JPH07282475A - Method for initializing phase transition type optical disk, and phase transition type optical disk - Google Patents

Abstract

PURPOSE:To obtain a method for initializing a phase transition type optical disk capable of initializing the optical disk under optimum conditions by a common simple method even if the material and constitution of the disk change. CONSTITUTION:While a laser beam is moved at a specified speed in the radial direction of the optical disk which has dielectric layers 2, 4 and a recording layer 3 on a substrate 1 and is not formed with a protective film 6, a laser power is increased and the focus error signal of this time is observed. The value of the laser power generating noise is set at a Pc value which is the value of the laser power at which sufficient crystallization is attained without thermal damage. The ordinary optical disk formed with the protective film 6 is initialized at the same rotating speed and the transfer speed of the same laser beam by using the laser beam of the power below this Pc value, by which the thermal damage of the optical disk is prevented and the sufficient crystallization is effected.

Description

Detailed Description of the Invention

[0001]

[0001]

[0002]

BACKGROUND OF THE INVENTION The present invention relates to the optical recording of information,
The present invention relates to a rewritable and erasable phase-change optical disc and an initialization method thereof.

[0003]

[0002]

[0004]

2. Description of the Related Art A magazine "Electronics" (March 1986 issue, page 38, "Optical phase change") describes a method of irradiating a rotating disk with a high-power argon laser for initialization. There is. This initialization method has a temperature distribution of not less than the glass transition point and not more than the melting point in the track direction, and spreads the beam spot in the radial direction to crystallize many information tracks at a time. It is described that the phase change type optical disk can be supplied at low cost. However, no specific initialization condition is disclosed here.

[0005]

Further, in Japanese Unexamined Patent Publication No. 02-42661, an optical recording layer of an optical recording medium in which a large number of arc-shaped recording tracks are provided in parallel is formed on a substrate and then a plurality of laser beams are formed by a single laser beam. An initialization method is disclosed, in which regions on adjacent substrates including tracks are sequentially scanned while partially overlapping each other. It is described that this initialization method can shorten the initialization time and reduce unerased residue and noise. However, there is no disclosure regarding an initialization method for suppressing deterioration of a recording signal at the time of repetition.

[0006]

[0004]

[0007]

The above-mentioned conventional examples are as follows.
The purpose is to crystallize the recording layer in an amorphous state in a short time, and no initialization method has been disclosed so that the state becomes the best when overwriting is repeated.

[0008]

In recent years, in order to increase the recording density, mark length recording indicating a signal of a plurality of bits according to the mark length is performed instead of mark position recording indicating a signal by a mark formed at a predetermined position. It's coming. In this mark length recording, since the detected signal changes depending on the mark length, it is necessary to prevent the detection error due to the increase of jitter by making the shapes of the front end and the rear end of the mark the same. The present inventor has observed a phenomenon in which, when the mark length recording is repeatedly overwritten, the jitter of the second overwrite extremely increases as compared with the first overwrite. This jitter gradually decreases and recovers to a constant value at about the 10th overwrite, but there is particularly much jitter due to deterioration of the disk at the 2nd overwrite, and if this is not reduced, subsequent recording / playback cannot be performed. It was necessary to reduce the second jitter. Although it has been known that the degree of deterioration of the disk largely depends on the initialization condition, there has been no example of solving the deterioration of the disk by paying attention to the initialization condition so far.

[0009]

Further, initialization involves many parameters such as the power of the initialization laser light, the rotational linear velocity of the disk, the moving speed of the initialization laser light in the radial direction of the disk, and is optimal for any disk. It was difficult to find an initialization condition that For this reason, conventionally, initialization is performed by changing initialization conditions variously every time the disc material or configuration is changed, and recording, reproduction, and overwriting are repeatedly performed for each disc to perform optimal initialization for that disc. The method of finding the condition was adopted.
However, this method requires time and cost because it needs to be repeated for each disk.

[0010]

Therefore, the present invention solves the above problems by providing a method for initializing a phase change type optical disk which can perform initialization under optimum conditions by a common simple method even if the material and the structure of the disk are changed. The purpose is to resolve.

[0011]

[0008]

[0012]

As a means for achieving the above object, there is provided a method for initializing a phase-change optical disk which reversibly changes its phase between a crystalline state and an amorphous state by irradiation with laser light. , Initialization is performed on the first phase change type optical disc in which a thin film including at least a recording layer, a dielectric layer and a reflective layer is formed on a substrate and a protective film is not formed, without destroying the thin film. The power value of the initialization laser beam that can be measured is measured in advance, and the power value of the second phase change type optical disk in which the protective film is formed on the optical disk having the same configuration as the first phase change type optical disk is less than or equal to the power value. It is an object of the present invention to provide a method for initializing a phase change type optical disc, which is characterized in that initialization is performed by using a laser beam of power.

[0013]

[0009]

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an initialization method for a phase change optical disk according to the present invention will be described with reference to the drawings. FIG. 1 is an enlarged cross-sectional view cut in the radial direction showing an embodiment of the phase change type optical disk of the present invention.

[0015]

In FIG. 1, a substrate 1 is a transparent substrate through which laser light can pass, and is provided with pregrooves 7 and prepits for guiding the laser light. As the material of the substrate 1, a plastic substrate such as polycarbonate, polyolefin, acrylic, or a glass substrate is used. The first dielectric layer 2 has a film thickness of 10 to 200 nm, preferably 80 to
Is a layer of _{150nm, ZnS-SiO 2, SiO} 2,
Materials such as Ta ₂ O ₅ , SiN, AlN and Al ₂ O ₃ are used.

[0016]

The recording layer 3 is a layer having a film thickness of 10 to 100 nm, preferably 20 to 60 nm, and is made of a phase change material which causes a change in reflectance or a change in refractive index due to a change in state between amorphous and crystalline. Ge as a changing material
Materials such as -Sb-Te series and Ag-In-Te-Sb series are mentioned. The second dielectric layer 4 has a film thickness of 5 to 200 n.
m, and the same material as the first dielectric layer 2 is used.
The thickness of the reflective layer 5 is 10 to 300 nm, preferably 50 to 300 nm.
It is a layer of 150 nm, and the material is Al, Au, A
Metals such as g, Cu, Ni, In, Ti, Cr and Pt or alloys thereof are used. The protective film 6 has a film thickness of 1
˜30 μm, and an ultraviolet curable resin is used as a material. A transparent substrate or another disk having the configuration shown in FIG. 1 may be attached.

[0017]

The phase change type optical disk is in an amorphous state having a low reflectance when formed. Therefore, the laser beam is radiated to perform the initialization of changing from the amorphous state having a low reflectance to the crystalline state having a high reflectance, and then the information is recorded. Normally, a phase change optical disk is initialized at the time of factory shipment and then put on the market as a product.

[0018]

An example of the initialization device is shown in FIG.
Here, the case of initializing a phase change type optical disc recorded at CLV (constant linear velocity) will be described.

In the figure, the spindle unit 20
Supplies a control signal to the spindle driver 24 to drive the spindle 23 and rotate the disk 11 so that the linear velocity becomes constant. And the potentiometer 15
The position of the pickup 12 detected by
It is supplied to the servo unit 21 to control the rotation of the disk 11 so as to keep the linear velocity constant, and is also supplied to the feed control unit 22. The feed control unit 22 supplies a control signal to the motor driver 14 to drive the DC feed motor 13,
The pickup 12 is moved in the radial direction of the disk 11. In the pickup 12, the laser driver 17 irradiates the disk 11 with laser light to perform initialization.
Then, the output of the laser light reflected by the disk 11 is supplied to the focus servo unit 19 via the preamplifier 16, and its output waveform is the oscilloscope 18.
Can be observed by. In addition, each unit 19
22 to 22 mutually control each other.

[0020]

In such an initialization device, the laser beam applied to the optical disk 11 by the pickup 12 has a beam diameter larger than the track width, and is preferably long in the radial direction so that a plurality of tracks are initialized at the same time. Is. A semiconductor laser device, a gas laser device, or the like is used as the laser light emitting device installed in the pickup 12.

[0021]

Then, the optimum laser light power value (Pc
Value) is determined as follows. The structure is the same as that of FIG. 1, and a substrate 1 / first dielectric layer 2 / recording layer 3 / second dielectric layer 4 / reflection layer 5 are formed in this order, and a protective film 6 is formed.
The optical disk 11 in which the disk is not formed is attached to the spindle 23, rotated at a constant linear velocity, and laser light is emitted from the substrate 1 side of the disk 11 by the pickup 12. Then, at this time, the focus error signal supplied to the focus servo unit 19 is measured by the oscilloscope 18. This is because when the recording layer 3 is crystallized by the irradiation of the laser beam, the reflectance of the recording layer 3 is increased and the disk 11 is focused. Then, if the laser power is weak, the recording layer 3 is not crystallized and focus cannot be applied. However, if the laser power is too strong, each layer constituting the disk 11 is destroyed. It is desirable that the laser power with as weak a power as possible be used in the range (focused range) to focus and the power be gradually increased.

[0022]

Therefore, the pickup 12 is moved in the radial direction at a constant speed and the laser power is gradually increased, and the focus error signal at this time is observed.
As a result, as the laser power is increased,
Noise occurs in the focus error signal, and this noise gradually increases. Then, destruction of each laminated layer starts, and when the laser power is further increased, cracks occur in the first and second dielectric layers 2 and 4, and finally the reflective layer 5 is also damaged. By measuring the noise state of the focus error signal in this way, the crystallization state of the recording layer 3 can be known, and thermal damage due to excessive laser power can be detected. Therefore, as the value of the laser power without heat damage and capable of performing sufficient crystallization, the value of the laser power at which noise is generated is defined as the Pc value,
Using the laser power below the Pc value, the protective film 6 is moved at the same disk rotation speed and the same moving speed of the pickup 12.
The present inventor has for the first time found that by performing initialization of a normal optical disc having a film formed therein, sufficient crystallization can be performed while preventing thermal damage.

[0023]

It should be noted that the disk on which the protective film 6 is formed has a P
Even if the disk is initialized by irradiating it with an excessive laser power exceeding the c value, the protective film 6 mainly suppresses the thermal damage caused by the thermal deformation, so that the initialization is achieved. However, if overwriting is repeated, a difference appears in the occurrence of jitter and the like. In particular, when the mark length recording is performed, a large difference does not occur in the jitter during the first recording, but a difference occurs in the jitter during the second overwriting.

[0024]

That is, if the initialization is carried out below the Pc value, the increase of the jitter is small, and if the initialization is carried out above the Pc value, the jitter is remarkably increased and sometimes deteriorates up to about twice. However, when overwriting is performed about 10 times, the difference in jitter approaches. The cause of this is currently under investigation, and the exact cause is unknown, but it is considered that the stress remains in the laminated medium due to thermal deformation and the internal stress is gradually released by repeating. However, no matter how many times overwrite can be repeated, if the jitter increases and the error state occurs in the second time, the disk cannot be used after that and it becomes useless. It is necessary to perform initialization with laser power equal to or lower than the Pc value so as to reduce the jitter.

[0025]

The present invention described above will be demonstrated using Examples 1 and 2. <Example 1> Track pitch 1.6 μm, groove depth 60 n
Layers 2 to 5 to be recording media were formed on a polycarbonate substrate 1 provided with m pregrooves 7 by a DC magnetron sputtering apparatus. First, after evacuating the inside of the sputtering apparatus to a vacuum degree of 1 × 10 ⁻⁶ Torr, Ta was reactively sputtered with a mixed gas of Ar and O ₂ to form Ta ₂ O ₅ having a thickness of 105 nm as the first dielectric layer 2. Provided. Then, a Ge ₁ Sb ₃ Te ₄ film having a thickness of 20 nm was formed as the recording layer 3. On top of this, as a second dielectric layer 4, a T layer having a thickness of 10 nm is formed.
a ₂ O ₅ is deposited, and the reflective layer 5 is formed to a thickness of 100 n.
An Al-Zr alloy of m was provided to prepare an optical disk. Normally, an ultraviolet curable resin is spin-coated on this as a protective film 6, but a disk without the protective film 6 is used when finding optimum initialization conditions. And a wavelength of 830n
m, a track direction is 2 μm, and a radial direction is 20 μm, and an initialization laser having a wide elliptical beam shape having a width of 20 μm is used.
The disk was rotated at a constant linear velocity, and the initialization laser was irradiated from the substrate side of the disk. Further, this initialization laser observes the focus error signal with the oscilloscope 18 while moving in the radial direction to the outer peripheral side of the disk at a speed of 5 μm / revolution, and noise is generated when the laser power is gradually increased. The Pc value, which is the starting laser power value, was measured. In addition, as a comparative example, a disk having a protective film formed by spin-coating a 5 μm ultraviolet curable resin as the protective film 6 is also measured in the same manner, and P is a laser power value at which noise starts to occur.
The c value was measured. The results are shown in Table 1.

[0026]

[0020]

[0027]

[Table 1]

[0028]

As can be seen from Table 1, in the case of the disk provided with the protective film 6, since the protective film 6 presses the layers 2 to 5, the deformation due to heating is less likely to occur. Therefore, the protective film 6
Even if the disc having the protective film 6 is irradiated with a laser beam having a power exceeding the Pc value in the case of the disc having no protective film, no noise is observed in the focus error signal. The Pc value at which
In any case, the linear velocity is higher than the Pc value of the disk without the protective film 6.

[0029]

Next, an optical disk having a 5 μm thick UV curable resin as a protective film 6 on the reflective layer 5 was attached to an initialization device, initialization was performed by changing the power of the initialization laser, and this disk was The change in jitter when the signal was overwritten on the recording / reproducing apparatus was measured. The recording conditions at this time are: linear velocity 2 m / s, recording laser wavelength 684 nm, lens numerical aperture (NA) 0.6, EF
The shortest mark length is 0.68 μm for M modulation mark length recording, 1
4. Beam overwrite recording, peak power (recording power) 12.3 mW, bias power (erase power) 5.
It is 1 mW. The results are shown in Table 2.

[0030]

[0023]

[0031]

[Table 2]

[0032]

When the initialization laser power is 76 mW, which is the Pc value when the linear velocity is 2 m / s, the second jitter is almost the same as the first jitter, and if the initialization is performed under the condition of Pc value or less. It can be seen that the increase in jitter after the second time is suppressed and good rewriting can be performed. Further, as shown in Table 1 above, the Pc value of the disk on which the protective film is formed is 134 mW. And Table 2
Then, the closer to the Pc value, the larger the second jitter tends to be. As a result, when the protective film 6 is provided, the laser power at the time of initialization is changed to follow the change in noise generated in the focus error signal.
It can be seen that it is not possible to obtain a laser power value with a small number of jitters. Therefore, the Pc value, which is the laser power value that causes thermal deformation, is measured on a disk that is not provided with the protective film 6 in advance, and the protective film 6 is provided (normally used) with a laser having a power not higher than this Pc value. Optimal initialization can be achieved by initializing the disk.

[0033]

Example 2 The same disk as in Example 1 was initialized this time at a linear velocity of 4 m / s. As shown in Table 1, the laser power value (Pc value) at which noise occurs in the focus error signal in the disc on which the protective film is not formed is 121 mW. Then, an optical disk provided with a 5 μm thick ultraviolet curable resin on the reflective layer 5 as the protective film 6 is attached to the initialization device, initialization is performed by changing the power of the initialization laser, and this disk is applied to the recording / reproducing device. The change in jitter when the signal was overwritten was measured. The results are shown in Table 3. The recording conditions are exactly the same as in Example 1.

[0034]

[0026]

[0035]

[Table 3]

[0036]

Even in this case, the initialization laser power is 1 which is less than or equal to the Pc value in the case of the disk in which the protective film is not formed.
At 14 mW and 119 mW, since the second jitter did not increase much compared to the first jitter, Pc
It is understood that if the initialization is performed under the condition of not more than the value, the increase of the jitter after the second time can be suppressed, and good rewriting can be performed. 119, which is closer to the Pc value than 114 mW
It is considered that the initialization is performed with mW so that the jitter is less, and the initialization with the Pc value is the best. Then, as shown in Table 1 above, the Pc value of the disk on which the protective film is formed is 198 mW. Then, Table 3 shows that the closer to the Pc value, the larger the second-time jitter becomes. As a result, if the laser power at the time of initialization is changed with the protective film 6 provided to follow the change in the noise generated in the focus error signal, it is impossible to obtain the laser power value with less jitter for the second time. I understand. Therefore, P is a laser power value that causes thermal deformation in a disk that is not provided with the protective film 6 in advance.
Optimum initialization can be realized by measuring the c value and initializing a disk having a structure (usually used) provided with the protective film 6 with a laser having a power less than or equal to the Pc value.

[0037]

[0028]

[0038]

According to the initialization method of the phase-change optical disk and the phase-change optical disk of the present invention, the initialization is performed without destroying the thin film by using the phase-change optical disk in which the protective film is not formed. Since the power Pc value of the initialization laser light that can be generated is measured in advance and the phase-change optical disk having the protective film formed thereon is initialized by using the laser light having the power equal to or lower than the Pc value, recording / erasing can be performed. Even if repeated, there is almost no increase in jitter, and excellent reliability can be obtained. In particular, it is more effective for a phase change type optical disc having an improved recording density. Then, when the phase change optical disc having the protective film formed thereon is initialized by using the laser having the Pc value which is the maximum power value in the range where the film is not thermally deformed in the state without the protective film, the initial jitter is minimized. It is possible to obtain the result that the jitter hardly increases even at the time of the overwriting for the first time.

[0039]

Further, since the optimum initialization condition can be known only by observing the focus error signal, there is an effect that good initialization can be easily performed.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view showing an embodiment of a phase change optical disc of the present invention.

FIG. 2 is a configuration diagram showing an example of an initialization device for a phase change optical disc of the present invention.

[Explanation of symbols]

 1 Substrate 2 First Dielectric Layer 3 Recording Layer 4 Second Dielectric Layer 5 Reflective Layer 6 Protective Film 7 Pregroove

Claims (3)

[Claims] 1. A method for initializing a phase-change optical disk which reversibly changes its phase between a crystalline state and an amorphous state upon irradiation with laser light, comprising at least a recording layer, a dielectric layer and a reflective layer on a substrate. For the first phase change type optical disc having a thin film consisting of and having no protective film formed thereon, the power value of the initialization laser beam capable of performing initialization without destroying the thin film was measured. Every other time, initialization is performed on the second phase change type optical disc in which a protective film is formed on the optical disc having the same configuration as the first phase change type optical disc, by using laser light having a power less than the power value. Initializing method for phase change optical disk. 2. The phase change according to claim 1, wherein the power value is measured from a focus error signal when the initialization laser beam is applied to the first phase change type optical disk in which the protective film is not formed. Type optical disc initialization method. 3. A phase-change optical disk which is initialized by using the phase-change optical disk initialization method according to claim 1.