U.S. patent application number 11/713035 was filed with the patent office on 2007-07-05 for optical recording medium and recording system for the same.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Hideki Hirata, Hiroyasu Inoue.
Application Number | 20070153671 11/713035 |
Document ID | / |
Family ID | 26622872 |
Filed Date | 2007-07-05 |
United States Patent
Application |
20070153671 |
Kind Code |
A1 |
Inoue; Hiroyasu ; et
al. |
July 5, 2007 |
Optical recording medium and recording system for the same
Abstract
An optical recording medium and a recording system for the same
are provided, which can dissipate heat produced by a laser beam
during recording operations to thereby increase the erasing power
margin of the laser beam which allows the playback jitter value to
take on a certain value or less. A recording system includes an
optical recording medium and an optical recording apparatus. The
optical recording medium has a reflective film, a second dielectric
layer, a recording layer, a heat sink layer, and a
light-transmitting layer, which are formed on a support substrate.
The heat sink layer is made of a material having a certain range of
thermal conductivity, e.g., alumina. The optical recording
apparatus allows a laser beam of 450 nm or less in wavelength to be
incident from the light-transmitting layer via a lens system having
an objective lens with a numerical aperture of 0.7 or more. The
optical recording medium dissipates heat produced by the laser beam
through the heat sink layer to thereby prevent an increase in
temperature of the recording layer, such that the relation between
the recording power Pw of the laser beam and the erasing power Pe
satisfies 0.7.ltoreq.Pe/Pw.ltoreq.1.0.
Inventors: |
Inoue; Hiroyasu; (Chuo-ku,
JP) ; Hirata; Hideki; (Chuo-ku, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TDK CORPORATION
Chuo-ku
JP
|
Family ID: |
26622872 |
Appl. No.: |
11/713035 |
Filed: |
March 2, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10485664 |
Feb 3, 2004 |
7203150 |
|
|
PCT/JP02/09797 |
Sep 24, 2002 |
|
|
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11713035 |
Mar 2, 2007 |
|
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Current U.S.
Class: |
369/275.5 ;
G9B/7.166; G9B/7.171; G9B/7.189 |
Current CPC
Class: |
G11B 7/0062 20130101;
G11B 2007/25715 20130101; G11B 2007/25708 20130101; G11B 2007/25716
20130101; G11B 7/2533 20130101; G11B 2007/2571 20130101; G11B
7/2403 20130101; G11B 2007/2431 20130101; G11B 7/2542 20130101;
G11B 2007/25706 20130101; G11B 2007/24316 20130101; G11B 2007/24308
20130101; G11B 2007/24314 20130101; G11B 7/252 20130101; G11B
7/2578 20130101; G11B 2007/24312 20130101; G11B 7/259 20130101;
G11B 7/2534 20130101 |
Class at
Publication: |
369/275.5 |
International
Class: |
G11B 7/24 20060101
G11B007/24 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 26, 2001 |
JP |
2001-294165 |
Sep 26, 2001 |
JP |
2001-292798 |
Claims
1. An optical recording medium having at least a recording layer,
for recording information in the form of the recording marks being
created in the recording layer with a recording laser beam, wherein
jitter of recording marks is 13% or less, the recording marks being
formed at a Pe/Pw setting of 1.0, where Pw is a recording power of
the recording laser beam and Pe is an erasing power.
2. The optical recording medium according to claim 1, wherein the
jitter of the recording marks is 11% or less, the recording marks
being formed at a Pe/Pw setting of 1.0.
3. The optical recording medium according to claim 1, wherein the
jitter of recording marks is 10% or less, the recording marks being
formed at a Pe/Pw setting of 0.7.
4. The optical recording medium according to claim 1, wherein the
jitter of recording marks is 9% or less, the recording marks being
formed at a Pe/Pw setting of 0.7.
5. The optical recording medium according to claim 1, further
including a light-transmitting layer provided on a side of
incidence of the recording laser beam, and a dielectric layer and a
heat sink layer provided between the recording layer and the
light-transmitting layer.
6. The optical recording medium according to claim 2, further
including a light-transmitting layer provided on a side of
incidence of the recording laser beam, and a dielectric layer and a
heat sink layer provided betweent he recording layer and the
light-transmitting layer.
7. The optical recording medium according to claim 3, further
including a light-transmitting layer provided on a side of
incidence of the recording laser beam, and a dielectric layer and a
heat sink layer provided between the recording layer and the
light-transmitting layer.
8. The optical recording medium according to claim 4, further
including a light-transmitting layer provided on a side of
incidence of the recording laser beam, and a dielectric layer and a
heat sink layer provided between the recording layer and the
light-transmitting layer.
9. The optical recording medium according to claim 5, wherein the
heat sink layer has a thickness of 10 to 200 nm.
10. The optical recording medium according to claim 6, wherein the
heat sink layer has a thickness of 10 to 200 nm.
11. The optical recording medium according to claim 7, wherein the
heat sink layer has a thickness of 10 to 200 nm.
12. The optical recording medium according to claim 8, wherein the
heat sink layer has a thickness of 10 to 200 nm.
13. The optical recording medium according to claim 5, wherein the
heat sink layer has a thickness of 30 to 100 nm.
14. The optical recording medium according to claim 6, wherein the
heat sink layer has a thickness of 30 to 100 nm.
15. The optical recording medium according to claim 7, wherein the
heat sink layer has a thickness of 30 to 100 nm.
16. The optical recording medium according to claim 8, wherein the
heat sink layer has a thickness of 30 to 100 nm.
Description
[0001] This is a Division of application Ser. No. 10/485,664 filed
Feb. 3, 2004. The disclosure of the prior application is hereby
incorporated by reference herein in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to an optical recording
medium, and more particularly to an optical recording medium which
has a wide power margin and to a recording system for the same.
BACKGROUND ART
[0003] Conventional optical recording media (discs) such as CDs
(Compact Discs) and DVDs (Digital Versatile Discs) are fabricated
such that their various characteristics (electrical and mechanical
properties) comply with predetermined specifications in their
as-fabricated (initial) conditions, and as a basic property, their
playback jitter values are particularly required to be equal to or
less than a certain value.
[0004] One of the factors responsible for variations in the
playback jitter value is the ratio between the recording power Pw
of a laser beam employed during recording operations and the
erasing power Pe of a laser beam applied to erase data before the
radiation with the laser beam for the recording operations.
[0005] In general, an increase in the ratio Pe/Pw, i.e., an
increase in Pe would cause self-erasing to occur during a recording
operation due to heat generated by a laser beam employed during an
erasing operation, thereby leading to degradation in playback
jitter value.
[0006] Therefore, such a recording strategy has to be employed
which makes the erasing power Pe of a laser beam as low as possible
to prevent degradation in playback jitter value
[0007] Therefore, such a recording strategy has to be employed
which makes the erasing power Pe of a laser beam as low as possible
to prevent degradation in playback jitter value even when the
erasing power Pe is increased due to manufacturing variations of
the semiconductor laser or variations of the control system.
[0008] Explaining this in more detail, the aforementioned recording
scheme employed to read data allows an optical recording medium to
be radiated with a reproducing laser beam along the tracks to
detect the reflected light, thereby reading information carried by
recording marks. On the other hand, to record data, the optical
recording medium is radiated with a recording laser beam along the
tracks, thereby forming recording marks having a predetermined
length. For example, a DVD-RW or a type of the user data-rewritable
optical recording medium employs recording marks having lengths
corresponding to 3T to 11T and 14T (where T is one clock cycle),
thereby recording data.
[0009] In general, when data is recorded on an optical recording
medium, the optical recording medium is not radiated with a
recording laser beam that has the same pulse width as the duration
corresponding to the length of a recording mark to be formed but
with a recording laser beam of a train of the number of pulses
determined in accordance with the type of the recording mark to be
formed, thereby forming recording marks having a predetermined
length. For example, to record data on the aforementioned DVD-RW,
pulses as many as n-1 or n-2 (where n indicates the type of
recording marks and takes on any one value of 3 to 11 and 14) are
successively impinged thereon, thereby forming any one of the
recording marks having lengths corresponding to 3T to 11T and 14T.
Accordingly, for n-2, to form a recording mark having a length
corresponding to 3T, one pulse is used, while to form a recording
mark having a length corresponding to 11T, nine pulses are used. On
the other hand, for n-1, to form a recording mark having a length
corresponding to 3T, two pulses are used, while to form a recording
mark having a length corresponding to 11T, ten pulses are used.
[0010] In general, to overwrite an optical recording medium, on
which data has been once recorded, with data different therefrom,
the train of recording marks corresponding to the currently
recorded data is directly overwritten with a train of recording
marks corresponding to the overwrite data.
[0011] However, in the case where the data that has been stored on
an optical recording medium for a long time is directly overwritten
with new data, the old recorded data may be insufficiently erased
in some cases. In particular, when an optical recording medium has
been exposed to a hot and humid environment after data had been
recorded thereon, the old recorded data is less prone to being
erased. Accordingly, the direct overwriting of the data that has
been stored on an optical recording medium for a long time with new
data would cause degradation in the jitter of the new overwrite
data, thereby causing a problem of being unable to reproduce the
data with accuracy in some cases. Such a problem becomes noticeable
in recording operations performed at a high setting of data
transfer rate (e.g., 35 Mbps or more).
[0012] To thoroughly erase such old data, the erasing power can be
effectively increased. However, to form recording marks having a
good shape, it is necessary to appropriately set the ratio (Pe/Pw)
of the erasing power to the recording power of a recording laser
beam for each target optical recording medium. If the ratio of the
erasing power to the recording power is out, of an appropriate
range, recording marks cannot be formed in a proper shape, thus
causing significant degradation in jitter. The proper range in
which the ratio of the erasing power to the recording power falls
is generally referred to as a "power margin," which is desired to
be wider for recording operations with better stability.
Accordingly, to thoroughly erase old data, such an optical
recording medium is demanded which can provide better jitter even
at a higher ratio of the erasing power to the recording power.
[0013] On the other hand, in recent years, there has been a great
demand for an optical recording medium operable at further improved
data transfer rates. However, since the laser for recording
operations needs to be driven at increased speeds to increase the
data transfer rate, a lower ratio (Pe/Pw) of the erasing power to
the recording power would cause improper pulse tracking. For this
reason, there is a need for an optical recording medium which can
provide good jitter even when a higher ratio (Pe/Pw) of the erasing
power to the recording power needs to be set for recording
operations at higher data transfer rates.
[0014] However, the aforementioned recording strategy requires a
complicated control of the semiconductor laser. In particular, in
high-speed recording operations, there is a problem that when
recording pulses for driving the semiconductor laser are
significantly reduced in pulse width, the actual waveform of the
laser beam could not properly follow the recording pulses at a
reduced Pe/Pw.
[0015] There is also a problem that the recording strategy employed
for DVD-RWs or the like operates at power levels of three values,
i.e., the recording power, the erasing power, and the bottom power,
which make the recording strategy complicated.
[0016] The present invention was developed in view of the
aforementioned conventional problems. It is therefore an object of
the invention to provide a recording system for an optical
recording medium which can prevent self-erasing to provide improved
playback jitter values and which can employ a recording strategy at
power levels of substantially two values.
[0017] It is another object of the present invention to provide an
optical recording medium having an increased power margin.
[0018] It is still another object of the present invention to
provide an optical recording medium which can provide good jitter
even when recording marks are formed with a recording laser beam at
a high ratio of the erasing power to the recording power.
DISCLOSURE OF THE INVENTION
[0019] That is, the following inventions achieve the aforementioned
objects.
[0020] The objects of the present invention are also achieved by
(1) an optical recording medium which has at least a recording
layer and records information in the form of recording marks being
created in the recording layer with a recording laser beam. The
optical recording medium is characterized in that jitter of
recording marks is 13% or less, the recording marks being formed at
a Pe/Pw setting of 1.0, where Pw is a recording power of the
recording laser beam and Pe is an erasing power.
[0021] According to the present invention, because of a wide margin
of the ratio of the erasing power to the recording power, data
recording can be performed with stability with reduced jitter in
direct overwriting of old data with new data even when the ratio of
the erasing power to the recording power is increased to thoroughly
erase the old data.
[0022] (2) An optical recording medium characterized in that the
jitter of recording marks is 11% or less, the recording marks being
formed at a Pe/Pw setting of 1.0.
[0023] According to the invention set forth in (2), because of a
wider margin of the ratio of the erasing power to the recording
power, data recording can be performed with better stability with
further reduced jitter even at an increased ratio of the erasing
power to the recording power.
[0024] (3) An optical recording medium characterized in that the
jitter of recording marks is 10% or less, the recording marks being
formed at a Pe/Pw setting of 0.7.
[0025] According to the invention set forth in (3), because of a
much wider margin of the ratio of the erasing power to the
recording power, data recording can be performed with much better
stability with much more reduced jitter even at an increased ratio
of the erasing power to the recording power.
[0026] (4) An optical recording medium characterized in that the
jitter of recording marks is 9% or less, the recording marks being
formed at a Pe/Pw setting of 0.7.
[0027] According to the invention set forth in (4), because of an
extremely wider margin of the ratio of the erasing power to the
recording power, data recording can be performed with far better
stability with significantly reduced jitter even at an increased
ratio of the erasing power to the recording power.
[0028] (5) An optical recording medium further including a
light-transmitting layer provided on the side of incidence of the
recording laser beam, and a dielectric layer and a heat sink layer
provided between the recording layer and the light-transmitting
layer.
[0029] (6) An optical recording medium characterized in that the
heat sink layer has a thickness of 10 to 200 nm.
[0030] According to the invention set forth in (6), it is possible
to obtain a wide power margin with stability without excessively
reducing the throughput of manufacturing processes.
[0031] (7) An optical recording medium characterized in that the
heat sink layer has a thickness of 30 to 100 nm.
[0032] According to the invention set forth in (7), it is possible
to obtain a wide power margin with better stability without
excessively reducing the throughput of manufacturing processes.
[0033] (8) A recording system for an optical recording medium, the
system including an optical recording medium provided with at least
a light-transmitting layer covered with a recording layer formed on
a support substrate, and a radiation optical system for recording,
reproducing, and erasing information on/from the recording layer by
radiating the optical recording medium from the light-transmitting
layer side with a laser beam at a recording power Pw and an erasing
power Pe. The radiation optical system is designed to radiate the
recording layer with a laser beam of wavelength 450 nm or less
through a lens system having an objective lens of numerical
aperture 0.7 or more. The optical recording medium is designed to
be able to record or erase information on the recording layer when
the relation between the recording power Pw of the laser beam and
the erasing power Pe satisfies 0.7.ltoreq.Pe/Pw.ltoreq.1.0.
[0034] (9) The recording system for an optical recording medium
according to (8), wherein the radiation optical system is designed
to radiate the recording layer to record information thereon with a
laser beam of wavelength 450 nm or less through a lens system
having an objective lens of numerical aperture 0.7 or more, and the
optical recording medium is designed to provide a playback jitter
value of 10% or less for the information recorded.
[0035] As used herein, the term "jitter" refers to the clock jitter
having a value that is determined as in .sigma./Tw (%), where
.sigma. is the signal fluctuation obtained by measuring a playback
signal with a time interval analyzer and Tw is the detection window
width.
[0036] (10) The recording system for an optical recording medium
according to (8) or (9), wherein the radiation optical system is
designed such that the laser beam has a wavelength of 380 nm or
more.
[0037] (11) The recording system for an optical recording medium
according to (8) or (9), wherein the radiation optical system is
designed such that the laser beam has a wavelength of 405 nm, and
the lens system is designed to have an objective lens of numerical
aperture 0.85.
[0038] (12) The recording system for an optical recording medium
according to any of (8) to (11), wherein the recording layer is
provided, on its light-transmitting layer side, with a heat sink
layer.
[0039] (13) The recording system for an optical recording medium
according to (12), wherein the heat sink layer has a thickness of
10 nm or more and 200 nm or less, preferably, has a thickness of 30
nm or more and 100 nm or less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0040] FIG. 1 is a block diagram illustrating a recording system
according to an embodiment of the present invention;
[0041] FIG. 2 is a schematic cross-sectional view illustrating the
layer structure of an optical recording medium employed for the
recording system;
[0042] FIG. 3 is a flowchart showing a method of fabricating an
optical recording medium 10;
[0043] FIG. 4 is a diagram showing the relation between the pulse
strategy and the emission waveform of a laser beam for recording
operations on an optical recording medium in a recording system
according to the embodiment;
[0044] FIG. 5 is a diagram showing the relation between the pulse
strategy and the emission waveform of a laser beam for an optical
recording medium having no heat sink layer according to the present
invention;
[0045] FIG. 6 is an exemplary view illustrating the recording
strategy for forming a recording mark having a length corresponding
to 2T;
[0046] FIG. 7 is a diagram showing the relation between the
playback jitter value and the ratio Pe/Pw of the erasing power Pe
to the recording power Pw of a laser beam according to Example 1 of
the present invention and Comparative example 1;
[0047] FIG. 8 is a diagram showing the relation between the
playback jitter value and the Pe/Pw with the recording power of a
laser beam varied according to Example 2 of the present
invention;
[0048] FIG. 9 is a diagram showing the relation between the
playback jitter value and the ratio Pe/Pw of the erasing power Pe
to the recording power Pw of a laser beam according to Example 3 of
the present invention and Comparative example 2;
[0049] FIG. 10 is a diagram showing the relation between the
playback jitter value and the Pe/Pw with the recording power of a
laser beam varied according to Example 4 of the present invention;
and
[0050] FIG. 11 is a diagram illustrating the relation between the
playback jitter value and the ratio Pe/Pw of the erasing power Pe
to the recording power Pw of a laser beam according to Example 5 of
the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0051] Now, the present invention will be explained below in more
detail with reference to the drawings in accordance with the
embodiment.
[0052] As shown in an enlarged schematic view in FIG. 2, an optical
recording medium 10 used with a recording system 1, shown in FIG.
1, according to this embodiment is provided with at least a
reflective film 16, a second dielectric layer 18, a recording layer
20, a first dielectric layer 22, and a light-transmitting layer 26,
which are formed in that order on top of ("under" in FIG. 2) a
support substrate 12 made of polycarbonate, and with a heat sink
layer 24 between the first dielectric layer 22 and the
light-transmitting layer 26, as required.
[0053] In this embodiment, the support substrate 12 is formed of
polycarbonate resin by injection molding in a thickness of about
1.1 mm. On top thereof, the reflective film 16, the second
dielectric layer 18, the recording layer 20, and the first
dielectric layer 22, as well as the heat sink layer 24 (as
required) are formed in that order by sputtering, with the
light-transmitting layer 26 being formed of acrylic-based resin by
spin coating in a thickness of about 100 .mu.m. There is provided a
hole 28 at the center portion of the optical recording medium 10.
The optical recording medium 10 having such a structure is radiated
with a recording laser beam from the light-transmitting layer 26
side to thereby record data, while being radiated with a
reproducing laser beam from the light-transmitting layer 26 side to
thereby reproduce data.
[0054] Accordingly, the light-transmitting layer 26 is formed to be
considerably thicker in thickness than a resin layer corresponding
to the position of the light-transmitting layer 26 in the optical
recording medium 10 or a protective layer (about 5 to 10 .mu.m in
thickness) on the reflective layer in conventional CDs or DVDs or
the like.
[0055] Only by way of example, the support substrate 12 is formed
of polycarbonate as mentioned above. Although the reflective film
16 can be formed of any type of metal materials without limitation
as long as it satisfies the required reflectivity, it is formed of
an alloy composed mainly of Ag in this embodiment. Although the
first and second dielectric layers 22, 18 can also be formed of any
type of materials, the second dielectric layer 13 is formed of
Al.sub.2O.sub.3 and the first dielectric layer 15 is formed of
ZnS--SiO.sub.2 in this embodiment in this embodiment. The recording
layer 20 is formed of AgInSbTeGe-based material having a phase
change recording-layer composition. The light-transmitting layer 26
is formed of an UV curable resin.
[0056] The heat sink layer 24 is formed of a material having a
thermal conductivity k, where k>1 Wm.sup.-1K.sup.-1, e.g.,
alumina (Al.sub.2O.sub.3).
[0057] The heat sink layer 24 is a layer for efficiently radiating
heat given to the recording layer 20, serving to provide an
additional power margin to the optical recording medium 10.
Accordingly, the thermal conductivity of the heat sink layer 24 is
required to be higher at least than that of the first dielectric
layer 22.
[0058] On the other hand, the support substrate 12 has a thickness
of about 1.1 mm, the reflective film 16 has a thickness of 10 to
300 nm, the second dielectric layer 18 has a thickness of 2 to 50
nm, the recording layer 20 has a thickness of 5 to 30 nm, the first
dielectric layer 22 has a thickness of 10 to 300 nm, and the
light-transmitting layer 26 has a thickness of 10 to 300 .mu.m,
preferably, 50 to 150 .mu.m. However, the present invention is not
limited thereto.
[0059] If the thickness of the heat sink layer 24 is below 10 nm,
the thickness is controlled with difficulty, while a slight
variation in thickness would cause a significant variation in the
power margin. On the other hand, at a thickness of 30 nm or more
would make it possible to obtain a noticeable effect of increasing
the power margin. In contrast, an excessively greater thickness of
the heat sink layer 24 would require elongated time for deposition,
thereby causing not only a decrease in throughput but also a danger
of thermal damage to a substrate 11. In consideration of the
foregoing, the heat sink layer 24 is set at 10 to 200 nm in
thickness, preferably, to 30 to 100 nm.
[0060] The recording layer 20 (AgInSbTeGe) of the optical recording
medium 10 is made of a phase change film having different values of
reflectivity between in the crystalline state and in the amorphous
state, which is utilized for recording data. More specifically, the
recording layer 20 of a non-recorded area is in the crystalline
state with 20% reflectivity, for example. To record any data onto
such a non-recorded area, a predetermined portion in the recording
layer 20 is heated to a temperature higher than the melting point
in accordance with the data to be recorded and then quickly cooled
down into an amorphous state. The portion in the amorphous state
has, e.g., 7% reflectivity, thus allowing the predetermined data to
be recorded. To overwrite data once recorded, the portion of the
recording layer 14 on which the data to be overwritten is recorded
is heated to a temperature equal to or higher than the
crystallization point or the melting point in accordance with data
to be recorded, and thus changed into the crystalline state or an
amorphous state.
[0061] In this case, the relation between the power Pw (recording
power) of a recording laser beam with which the recording layer 20
is radiated to melt, the power Pb (ground power) of a recording
laser beam with which the recording layer 20 is radiated to cool
down, and the power Pe (erasing power) of a recording laser beam
with which the recording layer 20 is radiated to crystallize is
expressed by Pw.gtoreq.Pe>Pb.
[0062] The optical recording medium 10 according to this embodiment
preferably stores "recording condition setting information," though
the present invention is not limited thereto The recording
condition setting information refers to various conditions
necessary to record/reproduce data on/from the optical recording
medium 10, e.g., information used for identifying the power of a
recording laser beam or a recording strategy. The recording
condition setting information includes not only those pieces
specifically indicative of each condition necessary to
record/reproduce data but also those pieces for identifying a
recording/reproduction condition by specifying any of the various
conditions pre-stored in an information recording apparatus.
[0063] On the other hand, the "recording strategy" refers to a
method of radiation with a recording laser beam to form recording
marks, i.e., the settings such as the number of recording laser
beam pulses, the pulse width of each pulse, the pulse interval, and
the power of recording laser beams (Pw, Pe, and Pb). The "recording
strategy" is determined in accordance with the recording condition
setting information stored in the optical recording medium 10.
[0064] To record data on the optical recording medium 10 according
to this embodiment, it is necessary to set the ratio (Pe/Pw) of the
erasing power Pe to the recording power Pw of a recording laser
beam within an appropriate range. If the ratio (Pe/Pw) of the
erasing power Pe to the recording power Pw is out of the
appropriate range, recording marks cannot be formed in a proper
shape, thus causing significant degradation in jitter. Suppose that
the jitter is defined as jitter (1.0) when the ratio (Pe/Pw) of the
erasing power Pe to the recording power Pw is 1.0. In this case,
the optical recording medium 10 according to this embodiment
satisfies the condition given by Jitter(1.0)<13% (1). Thus, the
optical recording medium 10 according to this embodiment allows old
data to be overwritten directly with new data, effectively
preventing degradation in jitter even when the ratio of the erasing
power to the recording power is increased to thoroughly erase the
old data. Additionally, the optical recording medium 10 according
to this embodiment preferably satisfies the condition given by
Jitter(1.0)<11% (2). With such a condition satisfied,
degradation in jitter is more effectively prevented in overwriting
old data directly with new data even when the ratio of the erasing
power to the recording power is increased to thoroughly erase the
old data.
[0065] Furthermore, suppose that the jitter is defined as jitter
(0.7) when the ratio (Pe/Pw) of the erasing power Pe to the
recording power Pw is 0.7. In this case, the optical recording
medium 10 according to this embodiment more preferably satisfies
the condition given by Jitter(0.7)<10% (3). With such a
condition satisfied, degradation in jitter is prevented much more
effectively in overwriting old data directly with new data even
when the ratio of the erasing power to the recording power is
increased to thoroughly erase the old data. Additionally, the
optical recording medium 10 according to this embodiment more
preferably satisfies the condition given by Jitter(0.7)<9% (4).
With such a condition satisfied, degradation in jitter is prevented
very effectively in directly overwriting old data with new data
even when the ratio of the erasing power to the recording power is
increased to thoroughly erase the old data.
[0066] Now, a method for fabricating the optical recording medium
10 according to this embodiment will be described below.
[0067] FIG. 3 is a flowchart showing the method for fabricating the
optical recording medium 10 according to this embodiment. As
described above, the light-transmitting layer 26 of the optical
recording medium 10 is as very thin as 10 to 300 .mu.m in
thickness, thus being deposited in the reverse order to that for
the typical conventional DVD-RWs.
[0068] First, a stamper is used to injection mold a substrate 11
having a thickness of about 1.1 mm, with a pre-groove of groove
width about 0.15 .mu.m, track pitch about 0.32 .mu.m, and groove
depth about 20 nm (step S1).
[0069] Then, the support substrate 12 is transported into a first
chamber (not shown) of a sputtering apparatus. The sputtering
apparatus is provided in the first chamber with an alloy composed
mainly of silver as a target. Then, the first chamber is pumped
into a vacuum of about 1.times.10.sup.-4 Pa. Subsequently, an argon
gas is introduced into the first chamber to set the gas pressure at
0.1 to 1.0 Pa. Thereafter, a DC or RF voltage is applied to the
target for sputtering. In this manner, on top of the support
substrate 12, formed is a reflective film 16 of 10 to 300 nm in
thickness (step S2).
[0070] Then, the support substrate 12 having the reflective film 16
formed thereon is transported from the first chamber to a second
chamber (not shown). In the second chamber of the sputtering
apparatus, provided is Al.sub.2O.sub.3 as a target. Then, the
second chamber is pumped into a vacuum of about 1.times.10.sup.-4
Pa. Subsequently, an argon gas is introduced into the second
chamber to set the gas pressure at 0.1 to 1.0 Pa for sputtering. In
this manner, on top of the reflective film 16, formed is a second
dielectric layer 18 having a thickness of 2 to 50 nm (step S3).
[0071] Then, the support substrate 12 having the reflective film 16
and the second dielectric layer 18 formed thereon is transported
from the second chamber to a third chamber (not shown). In the
third chamber of the sputtering apparatus, provided is a target
mixture of Ag, In, Sb, Te, and Ge. Then, the third chamber is
pumped into a vacuum of about 1.times.10.sup.-4 Pa. Subsequently,
an argon gas is introduced into the third chamber to set the gas
pressure at 0.1 to 1.0 Pa for sputtering. In this manner, on top of
the second dielectric layer 18, formed is a recording layer 20
having a thickness of 5 to 30 nm (step S4).
[0072] Then, the support substrate 12 having the reflective film 16
to the recording layer 20 formed thereon is transported from the
third chamber to a fourth chamber (not shown). In the fourth
chamber of the sputtering apparatus, provided is a target mixture
of ZnS and SiO.sub.2. Then, the fourth chamber is pumped into a
vacuum of about 1.times.10.sup.-4 Pa. Subsequently, an argon gas is
introduced into the fourth chamber to set the gas pressure at 0.1
to 1.0 Pa for sputtering. In this manner, on top of the recording
layer 20, formed is a first dielectric layer 22 having a thickness
of 10 to 300 nm (step S5).
[0073] Then, the support substrate 12 having the reflective film 16
to the first dielectric layer 22 formed thereon is transported from
the fourth chamber to a fifth chamber (not shown). In the fifth
chamber of the sputtering apparatus, provided is a target of
Al.sub.2O.sub.3. Then, the fifth chamber is pumped into a vacuum of
about 1.times.10.sup.-4 Pa. Subsequently, an argon gas is
introduced into the fifth chamber to set the gas pressure at 0.1 to
1.0 Pa for sputtering. In this manner, on top of the first
dielectric layer 22, formed is a heat sink layer 24 having a
thickness of 10 to 200 nm, preferably, 30 to 100 nm (step S6). The
sputtering of the heat sink layer 24 may also be carried out in the
second chamber.
[0074] In this manner, the reflective film 16, the second
dielectric layer 18, the recording layer 20, the first dielectric
layer 15, and the heat sink layer 24 are completely formed on the
support substrate 12. Then, the support substrate 12 having each of
these layers formed thereon is taken out of the fifth chamber of
the sputtering apparatus and then coated on the surface of the heat
sink layer 24 with an UV curable resin such as by spin coating, by
roll coating, or by screen printing. Then, the resulting substrate
12 is radiated with an ultraviolet radiation to thereby form a
light-transmitting layer 17 having a thickness of about 10 to 300
.mu.m (step S7). In the foregoing, the optical recording medium 10
according to this embodiment is completed. To form the
light-transmitting layer 26, a pre-molded resin sheet material such
as of polycarbonate or polyolefin may also be adhered to the
surface of the heat sink layer 24.
[0075] Now, an optical recording/reproducing apparatus 30 for
recording data onto the optical recording medium 10 in the optical
recording system 1 will be described with reference to FIG. 1.
[0076] FIG. 1 is a schematic view illustrating the main portion of
a preferred information recording apparatus for recording data on
the optical recording medium 10.
[0077] As shown in FIG. 1, the information recording/reproducing
apparatus 30 illustrated includes a spindle motor 2 for rotating
the optical recording medium 10, a head 3 for radiating the optical
recording medium 10 with a recording laser beam, a controller 4 for
controlling the operations of the spindle motor 2 and the head 3, a
laser drive circuit 5 for supplying a laser drive signal to the
head 3, and a lens drive circuit 6 for supplying a lens drive
signal to the head 3.
[0078] Furthermore, as shown in FIG. 1, the controller 4 includes a
focus servo follower circuit 7, a tracking servo follower circuit
8, and a laser control circuit 9. Activating the focus servo
follower circuit 7 would allow the recording surface of the optical
recording medium 10 being rotated to be focused, while activating
the tracking servo follower circuit 8 would allow the spot of a
laser beam to automatically follow an eccentric signal track of the
optical recording medium 10. The focus servo follower circuit 7 and
the tracking servo follower circuit 8 are each provided with an
automatic gain control function for automatically adjusting focus
gain and an automatic gain control function for automatically
adjusting tracking gain, respectively. The laser control circuit 9
generates a laser drive signal to be supplied by the laser drive
circuit 5, while generating an appropriate laser drive signal in
accordance with recording condition setting information stored in
the optical recording medium 10, if any.
[0079] These focus servo follower circuit 7, the tracking servo
follower circuit 8, and the laser control circuit 9 do not always
need to be a circuit incorporated into the controller 4 but may
also be a component separated from the controller 4. Furthermore,
these circuits need not to be always in the form of a physical
circuit but may also be in the form of software to be executed in
the controller 4.
[0080] Although not limited to the following particular
arrangement, the information recording apparatus suitable for
recording data onto the optical recording medium 10 employs
preferably a recording laser beam of wavelength 450 nm or less,
preferably 380 to 450 nm, more preferably 405 nm, and an objective
lens (not shown) or part of the head 3 for focusing a recording
laser beam, having an NA (numerical aperture) of 0.7 or more. In
recording data onto the optical recording medium 10 using such an
information recording apparatus, a distance (working distance) to
be set between the objective lens and the surface of the optical
recording medium 10 is very small (e.g., about 80 to 150 .mu.m),
thereby making it possible to realize a beam spot of a
significantly reduced diameter as compared with the conventional
one. This makes it possible to realize an extremely high data
transfer rate (e.g., 35 Mbps or greater) in recording data onto the
optical recording medium 10 using such an information recording
apparatus.
[0081] Additionally, as described above, in recording data onto the
optical recording medium 10 according to this embodiment using such
an information recording apparatus 30, a recording strategy
determined in accordance with recording condition setting
information stored on the optical recording medium 10, if any, is
used to determine the ratio of the erasing power Pe to the
recording power Pw of the recording laser beam.
[0082] More specifically, the recording layer 20 is radiated with
the aforementioned laser beam from the light-transmitting layer 26
side via the objective lens at the recording power Pw or the
erasing power Pe, thereby recording or erasing information on the
recording layer 20. The optical recording medium 10 is also
designed to provide a jitter value below 10% at the time of
reproducing the information that has been recorded by being
radiated with a laser beam under the condition of
0.7.ltoreq.Pe/Pw.ltoreq.1.0.
[0083] The heat sink layer 24 has a thickness of 10 nm or more
because a thickness of less than 10 nm would cause the power margin
of the laser beam to be significantly varied due to a slight
variation in thickness. Accordingly, the thickness is preferably
determined to be 30 nm or more.
[0084] Furthermore, the aforementioned thickness is 200 nm or less
because a thickness greater than 200 nm would require an excessive
time for its deposition during manufacturing, simultaneously
causing increased thermal damage to the support substrate 12.
Accordingly, the thickness is determined to be 200 nm or less, more
preferably 100 nm or less.
[0085] As described above, the optical recording medium 10
according to this embodiment makes the playback jitter value below
10% even when the erasing power Pe of an erasing laser beam is
within the range of 0.7.ltoreq.Pe/Pw.ltoreq.1.0 relative to the
recording power Pw. For example, as shown in FIG. 3, the emission
waveform of a laser beam actually emitted from a laser 36 (see FIG.
1) has a very good trackability to the recording pulse signal for
driving the laser 36. FIG. 4(A) shows a recording transfer rate of
35 Mbps, while FIG. 4(B) shows a rate of 100 Mbps.
[0086] In contrast to this, suppose that Pe/Pw is about 0.5. In
this case, as shown in FIGS. 5(A) and 5(B), the emission waveform
has a lower trackability to the recording pulse signal.
Particularly, in the case of a recording transfer rate of 100 Mbps
as shown in FIG. 5(B), the recording pulse signal having a narrow
pulse width will fall before the emission waveform completely
rises.
[0087] That is, the heat sink layer 24 is provided to accelerate
the radiation of heat from the recording layer 20 and prevent the
heat from being accumulated therein. Thus, this will not allow the
heat to cause self-erasing during recording operations even when
the erasing power Pe of a laser beam for erasing operations is made
higher than the conventional level relative to the recording power
Pw. Accordingly, it is possible to prevent degradation in playback
jitter value.
[0088] To record information onto the recording layer 20, the
recording power Pw of a laser beam multiplied by the pulse width of
a recording pulse equal to the amount of input heat has to be in a
predetermined range.
[0089] The optical recording medium 10 according to this embodiment
is provided with the heat sink layer 24 and thereby allows heat to
readily escape from the recording layer 20, thus making it possible
to set the pulse width in a wide range at a constant recording
power Pw. In contrast to this, without the heat sink layer 24, the
amount of target input heat can be reached in a short time, thus
providing a lower degree of flexibility in the setting range of
pulse width.
[0090] In the aforementioned embodiment, the heat sink layer 24 is
made of alumina. The present invention is not limited thereto but
may also employ a material having a thermal conductivity within the
aforementioned range and formable in the shape of film for covering
the recording layer 20 therewith, e.g., aluminum nitride or the
like.
[0091] Additionally, in the aforementioned embodiment, the
light-transmitting layer 26 is made of an acryl-based resin;
however, any type of material can also be selected from the group
of an energy beam curable resin that is hardened by an energy beam
such as an ultraviolet ray or a thermally curable resin that is
hardened by heat, thus making the acryl-based resin, the
epoxy-based resin, the urethane-based resin or the like applicable.
It is also possible to employ a preformed resin film such as of
polycarbonate or polyolefin for adhesion or the like.
[0092] Furthermore, the support substrate 12 may also be made of
polyolefin or the like other than the polycarbonate as employed in
the embodiment.
[0093] The aforementioned information recording apparatus 30 can
also employ a (1, 7) RLL modulation scheme, though the present
invention is not limited thereto. However, the information
recording apparatus for recording data onto the optical recording
medium 10 does not always need to employ such a modulation scheme
to record data but may also employ other modulation schemes for
recording data.
[0094] Now, an exemplary recording strategy will be described below
which employs the (1, 7) RLL modulation scheme.
[0095] FIG. 6 is a view illustrating an exemplary recording
strategy for forming a recording mark of a length corresponding to
2T.
[0096] As shown in FIG. 6, to form a recording mark of a length
corresponding to 2T, the number of recording laser beam pulses is
set at "1." In the foregoing, the number of recording laser beam
pulses is defined by the number of times of raising the power of
the recording laser beam up to Pw. In more detail, suppose that the
timing at which the recording laser beam is positioned at the start
point of a recording mark is time ts, and the timing at which the
recording laser beam is positioned at the end point of the
recording mark is time te. In this case, the power of the recording
laser beam is raised once up to Pw and then to power Pb during the
period from time ts to time te. The power of the recording laser
beam is set at Pe before time ts, allowing the recording laser beam
to start rising at time ts. On the other hand, the power of the
recording laser beam at time te is set at Pe or Pb.
[0097] During the duration of Tpulse, the recording layer 20 of the
optical recording medium 10 is subjected to a high energy to have a
temperature higher than the melting point, whereas during the
duration of Tcl, the recording layer 20 of the optical recording
medium 10 is quickly cooled down. This allows the recording mark of
a length corresponding to 2T to be formed in the recording layer 20
of the optical recording medium 10.
[0098] To form a recording mark of another length, as in the case
of forming the recording mark of the length corresponding to 2T,
the power of the recording laser beam is set at Pw, Pe, or Pb, thus
forming recording marks having a desired length each by a
predetermined number of pulses.
[0099] The optical recording medium 10 according to this embodiment
provides a wide power margin as described above. It is therefore
possible to reduce jitter in directly overwriting old data with new
data even when the ratio of the erasing power to the recording
power is increased to thoroughly erase the old data. Accordingly,
even with recording operations performed at a high setting of data
transfer rate (e.g., 35 Mbps or more), the old data can be
thoroughly erased.
[0100] Now, examples of the present invention will be explained in
detail below.
EXAMPLE 1
[0101] An optical recording medium was prepared in accordance with
the following procedures.
[0102] A disc-shaped support substrate was employed which was made
of a polycarbonate resin like in the aforementioned embodiment and
which had a surface having grooves formed thereon (the depth of the
grooves was .lamda./18 in terms of an optical path length at a
wavelength .lamda.=405 nm with a record track pitch of 0.32 .mu.m).
On top of this surface, a reflective film composed mainly of silver
was formed by sputtering in a thickness of 100 nm.
[0103] Then, on the surface of the reflective film, formed was a
second dielectric layer of Al.sub.2O.sub.3 by sputtering in a
thickness of 20 nm.
[0104] Additionally, a recording layer was formed by sputtering in
a thickness of 12 nm on the second dielectric layer using an alloy
target of a phase change material. This recording layer was chosen
to have a composition of AgInSbTeGe.
[0105] Furthermore, on the surface of the recording layer, a
dielectric layer was formed by sputtering in a thickness of 30 nm
using a ZnS (80 mol %)-SiO.sub.2 (20 mol %) target.
[0106] On the surface of this dielectric layer, as with the
aforementioned second dielectric layer, a heat sink layer of
Al.sub.2O.sub.3 was formed by sputtering in a thickness of 60
nm.
[0107] Then, the surface of the heat sink layer was coated by spin
coating with an UV curable resin, and then radiated with an
ultraviolet radiation to thereby obtain a light-transmitting layer
of 100 .mu.m in thickness.
COMPARATIVE EXAMPLE 1
[0108] Furthermore, an optical recording medium was prepared as
Comparative example 1 which had the heat sink layer removed from
the aforementioned example 1.
[0109] As with the aforementioned embodiment, recording operations
were performed with these examples under the conditions of a
wavelength .lamda.=405 nm and a numerical aperture of the objective
lens NA=0.85, at the recording power Pw of a laser beam fixed to
6.0 mW, with the erasing power Pe of a laser beam being varied so
that the Pe/Pw was 0.25 to 1.00. Thereafter, the playback jitter
value was measured as shown in FIG. 7.
[0110] As can be seen from FIG. 7, the upper limit value of the
Pe/Pw providing a playback jitter value of 10% or less is 0.67 in
the comparative example, whereas being 0.87 in the case of the
example of the present invention. Furthermore, the upper limit
value of the Pe/Pw providing a jitter value of 13% or less is about
0.75 in the comparative example, whereas being above 1.0 in the
example of the present invention.
[0111] This can be listed as shown in Table 1 below. TABLE-US-00001
TABLE 1 Playback jitter value (%) Pe/Pw Example Comparative example
0.5 7.5 8.0 0.6 7.5 8.3 0.7 8.3 11.0 0.8 8.5 >14 0.9 9.2 -- 1.0
11.1 --
EXAMPLE 2
[0112] In Example 2, with the heat sink layer changed to be 30 nm
in thickness, recording operations were performed on the optical
recording medium configured in the same manner as in Example 1 at
each recording power Pw of a laser beam selected from 3.8 mW, 4.2
mW, and 6.0 mW with the erasing power Pe being varied relative to
these recording powers Pw such that Pe/Pw was in the range of 0.3
to 1.1. Then, the playback jitter values were measured as shown in
FIG. 8.
[0113] From FIG. 8, it can be seen that even when the recording
power of a laser beam is varied, the playback jitter value can be
made 10% or less if the Pe/Pw is within the range of the
embodiment.
EXAMPLE 3
[0114] Example 3 employs the same optical recording medium as that
of Example 2. The optical recording medium of Example 3 was
provided with the first dielectric layer of 45 nm in thickness
without the heat sink layer to prepare Comparative example 2.
Recording operations were performed on the comparative example 2
and Example 3 with the Pe/Pw being varied in the range of 0.3 to
1.0. Then, the playback jitter values were measured as shown in
FIG. 9.
[0115] As seen from FIG. 9, the comparative example having no heat
sink layer provides a jitter value of above 10% at the point of
Pe/Pw exceeding 0.60, while providing a jitter value of above 13%
at 0.80.
[0116] In contrast to this, the optical recording medium of Example
3 never exceeds a playback jitter value of 10% even at a Pe/Pw of
1.0.
EXAMPLE 4
[0117] The aforementioned method was employed to fabricate an
optical recording medium 10-1 having the structure shown in FIG. 2,
with the support substrate 12 having a thickness of 1.1 mm, the
reflective film 16 having a thickness of 100 nm, the second
dielectric layer 18 having a thickness of 20 nm, the recording
layer 20 having a thickness of 12 nm, the first dielectric layer 22
having a thickness of 30 nm, the heat sink layer 24 having a
thickness of 30 nm, and the light-transmitting layer 26 having a
thickness of 100 .mu.m.
[0118] With the optical recording medium 10-1, under the conditions
shown in Table 2, the recording power Pw was set at 3.8 mW and a
signal mixture of recording marks having lengths corresponding to
2T to 8T was formed using various erasing powers Pe. Then, the
recording power Pw was set at 4.2 mW and a signal mixture of
recording marks having lengths corresponding to 2T to 8T was formed
using various erasing powers Pe. Furthermore, the recording power
Pw was set at 6.0 mW and a signal mixture of recording marks having
lengths corresponding to 2T to 8T was formed using various erasing
powers Pe. The ground power Pb was set at 0.1 mW in all the cases.
The (1, 7) RLL modulation scheme was employed for recording
operations to record data only on one track. TABLE-US-00002 TABLE 2
Clock frequency 66 MHz Clock cycle (1T) 15.15 nsec Linear speed 5.3
m/sec Modulation scheme (1, 7) RLL Format efficiency 80% Data
transfer rate (efficiency 35 Mbps considered) Channel bit length
0.12 .mu.m/bit Numerical aperture (NA) 0.85 Laser wavelength 405
nm
[0119] Then, the clock jitter of the signal mixture created on the
optical recording medium 10-1 was measured. In the measurements, a
time interval analyzer was used to determine the "fluctuation
.sigma." of the playback signal to calculate .sigma./Tw (where Tw
is one clock cycle).
[0120] The results of the measurements are shown in FIG. 10.
[0121] As shown in FIG. 10, at any setting of the recording power
Pw to 3.8 mW, 4.2 mW, or 6.0 mW, the optical recording medium 10-1
provides the jitter (1.0) as shown below when the ratio (Pe/Pw) of
the erasing power Pe to the recording power Pw is 1.0. That is,
Jitter(1.0)<11%. Furthermore, at any setting of the recording
power Pw to 3.8 mW, 4.2 mW, or 6.0 mW, the optical recording medium
10-1 provides the jitter (0.7) as shown below when the ratio
(Pe/Pw) of the erasing power Pe to the recording power Pw is 0.7.
That is, Jitter(0.7)<9%.
[0122] As described above, it was confirmed that irrespective of
the setting of the recording power Pw, the optical recording medium
10-1 provides reduced jitter and a very wide power margin even at a
high setting of the ratio (Pe/Pw) of the erasing power Pe to the
recording power Pw.
EXAMPLE 5
[0123] The aforementioned method was employed to fabricate an
optical recording medium 10-2 having the structure shown in FIG. 2,
with the support substrate 12 of 1.1 mm in thickness, the
reflective film 16 of 100 nm in thickness, the second dielectric
layer 18 of 20 nm in thickness, the recording layer 20 of 12 nm in
thickness, the first dielectric layer 22 of 45 nm in thickness, and
the heat sink layer 24 of 0 nm in thickness. The optical recording
medium 10-2 is different from the aforementioned optical recording
medium 10-1 in that the first dielectric layer 22 was changed to
have a thickness of 45 nm and the heat sink layer 24 was changed to
be 0 nm (no heat sink layer was provided).
[0124] With the optical recording medium 10-2, under the conditions
shown in Table 2, the recording power Pw was set at 5.8 mW and a
signal mixture of recording marks having lengths corresponding to
2T to 8T was formed using various erasing powers Pe. The (1, 7) RLL
modulation scheme was employed for recording operations to record
data only on one track.
[0125] Then, the clock jitter of the signal mixture created on the
optical recording medium 10-2 was measured.
[0126] The results of the measurements are shown in FIG. 11. FIG.
11 also shows the results of measurements made when the recording
power Pw was set at 6.0 mW with the optical recording medium
10-1.
[0127] As shown in FIG. 11, it is seen that the optical recording
medium 10-2 satisfies Jitter(1.0)<13%, and
Jitter(0.7)<10%.
[0128] As described above, defining Jitter (1.0) as the jitter at a
ratio (Pe/Pw) of the erasing power Pe to the recording power Pw
being 1.0, the optical recording medium 10 according to this
embodiment satisfies the condition given by Jitter(1.0)<13% (1).
It is therefore possible to reduce jitter in directly overwriting
old data with new data even when the ratio of the erasing power to
the recording power is increased to thoroughly erase the old
data.
[0129] The present invention is not limited to the aforementioned
embodiment, and various modifications may also be made thereto
within the scope of the invention defined in the claims, the
modifications also being contained within the scope of the present
invention.
[0130] For example, in the aforementioned embodiment, the structure
shown in FIG. 2 was cited as a specific structure of the optical
recording medium 10; however, the structure of the optical
recording medium according to the present invention is not limited
thereto.
[0131] The present invention is configured as described above, and
thus can provide an advantageous effect of efficiently dissipating
heat produced by a laser beam during recording operations to
thereby increase the erasing power relative to the recording power
of the laser beam.
[0132] Accordingly, a very wide power margin provided makes it
possible to record data with stability.
* * * * *