B, the first dielectric layer 2, the recording thin film layer 3, and the reflective layer 5 are respectively formed with 170 nm and 23 nm.
A graph of the relationship between the recording power and the signal amplitude when the film thickness of the second dielectric layer 4 is changed while fixing the values to 70 nm and 70 nm is shown. When the film thickness of the second dielectric layer 4 is 70 nm or less,
The signal amplitude is within -3 dB when the film thickness is 30 nm.
When it exceeds 70 nm, the signal amplitude becomes small, which is not preferable. The recording power was 12 mW or less at a film thickness of 30 nm or more. When the film thickness is 30 nm or less, the recording thin film layer 3 approaches the reflective layer 5, heat is likely to escape, and the sensitivity decreases, which is not preferable. (4) Next, the film thickness of the reflective layer 5 will be described. Reflective layer 5
Must be determined in consideration of heat capacity and mechanical strength in addition to optical characteristics. 2C, the film thicknesses of the first dielectric layer 2, the recording thin film layer 3, and the second dielectric layer 4 are 170 nm and 2 respectively.
The graph of the relationship with recording power when changing the film thickness of the reflective layer 5 with 3 nm and 40 nm fixed is shown. Film thickness 1
A recording sensitivity of 20 m or less and a recording power of 12 mW or less can be obtained. Further, when the film thickness is 70 nm or less, the recording power is 9 mW or less, and the change in the recording sensitivity is small with respect to the change in the film thickness of the reflective layer 5. An experiment of overwrite cycle characteristics was carried out for disks of different thicknesses. The overwrite experiment used a random signal that was "2-7" modulated by PPM (pit position modulation) recording. At the linear velocity of 5 m / s, 4.03 MHz was used as the highest recording frequency, and at the linear velocity of 12 m / s, 8.87 MHz was used as the highest recording frequency. The wavelength of the semiconductor laser is 780 nm, NA (NA is
Numerical Aperture is an abbreviation for the numerical aperture of a lens) is 0.5. Jitter (deviation of recorded signal from recorded signal) was measured with a time interval analyzer. As a result, it was observed that the mechanical strength was weak and deteriorated when the film thickness was less than 60 nm. With a film thickness of 60 nm or more, characteristics of 100,000 times or more were obtained. For the above reasons, it is preferable to select the film thickness of each layer in the range of 70 nm to 120 nm.

Z constituting the first and second dielectric layers 2 and 4
When the blending ratio of SiO _{2 in} the nS-SiO ₂ mixture is 5 mol% or less, the effect of reducing the crystal grain size is weakened, and when it is 40 mol% or more, Si is mixed.
The properties of the O ₂ film became large and the film strength was not sufficient.
Therefore, the molar fraction of SiO ₂ is 5 to 40 mol.
It was suitable to be in the range of%.

In the present invention, the recording pulse width of the inner circumference> the recording pulse width of the outer circumference is selected so that the temperatures reached during recording on the inner circumference and the outer circumference are substantially equal. For this reason, the recording marks have almost the same size on the inner and outer peripheries, the mass transfer of the recording film due to the overlapping marks is suppressed and the signal deterioration is small. The pulse width of the inner circumference at that time is 40 to 60 ns
Therefore, the pulse width of 30-40 ns was suitable for the outer circumference. By selecting the pulse width in such a range,
Overwriting experiments were conducted in the range of m / s to 12 m / s, but no deterioration of jitter was observed 100,000 times or more. Thus, the pulse width ratio of the inner and outer circumferences is 1.2 or more.

In the present invention, the first and second dielectric layers 2 and 4 made of a mixture of ZnS and SiO ₂ and Te and G are used.
e, a recording thin film layer 3 containing nitrogen in Sb, and a reflective layer 5 containing Al as a main component and having a disk diameter of 120 mm and a thickness t.
= 1.2mm substrate, total thickness of each layer is 25
It is formed in the range of 0 to 430 nm. When a four-layer thin film is formed on the signal surface side of the disk substrate, the thin film side is deformed to be convex, and compressive stress is generated. At that time, a tilt of about 3 mrad occurs. Therefore, by forming the overcoat resin protective layer 6 that generates tensile stress in the range of 3 to 15 μm on the reflective layer, it is possible to cancel the compressive stress generated in the four-layer thin film and also in the outer peripheral portion of the disk substrate. 1
It was possible to obtain a disc with almost no tilt of about 2 mrad. When the thickness of the overcoat resin protective layer 6 was less than 3 μm, the compressive stress generated in the four-layer thin film could not be offset, and the strength of the overcoat layer was insufficient. Further, when the film thickness is 15 μm or more, the curing shrinkage increases, that is, the tensile stress increases, so that the thin film forming surface of the disk substrate is deformed into a concave shape and the tilt increases. For these reasons, it was appropriate that the film thickness of the overcoat resin protective layer 6 be in the range of 5 to 15 μm. As the material of the overcoat resin protective layer 6, the above-mentioned effects could be obtained when an acrylic ultraviolet curing resin, for example, a mixture of urethane acrylate and acrylic ester monomer was used. The material of the overcoat resin protective layer is not limited to this, and the same effect can be obtained as long as the shrinkage rate by curing is about 10%. When a mixture resin of acrylic acid ester is used as the overcoat resin protective layer 6, the annealing (stress relaxation) treatment condition is preferably 100 ° C. for about 1 hour.

Further, the tilt of the surface on which information is recorded in advance is set to 1 to 2 mrad with respect to the inner peripheral reference surface of the substrate.
Using a substrate formed in a convex shape, the first dielectric layer 2, the recording thin film layer 3, the second dielectric layer 4, and the reflective layer 5 are formed on the surface on which information is recorded, and four layers are formed. The sum of thin films is 250-4
In the range of 30 nm, compressive stress of 4 layers of thin film is 0.5 ×
By forming a film to have a film thickness of 10 ⁹ dyn / cm ² or less and forming the ultraviolet curable resin of the overcoat protective layer 6 which generates tensile stress on the reflective layer 5 to a film thickness of 3 to 15 μm, the tilt can be further reduced. I was able to make it smaller. In addition, after forming an overcoat protective layer on the four thin films, a heat treatment is performed at 100 ° C. for about 1 hour in order to relax the stress of the substrate, the stress of the thin film, and the stress of the overcoat protective layer during formation. For example, it was effective against changes over time. As a result, it was possible to reduce the influence of tilt on the recording characteristics such as off-track. Here, the surface on which information is recorded is 1 to 2 mra with respect to the inner peripheral reference surface of the disk substrate 1.
The substrate formed in the convex shape of d can be easily obtained by changing the temperature distribution of the mold by the injection method. With such a manufacturing method, the tilt can be set to 5 mrad or less even for a disk having a single plate structure. The disc thus produced was placed in an environment of 90 ° C. and 80% relative humidity for 20 hours, taken out, and allowed to stand at room temperature, and tilt was measured at each elapsed time. The film side warps convexly for a few hours immediately after taking it out, but it stabilizes after 48 hours after leaving it, and the tilt at that time is as follows:
As a result of measurement with LM-110 (manufactured by Ono Sokki Co., Ltd.), as shown in FIG. 3, a good result of 5 mrad or less was obtained although slightly increased in the outer peripheral portion as compared with before the acceleration test.

Further, according to the present invention, the recording frequency is changed in accordance with the linear velocity to perform recording with MCAV (Modified Constant).
t Angular Velocity) Recording system linear velocity 5m / s-12
At m / s, recording is performed by changing the recording start point within the range where the information fits in the sector, and the sector is overwritten almost uniformly. This makes it possible to make uniform the mass transfer that occurs when the next mark overlaps the already recorded mark and is recorded. Therefore, it is possible to eliminate the phenomenon that the recording film is moved and deposited at a place where the same signal is always recorded, such as the resync portion, and the recording sensitivity is lowered and recording cannot be performed. This effect was great on the low power side where the marks did not overlap each other. Therefore, the power margin of the overwrite characteristic is expanded. Here, the recording start point is changed by a maximum of 7.75 μm, and when it is moved in 0.484 μm intervals during this period,
Even if overwriting was performed 100,000 times or more, no deterioration was observed as shown in FIG. 4 (trace diagram of waveform photograph), and the effect was large.

Specific examples will be described below. (Example 1) 170 m of a first dielectric layer having a mixture of ZnS and SiO ₂ and having an amount of SiO ₂ of 20 mol% was formed on a signal surface of a polycarbonate substrate having a diameter of 120 mm and a thickness of 1.2 mm.
m, a recording thin film layer of 26 nm is formed on the first dielectric layer by using a material containing Te, Ge, and Sb containing nitrogen, and a first thin film layer made of the same material as the first dielectric layer is formed on the recording thin film layer. The second dielectric layer was 44 nm thick, and the Al alloy reflective layer was sequentially formed in-line on the second dielectric layer by a 95 nm sputtering method.

The first and second dielectric layers were formed by a high frequency sputtering method using Ar gas at a pressure of 2 mTorr during sputtering. The recording thin film layer has a sputtering pressure of 1 mTorr.
It was formed by DC sputtering using a mixed gas of Ar and N _{2 at} r. The reflective layer has a sputtering pressure of 2 mTorr.
It was formed by the DC sputtering method using r gas. Further, in order to protect the four thin films on the reflective layer, SD101 (DAINIPPON INK & CHEMI) whose composition is a mixture of acrylic ultraviolet curing resin, for example, urethane acrylate and acrylic ester monomer.
CALS) was applied to a thickness of 5 μm by a spin coating method to obtain a single disk. The disc thus obtained was evaluated for disc tilt with an optical disc tester: LM110 (manufactured by Ono Sokki Co., Ltd.), and a value of 3 mrad was obtained.

The rotation speed of this disk is 2026 rp.
m, semiconductor laser wavelength: 780 nm, objective lens N
A: Recording / erasing characteristics were measured using an optical disk drive incorporating an optical pickup of 0.5. Recording frequency 8.87MHz at the outermost linear velocity of 12m / s
Signal was recorded with a pulse width of 32 ns, and the C / N ratio was measured with a spectrum analyzer.
An N ratio of 50 dB or more was obtained. The rising power of the C / N ratio at that time was 12 mW. The erase ratio was measured at 3.32MHz after recording the 8.87MHz signal.
Signal is overwritten and the spectrum is recorded by a spectrum analyzer at 8.87 MHz from the spectrum at 3.32 MH
The value was obtained by subtracting the spectrum when the z signal was overwritten. An erase ratio of 25 dB was obtained.

Next, an experiment of overwrite cycle characteristics was conducted. The overwrite experiment used a random signal modulated by "2-7" in PPM (pit position modulation) recording.

Further, a method of recording by changing the recording start point within the range where the recording information is stored in the sector is used. The recording start point at that time was changed by a maximum of 7.75 μm, and during this interval,
It was moved randomly in 484 μm increments.

At the linear velocity of 5 m / s on the inner circumference, 4.03 MHz was set as the highest recording frequency, and 12 m / s on the outer circumference.
At the linear velocity of 8.8, the highest recording frequency is 8.8.
7 MHz was used. Jitter was measured with a time interval analyzer. As a result, at both linear velocities of 5 m / s and 12 m / s, deterioration was not seen 100,000 times or more from the initial stage.

Example 2 Using the same means as in Example 1, an experiment was conducted by changing the film thicknesses of the first dielectric layer, the second dielectric layer and the reflective film. The conditions and results are shown in Table 1 below.

[0048]

[Table 1]

As shown in Table 1 above, the thickness of the second dielectric layer is smaller than that of the first dielectric layer, and the thickness of the second dielectric layer is within the range of 35 nm to 70 nm. It was confirmed that by setting the film thickness of the reflective layer in the range of 70 nm to 120 nm, it is possible to obtain an optical recording medium having high recording sensitivity and excellent recording / erasing repetition characteristics.

[0050]

As described above, according to the present invention, the first dielectric layer formed on one surface of the transparent substrate and the laser light formed on the upper surface of the first dielectric layer A recording thin film layer having a property of absorbing the energy by irradiation, heating, melting, and rapidly cooling to become amorphous, and a property of crystallizing by heating the amorphous state, and the recording thin film layer. An optical recording medium having a second dielectric layer formed on the upper surface of the second dielectric layer and a reflective layer formed on the upper surface of the second dielectric layer, wherein the second dielectric layer is formed from the first dielectric layer. The thickness of the second dielectric layer is reduced to 35 nm and the thickness of the second dielectric layer is reduced to 35 nm.
The thickness of the reflective layer in the range of 70 nm to 1 nm
By setting the thickness in the range of 20 nm, an optical recording medium having high recording sensitivity and excellent recording / erasing repetition characteristics can be realized.

Next, according to the recording method of the present invention, in the MCAV recording system in which the recording frequency is changed according to the linear velocity to perform recording, a linear velocity of 5 m /
Select the recording pulse width from s to 12 m / s: inner circumference> outer circumference,
The temperatures reached at the inner and outer circumferences during recording are made substantially equal. For this reason, marks having substantially the same size are formed, and the mass transfer of the recording film due to the overlapping marks at the time of overwriting can be suppressed, and the cycle characteristics of overwriting can be improved.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an example showing the configuration of an optical recording medium according to the present invention.

2A is a diagram showing the relationship between the film thickness of the recording film and the amplitude and the recording power, FIG. 2B is a diagram showing the relationship between the film thickness and the amplitude of the second dielectric layer, and FIG. FIG. 4 is a diagram showing a relationship between a layer thickness and recording power.

FIG. 3 is a diagram showing tilt measurement results before and after an acceleration test of an optical recording medium according to an example of the present invention.

FIG. 4 is a waveform photograph of an optical recording medium according to an embodiment of the present invention after overwriting 100,000 times.

[Explanation of reference numerals] 1 disk substrate 2 first dielectric layer 3 recording thin film layer 4 second dielectric layer 5 reflective layer 6 overcoat resin protective layer

[Procedure amendment]

[Submission date] September 11, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of an example showing the configuration of an optical recording medium according to the present invention.

2A is a diagram showing the relationship between the film thickness of the recording film and the amplitude and the recording power, FIG. 2B is a diagram showing the relationship between the film thickness and the amplitude of the second dielectric layer, and FIG. FIG. 4 is a diagram showing a relationship between a layer thickness and recording power.

FIG. 3 is a diagram showing tilt measurement results before and after an acceleration test of an optical recording medium according to an example of the present invention.

FIG. 4 is a trace diagram of a waveform photograph of an optical recording medium according to an embodiment of the present invention after overwriting 100,000 times.

[Explanation of reference numerals] 1 disk substrate 2 first dielectric layer 3 recording thin film layer 4 second dielectric layer 5 reflective layer 6 overcoat resin protective layer

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location G11B 7/24 538 E 7215-5D F 7215-5D B41M 5/26 G11B 7/00 L 9464-5D F 9464-5D (72) Inventor Hidemi Isomura 1006 Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (26)

[Claims] 1. A first dielectric layer formed on one surface of a transparent substrate, and a first dielectric layer formed on the upper surface of the first dielectric layer. A recording thin film layer having a property of being melted and rapidly cooled to be amorphized and having a property of being crystallized by heating an amorphous state,
A second dielectric layer formed on the upper surface of the recording thin film layer;
An optical recording medium having a reflection layer formed on the upper surface of the second dielectric layer, wherein the second dielectric layer is thinner than the first dielectric layer, and 2. An optical recording medium, wherein the second dielectric layer has a thickness of 35 nm to 70 nm, and the reflective layer has a thickness of 70 nm to 120 nm. 2. The thickness of the recording thin film layer is 18 nm to 30 nm.
The optical recording medium according to claim 1, wherein 3. The film thickness of the first dielectric layer is 140 nm to 2
The optical recording medium according to claim 1, wherein the optical recording medium has a range of 10 nm. 4. The first and second dielectric layers are made of ZnS and Si.
It is a mixture of O _{2 and} the amount of SiO ₂ present is 5 to 40 mo.
The optical recording medium according to claim 1, wherein the amount of ZnS is in the range of 1%, and the amount of ZnS present is in the range of 60 to 95 mol%. 5. The reflection layer is composed of Al, which is the main component, of Ti, Ni,
The optical recording medium according to claim 1, containing at least one metal selected from Cr, Cu, Ag, Au, Pt, Mg, Si, and Mo. 6. The optical recording medium according to claim 1, wherein the recording thin film layer contains Te, Ge and Sb. 7. The optical recording medium according to claim 6, wherein the recording thin film layer further contains nitrogen. 8. The recording thin film layer comprises GeTe, Sb ₂ Te ₃ ,
The optical recording medium according to claim 1, comprising Sb and nitrogen. 9. The composition of the recording thin film layer is Sb / Sb ₂ Te.
The optical recording medium according to claim 8, wherein when the molar ratio of ₃ is b, 0.2 ≦ b ≦ 0.5. 10. The optical recording medium according to claim 1, further comprising an overcoat resin protective layer having a film thickness in the range of 3 to 15 μm that generates tensile stress, on the upper surface of the reflective layer. 11. The optical recording medium according to claim 10, wherein the overcoat resin protective layer is annealed for stress relaxation. 12. The total thickness of the first dielectric layer, the recording thin film layer, the second dielectric layer, and the reflective layer is 250 to 430n.
m within the range of 0.5, and the compressive stress of the four thin films is 0.5 × 1.
The optical recording medium according to claim 1, wherein the optical recording medium has a density of not more than ⁰⁹ dyn / cm ² . 13. Information is recorded on one surface of an optical recording medium, and the tangential line of a circumferential portion of the optical recording medium is horizontal with respect to a horizontal reference surface of the optical recording medium so that the side on which the information is recorded has a convex shape. The optical recording medium according to claim 1, wherein the angle formed with the reference plane is 1 to 2 mrad. 14. The transparent substrate has a single-plate structure, information is recorded on one surface of the transparent substrate, and a circular shape is formed so that a surface on which information is recorded is convex with respect to a horizontal reference surface of the substrate. The angle between the peripheral tangent and the horizontal reference plane is 1 to 2 mrad
2. The optical recording medium according to claim 1, wherein a first dielectric layer, a recording thin film layer, a second dielectric layer, and a reflective layer are sequentially formed on the surface of the transparent substrate on which information is recorded. 15. An MCAV (Modified Constant) for recording by changing a recording frequency according to a linear velocity.
A first dielectric layer formed on one surface of a transparent substrate using an angular velocity recording method;
Is formed on the upper surface of the dielectric layer, absorbs its energy by irradiation with laser light, and is heated and melted, and is rapidly cooled to become amorphous, and the amorphous state is crystallized by raising the temperature. A recording thin film layer, a second dielectric layer formed on the upper surface of the recording thin film layer, a reflective layer formed on the upper surface of the second dielectric layer, and the first dielectric layer. Light in which the thickness of the second dielectric layer is thinner than that of the layer, the thickness of the second dielectric layer is in the range of 35 nm to 70 nm, and the thickness of the reflective layer is in the range of 70 nm to 120 nm. A method of recording on a recording medium, wherein the linear velocity is 5 m / s to 12 m / s.
s, the recording pulse width is selected as inner circumference> outer circumference, and the ratio of the pulse widths of the inner circumference and the outer circumference is 1.2 or more. 16. Use of the optical recording medium according to claim 15, wherein the recording pulse width is 40 to 60 ns in the region of linear velocity of 5 m / s and 30 to 40 ns in the region of linear velocity of 12 m / s. Method. 17. A linear velocity of 5 m / s to 12 m / of an MCAV recording system for recording by changing the recording frequency according to the linear velocity.
The method of using the optical recording medium according to claim 15, wherein recording is performed while changing the recording start point by a maximum of 7.75 μm in the range of s. 18. The thickness of the recording thin film layer is 18 nm to 30 n.
The method of using the optical recording medium according to claim 15, wherein the range is m. 19. The film thickness of the first dielectric layer is from 140 nm to
The method of using the optical recording medium according to claim 15, wherein the range is 210 nm. 20. The first and second dielectric layers are ZnS and S.
It is a mixture of iO ₂ and the abundance of SiO ₂ is 5 to 40 mo.
16. The method of using an optical recording medium according to claim 15, wherein the amount of ZnS present is 60 to 95 mol%. 21. The reflection layer comprises a main component of Al containing Ti and N.
i, Cr, Cu, Ag, Au, Pt, Mg, Si and M
The method of using the optical recording medium according to claim 15, which contains at least one metal selected from o. 22. The method of using an optical recording medium according to claim 15, wherein the recording thin film layer contains Te, Ge and Sb. 23. The method of using an optical recording medium according to claim 22, wherein the recording thin film layer further contains nitrogen. 24. The recording thin film layer is made of GeTe, Sb ₂ T.
The method of using the optical recording medium according to claim 15, comprising e ₃ , Sb and nitrogen. 25. The composition of the recording thin film layer is Sb / Sb ₂ T.
The method of using the optical recording medium according to claim 15, wherein 0.2 ≦ b ≦ 0.5 where the molar ratio of e ₃ is b. 26. The method of using an optical recording medium according to claim 15, further comprising an overcoat resin protective layer having a film thickness in the range of 3 to 15 μm that generates tensile stress, on the upper surface of the reflective layer.