Title of Invention

AN OPTICAL INFORMATION RECORDING MEDIUM

Abstract The invention relates to an optical information recording medium comprising a disk-like substrate and a plurality of information layers formed on the substrate having a first information layer and a second information layer, the first information layer having a BCA which comprises a plurality of band-like portions having different reflectivities, extending in the radial direction, and being arranged like a bar code, the second information layer not including a BCA, wherein the BCA is formed by providing initialized portions and uninitialized portions in a first area that is an area corresponding to the radius range of r1-r2 on the first information layer, each of the plurality of information layers comprises at least a recording layer that generates a reversible change between an amorphous phase and a crystalline phase by irradiation with the laser beam, the reversible change being optically detectable, and the first information layer is located on the far side from the laser beam incident side, the second information layer comprises a third area that is an area corresponding to the radius range of r1-r2, and a fourth area that is other than the third area, a difference in reflectivities between the radial positions r3 and r4 is 0.2% or more on the second information layer and a reflectivity at radial position r3 is higher than a reflectivity at radial position r4, where r3 denotes a radial position of an initialized portion in the third area and close to the fourth area, and r4 denotes a radial position of an initialized portion in the fourth area and close to the third area.
Full Text OPTICAL INFORMATION RECORDING MEDIUM AND METHOD FOR MANUFACTURING THE
MEDIUM
BACKGROUND OF THE INVENTION
5 1. Field of the Invention
The present invention relates to an optical information
recording medium for recording and reproducing information by using
optical means such as a laser beam, and a method for manufacturing
the medium.
10 2. Description of the Prior Art
There is conventional technology available for reproducing or
recording information at high density by utilizing a laser beam.
This conventional technology is commercialized mainly as optical
disks.
Optical disks can be divided roughly into the read-only type,
the write-once read-many type and the rewritable type.
The read-only type is commercialized as compact discs or laser
disks, and the write-once read-many type and the rewritable type are
commercialized as disks for recording document files and data files.
20 As the rewritable type optical disk, a magneto optical disk and a
phase-change type optical disk are mainly known.
The phase change type optical disk utilizes the reversible
change of state of a recording layer between amorphous and
crystalline states (or between a crystalline state and another
25 crystalline state having a different structure) by irradiation with a
laser beam. More specifically, when a laser beam is irradiated onto
a phase-change type optical disk, at least one of a refractive index
and an attenuation coefficient of a thin film for recording changes.
In addition, when a laser beam is irradiated onto a recorded part of
30 the phase-change type optical disk, the amplitude of light that
passes through the recorded part, or light that is reflected by the
recorded part, changes. As a result, the amount of the passed light
or the reflected light that reaches the detection system changes so
that the signal can be reproduced.
Generally in a phase-change type optical disk, the crystalline
state of a recording layer material is used as the unrecorded state,
while the amorphous state of the recording layer material is used as
the recorded state. Here, the amorphous state is obtained by
irradiating the laser beam so as to melt the recording layer material
40 and by cooling the recording layer material rapidly. In addition,
when erasing the signal, a laser beam of a smaller power than the
power for recording is irradiated so that the recording layer becomes
crystalline.
A chalcogen compound is often used as the recording layer
material. The recording layer made of a chalcogen compound is
deposited in the amorphous state, so it is necessary to crystallize
the entire recording area in advance to give it the unrecorded state.
This crystallization of the entire area is called "initialization".
The initialization process is included in a process for
manufacturing the disk, and a laser beam or a flash light source is
used to crystallize the recording layer. When using a laser beam,
the disk is rotated while the laser beam is irradiated and focused
onto an information layer. Then, the position of the optical head is
shifted in the radial direction of the disk, so that the entire
surface of the disk can be initialized.
Initialization conditions including a laser power, a linear
speed, a defocus amount and a feed pitch in this initialization are
determined so as to satisfy the following criterion. Namely, the
initialization conditions are generally determined so that the entire
initialization area is crystallized uniformly without remaining in
the amorphous state, and so that the quality of signal is constant
during the period from the first recording to after a plurality of
times (a few tens of times) of overwriting information.
In order to determine the initialization conditions, the
initialization conditions are detected at a middle position in the
radial direction of the disk (a predetermined position within a data
area for recording and reproducing information). Furthermore, the
detected initialization conditions are used for initializing the
entire surface of the disk, including a burst cutting area that will
be described later. Namely, the same conditions are used for
initializing the entire surface of the disk.
Note that a single-sided two-layer structure and a method for
manufacturing the structure have been proposed for increasing the
recording capacity per unit area of an optical disk, and a technique
for changing the initialization conditions for each of the layers is
known (for example, see Japanese unexamined patent publication No.
10-132982). In addition, there is a document that describes a method
for manufacturing a phase-change optical disk that has the single-
sided two-layer structure and is used with a blue violet laser beam
(for example, see Japanese unexamined patent publication No. 2000-
400442).
The standards for a DVD-RAM and a Blu-ray disk describe that a
Burst cutting area (hereinafter referred to as "BCA") is provided to
a disk for identifying each disk.
This BCA is formed by cutting the film using a high power laser
beam, or in a normal initialization process by providing initialized
portions and uninitialized portions in the radial direction like a
bar code (see Fig. 1), for example.
When forming the BCA in the initialization process, a relative
angular velocity between the optical head of the laser beam for
initialization and the disk is maintained at a constant value while
the laser beam is turned on and off so that the initialized portions
and the uninitialized portions are provided.
In addition, when reading information of the BCA, the disk is
rotated, and the laser beam is focused onto a BCA region where the
BCA is formed. Thus, the information of the BCA is read from the
difference in reflectivity between a portion with the film and a
portion without the film, or between the initialized portion and the
uninitialized portion. Note that standards for a DVD-RAM and a Blu-
ray disk describe that the BCA is provided to the innermost
circumference on the rearmost layer viewed from the laser beam
incident side.
The present inventors have been developing an optical disk
having a phase-change type single-sided multi-layered structure using
a blue-violet color laser beam. For example, they have been
developing an optical disk including a transparent substrate on which
a first information layer, an optical separation layer, a second
information layer and a transparent layer are formed, as shown in Fig.
1. In addition, this optical disk has the BCA that is formed on the
first information layer in the initialization process.
According to a study by the inventors, two problems are found
in this initialization process as follows.
The first problem is that the second information layer may be
initialized in part in the process for providing the BCA on the first
information layer, when performing the initialization process on the
first information layer and the second information layer one by one
in this order.
The second problem is that a defocus may occur at the same
radial area as the BCA region on the first information layer so that
the initialization process is stopped during the initialization
process of the second information layer after the initialization of
the first information layer.
SUMMARY OF THE INVENTION
A main object of the present invention is provide a method for
manufacturing an optical information recording medium having a
single-sided multi-layered structure in which the above-mentioned
problems are solved, and the optical information recording medium
itself.
(i) A first method according to the present invention is a
method for manufacturing an optical information recording medium that
includes a disk-like substrate and an information layer formed on the
substrate, the information layer including a BCA which comprises a
plurality of band-like portions having different reflectivities,
extending in the radial direction, and being arranged like a bar code.
The BCA is formed by providing initialized portions and uninitialized
portions in an area corresponding to the radius range of rl-r2 on the
information layer. Furthermore, at least one of a laser power, a
linear speed and a focal point of the laser beam for the information
layer is changed between initializing an area of the radius range of
rl-r2 and initializing an area of another radius range.
More specific description is as follows.
(1) The optical information recording medium includes a
plurality of information layers and a transparent layer formed on a
disk-like substrate in this order, and an optical separation layer is
provided between the plurality of information layers. The
information layer has at least a recording layer that generates an
optically detectable reversible change between an amorphous phase and
a crystalline phase by irradiation with the laser beam. At least one
of the plurality of information layers has the BCA which comprises a
plurality of band-like portions having different reriecEivities,
extending in the radial direction, and being arranged like a bar code.
(2) An initialization power for an information layer with the
BCA is set to a lower value when initializing the area of the radius
range of rl-r2 than when initializing the area of other radius range.
(3) An initialization linear speed for an information layer
with the BCA is set to a higher value when initializing the area of
the radius range of rl-r2 than when initializing the area of other
radius range.
(4) A focal point of the initialization laser beam for an
information layer with the BCA is set farther from the information
layer to be initialized when initializing the area of the radius
range of rl-r2 than when initializing the area of other radius range.
(ii) A second method according to the present invention is a
method for manufacturing an optical information recording medium that
includes a disk-like substrate and a plurality of information layers
formed on the substrate, the plurality of information layers
including a first information layer that includes a BCA which
comprises a plurality of band-like portions having different
reflectivities, extending in the radial direction, and being arranged
like a bar code. The BCA is formed by providing initialized portions
and uninitialized portions in an area corresponding to the radius
range of rl-r2 on the first information layer. Furthermore, for an
information layer without the BCA, at least one of a laser power, a
linear speed, a focal point of the laser beam, and a feed pitch of
the laser beam is changed between initializing the area of the radius
range of rl-r2 and initializing the area of other radius range.
Here, the optical information recording medium may be as
follows. Namely, the optical information recording medium includes a
plurality of information layers and a transparent layer formed on a
disk-like substrate in this order, and the optical information
recording medium further includes an optical separation layer
disposed between the plurality of information layers. Each of the
information layers has at least a recording layer that generates an
optically detectable reversible change between an amorpnous pnase and
a crystalline phase by irradiation with an energy beam. At least "one
of the plurality of information layers (a first information layer)
has the BCA which comprises a plurality of band-like portions having
different reflectivities, extending in the radial direction, and
being arranged like a bar code.
More specific description for the second method is as follows.
(1) An initialization laser beam power for an information layer
without the BCA is set to a higher value when initializing the area
of the radius range of rl-r2 than when initializing the area of other
radius range.
(2) An initialization linear speed for an information layer
without the BCA is set to a lower value when initializing the area
of the radius range of rl-r2 than when initializing the area of other
radius range.
(3) A focal point of the initialization laser beam for an
information layer without the BCA is set closer to the information
layer to be initialized when initializing the area of the radius
range of rl-r2 than when initializing the area of other radius range.
(4) A feed pitch of the initialization laser beam for an
information layer without the BCA is set to a smaller value when
initializing the area of the radius range of rl-r2 than when
initializing the area of other radius range.
Furthermore, the optical information recording medium itself in
the first and the second method for manufacturing an optical
information recording medium satisfies the inequalities Ral > Ra2 and
Rcl in the amorphous state and in the crystalline state of an information
layer with the BCA (hereinafter referred to as "first information
layer")-"at a wavelength of the laser beam for crystallization. Ra2
and Rc2 respectively denote reflectivities in the amorphous state and
in the crystalline state of an information layer without the BCA
(hereinafter referred to as "first informaticj3.,.JLay.ex.l)._iat-^a,
wavelength of the laser beam for crystallization.
In addition, the first information layer and the second
information layer are initialized by using one optical head in the
order of the first information layer and then the second information
layer.
(iii) A first structure of the optical information recording
medium according to the present invention includes a disk-like
substrate and an information layer formed on the substrate, the
information layer including a BCA which comprises a plurality of
band-like portions having different reflectivities, extending in the
radial direction, and being arranged like a bar code. The BCA is
formed by providing initialized portions and uninitialized portions
in the area corresponding to the radius range of rl-r2 (hereinafter
referred to as "BCA region") on the information layer. Furthermore,
reflectivities are different between radial positions r3 and r4 on
the information layer with the BCA, where r3 denotes a radial
position of an initialized portion in the BCA region and a position
being close to "a~^al:a~"area, and r4 denotes a radial position of an
initialized portion in the jiajta _area,_and"a 'position being close to
the BCA region......
More specific description is as follows.
(1) The optical information recording medium includes a
plurality of information layers and a transparent layer formed on a
disk-like substrate in this order and the optical information
recording medium further includes an optical separation layer
disposed between the plurality of information layers. The
information layer has at least a recording layer that generates an
optically detectable reversible change between an amorphous phase and
a crystalline phase by irradiation with an energy beam. At least one
of the plurality of information layers has the BCA which comprises a
plurality of band-like portions having different reflectivities,
extending in the radial direction, and being arranged like a bar code.
(2) An information layer with the BCA of the optical
information recording medium has a reflectivity at a radius r3 lower
than a reflectivity at a radius r4.
(3) The optical information recording medium is manufactured by
the initialization process in which at least one of the
initialization conditions for an information layer with the BCA is
changed between initializing the area of a radius range rl-r2 and
initializing the area of other radius range. Here, the initialization
conditions include a laser power, a linear speed, and a focal point
of the laser beam for the information layer with the BCA.
(4) The optical information recording medium is manufactured by
the initialization process in which a laser power for an information
layer with the BCA is set to a lower value when initializing the
area of a radius range rl-r2 than when initializing the area of other
radius range.
(5) The optical information recording medium is manufactured by
the initialization process in which an initialization linear speed
for an information layer with the BCA is set to a higher value when
initializing the area of a radius range of rl-r2 than when
initializing the area of other radius range.
(6) The optical information recording medium is manufactured by
the initialization process in which a focal point of the
initialization laser beam for an information layer with the BCA is
set farther from the information layer to be initialized when
initializing the area of a radius range of rl-r2 than when
initializing the area of other radius range.
(iv) A second structure of the optical information recording
medium according to the present invention includes a disk-like
substrate and a plurality of information layers formed on the
substrate, the plurality of information layers including a first
information layer that includes a BCA which comprises a plurality of
band-like portions having different reflectivities, extending in the
radial direction, and being arranged like a bar code. The BCA is
formed by providing initialized portions and uninitialized portions
in an area corresponding to the radius range of rl-r2 (hereinafter
referred to as "BCA region") on the first information layer.
Furthermore, reflectivities are different between radial positions r3
and r4 on the information layer without the BCA, where r3 denotes a
radial position of an initialized portion in the BCA region and a
position being close to a data area, and r4 denotes a radial position
of an initialized portion in the data area and a position being cl'ose
to the BCA region.
Here, the optical information recording medium may be as
follows. Namely, the optical information recording medium includes a
plurality of information layers and a transparent layer formed on a
disk-like substrate in this order, and the optical information
recording medium further includes an optical separation layer
disposed between the plurality of information layers. Each of the
information layers has at least a recording layer that generates an
optically detectable reversible change between an amorphous phase and
a crystalline phase by irradiation with an energy beam. At least one
of the plurality of information layers (a first information layer)
has the BCA which comprises a plurality of band-like portions having
different reflectivities, extending in the radial direction, and
being arranged like a bar code.
More specific description is as follows.
(1) An information layer without the BCA of the optical
information recording medium has a reflectivity at a radius r3 higher
than a reflectivity at a radius r4.
(2) The optical information recording medium is manufactured by
the initialization process in which at least one of the
initialization conditions for an information layer without the BCA is
changed between initializing the area of a radius range rl-r2 and
initializing the area of other radius range. Here, the initialization
conditions include a laser power, a linear speed, and a focal point
of the laser beam for the information layer without the BCA.
(3) The optical information recording medium is manufactured by
the initialization process in which a laser power for an information
layer without the BCA is set to a higher value when initializing the
area of a radius range rl-r2 than when initializing the area of other
radius range.
(4) The optical information recording medium is manufactured by
the initialization process in which an initialization linear speed
for an information layer without the BCA is set to a lower value when
initializing the area of a radius range of rl-r2 than when
initializing the area of other radius range.
(5) The optical information recording medium is manufactured by
the initialization process in which a focal point of the
initialization laser beam for an information layer without the BCA is
set closer to the information layer to be initialized when
initializing the area of a radius range of rl-r2 than when
initializing the area of other radius range.
(6) The optical information recording medium is manufactured by
the initialization process in which a feed pitch for an information
layer without the BCA is set to a smaller value when initializing the
area of a radius range of rl-r2 than when initializing the area of
other radius range.
Furthermore, the first or the second optical information
recording medium preferably has a difference in reflectivities
between radial positions r3 and r4 on an information layer with the
BCA or an information layer without the BCA, and the difference is
0.2% or more.
In addition, a difference in the distances between radial
positions r3 and r4 is 0.2 mm or less.
According to the present invention, the initialization of an
optical information recording medium can be performed appropriately.
Stopping of the initialization process on a track is prevented so
that yield of manufacturing optical information recording media can
be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a structure of an optical disk used for an
embodiment of the present invention.
Fig. 2 shows a focus error signal for initialization of the
optical disk used for an embodiment of the present invention.
Fig. 3 shows a structure of the optical disk used for the
embodiment of the present invention.
Fig. 4 shows a structure of an initialization device for the
optical disk used for the embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
(General outlines of the invention)
(A principle of an initialization process)
First, a principle of an initialization process for a first information layer and a
second information layer will be described in detail with reference to Fig. 2.
When the optical head for irradiating an initialization laser beam approaches a
transparent layer as shown in Fig. 2, three focus error signals (that are
respectively from the transparent layer, the second information layer, and the first
information layer (see Fig. 1)) are detected sequentially. Amplitudes of the three
focus error signals are detected to be large when the reflectivity of each
information layer is high, and detected to be small when it is low.
The reflectivity of each information layer varies depending on a combination of
the structure of the thin film and the phase state thereof (amorphous or
crystalline). If the detected focus error signal is small, the probability of failure in
the initialization process increases.
The structure or the information layer used here satisfies the inequalities Ra1 >
Ra2 and Rc1 information layer and the second information layer. Here, Ra1 and Rc1
respectively denote reflectivities in the amorphous state and in the crystalline
state of the first information layer, while Ra2 and Rc2 respectively denote
reflectivities in the amorphous state and in the crystalline state of the second
information layer. If the first information layer and the second information layer
are in the uninitialized state, when the initialization laser beam is irradiated, the
initialization laser beam can be focused onto the first information layer because
of Ra1> Ra2, and the first information layer can be initialized. Next, in order to
initialize the second information layer, an initialized portion ( a crystallized
portion), even if small, is made on the second information layer. Then Rc1 is satisfied, and the laser beam can be focused onto the second information
layer. Thus, the second information layer can be initialized.
(Reasons why the problems occur)
According to a study by the present inventors, the abovementioned problems are
considered to occur due to the following reasons.
First, the reason why the second information layer is
initialized partially during initialization of the first information
layer, which is the first problem, is considered as below.
When the first information layer is initialized, the
initialization laser beam is also irradiated onto the second
information layer in an unfocused state. For the disk that the
inventors are developing, an initialization laser power that is
necessary for initializing the second information layer must be
higher than a laser power that is necessary for initializing the
first information layer. Therefore, during initialization of the
first information layer, the second information layer is not to be
initialized.
However, the energy amount that is necessary for being
crystallized (initialized) varies depending on the disk structure.
The disk that is adopted here has a disk structure in which
initialization sensitivity of the first information layer is lower
than usual and initialization sensitivity of the second information
layer is higher than usual. In addition, a multi-layered film that
constitutes each information layer has variable film thickness in the
radial direction of each disk. This film thickness variation causes
a variation of the initialization sensitivity in the direction of the
disk, too. The second information layer of the disk that is adopted
here is considered to have a much higher initialization sensitivity
at the innermost circumference of the disk where the BCA is formed
due to the film thickness variation.
Therefore, if the same initialization method as the
conventional one is used, the second information layer is partially
initialized during initialization of the first information layer.
Next, the reason why a defocus occurs on the same radial area
of the second information layer as the BCA region of the first
information layer during initialization of the second information
layer causing the initialization to be stopped, which is the second
problem, is considered as below.
The disk that is adopted here has a structure in which the
difference between Ral and Rc2 is smaller than usual at the same
radial area as the BCA region having the uninitialized portion due to
the film thickness variation in the radial direction. Therefore,
when the laser beam that is initializing the second information layer
approaches the same radial area as the BCA region, focusing becomes
unstable.
Therefore, if the same initialization method as the
conventional one is used, defocus occurs in the same radial area as
the BCA region during initialization of the second information layer
resulting in the initialization stopping.
(First embodiment)
Hereinafter, an embodiment of the present invention will be
described with reference to the drawings.
The technology that is described in this embodiment is for
solving the above-mentioned first problem, i.e., for preventing the
second information layer from being initialized partially during the
time when the first information layer is initialized.
(Disk structure)
A structure of the disk used in this embodiment will be
described with reference to Fig. 3. In Fig. 3, the laser beam for
recording or reproducing information or initializing the information
layer enters from the side of a transparent layer 7. A substrate 1
is made of a resin plate such as polycarbonate or PMMA or a glass
plate. A surface of a substrate 2 is covered with a spiral groove or
concentric grooves.
A first information layer 3 is formed on the substrate 1 (at
the laser beam incident side). The first information layer 3
includes at least a reflection layer 8, protection layers 9 and 11,
and a recording layer 10.
An optical separation layer 4 is formed on the first
information layer 3. The optical separation layer 4 is made of a
material which is transparent for a wavelength of the laser beam
irradiated for recording and reproducing a signal on the first
information layer 3. The optical separation layer 4 has the function
of optically separating the first information layer from the second
information layer. The optical separation layer 4 is formed by a
spin coat method for forming a layer made of an ultraviolet curing
resin or the like, or by a method for bonding a transparent film by
using an adhesive tape or an ultraviolet curing resin. A surface 5
of optical separation layer is covered with a spiral groove or
concentric grooves.
A second information layer 6 is formed on the optical
separation layer 4. The second information layer 6 includes at least
a reflection layer 12, protection layers 13 and 15, and a recording
layer 14.
The transparent layer 7 is formed on the second information
layer 6. The transparent layer 7 is formed by a spin coat method for
forming a layer made of an ultraviolet curing resin or the like, or
by a method for bonding a transparent film onto the information layer
6 by using an adhesive tape or an ultraviolet curing resin.
The protection layers 9, 11,13 and 15 can be made of a material
containing an oxide of Al, Si, Ta, Mo, W, Zr or the like, a sulfide
of ZnS or the like, a nitride of Al, B, Ge, Si, Ti, Zr or the like,
or a fluoride of Pb, Mg, La or the like as a principal component. In
this embodiment, a material having a composition of ZnS-20mol%Si02 is
used.
The recording layers 10 and 14 can be made of a material that
is a phase change material containing Te, In, Se or the like as a
principal component. As a principal component of a well-known phase
change material, there are TeGeSb, TeGeSn, TeGeSnAu, SbSe, SbTe,
SbSeTe, In-Te, In-Se, In-Se-Tl, InSblnSbSe, GeSbTeAg and the like.
Material systems that are commercialized or often researched at
present for a phase change optical disk include the GeSbTe system,
the AgGeSbTe system or the like. The recording layer is usually
formed in the amorphous state. When these recording layer materials
are used, transmittance in the crystalline state is smaller than
transmittance in the amorphous state at an infrared wavelength that
is usually used for initialization of a recording layer. In this
embodiment, a recording layer material of the GeSbTe system is mainly
used.
The reflection layers 8 and 12 can be made of a material
containing a metal element such as Ag, Au, Al or the like as a
principal component. In addition, instead of a metal reflection
layer, two or more types of protection layers having different
refractive index values may be laminated so as to obtain optical
characteristics similar to that of the reflection layer. In this
embodiment, a metal reflection layer containing Ag as a principal
component is used.
Each of the protection layer, the recording layer, and the
reflection layer is usually formed by an electron beam evaporation
method, a sputtering method, a CVD method, a laser sputtering method
or the like. In this embodiment, the sputtering method is used.
(Initialization process)
Next, a process for initializing the optical information
recording medium having the above-mentioned single-sided two-layer
structure by using a laser beam will be described.
An outline of the initialization device will be described with
reference to Fig. 4. The laser beam emitted by a laser beam source
is focused by an objective lens on the second information layer 6 or
the first information layer 3 by an astigmatic aberration method, for
example. The focusing is performed by using focus error signals
obtained from the first information layer 3 and the second
information layer 6. A focusing control is performed by a knife edge
method or other various methods.
Next, a procedure for focusing the initialization laser beam on
a desired information layer will be described, in which the first
information layer 3 and the second information layer 6 are
distinguished from each other when initializing the formed
information layers (the first information layer 3 and the second
information layer 6).
First, when the optical head that irradiates the laser beam for
the initialization approaches the transparent layer, three focus
error signals from the transparent layer 7, the second information
layer 6 and the first information layer 3 are detected sequentially
(see Fig. 2) . For example, in order to initialize the second
information layer 6, the focusing is performed by the second focus
error signal among the focus error signals when the optical head
approaches the transparent layer. Alternatively, the initialization
device performs the process of detecting the focus error signal from
the first information layer 3, and then focusing is performed by the
second focus error signal while moving the optical head away from the
transparent layer (Note that the same method is used for the focus
also in the case of more than two information layers).
There are a plurality of ways of initializing the first and the
second information layers 3 and 6, as follows.
(1) The initialization of each of the information layers is
performed just after forming each of the information layers.
(2) The initialization is performed just after forming each of
the information layers and the optical separation layer 4 thereon
(the transparent layer 7 on the second information layer 6).
(3) The initialization is performed after forming the first
information layer 3, the optical separation layer 4, the second
information layer 6, and the transparent layer 7 on the substrate 1
(Note that the transparent layer 7 may be formed after the
initialization).
(4) In the case of (3), the first information layer 3 is
initialized prior to the initialization of the second information
layer 6 (Note that the opposite order is possible).
In addition, a high laser power is necessary for
crystallization (initialization) by using a laser beam, so an
infrared laser having a wavelength of approximately 800 nm is usually
used.
In this embodiment, the BCA is provided by utilizing the
initialization process. The initialization area to be initialized is
an area of the radius range of 21-59 mm on the disk, and the BCA is
formed in the area corresponding to the radius range of 21-22 mm on
the disk by providing band-like uninitialized portions (uninitialized
portions) which extend in the radial direction and are arranged like
a bar code. In addition, when forming the BCA (within the radius
range of 21-22 mm), the disk is rotated at a constant angular speed
(2728 rpm) for performing the initialization. The angular speed
corresponds to a linear speed of 6.0 m/sec at a radius 21 mm and 6.28
m/sec at a radius 22 mm.
The structure of the disk used in this embodiment will now be
described in more detail.
As an example of a structure of the disk, a polycarbonate plate
is adopted as the substrate 1, which has a diameter of 120 mm and a
thickness of 1.1 mm, and a surface of which is covered with a guide
groove having a depth of 20 nm and a track pitch of 0.3 urn. On the
substrate 1, an Ag reflection layer, GeN, ZnS-20mol%SiO2,
Ge22Sb25Te53(at%) and ZnS-20mol%SiO2 are formed in this order by a
magnetron sputtering method so as to form the first information layer
3. Then, a polycarbonate plate having a diameter of 120 mm, a
thickness of 25 µm and a surface covered with a guide groove having a
depth of 20 nm and a track pitch of 0.3 µm is formed by an
ultraviolet curing resin so as to form the optical separation layer 4
having a total thickness of 30 µm on the first information layer 3.
After that, on the optical separation layer 4, an Ag reflection layer,
GeN, Ge22Sb25Te53(at%) and ZnS-20mol%SiO2 are formed in this order by
a magnetron sputtering method so as to form the second information
layer 6. Then, the transparent layer 7 having a thickness of 0.1 mm
is formed by a spin coat method.
The structure of the disk used for the study, especially the
structure of the information layer, is as follows.
The first information layer 3 has a structure in which an Ag
reflection layer of 100 nm, a GeN layer of 5 nm, a ZnS-20mol%SiO2
layer of 25 nm, a GeSbTe recording layer of 15 nm and a ZnS-
20mol%Si02 layer of 60 nm are formed on the substrate 1.
The second information layer 6 has a structure in which the
optical separation layer 4 is formed on the first information layer 3,
and then an Ag reflection layer of 10 nm, a GeN layer of 5 nm, a ZnS-
20mol%SiO2 layer of 24 nm, a GeSbTe recording layer of 6 nm and a
ZnS-Si02 layer of 50 nm are formed. Furthermore, the transparent
layer 7 is formed on the second information layer 6.
The initialization of each information layer is performed by
using the initialization device having the laser beam source of a
wavelength 810 nm as shown in Fig. 4. The initialization condition
is determined in advance to be a condition without deterioration of
the signal quality (a condition without a increase of jitter) at a
radius of 40 mm on the disk when overwriting information.
On the first information layer 3, the determined initialization
condition (a second initialization condition) includes the defocus
amount of the laser beam at +3 µm (a plus sign means the state where
a correct focus position is located at the back side of the first
information layer 3 viewed from the laser incident side, while a
minus sign means the state where the correct focus position is
located at the front side), a linear speed of 6 m/sec, a feed pitch
of 40 µm, a laser power of 1650-1750 mW (in this embodiment, the
laser power is set to 1700 mW).
On the second information layer 6, the determined
initialization condition (a fourth initialization condition) includes
a defocus amount of +3 µm, the linear speed of 3 m/sec, the feed
pitch of 40 µm and the laser power of 870-930 mW (in this embodiment,
the laser power is set to 900 mW).
Note that the laser beam having a width of 100 µm in the radial
direction of the disk is used for the initialization.
The initialization of each of the information layers is
performed after forming the first information layer 3, the optical
separation layer 4, the second information layer 6 and the
transparent layer 7.
When initializing the first information layer 3, the
initialization laser power, the linear speed and the defocus amount
are changed between the BCA region (a first area, see Fig. 1) where
the BCA is formed and another initialization area (a second area, see
Fig. 1), so as to study the stability of the initialization. The
result of the study is as follows.
In this embodiment, when initializing the BCA region
(corresponding to the radius range of 21-22 mm) and the data area
(corresponding to the radius range of 22-59 mm) on the first
information layer 3, the initialization condition is changed (i.e.,
the first initialization condition and the second initialization
condition are respectively used). When the initialization of the
first information layer 3 is finished, initialized states are checked
by observation using an optical microscope. On this occasion, it is
checked whether or not the second information layer 6 is initialized
in error.
Table 1 shows the result in which the initialization laser
power is changed while the linear speed is maintained at 6 m/sec and
the defocus amount is maintained at +3 urn. Table 2 shows the result
in which the linear speed is changed while the initialization laser
power is maintained at 1700 mW and the defocus amount is maintained
at +3 urn. Table 3 shows the result in which the defocus amount is
changed while the initialization laser power is maintained at 1700 mW
and the linear speed is maintained at 6 m/sec.
Furthermore, each of Tables 1-3 show the reflectivities at the
radial position r3 = 21.9 mm and the radial position r4 = 22.1 mm on
the first information layer 3 when using each initialization
condition (see Fig. 1) . More specifically, the radial position r3 is
located in the BCA region (the first area) and is close to the data
area (the second area) . In addition, the radial position r4 is
located in the data area (the second area) and is close to the BCA
region (the first area) on the first information layer 3.
Furthermore, there are shown the reflectivities from the radial
position r3 and the radial position r4 at the wavelength of 405 nm in
a mirror portion of the reflected light.
The following fact is confirmed from Table 1.
When the initialization laser power for the BCA region is set
to a value more than or equal to 1650-1750 mW which is the optimal
power for the data area, a part of the second information layer 6 is
initialized in error. When initialization laser power for the BCA
region is set to a value less than 1650 mW which is an optimal power
for the data area (namely, the laser power density in a unit area is
small), the second information layer 6 is not initialized. The BCA
is used only for reading a signal as a difference in reflectivities
between the initialized portion and the uninitialized portion, so it
is sufficient if the BCA is crystallized uniformly. Thus, for
example, the BCA may be formed with 1550 mW power, because there is
no large influence to the reflectivity. However, if the
initialization laser power is reduced to 1450 mW for example, uneven
initialization of the BCA may occur. Therefore, it is preferable to
perform the initialization by an initialization laser power within
the range of more than 1450 mW and less than 1650 mW, more preferably
within the range of no less than 1500 mW and no more than 1600 mW.
In addition, a good result is obtained when the initialization
laser power for the BCA region is set to a value 5.9-11.8% lower than
the initialization laser power for the data area (when the laser
power is reduced). Note that this value range is merely determined
corresponding to the structure of the disk that is used in this
embodiment and the structure of the initialization device, and does
not limit an effective range of the present invention. For example,
the optimal range can be changed depending on a structure of the disk
or a structure of the initialization device.
The following fact is confirmed from Table 2.
When the initialization linear speed for the BCA region is set
to a value lower than 6 m/sec which is the linear speed for the data
area, a part of the second information layer 6 is initialized in
error. On the other hand, when the initialization linear speed is
set to a value higher than 6.5 m/sec (namely, when the laser power
density in a unit area is small), the second information layer 6 is
not initialized. However, if the initialization linear speed is
increased to 7.5 m/sec for example, uneven initialization of the BCA
may occur. Therefore, it is preferable to perform the initialization
by an initialization linear speed within the range of more than 6.0
m/sec and less than 7.5 m/sec, more preferably within the range of no
less than 6.5 m/sec and no more than 7.0 m/sec.
)5| In addition, a good result is obtained when the initialization
linear speed for the BCA region is set to a value 8.3-16.7% higher
than the initialization linear speed for the data area (when the
linear speed is increased). Note that this value range is merely
determined corresponding to the structure of the disk that is used in
this embodiment and the structure of the initialization device, and
does not limit the effective range of the present invention. For
example, the optimal range can be changed depending on the structure
of the disk or the structure of the initialization device.
The following fact is confirmed from Table 3.
When the defocus amount for initializing the BCA region is set
to a value which is closer to 0 urn (the "just focus" amount) than +3 µm which is the defocus amount for the data area, a part of the
second information layer 6 is initialized in error. However, if the
defocus amount is increased, the second information layer 6 is not
initialized. Therefore, it is preferable to perform the
initialization with a defocus amount larger than +3 µm, more
preferably +3.5 µm or more.
In addition, a good result is obtained when the defocus amount
for the BCA region is set to a value 16.7% or more larger than the
defocus amount for the data area (when the defocus amount is
increased). Note that this value range is merely determined
corresponding to the structure of the disk that is used in this
embodiment and the structure of the initialization device, and does
not limit the effective range of the present invention. For example,
the optimal range can be changed depending on the structure of the
disk or the structure of the initialization device.
As described above, the second information layer 6 is not
initialized in error when different initialization conditions are
used for the BCA region and the data area. More specifically, the
second information layer 6 is not initialized in error when the
initialization condition, in which a laser power, a linear speed and
a defocus amount are adjusted so that the laser power density in a
unit area is lower than that of the initialization condition for the
data area, is used for the BCA region.
In addition, as understood from Tables 1-3, the second
information layer 6 is not initialized when the difference in
reflectivities of the initialized portion between a radius of 21.9 mm
(a radial position in the BCA region) and a radius of 22.1 mm (a
radial position in the data area) is 0.2¥~"or more and when the
reflectivity at the radius 21.9 mm is-Tower than the other. Note
that th6TIgTi"T:Tie'Hi£ference in the reflectivities is also generated
when the laser power density in a unit area is too low, this causes
an initialization process error because the initialization is not
performed uniformly.
Here, it is considered that a distance in radial directions at
about 0.2 mm does not cause a difference in reflectivities due to the
film thickness distribution on each layer. Therefore, the difference
in the disk reflectivities shown in Tables 1-3 is considered to be
caused by a difference in the initialization conditions. For example,
if the laser power density in a unit area is high, the degree of
initialization increases so that the reflectivity becomes high.
However, if the laser power density exceeds a certain value, the
reflectivity becomes saturated. Therefore, if there is a difference
in reflectivities more than 0.2% within the radius 0.2 mm, the above--
mentioned difference in reflectivities can be ...attributed.,.to..the.
difference'in initialization conditions^.
Note that each of the parameters including a laser power, a
linear speed and a defocus amount is changed individually so that the
laser power density in a unit area is changed in this embodiment. A
similar result can be obtained if some of these parameters are
changed concurrently so as to change the laser power density.
Note that the initialization is performed from the inner
circumference to the outer circumference in this embodiment. A
similar result can be obtained if the initialization is performed
from the outer circumference to the inner circumference.
(Second embodiment)
The technology that is described in this embodiment is for
solving the above-mentioned second problem, i.e., for preventing the
stopping of the initialization of the second information layer after
a defocus occurs during the initialization.
When initializing the second information layer 6, the
initialization power, the linear speed and the defocus amount are
changed between an area (a third area, see Fig. 1) having the same
radius as the BCA region (the first area, see Fig. 1) on the first
information layer 3 and an area (a fourth area, see Fig. 1) having
the same radius as the data area (the second area, see Fig. 1) on the
first information layer 3, so as to study the stability of the
initialization. The result of the study is as follows. The disk
structure and the initialization device in this embodiment are the
same as in the first embodiment, so a detailed description thereof is
omitted.
On the first information layer 3, the BCA is formed in the BCA
region corresponding to the radius range of 21-22 mm by the
initialization process in advance, and further, the initialization is
performed in the data area corresponding to the radius range of 22-59
mm.
In this embodiment, consecutively, the area corresponding to
the radius range of 21-59 mm on the second information layer 6 is
initialized. On this occasion, the area corresponding to the radius
range of radius 21-22 mm, which is the same radius as the BCA region
on the first information layer 3, is initialized by an initialization
condition (a third initialization condition) which is a variation of
an appropriate initialization condition (a fourth initialization
condition) that is determined in advance for the area corresponding
to the radius range of 22-59 mm, while the area corresponding to the
radius range of 22-59 mm is initialized by the appropriate
initialization condition that is determined in advance. It is
checked whether or not the initialization process of the second
information layer 6 is completed without stopping.
As described in the first embodiment, the appropriate
initialization condition determined for the data area on the second
information layer 6 includes the defocus amount of +3 urn, the linear
speed of 3 m/sec, the feed pitch of 40 µm and the laser power of 870-
930 mW (900 mW is used in this embodiment).
In the initialization of the area corresponding to the radius
range of 21-22 mm on the second information layer 6, the linear speed
and the defocus amount are kept at constant values of 3 m/sec and +3m
respectively, while the initialization laser power is changed. The
result is shown in Table 4. Table 5 shows the result when the
initialization laser power and the defocus amount are kept at
constant values of 900 mW and +3 µm respectively, while the linear
speed is changed. Table 6 shows the result when the initialization
laser power and the linear speed are kept at constant values of 900
mW and 3 m/sec respectively, while the defocus amount is changed.
Furthermore, each of the Tables show the reflectivities at the
radial position r3 = 21.9 mm and the radial position r4 = 22.1 mm on
the second information layer 6 when using each initialization
condition (see Fig. 1) . More specifically, the radial position r3 is
located on the second information layer 6 in the area (the third
area) corresponding to the BCA region (the first area) and is close
to the data area (the fourth area). In addition, the radial position
r4 is located on the second information layer 6 in the data area (the
fourth area) and is close to the area (the third area) corresponding
to the BCA region (the first area). Furthermore, there is shown the
reflectivities from the radial position r3 and the radial position r4
at the wavelength of 405 nm in the mirror portion of the reflected
light.
The following fact is confirmed from Table 4.
When the area corresponding to the radius range of 21-22 mm on
the second information layer 6 is initialized by a laser power lower
than or equal to 870-930 mW, which is an appropriate laser power for
the data area, the initialization process stops after a defocus
occurs in the area of radius 21-22 mm. When the laser power is
increased above the appropriate laser power, the initialization does
not stop due to the defocus during the process. Thus, initialization
yield is improved. For example, it is preferable to perform the
initialization process by a laser power more than 930 mW, more
preferably more than or equal to 960 mW.
In addition, a good result is obtained when the initialization
laser power for the area corresponding to the BCA region is set to a
value 6.7% or more higher than the initialization laser power for the
data area (when the laser power is increased). Note that this value
range is merely determined corresponding to the structure of the disk
that is used in this embodiment and the structure of the
initialization device, and does not limit the effective range of the
present invention. For example, the optimal range can be changed
depending on the structure of the disk or the structure of the
initialization device.
The following fact is confirmed from Table 5.
When the area corresponding to the radius range of 21-22 mm on
the second information layer 6 is initialized by a linear speed more
than or equal to 3.0 m/sec, which is an appropriate linear speed for
the data area, the initialization process stops after a defocus
occurs in the area of radius 21-22 mm. When the linear speed is
decreased below the appropriate linear speed, the initialization does
not stop due to the defocus during the process, so the initialization
yield is improved. For example, it is preferable to perform the
initialization process by a linear speed lower than 3.0 m/sec, more
preferably lower than or equal to 2.7 m/sec.
In addition, a good result is obtained when the linear speed
for the area corresponding to the BCA region is set to a value of -
10% or more lower than the linear speed for the data area (when the
linear speed is decreased). Note that this value range is merely
determined corresponding to the structure of the disk that is used in
this embodiment and the structure of the initialization device, and
does not limit the effective range of the present invention. For
example, the optimal range can be changed depending on the structure
of the disk or the structure of the initialization device.
The following fact is confirmed from Table 6.
When the area corresponding to the radius range of 21-22 mm on
the second information layer 6 is initialized by a defocus amount
larger than +3 urn, which is an appropriate defocus amount for the
data area, the initialization process stops after a defocus occurs in
the area of the radius 21-22 mm. When the defocus amount is set to a
value closer to "just focus", the initialization does not stop due to
the defocus during the process so that the initialization yield is
improved. For example, it is preferable to perform the
initialization process with a focal point less than +3 µm, more
preferably less than or equal to +2.5 um.
In addition, a good result is obtained when the defocus amount
for the area corresponding to the BCA region is set to a value of -
16.7% or more lower than the defocus amount for the data area (when
the defocus amount is decreased). Note that this value range is
merely determined corresponding to the structure of the disk that is
used in this embodiment and the structure of the initialization
device, and does not limit the effective range of the present
invention. For example, the optimal range can be changed depending
on the structure of the disk or the structure of the initialization
device.
As described above, it is understood that yield in the
initialization process is improved without a defocus during the
process if different initialization conditions are used between the
area of the radius 21-22 mm (the area having the same radius as the
BCA region) and the area of the radius 22-59 mm (the area having the
same radius as the data area on the first information layer) on the
second information layer 6. More specifically, it is understood that
yield in the initialization process is improved without a defocus
during the process when the area of the radius 21-22 mm is
initialized with the initialization condition including the laser
power, the linear speed and the defocus amount being adjusted so that
the laser power density in a unit area is higher than that of the
initialization condition for the area of radius 22-59 mm.
Here, the reason why a defocus does not occur during the
initialization is considered as follows.
The initialization process is performed by moving the laser
beam a little in the radial direction for every circumference (with a
little overlapping) . In this embodiment, the beam diameter is 100 urn
and the feed pitch is 40 µm, so the area of 60 urn in the area of 100
urn that is crystallized in the first circumference of initialization
is irradiated by the initialization laser beam in the next
circumference of initialization, too. It is considered that the
conventional defocus in the area having the same radius as the BCA
region on the second information layer 6 occurs because the
reflectivity of the uninitialized portion in the BCA region is high.
When the laser power density in a unit area is increased as described
in this embodiment, the initialized area expands in the radial
direction so that reflected light from the uninitialized portion in
the BCA region decreases, resulting in a small amount of defocus.
In addition, as understood from Tables 4-6, the initialization
of the second information layer 6 does not stop in the area of radius
21-22 mm if the difference in reflectivities of the initialized
portions is 0.2% or more between the radius of 21.9 mm (a radial
position in the area having the same radius as the BCA region) and
the radius of 22.1 mm (a radial position in the data area) and if the
reflectivity at the radius of 21.9 mm is higher than the other.
Here, it is considered that a distance in radial directions at
about 0.2 mm does not cause a difference in reflectivities due to the
film thickness distribution on each layer. Therefore, the difference
in the disk reflectivities shown in Tables 4-6 is considered to be
caused by a difference in the initialization conditions. For example,
if the laser power density in a unit area is high, the degree of
initialization increases so that the reflectivity becomes high.
However, if the laser power density exceeds a certain value, the
reflectivity becomes saturated. Therefore, if there is a difference
in reflectivities of more than 0.2% within the radius 0.2 mm, the
above-mentioned difference in reflectivities can be attributed to the
difference in initialization conditions.
Note that each of the parameters including a laser power, a
linear speed and a defocus amount is changed individually so that the
laser power density in a unit area is changed in this embodiment. A
similar result can be obtained if some of these parameters are
changed concurrently so as to change the laser power density.
Note that the initialization is performed from the inner
circumference to the outer circumference in this embodiment. A
similar result can be obtained if the initialization is performed
from the outer circumference to the inner circumference.
(Third embodiment)
The technology that is described in this embodiment is for
solving the above-mentioned second problem, i.e., for preventing the
stopping of the initialization of the second information layer after
a defocus occurs during the initialization.
When initializing the second information layer 6, the feed
pitch of the initialization laser beam is changed between the area
(the third area, see Fig. 1) having the same radius as the BCA region
(the first area, see Fig. 1) on the first information layer 3 and the
area (the fourth area, see Fig. 1) having the same radius as the data
area (the second area, see Fig. 1) on the first information layer 3,
so as to study the stability of the initialization. The result of
the study is as follows. The disk structure and the initialization
device in this embodiment are the same as in the first embodiment, so
a detailed description thereof is omitted.
On the first information layer 3, the BCA region is formed in
the area corresponding to the radius range of 21-22 mm by the
initialization process in advance, and further the initialization is
performed in the data area corresponding to the radius range of 22-59
mm.
In this embodiment, consecutively, the area corresponding to
the radius range of 21-59 mm on the second information layer 6 is
initialized. On this occasion, the area corresponding to the radius
range of radius 21-22 mm, which is the same radius as the BCA region
on the first information layer 3, is initialized by using a feed
pitch that is a variation of an appropriate feed pitch for the area
corresponding to the radius range of 22-59 mm determined in advance,
while the area corresponding to the radius range of 22-59 mm is
initialized by the appropriate feed pitch determined in advance. It
is checked whether or not the initialization process of the second
information layer 6 is completed without stopping.
As described in the first embodiment, the appropriate
initialization condition determined for the data area on the second
information layer 6 includes the defocus amount of +3 µm, the linear
speed of 3 m/sec, the feed pitch of 40 µm and the laser power of 870-
930 mW (900 mW is used in this embodiment).
In the initialization of the area corresponding to the radius
range of 21-22 mm on the second information layer 6, the linear speed,
the defocus amount and the initialization laser power are kept at
constant values of 3 m/sec, +3 µm and 900 mW respectively, while the
feed pitch is changed. The result is shown in Table 7.
0o7 Furthermore, Table 7 shows the reflectivities at the radial
position r3 = 21.9 mm and the radial position r4 = 22.1 mm on the
second information layer 6 when using each initialization condition.
More specifically, the radial position r3 is located on the second
information layer 6 in the area (the third area) corresponding to the
BCA region (the first area) and is close to the data area (the fourth
area). In addition, the radial position r4 is located on the second
information layer 6 in the data area (the fourth area) and is close
to the area (the third area) corresponding to the BCA region (the
first area). Furthermore, there is shown the reflectivities from the
radial position r3 and the radial position r4 at the wavelength of
405 nm in the mirror portion of the reflected light.
The following fact is confirmed from Table 7.
When the area corresponding to the radius range of 21-22 mm on
the second information layer 6 is initialized by a feed pitch larger
than or equal to 40 urn, which is an appropriate feed pitch for the
data area, the initialization process stops after a defocus occurs in
the area of radius 21-22 mm. When the feed pitch is decreased to be
smaller than the appropriate feed pitch for the data area, the
initialization does not stop due to the defocus during the process,
so initialization yield is improved. For example, it is preferable
to perform the initialization process by a feed pitch smaller than 40
urn, more preferably smaller than or equal to 30 urn.
0 | *Z- Here, the reason why a defocus does not occur during the
initialization is considered in the same way as described in the
second embodiment. Namely, it is considered that when the feed pitch
is decreased, reflected light from the uninitialized portion in the
BCA region decreases, resulting in a small amount of defocus.
In addition, a good result is obtained when the feed pitch for
the area corresponding to the BCA region is set to a value lower than
minus 25% of a feed pitch of the initialization laser beam for the
data area (when the feed pitch is decreased). Note that this value
range is merely determined corresponding to the structure of the disk
that is used in this embodiment and the structure of the
initialization device, and does not limit the effective range of the
present invention. For example, the optimal range can be changed
depending on the structure of the disk or the structure of the
initialization device.
In addition, as understood from Table 7, the initialization of
the second information layer 6 does not stop in the area of radius
21-22 mm if the difference in reflectivities of the initialized
portions is 0.2% or more between the radius of 21.9 mm (a radial
position in the area having the same radius as the BCA region) and
the radius of 22.1 mm (a radial position in the data area) and if the
reflectivity at the radius of 21.9 mm is higher than the other.
Here, it is considered that a distance in radial directions at
about 0.2 mm does not cause a difference in reflectivities due to the
film thickness distribution on each layer. Therefore, the difference
in the disk reflectivities shown in Table 7 is considered to be
caused by a difference in the initialization conditions. For
example, a small feed pitch means that the portion that is once
initialized (a crystallized portion) is given laser power again so
that the degree of the initialization is increased. As a result, the
reflectivity becomes high. If there is a difference in
reflectivities of more than 0.2% within the radius 0.2 mm, the above-
mentioned difference in reflectivities can be attributed to the
difference in initialization conditions.
Note that the initialization is performed from the inner
circumference to the outer circumference in this embodiment. A
similar result can be obtained if the initialization is performed
from the outer circumference to the inner circumference.
In addition, when viewing the disk used in this embodiment by
an optical microscope, the pitch of a stripe pattern due to a
difference between initialized states appears to be different
depending on the feed pitch of the initialization condition. This
stripe pattern is generated by a difference in initialization degrees
due to overlapping of the initialization laser beam. In this way,
the difference in feed pitch can be seen as the difference in the
stripe pattern by using an optical microscope.
(Variations of the first through the third embodiments)
The techniques described in the first through the third
embodiments can be used independently of each other or can be used in
combination. More specifically, the first information layer 3 may be
initialized by the technique described in the first embodiment, while
the second information layer 6 may be initialized by the technique
described in the second or the third embodiment.
Inaddition, the above embodiments are described about the
initialization of a disk having two information layers. However, it
is possible to apply the present invention to the initialization of a
disk having more information layers.
The optical information recording medium and the method for
manufacturing the medium according to the present invention is useful
for improving productivity in initialization of a single sided
multilayered optical disk.
We Claim:
1. A single-sided multilayered optical information recording medium
comprising a disk-like substrate and an information layer formed on the
substrate, the information layer including a BCA which comprises a
plurality of band-like portions having different reflectivities, extending in
the radial direction, and being arranged like a bar code, wherein the BCA
is formed by providing initialized portions and uninitialized portions in a
first area that is an area corresponding to the radius range of rl-r2 on the
information layer, and characterized in that reflectivities are different
between radial positions r3 and r4 on the information layer where r3
denotes a radial position of an initialized portion in the first area and that
is an area corresponding to the radius range rl-r2 and close to a second
area that is an area other than the first area on the information layer, and
r4 denotes a radial position of an initialized portion in the second area and
close to the first area.
2. The optical information recording medium as claimed in claim 1, comprising:
a disk-like substrate;
a plurality of information layers formed on the substrate and having at least a
recording layer that generates an optically detectable reversible change between
an amorphous phase and a crystalline phase by irradiation with the laser beam;
an optical separation layer disposed between the plurality of information layers;
and
a transparent layer formed on the plurality of information layers, wherein
one of the plurality of information layers has the BCA.
3. The optical information recording medium as claimed in claim 1 or 2, wherein
a reflectivity at the radial position r3 on the information layer having the BCA is
lower than a reflectivity at the radial position r4 on the same information layer.
4. The optical information recording medium as claimed in claim 1 or 2, wherein
the first area and the second area are initialized respectively by initialization
conditions having different values of at least one of a laser power, a linear speed
and a focal point of the laser beam for the information layer.
5. The optical information recording medium as claimed in claim 4, wherein a
laser power of the initialization condition for initializing the first area is lower
than a laser power of the initialization condition for initializing the second area.
6. The optical information recording medium as claimed in claim 4, wherein a
linear speed of the initialization condition for initializing the first area is higher
than a linear speed of the initialization condition for initializing the second area.
7. The optical information recording medium as claimed in claim 4, wherein a
focal point of the initialization condition for initializing the first area is farther
from the information layer than a focal point of the initialization condition for
initializing the second area.
8. The optical information recording medium as claimed in claim 1, wherein
reflectivities are different between radial positions r3 and r4 on a second
information layer that is an information layer without the BCA, where r3 denotes
a radial position of an initialized portion in a third area, that is an area
corresponding to the radius range of rl-r2 on the second information layer and
close to a fourth area that is an area other than the third area on the second
information layer, and r4 denotes a radial position of an initialized portion in the
fourth area and close to the third area.
9. The optical information recording medium as claimed in claim 8, wherein a
reflectivity at the radial position r3 on the second information layer is lower than
a reflectivity at the radial position r4 on the same information layer.
10. The optical information recording medium as claimed in claim 8, wherein the
third area and the fourth area are initialized respectively by initialization
conditions having different values of at least one of a laser power, a linear
speed, a focal point of the laser beam for the second information layer and a
feed pitch of the laser beam.
11. The optical information recording medium as claimed in claim 10, wherein a
laser power of the initialization condition for initializing the third area is higher
than a laser power of the initialization condition for initializing the fourth area.
12. The optical information recording medium as claimed in claim 10, wherein a
linear speed of the initialization condition for initializing the third area is lower
than a linear speed of the initialization condition for initializing the fourth area.
13. The optical information recording medium as claimed in claim 10, wherein a
focal point of the initialization condition for initializing the third area is closer to
the second information layer than a focal point of the initialization condition for
initializing the fourth area.
14. The optical information recording medium as claimed in claim 10, wherein a
feed pitch of the initialization condition for initializing the third area is narrower
than a feed pitch of the initialization condition for initializing the fourth area.
15. The optical information recording medium as claimed in any one of the
preceding claims, wherein a difference in reflectivities between the radial
positions r3 and r4 is 0.2% or more on an information layer with the BCA or an
information layer without the BCA.
16. The optical information recording medium as claimed in any one of the
preceding claims , wherein a difference in distances between radial positions r3
and r4 is 0.2 mm or less.
17. A method for manufacturing a single-sided multilayered optical information
recording medium, the recording medium comprising a disk-like substrate and
an information layer formed on the substrate, the information layer having a BCA
which comprises a plurality of band-like portions having different reflectivities,
extending in the radial direction, and being arranged like a bar code, the method
is characterized by comprising:
a first area initialization process for forming the BCA while initializing a first area,
that is an area corresponding to the radius range of rl-r2 on the information
layer, by providing initialized portions and uninitialized portions in the first area in
accordance with a first initialization condition comprising at least one of a laser
power, a linear speed and a focal point of the laser beam for the information
layer; and
a second area initialization process for initializing a second area, that is an area
other than the first area on the information layer, in accordance with a second
initialization condition that is different from the first initialization condition,
comprising at least one of a laser power, a linear speed and a focal point of the
laser beam for the information layer.
18. The method as claimed in claim 17, wherein
the optical information recording medium comprises a plurality of information
layers and a transparent layer formed on the disk-like substrate in this order, and
also includes an optical separation layer between the plurality of information
layers,
each of the plurality of information layers includes at least a recording layer that
generates a reversible change between an amorphous phase and a crystalline
phase by irradiation with the laser beam, the reversible change being optically
detectable, and
at least one of the plurality of information layers has the BCA.
19. The method as claimed in claim 17 or 18, wherein a laser power of the first
initialization condition for initializing the first area is lower than a laser power of
the second initialization condition.
20. The method as claimed in claim 17 or 18, wherein a linear speed of the first
initialization condition for initializing the first area is higher than a linear speed of
the second initialization condition.
21. The method as claimed in claim 17 or 18, wherein a focal point of the first
initialization condition for initializing the first area is farther from the information
layer than a focal point of the second initialization condition.
22. The method as claimed in claim 17, further comprising the steps of:
(a) forming a second information layer by providing initialized portions and
uninitialized portions in a radius range of rl-r2 on the first information
layer,
the second information layer being an information layer without the BCA;
(b) initializing a third area on the second information layer in accordance
with a third initialization condition, the third area being an area
corresponding to the radius range of rl-r2 on the second information
layer,
the third initialization condition comprising at least one of a laser power,
a linear speed, a focal point of the laser beam for the second information
layer and a feed pitch of the laser beam; and
(c) initializing a fourth area, that is an area other than the third area on the
second information layer, in accordance with a fourth initialization
condition that is different from the third initialization condition in respect
of at least one of a laser power, a linear speed, a focal point of the laser
beam for the second information layer and a feed pitch of the laser
beam.
23. The method as claimed in claim 22, wherein a laser power of the third
initialization condition for initializing the third area is higher than a laser
power of the fourth initialization condition.
24. The method as claimed in claim 22, wherein a linear speed of the third
initialization condition for initializing the third area is lower than a linear
speed of the fourth initialization condition.
25. The method as claimed in claim 22, wherein a focal point of the third
initialization condition for initializing the third area is closer to the second
information layer than a focal point of the fourth initialization condition.
26. The method as claimed in claim 22, wherein a feed pitch of the third
initialization condition for initializing the third area is smaller than a feed pitch
of the fourth initialization condition.
27. The method as claimed in any one of claims 17-26, wherein the optical
information recording medium satisfies inequalities Ral> Ra2 and Rcl where Ral and Rcl respectively denote reflectivities in the amorphous state
and in the crystalline state of the first information layer at a wavelength of
the laser beam for crystallization, while Ra2 and Rc2 respectively denote
reflectivities in the amorphous state and in the crystalline state of the second
information layer at a wavelength of the laser beam for crystallization, the
first information layer being an information layer with the BCA, the second
information layer being an information layer without the BCA
28. The method as claimed in claim 27, wherein the first information layer and
the second information layer are initialized by using one optical head in the order
of the first information layer and then the second information layer.


The invention relates to an optical information recording medium comprising a
disk-like substrate and a plurality of information layers formed on the substrate
having a first information layer and a second information layer, the first
information layer having a BCA which comprises a plurality of band-like portions
having different reflectivities, extending in the radial direction, and being
arranged like a bar code, the second information layer not including a BCA,
wherein the BCA is formed by providing initialized portions and uninitialized
portions in a first area that is an area corresponding to the radius range of r1-r2
on the first information layer, each of the plurality of information layers
comprises at least a recording layer that generates a reversible change between
an amorphous phase and a crystalline phase by irradiation with the laser beam,
the reversible change being optically detectable, and the first information layer
is located on the far side from the laser beam incident side, the second
information layer comprises a third area that is an area corresponding to the
radius range of r1-r2, and a fourth area that is other than the third area, a
difference in reflectivities between the radial positions r3 and r4 is 0.2% or more
on the second information layer and a reflectivity at radial position r3 is higher
than a reflectivity at radial position r4, where r3 denotes a radial position of an
initialized portion in the third area and close to the fourth area, and r4 denotes a
radial position of an initialized portion in the fourth area and close to the third
area.

Documents:

761-KOL-2004-ABSTRACT 1.1.pdf

761-kol-2004-abstract.pdf

761-KOL-2004-AMENDED CLAIMS.pdf

761-KOL-2004-AMENDED PAGES OF SPECIFICATION.pdf

761-kol-2004-cancelled docoment.pdf

761-kol-2004-claims.pdf

761-kol-2004-correspondence 1.2.pdf

761-KOL-2004-CORRESPONDENCE.pdf

761-KOL-2004-DESCRIPTION (COMPLETE) 1.1.pdf

761-kol-2004-description complate.pdf

761-kol-2004-drawings.pdf

761-kol-2004-examination report 1.1.pdf

761-kol-2004-form 1.pdf

761-kol-2004-form 13 1.1.pdf

761-KOL-2004-FORM 13.pdf

761-kol-2004-form 18 1.1.pdf

761-KOL-2004-FORM 2.1.1.pdf

761-kol-2004-form 2.pdf

761-kol-2004-form 26 1.1.pdf

761-KOL-2004-FORM 27.pdf

761-kol-2004-form 3 1.1.pdf

761-kol-2004-form 5 1.1.pdf

761-KOL-2004-FORM-27.pdf

761-kol-2004-gpa 1.1.pdf

761-kol-2004-granted-abstract.pdf

761-kol-2004-granted-claims.pdf

761-kol-2004-granted-description (complete).pdf

761-kol-2004-granted-drawings.pdf

761-kol-2004-granted-form 1.pdf

761-kol-2004-granted-form 2.pdf

761-kol-2004-granted-specification.pdf

761-kol-2004-others.pdf

761-KOL-2004-PA.pdf

761-kol-2004-petition under rule 137.pdf

761-kol-2004-priority document 1.1.pdf

761-kol-2004-reply to examination report 1.1.pdf

761-kol-2004-reply to examination report.pdf

761-kol-2004-translated copy of priority document.pdf


Patent Number 243346
Indian Patent Application Number 761/KOL/2004
PG Journal Number 41/2010
Publication Date 08-Oct-2010
Grant Date 06-Oct-2010
Date of Filing 25-Nov-2004
Name of Patentee PANASONIC CORPORATION
Applicant Address 1006 OAZA KADOMA, KADOMA SHI, OSAKA
Inventors:
# Inventor's Name Inventor's Address
1 YOSHITAKA SAKAUE 3-36-21 HIGASHIKORI, HIRAKATA CITY, OSAKA 573-0075
2 KEN'ICHI NAGATA 12-7 KAMINO-CHO, NISHINOMIYA CITY, HYOGO 663-8021
3 KENICHI NISHIUCHI 6-22, SHODAIHIRANO-CHO, HIRAKATA CITY, OSAKA 573-1115
PCT International Classification Number G11B 7/24
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2003-408594 2003-12-08 Japan