JP4322927B2 - Optical recording method, optical recording medium, and multilayer optical recording medium optical recording apparatus - Google Patents

Description

The present invention relates to an optical recording medium (hereinafter also referred to as “optical information recording medium” or “optical disk”) having a phase change optical recording layer such as a rewritable DVD and capable of high density recording, and the optical recording. The present invention relates to an optical recording method and an optical recording apparatus using a medium.
In the present invention, two or more information layers including a recording layer capable of recording and reproducing information and recording information can be recorded and reproduced by optically changing the recording layer material by irradiating a laser beam. The present invention relates to a multilayer optical recording medium having an optical recording method and an optical recording apparatus using the multilayer optical recording medium.

In recent years, the demand for high-speed recording of optical recording media has increased. In particular, in the case of a disk-shaped optical recording medium, since the recording and reproducing speed can be increased by increasing the rotational speed, the speed is increasing. Among optical discs, optical recording media that can be recorded only by intensity modulation of the light irradiated during recording can be reduced in price due to the simple recording mechanism, and at the same time, reproduction is also intensity modulated. Since the use of the emitted light enables high compatibility with a read-only device, it has become widespread. With the recent increase in capacity of electronic information, the demand for higher density and higher speed recording has increased.
Among such optical discs, those using phase change materials have become mainstream because they can be rewritten many times. In the case of an optical disk using a phase change material, recording is performed by making the recording layer material into a rapidly cooled state and a slowly cooled state by intensity modulation of the irradiated light beam. The recording layer material becomes amorphous when it is rapidly cooled, and becomes crystalline when it is slowly cooled. Since amorphous and crystal have different optical properties, information can be recorded. That is, the phase change type optical recording medium changes the disk reflectivity by irradiating the recording layer thin film on the substrate with laser light to heat the recording layer and changing the recording layer structure between crystal and amorphous. Information is recorded and erased. Normally, information is recorded by forming a non-recorded state as a high-reflectance crystal phase, and forming a mark composed of a low-reflectance amorphous phase and a space composed of a high-reflectance crystal phase.

Since the recording principle uses such a complicated mechanism of “rapid cooling” and “slow cooling” of the recording layer material, the pulse is divided and intensity-modulated into three values as is well known for high-speed recording. This is done by irradiating the medium with recording light.
As a waveform light emission pattern (recording strategy) for repeatedly recording data consisting of marks and spaces, there is one used in DVD + RW as shown in FIG. The amorphous mark is formed by pulse irradiation by alternately repeating the peak power (Pw = Pp) light and the bias power (Pb) light, and the space made of the crystal receives these intermediate level erasing power (Pe) light. It is formed by continuous irradiation. Of course, the space may be binarized with erasing power light and irradiated in a pulsed manner.
When a pulse train composed of peak power light and bias power light is irradiated, the recording layer repeats melting and quenching to form amorphous marks. When the erasing power light is irradiated, the recording layer is gradually cooled after being melted, or annealed in a solid state and crystallized to form a space. A pulse train composed of peak power light and bias power light is usually divided into a first pulse, an intermediate pulse, and a last pulse, and the shortest 3T mark is recorded only by the first pulse and the last pulse, and a mark of 4T or more is formed. An intermediate pulse is also used. The intermediate pulse is also called a multi-pulse, and is provided in a 1T cycle, and the number of pulses is increased by one every time the mark length becomes 1T longer. That is, the number of pulse trains is (n-1) with respect to the length nT.

  By the way, at the time of high-speed recording exceeding the quadruple speed of DVD, since the time of the basic clock period T is shortened, the load on the light source driving unit is increased. Further, when a pulse train having a 1T period is irradiated, both the heating time and the cooling time are shortened, resulting in a problem that an amorphous mark having a sufficiently large size cannot be formed. In order to avoid this problem, the number of pulses for forming the amorphous mark is reduced (the pulse cycle is made longer than 1T), sufficient time is ensured for both heating and cooling, and a sufficiently large amorphous film is formed. Various proposals have been made so that a quality mark can be formed (for example, see Patent Documents 1 to 3, and many others).

Further, at the time of high-speed recording, even if recording can be performed with low jitter at the first time, if the recording is repeatedly performed, the reduction in that the jitter rapidly increases becomes remarkable. FIG. 1 shows an example of jitter fluctuation when a random pattern is repeatedly recorded. The jitter that suddenly increased by the first repetitive recording is gradually lowered and settled by repetitive recording up to about 10 times, and the film quality deteriorates and the jitter increases again by repetitive recording from several thousand to several tens of thousands. The fluctuations up to are small. An increase in jitter at the initial stage of repeated recording is also observed during low-speed recording of about 1 to 2 times speed, but is not so remarkable, and even if the jitter increases, the standard value can be satisfied. However, as the recording linear velocity increases, even when good recording is possible after the first recording or repeated recording 10 times or more, the jitter of the first repeated recording is particularly large and exceeds the standard value. Often occurs.
Such an increase in jitter at the beginning of repeated recording is presumed to be caused by some difference between the initial crystal phase formed by the initialization process and the crystal phase formed during recording. For this reason, in the initial stage of repeated recording in which the initial crystal phase and the crystal phase formed at the time of recording are mixed, the shape of the mark varies and jitter increases. By repeating about 10 times, almost the entire recording track becomes a crystal phase formed at the time of recording, so that it is estimated that the variation in mark shape is reduced and the jitter is lowered.

Therefore, the jitter at the initial stage of repeated recording varies greatly depending on the state of the initial crystal. By setting the initial crystal phase to a state equivalent to the crystal formed at the time of recording, the jitter at the initial stage of repeated recording can be reduced. Specifically, when initializing a recording layer for high-speed recording, the jitter at the initial stage of repeated recording tends to be reduced by scanning a large-diameter beam at a higher linear velocity to cause melt crystallization.
However, the crystal state formed during high-speed recording is generally unstable, and even if it shows good characteristics immediately after the initialization process, it changes with time, and good recording cannot be performed under the same recording conditions. There is a tendency to end up. FIG. 2 shows this state. This is an example in which jitter was increased when recording was performed with low jitter even at the beginning of repeated recording immediately after initialization, but when re-recording was performed on the unrecorded portion under the same conditions one month later. Therefore, even when the initial crystal state is not equivalent to the crystal formed at the time of recording, it is necessary to reduce the jitter at the initial stage of repeated recording.

As a recording method effective for reducing jitter in the first repeated recording, Patent Document 4 describes that the start time of the heating pulse at the head portion is delayed by 1T or more. According to the study by the present inventors, this recording method is effective when the pulse train is set at a 1T period. However, the recording method is ineffective when the pulse period is longer than 1T in order to cope with higher speed recording.
Further, Patent Document 5 discloses that good recording can be performed by increasing the irradiation time of the heating pulse at the head. This recording method is also effective in reducing an increase in jitter at the initial stage of repeated recording. However, since the recording method generally has a high peak power value in the case of high-speed recording, there is a problem that when the irradiation time is lengthened, the film quality is likely to deteriorate and the repeated recording durability is deteriorated. Furthermore, there is a problem that marks recorded on adjacent tracks are partially erased and cross erase becomes large.

Further, a phase change optical recording medium such as CD-RW is generally provided with a recording layer containing a phase change material on a plastic substrate, and improves the light absorption rate of the recording layer on the recording layer, and A basic structure is formed with a reflective layer having a thermal diffusion effect, and information is recorded and reproduced by irradiating a laser beam from the substrate surface side.
Phase change recording materials used in the recording layer of phase change optical recording media undergo a phase change between the crystalline and amorphous states by repeating heating and cooling by laser light irradiation, and become amorphous when rapidly cooled after rapid heating. When it is slowly cooled, it crystallizes. The phase-change optical recording medium applies this property to information recording, and information reproduction utilizes a difference in reflectance caused by a difference in optical constant between a crystalline state and an amorphous state.
A phase change type optical recording medium is usually an upper protective layer (hereinafter referred to as a “lower dielectric layer”) between a substrate and a recording layer for the purpose of preventing oxidation, transpiration or deformation of the recording layer caused by heating by light irradiation. And a lower protective layer (hereinafter also referred to as “lower dielectric layer”) is provided between the recording layer and the reflective layer. These protective layers have a function of adjusting the optical characteristics of the recording medium by adjusting the thickness thereof. Furthermore, the upper protective layer also has a function of preventing the substrate from being softened by heat during recording on the recording layer.

In recent years, as the amount of information handled by computers and the like has increased, the signal recording capacity of rewritable optical discs such as DVD-RAM, DVD-RW, and DVD + RW has increased, and the density of signal information has been increasing. . The recording capacity of the current CD is about 650 MB, and the DVD is about 4.7 GB. However, it is expected that the demand for higher recording density will increase in the future.
As a method for increasing the recording density using such an optical recording medium, for example, the laser wavelength used is shortened to the blue region, or the numerical aperture (NA) of an objective lens used for a pickup for recording / reproducing is used. It has been proposed that the spot size of the laser beam irradiated onto the optical recording medium be reduced, and research and development has progressed and it has come to practical use.

  On the other hand, as a method of improving the recording capacity by improving the optical recording medium itself, at least two information layers consisting of a recording layer and a reflective layer are stacked on one side of the substrate, and these information layers are bonded with an ultraviolet curable resin or the like. Various types of two-layer optical recording media to be manufactured have been proposed. The intermediate layer, which is an adhesive portion between the information layers, has a function of optically separating the two information layers, and the laser beam used for recording / reproduction needs to reach the information layer on the back side as much as possible. It is made of a material that absorbs as little light as possible. However, many problems still exist with this two-layer optical recording medium. For example, if the laser beam is not sufficiently transmitted through the information layer (first information layer) on the front side when viewed from the laser beam irradiation side, information is recorded on the recording layer of the information layer (second information layer) on the back side. In order not to be able to record and reproduce it, the reflective layer constituting the first information layer must be a very thin translucent reflective layer.

Recording on a phase change optical recording medium is performed by forming a mark by changing the crystalline state to an amorphous state by irradiating the phase change material of the recording layer with laser light and heating and quenching above the melting point. Done. Information is erased by changing the amorphous state to the crystalline state by raising the temperature above the crystallization temperature and gradually cooling it.
In the conventional single-layer optical recording medium, the reflective layer can be formed sufficiently thick, so that the residual heat of the irradiated laser light can be quickly released. For this reason, the rapid cooling effect is promoted to easily form an amorphous state. Similarly, since the second information layer of the two-layer type optical recording medium does not need to transmit light, the second reflective layer and the second recording layer may have the same thickness as a conventional single-layer type optical recording medium. If the transmittance of the first information layer is high, good recording characteristics can be obtained and reproduction can be easily performed.

However, when recording is performed on the first information layer of the two-layer type optical recording medium, an amorphous mark is formed because the heat dissipation effect is reduced in the case of a very thin translucent reflective layer having a thickness of about 10 nm. It becomes difficult. Further, it is desirable that the first information layer has a high light transmittance so that information can be recorded and reproduced on the recording layer of the second information layer. Therefore, in order to record and erase the amorphous mark of the first information layer in the two-layer optical recording medium, it is necessary to irradiate the recording or erasing power higher than that of the single-layer optical recording medium in which the reflective layer can be thickened. There is sex. For example, the erasing power Pe of a conventional DVD single-layer optical recording medium has good characteristics at about 6 to 9 mW when the recording linear velocity is in the range of 3.5 m / s to 27.9 m / s. I know. On the other hand, the erasing power Pe applied to the first information layer of the dual-layer optical recording medium of DVD requires about 6 to 9 mW when the recording linear velocity is in the range of 3.5 to 14 m / s. An erasing power with a high energy density is required in a situation where the recording linear velocity is slower than that of the mold.
In addition, since the two-layer type optical recording medium not only requires a high erasing power Pe, but also the first reflective layer is thin, the first information layer has significantly poorer heat dissipation than a single-layer optical recording medium. The thermal effect on the first recording layer, which is extremely thin, becomes a problem. The recording power Pp requires about twice or more power than the erasing power when recording is performed at a recording linear velocity in the range of 3.5 to 14 m / s. Due to the residual heat generated by the above, there is a problem that thermal damage is further applied to the first recording layer, which must be prevented.

For example, Patent Document 6 proposes a method in which erasing power light is binarized and irradiated in a pulsed manner when forming a space. However, in this proposal, the immediately preceding head pulse having the peak power Pp for forming the mark is not lowered to the level of the bias power Pb. When recording is performed by this recording method, excessive heat is applied due to the effect of residual heat. Is a problem.
Further, as in Patent Document 7, too much heat is a problem when recording is performed by a recording method on an optical recording medium in which the erasing power immediately before forming a recording mark is temporarily increased.
In addition, the method in which only the bias power Pb is set immediately before the head pulse as in Patent Documents 8 to 10 can be sufficiently effective in a single-layer optical recording medium, but a two-layer light When recording and erasing are performed on the first information layer with poor heat dissipation like a recording medium, there is a problem that the effect is not sufficient and it is difficult to obtain good recording characteristics.

  Therefore, it has two or more information layers including a phase change recording layer that can record and reproduce information by irradiating a laser beam to cause an optical change in the recording layer material and can be rewritten and record information. When recording on the first recording layer in the first information layer in front of the multilayer optical recording medium as viewed from the side irradiated with the laser beam, thermal damage to the recording layer is suppressed, and recording or erasing is performed. However, a recording method for a multilayer optical recording medium that can accurately perform recording and improve recording characteristics has not yet been provided, and the rapid development thereof is desired.

Japanese Patent Laid-Open No. 2002-237051 JP 2002-288837 A JP 2001-331936 A JP 2004-46956 A Japanese Patent No. 3223907 JP 2004-63005 A JP 2002-288830 A JP 2001-273638 A JP 2004-47053 A JP 2005-63586 A

The present invention reduces the increase in jitter at the initial stage of repeated recording regardless of the initial crystal state without deteriorating the durability of repeated recording or increasing crosstalk even during high-speed recording equivalent to 6-8 times the speed of DVD. It is an object to provide an optical recording medium capable of recording, an optical recording method and an optical recording apparatus using the optical recording medium.
The present invention relates to a case where recording is performed on the first recording layer in the first information layer in front of the multilayer optical recording medium having two or more information layers including the phase change recording layer when viewed from the side irradiated with the laser beam. The multilayer optical recording medium can suppress thermal damage to the recording layer, can perform recording and erasure accurately, has good repetitive recording characteristics, and has good recording sensitivity of the second and higher recording layers An object of the present invention is to provide an optical recording method and an optical recording apparatus using the multilayer optical recording medium.

In the first aspect of the present invention, when recording is performed on a multilayer optical recording medium having M phase change recording layers (M ≧ 2), the first recording layer is the foremost when viewed from the laser beam side. The recording layer is a recording layer, the Mth recording layer is the recording layer that is the farthest back as viewed from the laser beam side, T is the clock cycle, and the Kth recording layer uses a recording pulse train that consists of a plurality of laser beam pulses. When the period of the recording pulse train when recording the mark by irradiating light is t _(K) [T], the relationship of the following formula, t ₍₁₎ <t _(M) is satisfied, and the period of the recording pulse train Provides an optical recording method for a multi-layer optical recording medium, characterized in that it does not decrease from the first recording layer to the next recording layer in the direction of laser light irradiation.
In the first aspect of the present invention, the repetitive recording characteristics of the recording layer on the front side as viewed from the laser irradiation side and the recording sensitivity of the recording layer on the back side can be improved.

In this case, the following effects can be obtained by setting the front side to the 1T strategy and the back side to the 2T strategy.
(1) Good jitter characteristics on the near side.
(2) The recording sensitivity on the back side can be improved (recording can be performed with low power).
Other possible effects include
(3) The effect of improving the maximum value of the modulation factor on the back side (as shown in FIG. 32, the saturation value of the modulation factor on the high power side is increased by about 2%) is obtained.

Here, as shown in FIG. 34, the 1T strategy uses (n−1) pulses to record a mark of length nT.
In the 2T strategy , when a mark of length nT is recorded using m pulses, n = 2m is satisfied when n is an even number, and n = 2m + 1 is satisfied when n is an odd number (m ≧ 1).
As shown in FIG. 36, the 3T strategy has the following relationship when a mark of length nT is recorded using m (m ≧ 1) pulses.
When n is a remainder of 1 divided by 3, n = 3m−2.
When n is a remainder of 2 divided by 3, n = 3m-1.
When n is a multiple of 3, n = 3 m.

In the present invention, there is provided an optical recording method for a multilayer optical recording medium that satisfies the relationship of the following expression, t ₍₁₎ <t ₍₂₎ , for the recording pulses used in the first and second recording layers. it can.
The present invention is characterized in that a mark is recorded on the first recording layer using a 1T period recording pulse train, and a mark is recorded on the second recording layer using a 2T period recording pulse train.
The present invention is characterized in that a mark is recorded on the first recording layer using a 1T period recording pulse train, and a mark is recorded on the other recording layer using a 2T period recording pulse train.
In the present invention, when recording a mark having a length of nT on a recording layer other than the Mth recording layer in the M phase change recording layer, the following equation is satisfied. A recording method can be provided. However, n is an integer greater than or equal to 1, and Tr represents the space | interval of the front-end | tip of a top pulse, and the rear end of the last pulse.
The present invention can provide an optical recording method for a multilayer optical recording medium that satisfies the following formula: 0.12T ≦ Tmp ≦ 0.3T (where Tmp represents a recording pulse width).
In the present invention, the recording method is for recording on a recording layer other than the innermost side as viewed from the laser beam irradiation side, modulated between the bias power level Pb and the recording power level Pp, and the erasing power level Pe. , PcN (where N represents an integer equal to or greater than 1) between at least one of the bias power levels Pb before the first pulse and after the last pulse. , Pp>Pe>Pc1>Pc2...>PcN> Pb can be provided. An optical recording method for a multilayer optical recording medium in which marks are formed by a recording pulse train satisfying the relationship of Pp>Pe>Pc1> Pc2.

In the present invention, the recording mark is modulated between the bias power level Pb and the recording power level Pp, and the cooling power level Pc1 between the erasing power level Pe and the bias power level Pb before the first pulse, Pc2,..., PcN (where N represents an integer greater than or equal to 1), a multilayer formed by a recording pulse train that satisfies the following formula: Pp>Pe>Pc1>Pc2...>PcN> Pb Can be provided.
In the present invention, the recording mark is modulated between the bias power level Pb and the recording power level Pp, and the cooling power level Pc1 between the erasing power level Pe and the bias power level Pb after the last pulse, Pc2,..., PcN (where N represents an integer greater than or equal to 1), a multilayer formed by a recording pulse train that satisfies the following formula: Pp>Pe>Pc1>Pc2...>PcN> Pb Can be provided.
In the present invention, the recording mark is modulated between the bias power level Pb and the recording power level Pp, and between the erasing power level Pe and the bias power level Pb before the first pulse and after the last pulse. .., PcN (where N represents an integer equal to or greater than 1), the pulse train satisfying the following formula: Pp>Pe>Pc1>Pc2...>PcN> Pb The optical recording method of the multilayer type optical recording medium formed by the above can be provided.
In this case, in the cooling power levels Pc1, Pc2,..., PcN, the value of N is any one of 1 to 3.
Recording can be performed on two or more phase change recording layers, and the ratio e (= Pe / Pp) between the recording power level Pp and the erasing power level Pe, the recording power level Pp and the cooling power levels Pc1, Pc2. ,..., PcN ratio d1,..., DN (= Pc1 / Pp,..., PcN / Pp) can be recorded by changing at least one of the recording layers.

In the present invention, the number of irradiation pulses of the recording power level Pp when recording a recording mark having a length nT (where n is an integer of 1 or more and T represents a clock period) is m (where m is 1). It is possible to provide an optical recording method for a multilayer optical recording medium that satisfies the relationship of n = 2m when n is an even number and n = 2m + 1 when n is an odd number.
In the present invention, it is possible to provide a recording method for a multilayer optical recording medium in which a pulse-like structure having an erase power level Pe ⁻ lower than Pe is included in the erase power level Pe with respect to the erase power level Pe.
In the present invention, when recording on each information layer of the multilayer optical recording medium, there is provided a recording method for a multilayer optical recording medium in which recording is performed in order from the information layer on the front side when viewed from the laser beam irradiation side. Can be provided.
In this case, T can be the same clock period for each recording layer.

In a second aspect of the present invention, an optical recording apparatus for a multilayer optical recording medium is provided. When performing recording on a multilayer optical recording medium having M phase change recording layers (M ≧ 2), the optical recording apparatus sets the first recording layer as the foremost recording layer when viewed from the laser beam side, A recording pulse train composed of a plurality of laser light pulses in the Kth recording layer (where 1 ≦ K ≦ M), with the Mth recording layer being the deepest recording layer when viewed from the laser light side and T being the clock cycle. When the period of a recording pulse train when recording a mark by irradiating a laser beam using t is defined as t _(K) [T], the relationship of t ₍₁₎ <t _(M) is satisfied, and In the optical recording apparatus of the multilayer optical recording medium, the period of the recording pulse train is configured not to decrease from the first recording layer to the next recording layer in the laser light irradiation direction.
With such an optical recording apparatus, it is possible to improve the repetitive recording characteristics of the recording layer on the near side when viewed from the laser light side and the recording sensitivity of the recording layer on the farthest side.

In the present invention, the optical recording apparatus of the multilayer optical recording medium is set so as to satisfy the relationship of t ₍₁₎ <t ₍₂₎ with respect to the recording pulses used for the first and second recording layers. Is done.
In the present invention, an optical recording apparatus for a multilayer optical recording medium records a mark on a first recording layer using a recording pulse train having a 1T cycle, and uses a recording pulse train having a 2T cycle on a second recording layer. Is set to record the mark.
In the present invention, an optical recording apparatus for a multilayer optical recording medium records a mark on a first recording layer using a recording pulse train having a 1T cycle, and uses a recording pulse train having a 2T cycle on the other recording layers. Is set to be recorded.
In the present invention, the optical recording apparatus of the multilayer optical recording medium satisfies the following formula when recording a mark of length nT in a recording layer other than the Mth recording layer in the M phase change recording layer. Set to
(N−1.5) T ≦ Tr ≦ (n−1) T
However, n is an integer greater than or equal to 1, and Tr represents the space | interval of the front-end | tip of a top pulse, and the rear end of the last pulse.
In the present invention, the recording apparatus for the multilayer optical recording medium is set so as to satisfy the following formula: 0.12T ≦ Tmp ≦ 0.3T (where Tmp represents the recording pulse width).

In the present invention, the optical recording apparatus of the multilayer optical recording medium performs recording between the bias power level Pb and the recording power level Pp when recording on a recording layer other than the innermost side when viewed from the laser light irradiation side. Cooling power levels Pc1, Pc2,..., PcN between the modulated and erase power level Pe and at least one bias power level Pb before the first pulse and after the last pulse (where N is 1 or more) Is set so as to form a mark by a recording pulse train satisfying the following formula: Pp>Pe>Pc1>Pc2...>PcN> Pb.
In the present invention, the optical recording apparatus of the multilayer optical recording medium modulates the recording mark between the bias power level Pb and the recording power level Pp, and erases the power level Pe and the bias power before the first pulse. Cooling power levels Pc1, Pc2,..., PcN (where N represents an integer equal to or greater than 1) between the levels Pb, Pp>Pe>Pc1>Pc2...>PcN> Pb The recording pulse train is set so as to satisfy the relationship.
In the present invention, the optical recording apparatus of the multilayer optical recording medium modulates the recording mark between the bias power level Pb and the recording power level Pp, and erases the power level Pe and the bias power after the last pulse. Cooling power levels Pc1, Pc2,..., PcN (where N represents an integer equal to or greater than 1) between the levels Pb, Pp>Pe>Pc1>Pc2...>PcN> Pb The recording pulse train is set so as to satisfy the relationship.
In the present invention, the optical recording apparatus of the multilayer optical recording medium modulates the recording mark between the bias power level Pb and the recording power level Pp, and erases the power level Pe before the first pulse and the last pulse. Cooling power levels Pc1, Pc2,..., PcN (where N represents an integer of 1 or more) between the following bias power level Pb, Pp>Pe>Pc1> Pc2. It is set so as to be formed by a pulse train satisfying the relationship of>PcN> Pb.
In this case, in the cooling power levels Pc1, Pc2,..., PcN, the value of N is any one of 1 to 3.

In the present invention, the optical recording apparatus of the multilayer optical recording medium has a ratio e (= Pe / Pp) between the recording power level Pp and the erasing power level Pe when recording on each of the two or more phase change recording layers. , PcN ratios d1,..., DN (= Pc1 / Pp,..., PcN / Pp) at least one of the recording power levels Pp and cooling power levels Pc1, Pc2,. It is set to record by changing.
In the present invention, an optical recording apparatus for a multilayer optical recording medium irradiates a recording power level Pp when recording a recording mark having a length nT (where n is an integer of 1 or more and T represents a clock period). When the number of pulses is m (where m is an integer of 1 or more), n = 2m is set when n is an even number, and n = 2m + 1 is set when n is an odd number. Only the shortest mark is recorded by incrementing one pulse.
In the present invention, the optical recording apparatus of the multilayer optical recording medium includes a pulse-like structure having an erasing power level Pe ⁻ lower than Pe with respect to the erasing power level Pe during the erasing power level Pe irradiation.
In the present invention, the optical recording apparatus of the multilayer optical recording medium records in order from the information layer on the near side when viewed from the laser beam irradiation side when recording on each information layer of the multilayer optical recording medium. It is set to go.
In this case, T can be the same clock period for each recording layer.

(Optical recording medium, optical recording method, and optical recording apparatus)
In the optical recording method of the present invention, the optical recording medium is irradiated with laser light, and the mark length recording in which the time length of the recording mark is represented by nT (where T is a basic clock period and n is a natural number). When recording information by method,
The recording mark is formed by alternately irradiating a heating pulse of power Pp and a cooling pulse of power Pb (where Pp> Pb) m times, satisfying the following formula, m ≦ (n / 2 + 1), and leading The cooling pulse irradiation time is 0.2T to 0.4T.
The optical recording medium of the present invention is used in the optical recording method of the present invention, and has a substrate, and at least a first protective layer, a phase change recording layer, a second protective layer, and a reflective layer on the substrate, and The phase change recording layer contains Sb and at least one element selected from Ge, Ga, In, Zn, Mn, Sn, Ag, Mg, Ca, Bi, Se, and Te.
The optical recording apparatus of the present invention irradiates an optical recording medium with laser light, and records the mark length in which the time length of the recording mark is represented by nT (where T is a basic clock period and n is a natural number). Record the information by the method,
A rotation drive mechanism for rotating the optical recording medium;
A laser light source that emits laser light to irradiate the optical recording medium;
Light source driving means for emitting the laser light source;
A light emission waveform control means for controlling the light source driving means by setting a recording strategy related to the light emission waveform of the light beam emitted from the laser light source, and
In the recording strategy, recording marks are formed by alternately irradiating a heating pulse with power Pp and a cooling pulse with power Pb (where Pp> Pb) m times, and m ≦ (n / 2 + 1). The irradiation time of the first cooling pulse is set to be 0.2T to 0.4T.

  The present invention relates to an optical recording medium that records, erases, or rewrites by intensity modulation of irradiation light, and particularly performs recording on a phase change optical recording medium at a high speed equivalent to, for example, 6 to 8 times the speed of DVD. It can be applied to a method and an optical recording apparatus (including an optical information reproducing apparatus).

First, FIG. 3 shows an example of a phase change type optical recording medium of DVD specification and high-speed specification suitable for the optical recording method of the present invention.
The phase change optical recording medium 106 has at least a first protective layer 102, a phase change recording layer 103, a second protective layer 104, and a reflective layer 105 on a transparent substrate 101 having guide grooves. Reference numeral 107 denotes an anti-sulfurization layer, and reference numeral 108 denotes an organic protective layer, which may further include other layers as required.

The material for the transparent substrate 101 is not particularly limited and may be appropriately selected depending on the intended purpose. However, polycarbonate resin is preferable from the viewpoints of heat resistance, impact resistance, low water absorption, and the like.
The refractive index of the substrate 101 is preferably 1.5 to 1.65. If the refractive index is greater than 1.65, the reflectivity of the entire disk is reduced, and if it is less than 1.5, the degree of modulation may be insufficient due to an increase in reflectivity. The thickness of the substrate 101 is preferably 0.59 to 0.62 mm. If the thickness exceeds 0.62 mm, there may be a problem in the focus performance of the pickup, and if it is less than 0.59 mm, the rotation speed becomes unstable due to the sweetness of the clamp of the recording / reproducing apparatus. In addition, when the thickness unevenness in the circumferential direction exceeds this range, there may be a problem that the signal intensity varies within the circumference.

The phase change recording layer 103 is made of a material containing at least one element selected from Sb and Ge, Ga, In, Zn, Mn, Sn, Ag, Mg, Ca, Ag, Bi, Se, and Te. Use.
When combined with an element that is based on Sb and has a eutectic point with a melting point of about 600 ° C. or lower in a binary system with Sb, or in combination with an element that forms a solid solution, repeated recording of amorphous and crystals is possible. A suitable recording layer can be formed. Properties such as crystallization speed, recording characteristics, storage stability, and ease of initialization are adjusted according to the type and amount of elements to be combined. There are one or more elements to be combined with Sb, and any number may be used as necessary. Moreover, you may add another element to the binary or more alloy of the element mentioned above and Sb.
When performing repetitive recording at a high speed, it is necessary to crystallize the amorphous mark at a high speed. Therefore, especially when recording at a speed equivalent to 6 to 8 times the speed of DVD, Sb is 50 to 90 atomic%, preferably 60 to 85 atomic%. If it is less than 50 atomic%, the crystallization speed is too slow, and amorphous marks remain unerased during repeated recording, leading to an increase in jitter and errors. When the content is more than 90 atomic%, it becomes difficult to form an amorphous material.
If the thickness of the phase change recording layer 103 is less than 8 nm, the modulation degree is small, and the stability of the reproduction light decreases. If it is thicker than 22 nm, the increase in jitter due to repetitive recording is large. . When the thickness is preferably 11 to 16 nm, the repeated recording durability is particularly improved.

  Conventionally, an alloy mainly composed of Al is used for the reflective layer 105. In addition to high reflectivity and high thermal conductivity, Al is also excellent in stability over time when made into a disk. However, when the crystallization speed of the recording layer material is high, the recording mark tends to be thin on a disc using an Al alloy for the reflective layer, and it may be difficult to perform recording with a sufficient degree of modulation. The reason for this is that if the crystallization speed is high, the recrystallized area of the melted area becomes large during recording, and the formed amorphous area becomes small. In order to reduce the recrystallization region, the second protective layer 104 may be thinned to have a rapid cooling structure. However, the recording layer is not sufficiently heated only by thinning the second protective layer, Since the melted region becomes small, even if the recrystallized region can be made small, the amorphous region to be formed eventually becomes small. However, when a metal having a refractive index (n + ik) at a wavelength of 650 to 670 nm, which is smaller than both n and k, is used for the reflective layer, the absorptance of the recording layer can be improved and the degree of modulation can be increased. Examples of metals smaller than Al for both n and k include Au, Ag, Cu, and alloys containing them as main components. Here, the main component means containing 90 atomic% or more, and preferably 95 atomic% or more.

Au, Ag, and Cu all have higher thermal conductivity than Al, and using them as a reflective layer has the effect of improving the light absorptance of the recording layer, increasing the temperature of the recording layer, and increasing the melting region. At the same time, since the cooling rate is also improved, the recrystallized region at the time of cooling becomes small, and it becomes possible to form a larger amorphous region than when using an Al alloy. The modulation degree of the recording mark is determined by the optical modulation degree and the size of the mark. The optical modulation degree is large, and the larger the mark is, the larger the recording mark is. Therefore, even when high linear velocity recording is performed using a material having a high crystallization speed as the recording layer, if such a reflective layer is used, a large recording mark can be formed because the absorption rate is large and the cooling speed is high. In addition, since the difference in reflectance between the crystal and the amorphous is large, recording with a high degree of modulation becomes possible.
Among Au, Ag, Cu, and alloys based on them, in particular, Ag and Ag alloys are relatively inexpensive, and are also less susceptible to oxidation than inexpensive Cu and Cu alloys, so they are stable over time. A medium excellent in properties can be formed, which is preferable as a reflective layer.
If the thickness of the reflective layer is 90 nm or more, the transmitted light is almost eliminated and the light can be used efficiently. The thicker the reflective layer, the faster the cooling rate, which is advantageous when using a recording layer with a high crystallization rate, but the cooling rate is saturated at 200 nm or less, and the recording characteristics change even when the thickness is greater than 200 nm. However, since it takes only a long time to form a film, the thickness is preferably 200 nm or less.

When Ag or an Ag alloy is used as the reflective layer 105, the anti-sulfurization layer 107 is required when a material containing S is used for the second protective layer. Properties required for the sulfidation preventive layer include not containing S, not transmitting S, and the like. The inventors of the present invention formed various oxide films, nitride films, etc. as an anti-sulfurization layer, and evaluated the recording characteristics and storage reliability. Was found to have excellent functionality. Here, the main component means that the material contains 90 mol% or more of SiC or Si, and preferably 95 mol% or more.
The thickness of the antisulfurization layer 107 is preferably 3 to 22 nm. If the thickness is 3 nm or more, the film formed by sputtering becomes almost uniform and exhibits a sulfidation preventing function. However, if the thickness is smaller than this, the probability that a defect is partially generated increases rapidly. Further, if the thickness exceeds 22 nm, the reflectivity decreases as the thickness increases, and the film formation rate is almost the same as that of the recording layer even if it is largely estimated. Therefore, if the thickness is thicker than the recording layer, the production efficiency decreases. Therefore, it is desirable not to exceed the thickness of the recording layer at the maximum, and the preferable upper limit is 22 nm after all.

The first protective layer 102 and the second protective layer 104 function as a protective film such as heat resistance, as well as having a high refractive index and high heat insulation, so that incident light can be efficiently used by adjusting the thickness. A mixture of ZnS and SiO ₂ having a molar ratio of about 8: 2 is used.
The thickness of the first protective layer 102 is preferably 40 to 220 nm, and more preferably 40 to 80 nm. This is a value mainly determined from the reflectance. Within this range, a thickness that can achieve both sufficient reflectance and recording sensitivity is selected. When the thickness is less than 40 nm, the heat resistance is poor, the damage to the substrate 1 is increased, and the increase in jitter due to repeated recording is increased. On the other hand, if it is thicker than 220 nm, the reflectivity becomes too high and the recording sensitivity is lowered.
The thickness of the second protective layer 104 is preferably 2 to 20 nm, and more preferably 6 to 14 nm. This is a value mainly determined from heat conduction. Since the reflective layer is further provided on the second protective layer, the heat absorbed by the recording layer diffuses to the reflective layer through the second protective layer and is cooled. Therefore, if it is too thin, the thermal diffusion is too fast and the recording layer cannot be heated sufficiently and the recording sensitivity is lowered. If it is too thick, the cooling rate will be insufficient and it will be difficult to form amorphous marks.

A film as described above is formed on the substrate 1 by sputtering in order of the first protective layer 102, the phase change recording layer 103, the second protective layer 104, the antisulfuration layer 107, and the reflective layer 105, and then organically protected on the reflective layer. The film 108 is formed by spin coating. In this state or after a further bonding process, the optical recording medium 6 is used through an initialization process. Bonding is a process of bonding a plate having the same size and usually the same material as the substrate through an organic protective film.
Initialization is a process of crystallizing the phase change recording layer 103 that is in an amorphous state immediately after film formation by irradiating a laser beam of about 1 to 2 W formed to about 1 × (several 10 to several 100) μm. It is.

Next, the optical recording method of the present invention for the high-speed optical recording medium 6 as described above, particularly the recording strategy will be described.
Here, it is assumed that information is recorded by a recording mark length / inter-mark length modulation method in which PWM (Pulse Width Modulation) is applied to the optical recording medium 106. In this recording method, information can be recorded by controlling the length of the recording marks and the length between the recording marks in units of the basic clock period T. Since the recording density can be made higher than that of the mark position modulation method which is one of the recording methods of the optical recording medium, the recording density can be increased, and EFM adopted in CD and DD (Double Density) CD. This is a modulation method employed in an optical disk such as EFM + employed in DVD. In the recording mark length and mark length modulation system, it is important to accurately control the recording mark length and the mark length (hereinafter referred to as space length). In these modulation methods, both the recording mark length and the space length are set to a time length of nT (n is a natural number of 3 or more) with respect to the basic clock period T.

  In the present invention, the recording strategy using the three values of the peak power Pp, the erasing power Pe, and the bias power Pb is a high-speed specification that reduces the number of pulses so that sufficient heating and cooling can be performed, that is, the peak power Pp light. And an amorphous mark having a length of nT is formed by irradiation with m pulses (m is an integer) where m ≦ (n / 2 + 1) by repetition of the bias power Pb light and irradiation with the erasing power Pe light. It is assumed that a crystal space having a length nT between amorphous marks is formed. Therefore, 3T, which is the minimum mark formed according to the EFM + modulation method, is 2 pulses or less, 4T, 5T is 3 pulses or less, 6T, 7T is 4 pulses or less, 8T, 9T is 5 pulses or less, 10T, 11T is 6 pulses or less. , 14T is formed with 8 pulses or less. The number of pulses is mainly determined by the recording linear velocity, and it is better to reduce the number of pulses as the recording linear velocity is faster.

Under such high-speed specification conditions, the first cooling pulse time of the pulse train of the heating pulse and cooling pulse forming the amorphous mark is set to 0.2T to 0.4T. Furthermore, when the mark is formed by irradiation of three or more sets of heating pulses and cooling pulses, the second cooling pulse time is set to 1.0T to 2.5T. At this time, the ratio of the erase power to the peak power is set to 0.1 ≦ Pe / Pp ≦ 0.4.
These ideas make it possible to make the tip of the amorphous mark thicker, making the tip shape less susceptible to the state of the surrounding crystal, suppressing the rise in jitter at the beginning of repeated recording, and durability for repeated recording. Cross-erase can also be suppressed without deteriorating performance.

When the mark tip is thin, it is easy to reflect the difference in crystal state as an increase in jitter, and the increase in jitter at the beginning of repeated recording becomes large. This is because in the case of a recording layer containing Sb as a main component, crystallization proceeds by crystal growth from the boundary with the crystal.
In general, the higher the temperature, the faster the crystal growth rate. For this reason, if the boundary between the crystal and the amorphous is in the center of the track where the temperature is higher, the crystallization is likely to proceed, and if there is a difference in the crystal state, the shape of the mark tip in the process of irradiating the pulse train Variations are likely to occur. If the tip of the mark is thick and the boundary between the crystal and the amorphous material is further away from the center of the track, the temperature is low and the crystal growth rate is slow. Difficult to cause variation.
Furthermore, since the recording / reproducing beam usually has a Gaussian distribution, during reproduction, the recording / reproducing beam is more affected by the change in the mark shape at the center of the track than the change in reflectance due to the change in the mark shape away from the center of the track. Become. For the above reasons, it can be said that when the shape of the mark tip is originally thick, it is not easily affected by the difference in crystal state, and when it is thin, it is easily affected. Therefore, it is an effective method to record the mark tip thickly.

  Since the crystallization speed of the phase change recording layer used for high-speed recording is generally high, it has hardly been studied to shorten the cooling pulse irradiation time as in the setting of the leading cooling pulse of the present invention. If the cooling pulse irradiation time is shortened, the amorphous mark formed by the immediately preceding heating pulse is recrystallized, and a sufficiently large amorphous mark cannot be formed, resulting in an increase in jitter. However, the present inventors have found that the tip of the mark can be formed larger by deliberately shortening the leading cooling pulse time. As a result of examination by simulation, observation of a TEM photograph, etc., the amorphous part formed by the first heating pulse disappears by recrystallization, but the preheating effect of the first heating pulse causes the second heating pulse to It was found that the temperature at the time of irradiation increased and the melting region expanded, resulting in a larger mark tip. This is schematically shown in FIG.

Similarly, when the first heating pulse is lengthened in such a manner that the first and second heating pulses are continued without providing the first cooling pulse, it is possible to form a large mark tip. However, in this case, since the peak power is continuously irradiated, the temperature rises excessively, the film quality deteriorates, and the repeated recording durability deteriorates. Further, since the temperature rises to the adjacent track, a cross erase that partially erases the amorphous mark already recorded on the adjacent track also occurs.
The leading cooling pulse is set between 0.2T and 0.4T. When the time is shorter than 0.2T, the cooling effect is hardly obtained, and the behavior is similar to that when the leading heating pulse is lengthened, and the repeated recording durability is deteriorated and the crosstalk is increased. If it is set longer than 0.4T, the amorphous portion formed by the first heating pulse remains, and as a result, the tip portion becomes a thin mark and the jitter at the initial stage of repeated recording increases.

Further, the second cooling pulse in the case where the mark is formed by three or more pulse trains needs to be sufficiently long as conventionally studied. Thereby, recrystallization due to the third heating pulse can be prevented, and the mark tip can be formed large. The second cooling pulse is set between 1.0T and 2.5T. If it is shorter than 1.0 T, recrystallization of the formed amorphous part proceeds in the process of irradiation with the second cooling pulse due to the influence of the third heating pulse, and the jitter becomes large. If it is longer than 2.5T, continuous marks cannot be formed.
Such a recording strategy is effective when the ratio of the erasing power Pe to the peak power Pp is 0.4 or less. As a result of investigations by the present inventors, when recording is performed at a DVD speed of 6 times or higher, if the ratio of the erasing power Pe to the peak power Pp is larger than 0.4, the jitter becomes large even in the first recording. The reason is not clear, but since the recording time is shortened in the case of high-speed recording, the recording layer cannot be heated sufficiently unless the value of Pp is increased. However, if the value is increased to Pe, the cooling is insufficient and the jitter increases. Conceivable. However, when Pe is low, the temperature rise due to the peak power at the head tends to be insufficient. In such a case, the jitter at the beginning of repeated recording tends to increase, but this problem can be solved by using the leading heating pulse as a preheating pulse as in the present invention. However, if Pe / Pp is less than 0.1, erasure is likely to be insufficient, and even if the initial recording is good, the jitter increases over the entire repeated recording.

Next, a configuration example of an optical recording apparatus for realizing the optical recording method based on the above-described recording strategy will be described with reference to FIG.
This apparatus is provided with a rotation control mechanism 122 including a spindle motor 121 for rotating the optical recording medium 106, an objective lens for condensing and irradiating the optical recording medium 106 with a laser beam, a semiconductor laser LD 123, and the like. An optical head 124 having the laser light source is provided so as to be seekable in the radial direction of the disk. An actuator control mechanism 25 is connected to the objective lens driving device and output system of the optical head 124. The actuator control mechanism 25 is connected to a wobble detection unit 27 including a programmable BPF 26. The wobble detection unit 27 is connected to an address demodulation circuit 28 that demodulates an address from the detected wobble signal. A recording clock generator 30 including a PLL synthesizer circuit 29 is connected to the address demodulating circuit 28. A drive controller 31 is connected to the PLL synthesizer circuit 29. The rotation controller 122, the actuator controller 25, the wobble detector 27, and the address demodulator 28 are also connected to the drive controller 31 connected to the system controller 32.

The system controller 32 has a so-called microcomputer configuration including a CPU and the like. Further, an EFM encoder 34, a mark length counter 35, and a pulse number control unit 36 are connected to the system controller 32. The EFM encoder 34, the mark length counter 35, the pulse number control unit 36, and the system controller 32 are connected to a recording pulse train control unit 37 serving as a light emission waveform control unit. The recording pulse train controller 37 includes a multi-pulse generator 38 that generates multi-pulses (on pulse for peak power Pp, off-pulse for bias power Pb) defined by a recording strategy, an edge selector 39, and a pulse edge generator. 40 is included.
On the output side of the recording pulse train controller 37, the semiconductor laser LD 123 in the optical head 124 is driven by switching the driving current sources 41 of the recording power Pw (peak power Pp), the erasing power Pe, and the bias power Pb. An LD driver unit 42 is connected as a light source driving means.

  In order to record on the optical recording medium 106 in such a configuration, the rotation control mechanism 122 controls the rotation speed of the spindle motor 121 under the control of the drive controller 31 so that the recording linear velocity corresponds to the target recording velocity. After the control, the address demodulation is performed by the wobble signal separated and detected by the programmable BPF 26 from the push-pull signal obtained by the optical head 124, and the recording channel clock is generated by the PLL synthesizer circuit 29. Next, in order to generate a recording pulse train by the semiconductor laser LD 123, a recording channel clock and EFM + data as recording information are input to the recording pulse train controller 37, and the multi-pulse generator 38 in the recording pulse train controller 37 7 is generated, and a multi-pulse is generated according to the recording strategy as shown in FIG. 7, and the driving current source 41 set so as to have the respective irradiation powers corresponding to the aforementioned Pp, Pe, and Pb is switched by the LD driver unit 42. The LD emission waveform according to the recording pulse train can be obtained.

Further, in the recording pulse train controller 37 configured as shown in FIG. 5, a mark length counter 35 for counting the mark length of the EFM + signal obtained from the EFM encoder 34 is arranged, and the mark count value is increased by 2T. Each time, a multi-pulse is generated via the pulse number control unit 36 so that one set of pulses (on-pulse with recording power Pw = peak power Pp and off-pulse with bias power Pb) is generated.
Another configuration of the multi-pulse generation unit is to generate a recording frequency-divided clock obtained by dividing the recording channel clock by two, generate an edge pulse from the multi-stage delay circuit, and select the front and rear edges with an edge selector. Thus, every time the recording channel clock increases by 2T, one set of pulses (recording power Pw = on pulse with peak power Pp and off pulse with bias power Pb) can be generated. In the case of this configuration, the substantial operating frequency of the multi-pulse generator is halved, and further high-speed recording operation is possible.

  According to the present invention, the mark tip can be formed thick at the time of high-speed recording equivalent to 6 to 8 times the speed of DVD, so that it is repeated regardless of the initial crystal state without causing deterioration of repeated recording durability and increase of crosstalk. An optical recording method and an optical recording apparatus capable of reducing an increase in jitter at the initial stage of recording can be provided.

(Optical recording method and optical recording apparatus for multilayer optical recording medium)
The optical recording method for a multilayer optical recording medium of the present invention comprises irradiating a laser beam to a multilayer optical recording medium having at least M phase change recording layers (where M represents an integer of 2 or more) on a substrate. When forming a recording mark, the emission waveform of the laser beam is a recording pulse train composed of a plurality of pulses, and recording is performed by modulating the recording pulse train,
The period of the recording pulse train when recording is performed on the Kth recording layer (which is an integer satisfying 1 ≦ K ≦ M) under the clock period T as viewed from the laser light irradiation side, t _(K) [T] , The following formula, 1 ≦ t ₍₁₎ ≦ t ₍₂₎ ≦... T _(K) ≦ t _{(K + 1)} (except when all are equal signs). In this case, it is preferable to satisfy the following formula, t ₍₁₎ <t ₍₂₎ .
In another embodiment, in the optical recording method for a multilayer optical recording medium having M phase change recording layers (M ≧ 2), the first recording layer is the foremost recording layer when viewed from the laser beam side. The Mth recording layer is the deepest recording layer when viewed from the laser beam side, T is the clock cycle, and the Kth recording layer is irradiated with the laser beam using a recording pulse train composed of a plurality of laser beam pulses. _Assuming that the period of the recording pulse train when recording the mark is t _(K) [T], the relationship of the following equation, t ₍₁₎ <t _(M) is satisfied, and the period of the recording pulse train is the laser It does not decrease from the first recording layer to the next recording layer in the direction of light irradiation.
Here, in many cases, T1 = 1. In the case of T1 = 1, when recording is performed on the second and subsequent layers, an effect appears if recording is performed with a period of 1.5T or more. In general, it is also possible to record with a strategy of 3T period. In other words, preferably 1.5 ≦ T _(K) ≦ 3 as the range of T _(K) If the K ≧ 2. However, in practice, it is preferable to record at a 2T period in order to avoid an increase in the number of parameters of the recording strategy. Therefore, in particular, it is preferable to use the 1T cycle strategy when recording to the foremost side and to use the 2T cycle strategy when recording to other recording layers.
When recording on the foremost recording layer, the overwrite characteristics are improved if the recording pulse train has a 1T period. If the 2T period is used, recording is possible. However, since the shift of the length of the shortest mark mainly affects, the jitter becomes worse as compared with the 1T period when the number of repeated recordings increases (see FIG. 25). . In this example, an experiment was conducted using the two-layer optical recording medium used in Example B-17 described later.
When recording on other recording layers, if the recording pulse train has a 2T period, the pulse width of the recording pulse train can be increased and the cooling time can be increased, so that the recording sensitivity is improved. be able to. If the period is 1T, recording is possible, but the recording sensitivity is deteriorated by about 15% (see FIGS. 26 and 27).

In the optical recording method of the present invention, the length nT (where T is a clock period and n is 2 or more) is added to a recording layer other than the Mth (where M represents an integer of 2 or more) as viewed from the laser light irradiation side. When the recording mark (which is an integer) is formed, the rising interval Tr of the first pulse and the last pulse is set so as to satisfy the following expression: (n−1.5) T ≦ Tr ≦ (n−1) T By setting, the recording characteristics of the recording layers other than the innermost side when viewed from the light irradiation side of the multilayer optical recording medium having two or more phase change recording layers can be improved.
As shown in FIG. 24, in a conventional single-layer rewritable optical recording medium such as DVD + RW, for example, when a 1T periodic strategy is used, a recording method that starts recording from a time position delayed by 1T with respect to data is mainly used. (1 in FIG. 24). However, as a recording method for recording layers other than the innermost side when viewed from the light irradiation side of the multilayer optical recording medium having two or more phase change recording layers , (2) in FIG. 24 and (3) in FIG. As described above, when forming a mark having a length nT, it is better to use a recording method in which the rising time width Tr of the first pulse and the last pulse is widened.
This is because it is necessary to secure a high transmittance in the information layer other than the innermost side when viewed from the light irradiation side of the multilayer optical recording medium, so that a thick metal layer cannot be formed, and the transparent dielectric This is because the heat dissipation effect is compensated by using. If the metal layer is thick, sufficient heat dissipation is obtained and recording marks are easily formed, but if a transparent dielectric is used, the thermal conductivity is lower than that of the metal, so that sufficient heat dissipation effect cannot be obtained and recrystallization of amorphous marks It tends to occur. Therefore, it is aimed to obtain a desired mark length by setting Tr wide.

This optical recording method may be a method in which the leading pulse rises early in time as shown in (2) of FIG. 24 and the last pulse rises in time late as shown in FIG. 24, or only the leading pulse as shown in (3) of FIG. You just have to get up early. The range of the Tr value is preferably (n−1.5) T ≦ Tr ≦ (n−1) T. For example, when recording an 8T mark, Tr that satisfies 6.5T ≦ Tr ≦ 7T is used. Further, in order to make the formation region of the amorphous mark as large (thick) as possible, it is necessary to take a long cooling time after heating. Therefore, it is preferable to make the width Tmp of the recording pulse as small as possible. When the clock period is T, it is preferable to satisfy 0.12T ≦ Tmp ≦ 0.3T regardless of the recording speed. When Tmp is shorter than 0.12T, a high recording power is required. In particular, when the recording speed is as high as 9.2 m / s, the clock cycle T = 15.9 nsec, so Tmp = 0.12T = 1. 9 nsec, and the response time (rise time and fall time) of the laser emitted from the LD (laser diode) in the recording apparatus is not in time, and it becomes difficult to perform recording with a desired recording power. Further, if Tmp is longer than 0.3T, the cooling time is insufficient, so that recrystallization occurs due to the remaining heat of the next pulse, resulting in a problem that a desired modulation degree cannot be secured.
In general, it is preferable to use the parameters of the recording pulse strategy as shown in FIG. 28 while maintaining the range of Tr, but this is not restrictive. For example, in DVD, the data modulation method is the EFM + method, and the 3T mark and 4T mark have a larger number of appearances than other long marks, so that the recording characteristics (jitter) are most affected. Therefore, parameters such as (dTtop3), (dTtop4), (dTlp3), (dTlp4), (dTera3), and (dTera4) can be set individually for 3T and 4T recording. 19 and 20 compare the recording characteristics (jitter) when the number of parameters is changed. It can be seen that when the final pulses of 3T and 4T are individually set, the recording characteristics are improved. Recording was performed with a recording strategy represented by the parameters in FIG. “−” In the parameter means that it is delayed in time from the reference (rising edge) of the clock.

  According to the optical recording method of the present invention, the recording characteristics of the multilayer optical recording medium are improved. Further, as a recording method applied to a recording layer other than the innermost side when viewed from the laser beam irradiation side, a recording mark is formed by irradiating a multilayer optical recording medium having at least two phase change recording layers on a substrate with a laser beam. , The laser light emission waveform is used as a recording pulse train composed of a plurality of pulses, recording is performed by modulating the recording pulse train, and a recording mark is placed between the bias power level Pb and the recording power level Pp. Cooling power levels Pc1, Pc2,..., PcN between the modulated and erase power level Pe and at least one bias power level Pb before the first pulse and after the last pulse (where N is 1 or more) Is a pulse train satisfying the relationship represented by the following formula: Pp> Pe> Pc1> Pc2...> PcN> Pb It is formed.

The optical recording apparatus for a multilayer optical recording medium of the present invention is set so that the optical recording method of the multilayer optical recording medium of the present invention can be carried out, and laser light emitted from a laser light source is used. The light is guided to a condensing lens by an optical element, and recording is performed on the optical recording medium by condensing and irradiating laser light to the multilayer optical recording medium by the condensing lens. At this time, the optical recording apparatus guides a part of the laser light emitted from the laser light source to the laser light detector, and controls the light amount of the laser light source based on the detection amount of the laser light of the laser light detector. The laser light detector converts the detected amount of the detected laser light into a voltage or current and outputs it as a detection amount signal.
The optical recording apparatus is further provided with various control means as required. The control means is not particularly limited as long as the movement of each means can be controlled, and can be appropriately selected according to the purpose. Examples thereof include devices such as a sequencer and a computer.

The optical recording method for a multilayer optical recording medium of the present invention comprises any one of the following first to third embodiments.
In the first mode, the recording mark is modulated between the bias power level Pb and the recording power level Pp, and the cooling power level Pc1 between the erasing power level Pe and the bias power level Pb before the first pulse, Pc2,..., PcN (where N represents an integer greater than or equal to 1) is formed by a pulse train that satisfies the following formula: Pp>Pe>Pc1>Pc2...>PcN> Pb. is there.
In the second mode, the recording mark is modulated between the bias power level Pb and the recording power level Pp, and the cooling power level Pc1 between the erasing power level Pe and the bias power level Pb after the last pulse. , Pc2,..., PcN (where N represents an integer greater than or equal to 1), and formed by a pulse train satisfying the following formula: Pp>Pe>Pc1>Pc2...>PcN> Pb It is.
In the third mode, the recording mark is modulated between the bias power level Pb and the recording power level Pp, and between the erasing power level Pe and the bias power level Pb before the first pulse and after the last pulse. , PcN (where N represents an integer greater than or equal to 1) satisfies the relationship of the following formula: Pp>Pe>Pc1>Pc2...>PcN> Pb It is formed by a pulse train.
In the first to third embodiments, it is preferable that N in the cooling power levels Pc1, Pc2,..., PcN is any one of 1 to 3.

Here, as a specific laser waveform light emission pattern, for example, there is a pattern used in DVD + RW or the like as shown in FIGS. The mark in the amorphous state is formed by pulse irradiation by alternately repeating peak power (Pp) light and bias power (Pb) light. On the other hand, the space consisting of the crystalline state is formed by continuously irradiating an intermediate level erase power (Pe) light between Pp and Pb.
When a recording pulse train composed of peak power (Pp) light and bias power (Pb) light is irradiated, the recording layer is repeatedly melted and rapidly cooled to form amorphous marks. On the other hand, when the erasing power (Pe) light is irradiated, the recording layer is gradually cooled after being melted or annealed in a solid state to be crystallized to form a space.
A recording pulse train composed of peak power (Pp) light and bias power (Pb) light is usually divided into a head pulse, an intermediate pulse, and a final pulse. The shortest 3T mark is recorded by only the first pulse and the last pulse, and an intermediate pulse is also used when forming a mark of 4T or more. The intermediate pulse is also called a multi-pulse, and is provided with a 1T period, and a method of increasing the number of pulses by one every time the mark length becomes 1T longer is used. This recording method is called a 1T period recording strategy, and the number of recording pulses when forming a mark of length nT is (n-1). However, T means a clock cycle. Incidentally, in DVD + RW, when recording at a speed exceeding 4 × speed, since the clock period is shortened, a recording method with a 2T period (2T period recording strategy) is often used.

In the optical recording method of the multilayer optical recording medium in the first embodiment, when N = 1, as shown in FIG. 11, the recording mark is modulated between the bias power level Pb and the recording power level Pp. In addition, the cooling power level Pc1 between the erasing power level Pe and the bias power level Pb before the first pulse satisfies the relationship of the following expression, Pp>Pe>Pc1> Pb.
When N = 2, as shown in FIG. 12, the recording mark is modulated between the bias power level Pb and the recording power level Pp, and the bias power before the erasing power level Pe and the first pulse. The cooling power levels Pc1 and Pc2 with the level Pb satisfy the following relationship: Pp>Pe>Pc1>Pc2> Pb.

In the optical recording method of the multilayer optical recording medium according to the second embodiment, when N = 1, as shown in FIG. 13, the recording mark is modulated between the bias power level Pb and the recording power level Pp. In addition, it is clear that the cooling power level Pc1 between the erase power level Pe and the bias power level Pb after the final pulse satisfies the relationship of the following equation: Pp>Pe>Pc1> Pb.
In the optical recording method of the multilayer optical recording medium in the third embodiment, when N = 1, as shown in FIG. 14, the recording mark is modulated between the bias power level Pb and the recording power level Pp. In addition, it is clear that the cooling power level Pc1 between the erase power level Pe and the bias power level Pb before the first pulse and after the last pulse satisfies the relationship of the following equation: Pp>Pe>Pc1> Pb. is there.

  The multilayer optical recording medium optical recording method of the present invention can utilize at least one of the remaining heat before the first pulse and after the last pulse by satisfying any one of the first to third embodiments. Therefore, thermal damage to the first recording layer can be further suppressed, recording and erasing can be performed accurately, recording characteristics can be improved, and it can be applied to various optical recording media. It is suitably used for the multilayer optical recording medium of the present invention described in (1).

  In the conventional recording method as shown in FIGS. 15 and 16, a method of performing recording with the ratio ε (= Pe / Pp) of the recording power Pp and the erasing power Pe constant is often used. This is a method devised for maintaining good jitter and asymmetry in a wider recording power range by the balance between the recording power Pp and the erasing power Pe. Here, the jitter is expressed by standardizing the time lag between the boundary and the clock with the window width when the reflectance level of the mark and space is binarized at the slice level. The lower this value, the better the recording characteristics. The asymmetry is an average value of the crystalline reflectance I14H corresponding to 14T space and the amorphous reflectance I14L corresponding to 14T mark, and the crystalline reflectance I3H corresponding to 3T space and the amorphous reflectance I3L corresponding to 3T mark. It is a characteristic value that represents how much the average value of the deviation is. The expression is expressed by (I14H + I14L) − (I3H + I3L) / 2 (I14H−I14L) (see FIG. 19). Since the reflectance signal is binarized by the slice level, it is better that the asymmetry is closer to zero. If the asymmetry is broken, the boundary between the mark and the space may not be recognized correctly. If the recording power Pp is too high or too low, or if the erasing power Pe is too high or too low, the asymmetry is broken, resulting in poor jitter. Therefore, the recording characteristics are prevented from deteriorating by fixing the ratio and balancing the power.

Therefore, in the optical recording method of the present invention, not only the ratio ε of the recording power Pp and the erasing power Pe set individually for the first recording layer and the second recording layer, but also the recording power Pp and the cooling power Pc1, Pc2 ,..., PcN ratios δ1,... ΔN (= Pc1 / Pp,... PcN / Pp) are preferably set individually at the same time.
For example, consider the case where the phase change recording material used for the first recording layer and the second recording layer and the composition thereof are the same. At the same recording speed on each information layer, the recording mark is modulated between the bias power level Pb and the recording power level Pp, and at least one of the erasing power level Pe, before the first pulse and after the last pulse. Cooling power levels Pc1, Pc2,..., PcN (where N represents an integer equal to or greater than 1) between the bias power level Pb and the following expression, Pp>Pe>Pc1>Pc2...>PcN> When recording using an optical recording method formed by a pulse train that satisfies the relationship represented by Pb, the values of ε and δ1,. As a result of the examination, a result as shown in FIG. 20 was obtained. FIG. 20 shows data obtained by recording on the two-layer phase change optical recording medium described in Example B-19 using the recording strategy shown in FIG. 11 (Example B-28 and Comparative Example B described later). Corresponds to -23).
As can be seen from FIG. 20, compared to the case where recording is performed on the second information layer at the same power ratio as the optimal power ratio (ε = 0.18, δ1 = 0.09) in the first information layer, The recording characteristics are superior when recording is performed on the second information layer at different power ratios (ε = 0.38, δ1 = 0.19). In particular, the jitter at the optimum recording power (referred to as bottom jitter) is 8.7% when recording at the same power ratio, and 8.1% when recording at different power ratios. Thus, it can be seen that there is an optimum power ratio for each information layer.

Furthermore, as shown in Table 1 below, when recording on the second information layer was performed at a power ratio of (ε = 0.38, δ1 = 0.09), the bottom jitter was 8.3%. It can be seen that not only the ratio ε but also the effect of the ratio δ1 affects the recording characteristics.

In the optical recording method of the present invention, the number of irradiation pulses of the recording power level Pp when recording a recording mark having a length nT (where T is a clock period and n is an integer of 1 or more) is m (m: 1). When n is an even number, the recording sensitivity can be improved by satisfying the relationship of n = 2m when n is an even number and n = 2m + 1 when n is an odd number.
Conventionally, when recording on a single-layer phase change optical recording medium compatible with DVD 1 to 4 times speed, the scanning linear velocity of the medium is slow, so one set of heating irradiation pulse and cooling irradiation pulse is repeated every clock cycle. The method is widely used (1T periodic strategy). In this recording method, when recording an amorphous mark having a length of nT, (n-1) heating irradiation pulses and cooling irradiation pulses are alternately irradiated. However, since the clock cycle is shortened as the recording linear velocity is improved, when the heating irradiation pulse and one set of cooling pulse are performed in the 1T cycle as in the prior art, sufficient cooling time cannot be obtained. That is, even if irradiation with a certain heating pulse and cooling pulse is performed to form an amorphous mark, the amorphous mark once formed is recrystallized due to the residual heat generated from the heating pulse after the next 1T cycle, In particular, there is a problem that a long mark becomes thin and it is difficult to obtain a modulation degree. In order to solve such a problem, it is essential to take as long a cooling pulse irradiation time as possible.

Therefore, in high-speed recording exceeding DVD quadruple speed, a thick and uniform amorphous mark is formed by adopting a recording method (2T period strategy) in which one set of heating irradiation pulse and cooling irradiation pulse is repeated every two clock periods. And a high degree of modulation can be ensured. In this recording method, when recording an amorphous mark having a length of nT, if the number of heating irradiation pulses is m (where m is an integer of 1 or more), n = 2m + 1 when n is an odd number, When n is an even number, n = 2 m is preferable. Recording can be easily performed even when the 2T cycle strategy is used at a recording linear velocity of about 1 to 4 times the DVD speed. Furthermore, since the cooling time can be made longer as described above, the rapid cooling effect is promoted, so that the recording power can be made lower than that in the case of recording with the 1T cycle strategy, and recording can be performed with high sensitivity. Also in the recording method for the multilayer optical recording medium of the present invention, it is preferable to use the 2T periodic strategy because the recording sensitivity of each recording layer such as the first information layer and the second information layer is improved.
In this case, the repeated recording of the multilayer type optical recording medium can be performed more satisfactorily by recording the shortest mark by increasing one pulse.

In the optical recording method of the present invention, a pulse-like structure having an erasing power level Pe ⁻ lower than Pe is included in the Pe irradiation with respect to the erasing power level Pe. Damage can be further reduced.
FIG. 21 illustrates a laser emission waveform. JP-A-2004-63005 can be cited as a known technique similar to such a laser irradiation waveform. According to the technique of this publication, in order to prevent the recorded mark from being left in the space portion without being erased as the recording linear velocity is improved, the energy required for erasing by arranging Pe + in a pulse shape in the Pe region. Is to supply. On the other hand, in the present invention, in order to reduce as much as possible the thermal damage to the information layer on the near side of the multilayer recording medium by irradiating a relatively high erasing power Pe, Pe− Arrange a pulse-like structure. Thereby, the repeated recording characteristics of the information layer on the near side can be improved.

In the optical recording method of the present invention, when recording on each information layer of the multilayer optical recording medium, it is preferable that recording is performed in order from the information layer on the front side as viewed from the laser beam irradiation side.
The optical constants of the phase change material used in the recording layer of the multilayer optical recording medium are different between the crystalline state and the amorphous state, and the crystalline state has a higher absorption coefficient than the amorphous state. In other words, the amorphous state has a higher light transmittance because it absorbs less light. Therefore, if recording is performed in order from the information layer on the front side when viewed from the side irradiated with the laser beam, an amorphous mark can be formed on the information layer by recording, so that the area area of the amorphous mark is wide on the front side. Therefore, when recording is performed on the information layer on the back side as viewed from the side irradiated with the laser beam, light is easily transmitted and recording on the information layer on the back side is facilitated.
Further, when information is actually recorded on the optical recording medium by the recording device, the information recorded from the first information layer may be recorded with a power lower by several percent than the information recorded from the second information layer. it can. The light transmittance of the first information layer acts on the recording power necessary for recording on the second information layer, and there is an effect of relatively improving the recording sensitivity.

Here, FIG. 33 is a diagram showing an example of an optical recording apparatus according to an embodiment of the present invention. This optical recording apparatus 220 drives a spindle motor 222, an optical pickup apparatus 223, and the optical pickup apparatus 223 in the sledge direction for rotationally driving an optical disk 215 as a single-sided multilayer optical recording medium according to an embodiment of the present invention. And a seek motor 221, a laser control circuit 224, an encoder 225, a drive control circuit 226, a reproduction signal processing circuit 228, a buffer RAM 234, a buffer manager 237, an interface 238, a flash memory 239, a CPU 240, and a RAM 241.
Note that the arrows in FIG. 33 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block. In the present embodiment, the optical recording apparatus 220 is compatible with a single-sided multilayer optical recording medium.

(Multilayer type optical recording medium)
The multilayer optical recording medium of the present invention is used in the optical recording method of the multilayer optical recording medium of the present invention, and causes a reversible phase change between a crystalline state and an amorphous state by irradiation with a laser beam. The information layer includes at least two information layers including a phase change recording layer for recording information, and further includes other layers as necessary. The multilayer optical recording medium includes at least an upper protective layer, a phase change recording layer, a lower protective layer, a reflective layer, and other information layers other than the innermost information layer as viewed from the side irradiated with the laser beam. An embodiment having a thermal diffusion layer is preferred.
In this case, the light transmittance in each information layer other than the information layer on the innermost side when viewed from the side irradiated with the laser beam is preferably 30 to 70%, and more preferably 40 to 70%. If the light transmittance is lower than 30%, recording, erasing and reproducing on the back second information layer may be difficult. If it is higher than 70%, recording and erasing on the first information layer may be difficult. And playback may be difficult.
Here, the light transmittance can be measured by, for example, Etaoptics manufactured by STEAG. In the case of a two-layer optical recording medium, the light transmittance is measured from the transmitted light intensity and the reflected light intensity obtained by irradiating only the first substrate on which the first information layer is formed. Measure transmittance, reflectance, and absorption. That is, the light transmittance is measured before being bonded to the second substrate.

As the multilayer optical recording medium, a two-layer optical recording medium having a first information layer and a second information layer from the side irradiated with the laser beam is particularly preferably used.
Here, FIG. 17 is a schematic sectional view of a two-layer optical recording medium according to an embodiment of the present invention. This two-layer optical recording medium is formed by laminating a first information layer 1, an intermediate layer 4, a second information layer 2, and a second substrate 5 in this order on a first substrate 3, and further if necessary. And other layers.
The first information layer 1 includes a first lower protective layer 11, a first recording layer 12, a first upper protective layer 13, a first reflective layer 14, and a thermal diffusion layer 15.
The second information layer 2 includes a second lower protective layer 21, a second recording layer 22, a second upper protective layer 23, and a second reflective layer 24.
A barrier layer may be provided between the first upper protective layer 13 and the first reflective layer 14 and between the second upper protective layer 23 and the second reflective layer 24.

-First substrate-
The first substrate needs to be sufficiently transparent to the light irradiated for recording and reproduction, and can be appropriately selected from those conventionally known in the technical field.
As the material of the first substrate, glass, ceramics, resin, or the like is usually used, but resin is preferable in terms of moldability and cost.
Examples of such resins include polycarbonate resins, acrylic resins, epoxy resins, polystyrene resins, acrylonitrile-styrene copolymers, polyethylene resins, polypropylene resins, silicone resins, fluorine resins, ABS resins, urethane resins, and the like. Among them, among these, acrylic resins such as polycarbonate resin and polymethyl methacrylate (PMMA) which are excellent in terms of moldability, optical characteristics, and cost are preferable.
On the surface on which the information layer of the first substrate 3 is formed, a spiral or concentric groove for tracking laser light, if necessary, is provided with a concavo-convex pattern usually referred to as a groove portion or a land portion. It may be formed, and this is usually formed by an injection molding method or a photopolymer method.
There is no restriction | limiting in particular in the thickness of a 1st board | substrate, According to the objective, it can select suitably, About 10-600 micrometers is preferable.

As the material of the second substrate 5, the same material as that of the first substrate 3 may be used, but a material that is opaque to the recording / reproducing light may be used. May be different.
The thickness of the second substrate 5 is not particularly limited and can be appropriately selected according to the purpose. The thickness of the second substrate is selected so that the total thickness with the first substrate 5 is 1.2 mm. Is preferred.

-Phase change recording layer (first recording layer and second recording layer)-
Regarding the phase change recording layer, from the viewpoint of material development of the conventional recording layer, there are roughly two types of material development flows. That is, it is composed of GeTe which is a write-once recording layer material, Sb ₂ Te ₃ which is an alloy of Sb and Te capable of reversibly changing phase, and a ternary alloy of GeSbTe from the solid solution or eutectic composition of these two materials. The recording layer material is one flow. Another flow is an alloy of Sb and Te, but a recording layer in which a trace element is added to an SbTe system in which the Sb content, which is a eutectic composition of Sb and Sb ₂ Te ₃ , is about 70%. The material is known.

In an optical recording medium having a two-layer recording layer, the first information layer is required to have a high transmittance in consideration of recording and reproduction of the second information layer. Therefore, in parallel with efforts to reduce the absorption rate of the reflective layer, attempts have been made to make the recording layer thin. Since the crystallization speed decreases as the recording layer is made thinner, it is advantageous to make the recording layer material itself have a high crystallization speed. Therefore, the SbTe eutectic composition in which the latter Sb content is around 70% is preferable in the flow of this material series.
However, if the amount of Sb is increased in order to increase the crystallization speed, that is, in order to increase the corresponding linear speed, the crystallization temperature is lowered. Even if recording can be performed, there is a concern that the storage characteristics of the recording mark will deteriorate. In view of this, a material system has been studied which has a high crystallization speed with a small amount of Sb, that is, a high linear velocity that can be accommodated, as compared with a GeSbTe system, an SbTe system, or the like. It was found that the linear velocity can be improved with a small amount of Sb in the InSb system. Therefore, it is preferable to use InSb as the recording layer material of the first information layer that requires a thin recording layer thickness.
Then, as shown in FIG. 28, the amorphous mark is not recrystallized, and the storage state can be stabilized. Therefore, it is preferable to use the phase change material as described above for the recording layer included in the first information layer used in the two-layer type optical recording medium.

The first recording layer and the second recording layer can be formed by various vapor phase growth methods such as vacuum deposition method, sputtering method, plasma CVD method, photo CVD method, ion plating method, electron beam evaporation method, etc. Among them, the sputtering method is preferable because it is excellent in mass productivity, film quality, and the like. This is preferable in that abnormal discharge on the sputtering film formation such as arcing or delay of start of discharge can be reduced.
The thickness of the first recording layer is preferably 4 to 15 nm, more preferably 6 to 12 nm. If the thickness is less than 4 nm, it may be difficult to form a uniform film, and if it exceeds 15 nm, the transmittance may be reduced.
There is no restriction | limiting in particular in the thickness of a 2nd recording layer, According to the objective, it can select suitably, 3-25 nm is preferable. If the thickness is less than 3 nm, it may be difficult to form a uniform film, and if it exceeds 25 nm, the recording sensitivity may be lowered.

-Reflective layer (first reflective layer and second reflective layer)-
As shown in FIG. 17, in an optical recording medium including two recording layers, it is necessary to transmit recording / reproducing laser light as much as possible to the second information layer. Therefore, the first reflective layer is preferably made of a material that hardly absorbs laser light and easily transmits. Specifically, Ag and Cu are mentioned. On the other hand, the second reflective layer does not need to be translucent like the first reflective layer.
Examples of the film formation of the first reflective layer and the second reflective layer include various vapor phase growth methods, such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electrons. It can be formed by a beam evaporation method or the like. Among these, the sputtering method is excellent in mass productivity and film quality.

−Protective layer (upper protective layer and lower protective layer) −
The material used for the upper protective layer in the single-layer type optical recording medium is preferably a material that is transparent and allows light to pass through and has a melting point higher than that of the recording layer, to prevent deterioration and deterioration of the recording layer and to increase the adhesive strength with the recording layer. The metal oxide, nitride, sulfide, carbide, etc. are mainly used. Specifically, metal oxides such as SiO, SiO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ , Ta ₂ O ₅ ; Si ₃ N ₄ , AlN, Nitrides such as TiN, BN, ZrN; sulfides such as ZnS, In ₂ S ₃ , TaS ₄ ; carbides such as SiC, TaC, B ₄ C, WC, TiC, ZrC; diamond-like carbon (DLC), or these The mixture of these is mentioned. These materials can be used alone as a protective film, but may also be a mixture of each other. Moreover, you may contain an impurity as needed. For example, _{Ta 2 O} 5 -SiO 2 of a mixture of ZnS and _ZnS-SiO 2 of a mixture of SiO _{2, Ta} 2 _{O 5} and SiO ₂ and the like. Among these, ZnS—SiO ₂ is particularly preferable. In this case, (ZnS) ₈₀ (SiO ₂ ) ₂₀ is most preferable as the mixing molar ratio.

However, in the case of a multilayer optical recording medium, when information is recorded on the first recording layer, there is a problem that only the first reflective layer is thin, so that heat dissipation becomes poor and recording becomes difficult. Therefore, it is better to use a material having as good thermal conductivity as possible for the first upper protective layer. Therefore, it is better to use a material having higher heat dissipation than ZnS—SiO ₂ . For example, it is preferable to use an oxide of Sn. Further, the oxide of Sn may include a metal-based oxide (for example, In oxide, Zn oxide, Ta oxide, Al oxide). By using Sn oxide, it is easy to form an amorphous mark on the first recording layer even if the thickness of the first reflective layer is relatively thin. Each of the Sn oxide, Ta oxide, and Al oxide is a material that does not promote deterioration with respect to the reflective layer, and the respective composition ratios may be selected according to the production process, cost, allowable production time, and the like. However, when there are many Sn oxides, the power required for recording tends to increase. When there is a large amount of Ta oxide, it is a material that does not decrease the film formation speed, but it becomes difficult to obtain recording characteristics in the first information layer. When the amount of Al oxide is large, the deposition rate tends to decrease.

As for the second upper protective layer, ZnS—SiO ₂ may be used as usual, or Sn oxide may be used. The reason is that when recording on the second recording layer, the second reflective layer can be formed sufficiently thick, so that sufficient heat dissipation is obtained. When ZnS—SiO ₂ is used for the second upper protective layer and Ag is used for the second reflective layer, an interface layer such as TiC—TiO ₂ may be sandwiched between the second upper protective layer and the second reflective layer. This is to prevent the optical recording medium from being defective due to the reaction between sulfur S and Ag.

The first lower protective layer and the second lower protective layer are preferably made of a material that is transparent, allows light to pass through, and has a higher melting point than the recording layer, prevents deterioration and deterioration of the recording layer, increases the adhesive strength with the recording layer, and A metal oxide, nitride, sulfide, carbide or the like is mainly used because it has an effect of improving recording characteristics. Specifically, metal oxides such as SiO, SiO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ , Ta ₂ O ₅ ; Si ₃ N ₄ , AlN, Nitrides such as TiN, BN, ZrN; sulfides such as ZnS, In ₂ S ₃ , TaS ₄ ; carbides such as SiC, TaC, B ₄ C, WC, TiC, ZrC; diamond-like carbon (DLC), or these And the like. These materials can be used alone as a protective film, but may also be a mixture of each other. Moreover, you may contain an impurity as needed. For example, _{Ta 2 O} 5 -SiO 2 of a mixture of ZnS and _ZnS-SiO 2 of a mixture of SiO _{2, Ta} 2 _{O 5} and SiO ₂ and the like. Among these, ZnS—SiO ₂ is particularly preferable. In that case, the mixing molar ratio is most preferably (ZnS) ₈₀ (SiO ₂ ) ₂₀ . Since ZnS-SiO ₂ has a high refractive index n and an extinction coefficient k of almost zero, the light absorption efficiency of the recording layer is increased, and the thermal conductivity is small, so that the diffusion of heat generated by light absorption is reduced. Since it can be moderately suppressed, the temperature of the recording layer can be raised to a melting temperature.

  Examples of the film formation of the first upper protective layer, the second upper protective layer, the first lower protective layer, and the second lower protective layer as described above include various vapor deposition methods, such as a vacuum deposition method, a sputtering method, It can be formed by a plasma CVD method, a photo CVD method, an ion plating method, an electron beam evaporation method, or the like. Among these, the sputtering method is superior in terms of mass productivity, film quality, and the like.

-Thermal diffusion layer-
As the thermal diffusion layer, it is desirable that the thermal conductivity be high in order to quench the first recording layer irradiated with the laser. It is also desirable that the absorption rate at the laser wavelength is small so that the second information layer on the back side can be recorded and reproduced. From the above, it is preferable that at least one of nitride, oxide, sulfide, carbide and fluoride is included. Examples thereof include AlN, Al ₂ O ₃ , SiC, SiN, IZO (indium oxide-zinc oxide), ITO (indium oxide-tin oxide), DLC (diamond-like carbon), and BN. Among these, IZO and ITO are considered most preferable. First, it is preferable that the tin oxide contained in ITO (indium oxide tin oxide) is contained 1-10 mass%. If it is less or more than this, the thermal conductivity and the transmittance will decrease. Further, other elements may be added for the purpose of improving storage stability. These elements can be added within a range that does not affect the optical properties, and are preferably contained in an amount of 0.1 to 5% by mass. If it is less than this, the effect cannot be obtained. When the amount is large, light absorption increases and the transmittance decreases. The absorption coefficient is preferably 1.0 or less at the wavelength of the laser beam used for recording / reproducing information. Furthermore, it is preferable that it is 0.5 or less. If it is greater than 1.0, the absorptance in the first information layer increases, and recording / reproduction of the second information layer becomes difficult.
In addition, by using IZO (indium oxide-zinc oxide) instead of ITO (indium oxide-tin oxide), the internal stress in the optical recording medium is reduced, so that a very small thickness change is unlikely to occur. preferable.

  Examples of the thermal diffusion layer as described above include various vapor phase growth methods, and can be formed by, for example, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method, an electron beam evaporation method, or the like. Among these, the sputtering method is superior in terms of mass productivity, film quality, and the like.

-Intermediate layer-
The intermediate layer preferably has low light absorption at the wavelength of light irradiated for recording / reproduction, and as the material, a resin is suitable in terms of moldability and cost, and an ultraviolet curable resin, a slow-acting resin, a heat A plastic resin or the like can be used. The second substrate and the intermediate layer may be provided with an uneven pattern such as a groove and a guide groove formed by an injection molding method or a photopolymer method similar to the first substrate. The intermediate layer allows the pickup to discriminate between the first information layer and the second information layer and perform optical separation when performing recording and reproduction.
There is no restriction | limiting in particular in the thickness of the said intermediate | middle layer, According to the objective, it can select suitably, 10-70 micrometers is preferable. If the thickness is less than 10 μm, crosstalk between information layers may occur. If the thickness is more than 70 μm, spherical aberration may occur when recording and reproducing the second recording layer, and recording and reproduction may be difficult.

-Barrier layer-
In the multilayer optical recording medium of the present invention, a barrier layer may be provided between the upper protective layer and the reflective layer. The reflective layer is most preferably an Ag alloy, and the upper protective layer is most preferably a mixture of ZnS and SiO ₂ , but when these two layers are adjacent, sulfur in the protective layer may corrode Ag in the reflective layer. The storage reliability may be reduced. In order to eliminate this problem, it is preferable to provide a barrier layer when an Ag-based material is used for the reflective layer. The barrier layer does not contain sulfur and must have a higher melting point than the recording layer. Specifically, SiO, ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ Metal oxides such as: Si ₃ N ₄ , AlN, TiN, ZrN, etc. nitrides; ZnS, In ₂ S ₃ , TaS ₄ etc. sulfides; SiC, TaC, B ₄ C, WC, TiC, ZrC etc. Carbides; or mixtures thereof. These barrier layers are desired to have a low absorptance at the laser wavelength.

The barrier layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among these, the sputtering method is excellent in terms of mass productivity, film quality, and the like.
The thickness of the barrier layer is preferably 2 to 10 nm. When the thickness is less than 2 nm, the effect of preventing corrosion of Ag may not be obtained, and the storage reliability is lowered. On the other hand, if it is thicker than 10 nm, the heat dissipation effect cannot be obtained, or the transmittance tends to decrease.

Next, the two-layer optical recording medium of the present invention is not particularly limited and can be appropriately selected according to the purpose, but is preferably manufactured as follows. The manufacturing method includes a film forming process, an initialization process, and an adhesion process, and each process is basically performed in this order.
As the film forming step, in FIG. 17, the first information layer is formed on the surface of the first substrate on which the groove is provided, and the second information layer is formed on the surface of the second substrate on which the groove is provided. The first information layer and the second information layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among them, the sputtering method is excellent in mass productivity and film quality. In the sputtering method, film formation is generally performed while flowing an inert gas such as argon. At this time, reactive sputtering may be performed while oxygen, nitrogen, or the like is mixed.

As an initialization step, the entire surface is initialized by irradiating the first information layer and the second information layer with energy light such as laser light, that is, the recording layer is crystallized. If there is a possibility that the film may float due to laser light energy during the initialization process, before the initialization process, spin coat UV resin or the like on the first information layer and the second information layer, It may be cured by irradiating with ultraviolet rays, and an overcoat may be applied. Moreover, after performing the next contact | adherence process previously, you may initialize a 1st information layer and a 2nd information layer from the 1st board | substrate side.
As the adhesion process, the first substrate and the second substrate are bonded to each other through the intermediate layer while the first information layer and the second information layer face each other. For example, UV resin can be applied to any one of the film surfaces, the film surfaces face each other, both substrates can be pressed and adhered, and the resin can be cured by irradiating ultraviolet rays.

  According to the present invention, the conventional problems can be solved, and the first of the multilayer optical recording medium having two or more information layers including the phase change recording layer as viewed from the side irradiated with the laser beam. When recording on the first recording layer in the information layer, thermal damage to the recording layer can be suppressed, recording and erasing can be performed accurately, and a multilayer optical recording medium having good recording characteristics and the recording medium A recording method for a multilayer optical recording medium and a recording apparatus for the multilayer optical recording medium can be provided. It is also possible to improve the recording sensitivity of the second and higher recording layers.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited at all by these Examples.

(Example A-1)
On a polycarbonate disk substrate with a guide groove having a diameter of 12 cm, a thickness of 0.6 mm, and a track pitch of 0.74 μm, ZnS—SiO ₂ is 60 nm thick as the first protective layer, and In ₃ Sb ₁₇ Te ₈₀ is 15 nm thick as the recording layer. (2) ZnS—SiO ₂ was formed to a thickness of 12 nm as a protective layer, SiC was formed to a thickness of 4 nm as an anti-sulfurization layer, and Ag was formed as a reflective layer by a sputtering method sequentially to a thickness of 140 nm. The obtained reflective layer was overcoated with an organic protective film, and a 0.6 mm-thick polycarbonate disk was further bonded thereon to produce a phase change optical recording medium. Next, initial crystallization was performed using a large-diameter LD.
Recording was performed on the obtained optical recording medium under the following conditions, and the jitter of repeated recording was examined.
For recording, an optical head having a wavelength of 660 nm and a numerical aperture NA of 0.65 was used, and a random pattern with a linear density of 0.267 μm / bit was recorded at 42 m / s corresponding to DVD 12-times speed by an EFM + modulation method. FIG. 8 shows a waveform light emission pattern (recording strategy) for each mark length in this example. Table 2 shows the time that each power is held from the start position of the mark as a starting point as a value normalized by the reference clock T. In this example, all the leading cooling pulses were set to 0.2T. The second cooling pulse was set between 1.0T and 1.8T, depending on the mark length.
FIG. 6 shows jitter when the set values of the respective powers are Pp = 38 mW, Pb = 0.1 mW, and Pe = 6.5 mW. As can be seen from the results shown in FIG. 6, there is no sudden increase in jitter even in the first repetitive recording, indicating good repetitive recording characteristics.
FIG. 9 shows the results of examining the jitter at the beginning of the mark for the initial recording and the repeated recording 10 times when the random pattern is recorded while changing the length of the second cooling pulse of the mark of 6T or more. When the length of the second cooling pulse of the mark of 6T or more was smaller than 1.0T, the jitter at the mark head portion suddenly increased. On the other hand, when the time is longer than 2.5T, the jitter of the first recording is small, but the jitter of 10 repeated recordings rapidly increases.
FIG. 10 shows the jitter values of the initial recording and the repeated recording 10 times when Pp = 38 mW is fixed and the value of Pe is changed to change the value of Pe / Pp to record a random pattern. When Pe / Pp <0.1, the jitter in the initial recording was small, but the jitter increase was large due to repeated recording. In the case of Pe / Pp> 0.4, the jitter became large in both the initial recording and the repeated recording.

(Example A-2)
For the same optical recording medium as in Example A-1, the recording characteristics were examined in the same manner as in Example A-1, except that the recording strategy was set under the conditions shown in Table 3. When the mark length is 6T or more, the irradiation time of the first cooling pulse is 0.4T, and the irradiation time of the second cooling pulse is 1.3T.
FIG. 6 shows jitter when the set values of the respective powers are Pp = 38 mW, Pb = 0.1 mW, and Pe = 6.5 mW. As can be seen from the results shown in FIG. 6, there is no sudden increase in jitter even in the first repetitive recording, indicating good repetitive recording characteristics.

(Example A-3)
Recording characteristics were examined in the same manner as in Example A-1, except that the recording strategy was set under the conditions shown in Table 4 for the same optical recording medium as in Example A-1. When the mark length was 6T or longer, the irradiation time of the second cooling pulse was 2.5T, and the number of pulses when the mark length was an even multiple of T was reduced by one from that in Example A-1.
FIG. 6 shows jitter when the set values of the respective powers are Pp = 38 mW, Pb = 0.1 mW, and Pe = 6.5 mW. As can be seen from the results shown in FIG. 6, there is no sudden increase in jitter even in the first repetitive recording, indicating good repetitive recording characteristics.

(Example A-4)
In Example A-1, an optical recording medium was produced in the same manner as in Example A-1, except that the recording layer material was changed to In ₅ Sb ₁₇ Te ₇₈ having a slightly low crystallization rate.
Recording characteristics for this optical recording medium were the same as in Example A-1 except that the recording speed was changed to 8 × DVD (about 27.9 m / s) (that is, the recording strategy settings are the same as in Table 2). I investigated.
FIG. 6 shows the jitter when the set values of each power are Pp = 30 mW, Pb = 0.1 mW, and Pe = 6 mW. As can be seen from the results shown in FIG. 6, there is no sudden increase in jitter even in the first repetitive recording, indicating good repetitive recording characteristics.

(Comparative Example A-1)
Recording characteristics were examined in the same manner as in Example A-1, except that the recording strategy was set under the conditions shown in Table 5 for the same optical recording medium as in Example A-1. All the first cooling pulses were set to 0.1 T, and the second cooling pulse was set between 1.0 T and 1.8 T, although it varied depending on the mark length.
FIG. 6 shows jitter when the set values of the respective powers are Pp = 38 mW, Pb = 0.1 mW, and Pe = 6 mW. As can be seen from the results of FIG. 6, the jitter increase at the initial stage of repeated recording was relatively small and good, but the durability of repeated recording was poor, and the jitter increased greatly in the 1000th recording. In addition, when the influence of the cross erase was examined, when recording was performed on the adjacent track, the jitter of the track that had already been recorded increased by about 1% and the cross erase was large. I also understood that. It can be seen that at a setting of 0.1 T or less, the cooling effect is not obtained in the case of high-speed recording.

(Comparative Example A-2)
For the same optical recording medium as in Example A-1, the recording characteristics were examined in the same manner as in Example A-1, except that the recording strategy was set under the conditions shown in Table 6. When the mark length is 6T or more, the first cooling pulse is 0.5T and the second cooling pulse is 1.2T.
FIG. 6 shows jitter when the set values of the respective powers are Pp = 38 mW, Pb = 0.1 mW, and Pe = 6 mW. As can be seen from the results of FIG. 6, the jitter increase in the first repeated recording has increased. This is presumably because the leading edge cooling pulse is too long, the mark tip shape becomes thin, and the jitter at the mark leading edge becomes sensitive to the difference in crystal state.

ODU-1000 manufactured by Pulstec Corp. was used as an evaluation apparatus for optical recording media of Examples B-1 to B-47 and Comparative Examples B-1 to B-32 below, the laser wavelength irradiated during recording was 660 nm, and objective lens The numerical aperture (NA) was 0.65. The reproduction light power was 1.4 mW.
Evaluation was performed by recording on three adjacent tracks of the first recording layer and reproducing the middle track of them. The recording method uses a 1T periodic recording strategy, and the criteria for characteristic evaluation is that the data-to-clock jitter (DC jitter) when 3T to 11T and 14T marks and spaces are randomly recorded is 11% or less. did. The DC jitter represents a time lag between the boundary and the clock when the mark and space reflectivity levels are binarized at the slice level. The lower this value, the better the recording characteristics.

(Examples B-1 to B-4 and Comparative Examples B-1 to B-3)
ZnS (80 mol%)-SiO ₂ (20) on a first substrate made of polycarbonate resin having a diameter of 12 cm, a thickness of 0.6 mm, and having a tracking guide asperity formed by continuous meandering grooves having a meandering track pitch of 0.74 μm on one side. The first lower protective layer having a thickness of 70 nm composed of mol%), the first recording layer having a thickness of 7.5 nm composed of Ag _0.2 In _3.5 Sb _69.8 Te ₂₂ Ge _4.5 , In ₂ O ₃ (7. 5 mol%)-ZnO (22.5 mol%)-SnO ₂ (60 mol%)-Ta ₂ O ₅ (10 mol%) first upper protective layer having a thickness of 5 nm, containing 1.1% by mass of Mo the first reflective layer having a thickness of 7.5nm of Cu _was, in ₂ O 3 (90 mol%) - ZnO (10 mol%) in order sputtering in an Ar gas atmosphere thermal diffusion layer having a thickness of 65nm made of Deposited to form the first information layer. Sputtering was performed using an 8-chamber single wafer sputtering apparatus manufactured by Balzers.
Further, a substrate similar to the first substrate is used as the second substrate, a second reflective layer made of Ag having a thickness of 140 nm and a thickness of 4 nm made of TiC (70 mol%)-TiO ₂ (30 mol%) on the second substrate. Interface layer, ZnS (80 mol%)-SiO ₂ (20 mol%) second upper protective layer with a thickness of 20 nm, Ag _0.2 In _3.5 Sb _70.2 Te _22.6 Ge _3.5 A second recording layer having a thickness of 15 nm and a second lower protective layer having a thickness of 140 nm made of ZnS (80 mol%)-SiO ₂ (20 mol%) were sequentially formed in the same manner as in the case of the first information layer. Two information layers were formed.
Next, an ultraviolet curable resin (Kayarad DVD003M, manufactured by Nippon Kayaku Co., Ltd.) is applied on the film surface side of the first information layer, and the film surface side of the second information layer is bonded and spin-coated, and the first substrate side Were irradiated with ultraviolet light to cure the ultraviolet light curable resin to form an intermediate layer having a thickness of 55 μm, and a two-layer phase change optical recording medium having two information layers was produced.

Next, the first information layer and the second information layer were irradiated with laser light from the first substrate side to perform an initialization process. Initialization was performed by condensing laser light emitted from a semiconductor laser (emission wavelength 810 ± 10 nm) with an optical pickup (numerical aperture NA = 0.55). The initialization conditions of the first recording layer were as follows: the optical recording medium was rotated in the CLV (constant linear velocity) mode, the linear velocity was 5 m / s, the feed amount was 50 μm / rotation, the initialization power was 900 mW, and the radial position was 23 mm to 59 mm. The initialization conditions of the second recording layer were as follows: the optical recording medium was rotated in the CLV (constant linear velocity) mode, the linear velocity was 5 m / s, the feed amount was 40 μm / rotation, the initialization power was 1250 mW, and the radial position was 23 mm to 59 mm. The order of initialization was that the first information layer was initialized after the second information layer was initialized. The light transmittance of the first information layer after initialization was 42.5%, and it was confirmed that a sufficient light transmittance was obtained. The light transmittance was measured with Etaoptics manufactured by STEAG.
Recording was performed on the optical recording medium at a recording linear velocity of 9.2 m / s. As a recording strategy, a 1T period strategy was used, and its pulse width was set to 0.188T.
The experimental results are shown in Table 7. For example, DOW10 means 10 repeated recordings. Table 7 shows the optimum jitter value during recording with the recording power varied (changed) from 34 mW to 40 mW.
Recording on the second information layer was performed with a 1T cycle strategy and a 2T cycle strategy. As a result, the recording power at which a modulation factor of 60% was obtained was about 47 mW and about 40 mW, respectively, and the recording sensitivity was better when recording was performed at a 2T period. There was almost no difference in recording power due to the difference in Tr in Examples A-1 to A-4.

(Examples B-5 to B-8 and Comparative Examples B-4 to B-6)
In Example B-1, the first upper protective layer was formed of In ₂ O ₃ (9.2 mol%)-ZnO (27.5 mol%)-SnO ₂ (53.3 mol%)-Ta ₂ O ₅ (10 A two-layer type optical recording medium was prepared in the same manner as in Example B-1 except that it was changed to mol%), and a recording experiment was conducted in the same manner as in Example B-1. The light transmittance of the first information layer after initialization was 42.8%, and it was confirmed that sufficient light transmittance was obtained. The light transmittance was measured with Etaoptics manufactured by STEAG.
The experimental results are shown in Table 8. Table 8 shows the optimum jitter value of the recording performed with the recording power varying from 34 mW to 40 mW.
Recording on the second information layer was performed with a 1T cycle strategy and a 2T cycle strategy. As a result, the recording power at which a modulation degree of 60% was obtained was about 46 mW and about 39.5 mW, respectively, and the recording sensitivity was better when recording was performed at a 2T period. There was almost no difference in recording power due to the difference in Tr in Examples B-5 to B-8.

(Examples B-9 to B-12 and Comparative Examples B-7 to B-9)
In Example B-1, except that the thickness of the first recording layer was changed to 8 nm, a two-layer optical recording medium was produced in the same manner as in Example B-1, and recording was performed in the same manner as in Example B-1. The experiment was conducted. The light transmittance of the first information layer after initialization was 38.5%, and it was confirmed that sufficient light transmittance was obtained. The light transmittance was measured with Etaoptics manufactured by STEAG.
The experimental results are shown in Table 9. Table 9 shows the optimum jitter value among the recording performed by changing the recording power from 34 mW to 40 mW.
Recording on the second information layer was performed with a 1T cycle strategy and a 2T cycle strategy. As a result, the recording power at which a modulation factor of 60% was obtained was about 54 mW and about 46 mW, respectively, and the recording sensitivity was better when recording was performed at a 2T period. There was almost no difference in recording power due to the difference in Tr in Examples B-9 to B-12.

(Examples B-13 to B-16 and Comparative Examples B-10 to B-12)
Recording experiments were performed using the same two-layer optical recording medium as in Example B-1.
The recording linear velocity was 4.6 m / s, the recording strategy was a 1T period strategy, and the pulse width was 0.125T.
The experimental results are shown in Table 10. Table 10 shows the optimum jitter value among the recording performed by changing the recording power from 28 mW to 34 mW.
Recording on the second information layer was performed with a 1T cycle strategy and a 2T cycle strategy. As a result, the recording power at which a modulation factor of 60% was obtained was about 42 mW and about 35 mW, respectively, and the recording sensitivity was better when recording was performed at a 2T period. There was almost no difference in recording power due to the difference in Tr in Examples B-13 to B-16.

(Example B-17 and Comparative Example B-13)
Recording experiments were performed using the same two-layer optical recording medium as in Example B-1.
As a result, as shown in FIG. 25, the recording characteristics were improved repeatedly when the recording was performed on the first recording layer with the 1T cycle strategy. The recording power was 37 mW (1T cycle strategy) and 31 mW (2T cycle strategy).

(Example B-18 and Comparative Example B-14)
Recording experiments were performed using the same two-layer optical recording medium as in Example B-1.
As a result, as shown in FIGS. 26 and 27, recording sensitivity was better when recording was performed on the second recording layer with the 2T period strategy.

Next, as in the following Examples B-19 to B-35 and Comparative Examples B-15 to B-28, a two-layer optical recording medium having the structure as shown in FIG. 17 was prepared and evaluated. It was.
A first substrate made of a polycarbonate resin having a diameter of 12 cm and a thickness of 0.6 mm and having a tracking guide unevenness with a continuous meandering groove with a track pitch of 0.74 μm on one side is prepared. Each layer was formed by sputtering in an Ar gas atmosphere using a sputtering apparatus.
First, a 60 nm-thick first lower protective layer made of ZnS (80 mol%) — SiO ₂ (20 mol%) was formed on the first substrate.
Next, a first recording layer having a thickness of 8 nm made of Ag _0.2 In ₅ Sb _69.8 Ge ₅ Te ₂₀ was formed on the first lower protective layer.
Next, the first recording _layer, In ₂ O 3 (7.5 mol%) - ZnO (22.5 mol%) - _SnO 2 (60 mol%) _- consists of Ta ₂ O 5 (10 mol%) A first upper protective layer having a thickness of 5 nm was formed.
Next, a first reflective layer made of Cu and having a thickness of 8 nm was formed on the first upper protective layer.
Next, a 140-nm-thick thermal diffusion layer made of In ₂ O ₃ (90 mol%) — ZnO (10 mol%) was formed on the first reflective layer.
Thus, the first information layer was formed on the first substrate.
Here, the light transmittance in the first information layer was measured by Etaoptics manufactured by STEAG, and it was 41%.

Next, a substrate similar to the first substrate was prepared as a second substrate, and each layer was formed thereon by sputtering in the same manner as in the case of the first substrate.
First, a 140 nm-thick second reflective layer made of Ag was formed on the second substrate.
Next, a second upper protective layer having a thickness of 11 nm made of SnO ₂ (80 mol%)-Ta ₂ O ₅ (4 mol%)-Al ₂ O ₃ (16 mol%) is formed on the second reflective layer. did.
Next, a 14 nm thick second recording layer made of Ag _0.2 In _3.5 Sb _71.4 Te _21.4 Ge _3.5 was formed on the second upper protective layer.
Next, a 120 nm thick second lower protective layer made of ZnS (80 mol%) — SiO ₂ (20 mol%) was formed on the second recording layer.
Thus, the second information layer was formed on the first substrate.

Next, the first information layer and the second information layer were irradiated with laser light from the first substrate side and the film surface side of the second information layer, respectively, and an initialization process was performed. Initialization was performed by condensing the laser beam emitted from the semiconductor laser (emission wavelength 810 ± 10 nm) with an optical pickup (NA = 0.55). The initialization conditions were such that the optical recording medium was rotated in the CLV (constant linear velocity) mode, the linear velocity was 3 m / s, the feed amount was 36 μm / rotation, the radial position was 23 mm to 58 mm, and the initialization power was 700 mW.
Next, an ultraviolet curable resin (Kayarad DVD003M, manufactured by Nippon Kayaku Co., Ltd.) is applied onto the film surface side of the first information layer, and is bonded to the film surface side of the second information layer and spin-coated. Then, ultraviolet light was irradiated to cure the ultraviolet light curable resin to form an intermediate layer having a thickness of 55 μm, and a two-layer optical recording medium having two information layers was produced.

When the push-pull signal (PP) of the continuous meandering groove provided on the substrate was evaluated with the produced two-layer optical recording medium, the push-pull signal (hereinafter referred to as PP1) of the first information layer was 0.45, the second The information layer push-pull signal (hereinafter referred to as PP2) = 0.43. PP is a physical quantity necessary for facilitating tracking in a continuous meandering groove. If it is too small or too large, problems such as difficulty in tracking on the device that reproduces the signal occur. The values of PP1 and PP2 obtained here are good values. Further, when the carrier-to-noise (WCN) of the meandering groove (wobble) is measured, the signal of the first information layer (hereinafter referred to as WCN1) = 50 dB, the signal of the second information layer (hereinafter referred to as WCN2). ) = 46 dB was obtained. Here, if WCN is smaller than a certain value, a substrate with low wobble periodicity and poor uniformity is produced, which is not preferable. However, the values of WCN1 and WCN2 obtained here are good values.
Using the obtained two-layer optical recording medium, recording was performed under the following recording conditions.

(Example B-19)
Recording was performed using the pulse waveform shown in FIG. 11 with a recording linear velocity of 14 m / s, recording power Pp = 46 mW, erasing power Pe = 7 mW, cooling power Pc1 = 4 mW, and bias power Pb = 0.1 mW. . The width of the multipulse was 0.3T.
As a result, the DC jitter was 10.7%, which was favorable.

(Comparative Example B-15)
Recording was performed using the pulse waveform shown in FIG. 16 at a recording linear velocity of 14 m / s, recording power Pp = 46 mW, erasing power Pe = 7 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.3T.
As a result, the DC jitter was 13.7%, which was worse than that of Example B-19.

(Example B-20)
Using the pulse waveform shown in FIG. 11, the recording linear velocity is set to 8.41 m / s, the recording power Pp = 38 mW, the erasing power Pe = 6.8 mW, the cooling power Pc1 = 3.9 mW, and the bias power Pb = 0.1 mW. And recorded. The width of the multipulse was 0.2T.
As a result, the DC jitter was good at 10.3%.

(Comparative Example B-16)
Recording was performed using the pulse waveform shown in FIG. 16 at a recording linear velocity of 8.41 m / s, recording power Pp = 38 mW, erasing power Pe = 6.8 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
As a result, DC jitter was 12.5%, which was worse than that of Example B-20.

(Example B-21)
Using the pulse waveform shown in FIG. 11, the recording linear velocity is set to 7 m / s, the recording power Pp = 36 mW, the erasing power Pe = 6.6 mW, the cooling power Pc1 = 3.5 mW, and the bias power Pb = 0.1 mW. Recorded. The width of the multipulse was 0.18T.
As a result, the DC jitter was 10.4%, which was favorable.

(Comparative Example B-17)
Recording was performed using the pulse waveform shown in FIG. 16 at a recording linear velocity of 7 m / s, recording power Pp = 36 mW, erasing power Pe = 6.6 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.18T.
As a result, DC jitter was 12.9%, which was worse than that of Example B-21.

(Example B-22)
Using the pulse waveform shown in FIG. 11, the recording linear velocity is set to 3.5 m / s, the recording power Pp = 33 mW, the erasing power Pe = 6.3 mW, the cooling power Pc1 = 3.4 mW, and the bias power Pb = 0.1 mW. And recorded. The width of the multipulse was 0.13T.
As a result, the DC jitter was good at 9.8%.

(Comparative Example B-18)
Recording was performed using the pulse waveform shown in FIG. 16 at a recording linear velocity of 3.5 m / s, recording power Pp = 33 mW, erasing power Pe = 6.3 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.13T.
As a result, the DC jitter was 11.5%, which was worse than that of Example B-22.

(Example B-23)
Using the pulse waveform shown in FIG. 13, the recording linear velocity is set to 14 m / s, the recording power Pp = 46 mW, the erasing power Pe = 7.2 mW, the cooling power Pc1 = 4.2 mW, and the bias power Pb = 0.1 mW. Recorded. The width of the multipulse was 0.3T.
As a result, the DC jitter was 10.8%, which was favorable.

(Comparative Example B-19)
Recording was performed using the pulse waveform shown in FIG. 16 with a recording linear velocity of 14 m / s, recording power Pp = 46 mW, erasing power Pe = 7.2 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.3T.
As a result, the DC jitter was 13.9%, which was worse than that of Example B-23.

(Example B-24)
Using the pulse waveform shown in FIG. 13, the recording linear velocity is set to 8.41 m / s, the recording power Pp = 40 mW, the erasing power Pe = 7 mW, the cooling power Pc1 = 4 mW, and the bias power Pb = 0.1 mW. went. The width of the multipulse was 0.4T.
As a result, the DC jitter was 10.1%, which was favorable.

(Comparative Example B-20)
Recording was performed using the pulse waveform shown in FIG. 16 at a recording linear velocity of 8.41 m / s, recording power Pp = 40 mW, erasing power Pe = 7 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.4T.
As a result, DC jitter was 12.9%, which was worse than that of Example B-24.

(Example B-25)
Using the pulse waveform shown in FIG. 14, the recording linear velocity is set to 8.41 m / s, the recording power Pp = 40 mW, the erasing power Pe = 7.3 mW, the cooling power Pc1 = 4.3 mW, and the bias power Pb = 0.1 mW. And recorded. The width of the multipulse was 0.2T.
As a result, the DC jitter was 10.1%, which was favorable.

(Comparative Example B-21)
Recording was performed using the pulse waveform shown in FIG. 16 at a recording linear velocity of 8.41 m / s, recording power Pp = 40 mW, erasing power Pe = 7.3 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
As a result, DC jitter was 12.1%, which was worse than that of Example B-25.

(Example B-26)
Using the pulse waveform shown in FIG. 14, the recording linear velocity is set to 7 m / s, the recording power Pp = 36 mW, the erasing power Pe = 7.1 mW, the cooling power Pc1 = 4.1 mW, and the bias power Pb = 0.1 mW. Recorded. The width of the multipulse was 0.18T.
As a result, the DC jitter was 10.6%, which was favorable.

(Comparative Example B-22)
Recording was performed using the pulse waveform shown in FIG. 16 at a recording linear velocity of 7 m / s, recording power Pp = 36 mW, erasing power Pe = 7.1 mW, and bias power Pb = 0.1 mW.
The width of the multipulse was 0.18T.
As a result, DC jitter was 12.8%, which was worse than that of Example B-26.

(Example B-27)
Using the pulse waveform shown in FIG. 12, the recording linear velocity is set to 8.41 m / s, the recording power Pp = 39 mW, the erasing power Pe = 7 mW, the cooling power Pc1 = 4 mW, Pc2 = 2 mW, and the bias power Pb = 0.1 mW. And recorded. The width of the multipulse was 0.2T.
As a result, the DC jitter was 10.5%, which was favorable.

(Example B-28)
ZnS (80 mol%)-SiO ₂ (20 A first lower protective layer having a thickness of 60 nm, composed of Ag _0.2 In _3.5 Sb _71.4 Te _21.4 Ge _{3.5, a} first recording layer having a thickness of 8 nm, In ₂ O ₃ (7 0.5 mol%)-ZnO (22.5 mol%)-SnO ₂ (60 mol%)-Ta ₂ O ₅ (10 mol%)-thick first upper protective layer having a thickness of 5 nm, Mo of 1.0 mass% the first reflective layer having a thickness of 8nm of Cu was _contained, in ₂ O 3 (90 mol%) - heat diffusion layer having a thickness of 60nm made of ZnO (10 mol%) in order by a sputtering method in Ar gas atmosphere And film, to form the first information layer. The same sputtering apparatus as in Example B-19 was used.
Further, a substrate similar to the first substrate is used as the second substrate, and a second reflective heat radiation layer made of Ag and having a thickness of 140 nm, In ₂ O ₃ (7.5 mol%)-ZnO (22.5 mol%) is formed thereon. -SnO ₂ (60 mol%) _- Ta ₂ O 5 second upper protective layer having a thickness of 20nm made of (10 _mol%), the _{Ag 0.2 in 3.5 Sb 71.4 Te 21.4} Ge 3.5 A second recording layer having a thickness of 15 nm and a second lower protective layer having a thickness of 120 nm made of ZnS (80 mol%)-SiO ₂ (20 mol%) are formed in the same manner as in the case of the first information layer, A second information layer was formed.

Next, the first information layer and the second information layer were irradiated with laser light from the first substrate side and the film surface side of the second information layer, respectively, and an initialization process was performed. Initialization was performed by condensing laser light emitted from a semiconductor laser (emission wavelength 810 ± 10 nm) with an optical pickup (numerical aperture NA = 0.55). The initialization conditions of the first recording layer were as follows: the optical recording medium was rotated in the CLV (constant linear velocity) mode, the linear velocity was 3 m / s, the feed amount was 36 μm / rotation, the radial position was 23 mm to 58 mm, and the initialization power was 700 mW. The initialization conditions of the second recording layer were as follows: the optical recording medium was rotated in the CLV (constant linear velocity) mode, the linear velocity was 3 m / s, the feed amount was 36 μm / rotation, the radial position was 23 mm to 58 mm, and the initialization power was 500 mW.
The light transmittance of the first information layer after initialization was 40%, and it was confirmed that sufficient light transmittance was obtained. The light transmittance was measured with Etaoptics manufactured by STEAG.

Next, an ultraviolet curable resin (Kayarad DVD003M, manufactured by Nippon Kayaku Co., Ltd.) is applied on the film surface side of the first information layer, and the film surface side of the second information layer is bonded and spin-coated, and the first substrate side Were irradiated with ultraviolet light to cure the ultraviolet light curable resin to form an intermediate layer having a thickness of 55 μm, and a two-layer phase change optical recording medium having two information layers was produced.
When the continuous meandering groove provided on the substrate was evaluated with the produced two-layer type optical recording medium, PP1 = 0.47 and PP2 = 0.42. The values of PP1 and PP2 obtained here are good values. Moreover, WCN1 = 51 dB and WCN2 = 45 dB were obtained. The values of WCN1 and WCN2 obtained here are good values.
Recording was performed with the recording waveform shown in FIG. 11 at a recording speed of 8.4 m / s on the two-layer phase change optical recording medium thus manufactured. The power ratio when recording on the first information layer and the second information layer is different. The results are shown in Table 11 and FIG.

(Comparative Example B-23)
The ratio ε between the recording power level Pp and the erasing power level Pe of the first recording layer and the second recording layer, and the recording power for the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28 Recording was performed in the same manner as in Example B-28 except that the ratio δ1 between the level Pp and the cooling power level Pc1 was the same. The results are shown in Table 11 and FIG.

(Example B-29)
Recording was performed with a recording waveform shown in FIG. 11 at a recording speed of 9.9 m / s on a two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28. The power ratio when recording on the first information layer and the second information layer is different.

(Comparative Example B-24)
The ratio ε between the recording power level Pp and the erasing power level Pe of the first recording layer and the second recording layer, and the recording power for the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28 Recording was performed in the same manner as in Example B-29 except that the ratio δ1 of the level Pp and the cooling power level Pc1 was the same.

(Example B-30)
Recording was performed with a recording waveform shown in FIG. 11 at a recording speed of 11.5 m / s on a two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28. The power ratio when recording on the first information layer and the second information layer is different.

(Comparative Example B-25)
The ratio ε between the recording power level Pp and the erasing power level Pe of the first recording layer and the second recording layer, and the recording power for the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28 Recording was performed in the same manner as in Example B-30 except that the ratio δ1 of the level Pp and the cooling power level Pc1 was the same.

(Example B-31)
Recording was performed with a recording waveform shown in FIG. 13 at a recording speed of 8.4 m / s on a two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28. The power ratio when recording on the first information layer and the second information layer is different.

(Comparative Example B-26)
The ratio ε between the recording power level Pp and the erasing power level Pe of the first recording layer and the second recording layer, and the recording power for the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28 Recording was performed in the same manner as in Example B-31 except that the ratio δ1 of the level Pp and the cooling power level Pc1 was the same.

(Example B-32)
Recording was performed with a recording waveform shown in FIG. 14 at a recording speed of 8.4 m / s on a two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28. The power ratio when recording on the first information layer and the second information layer is different.

(Comparative Example B-27)
The ratio ε between the recording power level Pp and the erasing power level Pe of the first recording layer and the second recording layer, and the recording power for the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28 Recording was performed in the same manner as in Example B-32 except that the ratio δ1 of the level Pp and the cooling power level Pc1 was the same.

(Example B-33)
Recording was performed with a recording waveform shown in FIG. 12 at a recording speed of 8.4 m / s on a two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28. The power ratio when recording on the first information layer and the second information layer is different.

(Comparative Example B-28)
The ratio ε between the recording power level Pp and the erasing power level Pe of the first recording layer and the second recording layer, and the recording power for the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28 Recording was performed in the same manner as in Example B-33, except that the ratio δ1 between the level Pp and the cooling power level Pc1 was the same.

Table 11 summarizes the evaluation results of the recording characteristics of Examples B-28 to B-33 and Comparative Examples B-23 to B-28.

(Example B-34)
For the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28, the recording speed was 8.4 m / s, and the recording waveform shown in FIG. And recorded.
The results are shown in FIG. 22, and it can be seen that the recording sensitivity is about 10% better than Example B-28 in which recording was performed with the 1T cycle strategy.

(Example B-35)
For a two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-28, the recording linear velocity was 8.4 m / s, the recording power Pp = 42 mW, the erasing power Pe = 7 mW, and Pe ⁻ = 4 mW. Recording was done with a 1T strategy.
The results are shown in Table 12, and it can be seen that the repetitive recording characteristics of the first information layer are improved as compared with the conventional recording method as shown in FIGS. In addition, when the number of repeated recordings in the column of the conventional method is 2 times or more, it is clear that the number of repeated recordings is worse than the case of 1 time.

(Example B-36)
In Example B-28, both the first recording layer and the second recording layer were changed to Ag _0.5 In _3.9 Sb _69.6 Te ₂₄ Ge ₂ , and the second upper protective layer was ZnS (80 mol%) − A two-layer type optical recording medium having the same layer configuration and thickness as in Example B-28 except that SiO ₂ (20 mol%) was changed was prepared, and a recording linear velocity of 15.3 m was obtained from the pulse waveform shown in FIG. / S, recording power Pp = 30 mW, erasing power Pe = 7 mW, cooling power Pc1 = 4 mW, and bias power Pb = 0.1 mW were recorded. The width of the multipulse was 0.3T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.8%, which was good.

(Comparative Example B-29)
With respect to the two-phase phase change type optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity is 15.3 m / s, the recording power Pp = 30 mW, the erasing power Pe by the pulse waveform shown in FIG. = 7 mW and bias power Pb = 0.1 mW. The width of the multipulse was 0.3T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 11.3%, which was worse than that of Example B-36.

(Example B-37)
For the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity 9.2 m / s, recording power Pp = 28 mW, erasing power Pe according to the pulse waveform shown in FIG. = 6 mW, cooling power Pc1 = 3 mW, bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.6%, which was good.

(Comparative Example B-30)
With respect to the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity 9.2 m / s, recording power Pp = 28 mW, erasing power Pe by the pulse waveform shown in FIG. = 6 mW and bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 10.9%, which was worse than that of Example B-37.

(Example B-38)
With respect to a two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity 8.4 m / s, recording power Pp = 26 mW, erasing power Pe according to the pulse waveform shown in FIG. = 6 mW, cooling power Pc1 = 3 mW, bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 10%, which was good.

(Comparative Example B-31)
With respect to the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity 8.4 m / s, recording power Pp = 26 mW, erasing power Pe by the pulse waveform shown in FIG. = 6 mW and bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 11.1%, which was worse than that of Example B-38.

(Example B-39)
With respect to the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity is 15.3 m / s, the recording power Pp = 30 mW, the erasing power Pe by the pulse waveform shown in FIG. = 6.2 mW, cooling power Pc1 = 2.8 mW, bias power Pb = 0.1 mW The width of the multipulse was 0.3T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.5%, which was good.

(Example B-40)
With respect to the two-layer phase change optical recording medium having the same layer configuration and thickness as Example B-36, the recording linear velocity 9.2 m / s, recording power Pp = 30 mW, erasing power Pe by the pulse waveform shown in FIG. = 6 mW, cooling power Pc1 = 3 mW, bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.6%, which was good.

(Example B-41)
For the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity is 15.3 m / s, the recording power Pp = 30 mW, the erasing power Pe by the pulse waveform shown in FIG. Recording was performed by setting = 6.5 mW, cooling power Pc1 = 3.2 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.3T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.7%, which was good.

(Example B-42)
With respect to the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity 9.2 m / s, recording power Pp = 28 mW, erasing power Pe according to the pulse waveform shown in FIG. = 5.9 mW, cooling power Pc1 = 2.8 mW, bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.5%, which was good.

(Example B-43)
With respect to the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity is 15.3 m / s, the recording power Pp = 30 mW, the erasing power Pe by the pulse waveform shown in FIG. = 7 mW, cooling power Pc1 = 4 mW, Pc2 = 2 mW, bias power Pb = 0.1 mW. The width of the multipulse was 0.3T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.3%, which was good.

(Example B-44)
For the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity 9.2 m / s, recording power Pp = 28 mW, erasing power Pe by the pulse waveform shown in FIG. Recording was performed by setting = 6.2 mW, cooling power Pc1 = 4 mW, Pc2 = 2.1 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.2T.
When recording was repeated 100 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.4%, which was good.

(Example B-45)
For the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity is 15.3 m / s, the recording power Pp = 30 mW, the erasing power Pe according to the pulse waveform shown in FIG. Recording was performed by setting = 7.2 mW, Pe- = 4.2 mW, cooling power Pc1 = 6.6 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.3T.
When recording was repeated 1000 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.4%, which was good.

(Example B-46)
For the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, the recording linear velocity 9.2 m / s, recording power Pp = 28 mW, erasing power Pe by the pulse waveform shown in FIG. = 6.8 mW, Pe- = 3.8 mW, cooling power Pc1 = 3.8 mW, and bias power Pb = 0.1 mW were recorded. The width of the multipulse was 0.2T.
When recording was repeated 1000 times on the track of the first recording layer, the DC jitter of the first recording layer was 9.2%, which was good.

(Example B-47)
On the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, recording was first performed at a radial position of 24 to 58 mm of the first information layer at 9.2 m / s, and thereafter Recording was performed at 9.2 m / s at a radial position of 40 mm of the second information layer.
The result was as shown in FIG. From the results of FIG. 23, it can be seen that Example B-47 can achieve a higher modulation degree with lower power than Comparative Example B-32.

(Comparative Example B-32)
For the two-layer phase change optical recording medium having the same layer configuration and thickness as in Example B-36, no recording was performed on the first information layer, and the radial position of the second information layer was 40 mm at 9.2 m / s. Recorded.
The result was as shown in FIG. From the result of FIG. 23, it can be seen that the sensitivity is lower than that of Example B-47 and a higher power is required.

The optical recording medium, the optical recording method, and the optical recording apparatus of the present invention have an initial crystal state without causing repeated deterioration of recording durability or increase of crosstalk even at high-speed recording equivalent to 6 to 8 times the speed of DVD. Regardless of this, it is possible to reduce an increase in jitter at the initial stage of repeated recording, which can be applied to various CDs and DVDs.
The multilayer optical recording medium of the present invention, the optical recording method and the optical recording apparatus of the present invention can suppress thermal damage to the recording layer, accurately perform recording and erasing, and improve repeated recording characteristics. The present invention is suitably used for CD-type CDs, multi-layer DVDs, multi-layer blue wavelength compatible optical recording media, and the like.

FIG. 1 is a diagram showing an example of jitter fluctuation when a random pattern is repeatedly recorded. FIG. 2 is a diagram showing jitter immediately after initialization and after repeated recording one month later. FIG. 3 is a diagram showing an example of a phase change type optical recording medium of DVD specification and high speed specification. In FIG. 4, although the amorphous part formed by the first heating pulse disappears by recrystallization, the temperature at the time of irradiation of the second heating pulse becomes high due to the preheating effect of the first heating pulse. It is a figure which shows typically a mode that a fusion | melting area | region spreads and a mark front-end | tip part becomes large as a result. FIG. 5 is a block diagram showing an example of an optical recording apparatus for realizing the optical recording method of the present invention. FIG. 6 is a diagram showing jitter after repeated recording in Examples and Comparative Examples. FIG. 7 is a diagram showing a waveform light emission pattern (recording strategy) for repeatedly recording data consisting of marks and spaces used in DVD + RW and the like. FIG. 8 is a diagram showing a waveform light emission pattern (recording strategy) for each mark length in the example. FIG. 9 is a diagram showing the result of examining the jitter at the beginning of the mark for the initial recording and the repeated recording 10 times when the random pattern is recorded by changing the length of the second cooling pulse of the mark of 6T or more. FIG. 10 is a diagram showing the jitter values of the initial recording and the repeated recording 10 times when Pp = 38 mW is fixed, the value of Pe is changed and the value of Pe / Pp is changed to record a random pattern. Is FIG. 11 is a diagram showing an example of a laser emission pattern in the case of N = 1 in the recording method according to the first embodiment of the present invention in which the power levels of Pc1 to PcN are provided. FIG. 12 is a diagram showing an example of a laser emission pattern when N = 2 in the recording method according to the first embodiment of the present invention in which the power levels of Pc1 to PcN are provided. FIG. 13 is a diagram showing an example of a laser emission pattern when N = 1 in the recording method according to the second embodiment of the present invention in which the power levels of Pc1 to PcN are provided. FIG. 14 is a diagram showing an example of a laser emission pattern when N = 1 in the recording method according to the third embodiment of the present invention in which the power levels of Pc1 to PcN are provided. FIG. 15 is a diagram showing an example of a laser emission pattern in the conventional recording method. FIG. 16 is a diagram showing another example of the laser emission pattern in the conventional recording method. FIG. 17 is a diagram showing an example of the layer structure of the two-layer optical recording medium of the present invention. FIG. 18 is a graph showing the relationship between the Sb amount in the recording layer and the recording linear velocity. FIG. 19 is a diagram for explaining asymmetry. FIG. 20 is a diagram comparing the recording characteristics when recording is performed on the first information layer and the second information layer with the recording strategy of FIG. FIG. 21 is a diagram showing a laser emission waveform when Pe ⁻ is included. FIG. 22 is a diagram comparing the recording characteristics of Example B-34 with the recording characteristics of Example B-28 for the second information layer. FIG. 23 is a diagram comparing the modulation degrees of Example B-47 and Comparative Example B-32. FIG. 24A is a diagram illustrating a conventional single-layer optical recording medium, and FIG. 24B is a front-side information layer of the conventional two-layer optical recording medium as viewed from the light irradiation side. FIG. 24 (3) shows another example of the recording method of the information layer on the near side when viewed from the light irradiation side in the conventional two-layer optical recording medium. FIG. FIG. 25 is a diagram comparing jitter for Example B-17. FIG. 26 is a diagram comparing jitter for Example B-18. FIG. 27 is a diagram comparing the degree of modulation for Example B-18. FIG. 28 is a diagram showing parameters of the recording pulse strategy. FIG. 29 is a diagram comparing the recording characteristics of 10 repeated recordings in the front recording layer. FIG. 30 is a diagram comparing the recording characteristics of the front recording layer up to 500 times of repeated recording. FIG. 31 is a diagram showing recording strategy parameters actually used in FIGS. 29 and 30. FIG. 32 is a graph showing the relationship between recording power and modulation factor. FIG. 33 is a diagram showing an example of an optical recording apparatus equipped with the single-sided multilayer optical recording medium of the present invention. Figure 34 is a Ru waveform pattern der showing a 1T strategy. FIG. 36 is a waveform pattern showing a 3T strategy.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st information layer 2 2nd information layer 3 1st board | substrate 4 Intermediate layer 5 2nd board | substrate 11 1st lower protective layer 12 1st recording layer 13 1st upper protective layer 14 1st reflection layer 15 Thermal diffusion layer 21 2nd Lower protective layer 22 Second recording layer 23 Second upper protective layer 24 Second reflective layer 25 Actuator control mechanism 26 Programmable BPF
27 Wobble detection unit 28 Address demodulating circuit 101 Substrate 102 First protective layer 103 Phase change recording layer 104 Second protective layer 105 Reflective layer 106 Phase change type optical recording medium 107 Antisulfuration layer 108 Organic protective layer 121 Spindle motor 122 Rotation control mechanism 123 laser light source 124 optical head 215 optical disk 220 optical recording device 221 seek motor 222 spindle motor 223 optical pickup device 224 laser control circuit 225 encoder 226 drive control circuit 228 reproduction signal processing circuit 234 buffer RAM
237 Buffer manager 238 Interface 239 Flash memory 240 CPU

Claims (8)

A substrate, and at least a first protective layer, a phase change recording layer, a second protective layer, and a reflective layer on the substrate, wherein the phase change recording layer comprises Sb, Ge, Ga, In, Zn, Mn, Sn , Ag, Mg, Ca, Bi, Se, and Te , a laser beam applied to a phase change type optical recording medium that is recorded at a recording speed of 27.9 m / s or more and 42 m / s or less. an optical recording method of irradiating,
When recording information by the mark length recording method in which the time length of the recording mark is represented by nT (where n is a natural number and T is the basic clock period), the recording mark is formed by heating with power Pp. A pulse and a cooling pulse of power Pb (where Pp> Pb) are alternately applied by irradiating the heating pulse m times and the cooling pulse m−1 times , satisfying the following formula, m ≦ (n / 2 + 1), An optical recording method, wherein the irradiation time of the leading cooling pulse is 0.2T to 0.4T.   2. The optical recording method according to claim 1, wherein when the value of m is m ≧ 3, the irradiation time of the second cooling pulse is 1.0T to 2.5T. The optical recording method according to claim 1, wherein the Sb content in the phase change recording layer is 50 to 90 atomic%. The optical recording method according to claim 1, wherein the reflective layer contains Ag and an Ag alloy. The first protective layer and the second protective layer are made of ZnS and SiO. ₂ The optical recording method according to claim 1, comprising a mixture of The phase change optical recording medium further includes an antisulfurization layer between the reflective layer and the second protective layer, the reflective layer is made of either Ag or an Ag alloy, and the second protective layer is made of ZnS and SiO. ₂ The optical recording method according to claim 1, comprising a mixture of the above. As a recording strategy for a rotation drive mechanism for rotating an optical recording medium, a laser light source for emitting laser light to be irradiated on the optical recording medium, a light source driving means for emitting light from the laser light source, and an emission waveform of a light beam emitted from the laser light source An optical recording device comprising a light emission waveform control means for controlling a light source drive means,
A substrate, and at least a first protective layer, a phase change recording layer, a second protective layer, and a reflective layer on the substrate, wherein the phase change recording layer comprises Sb, Ge, Ga, In, Zn, Mn, Sn A phase change optical recording medium containing at least one element selected from Ag, Mg, Ca, Bi, Se, and Te and having a recording speed of 27.9 m / s to 42 m / s.
Information is recorded by a mark length recording method in which the time length of a recording mark is represented by nT (where n is a natural number and T is a basic clock period). Pp heating pulse and power Pb cooling pulse (where Pp> Pb) are alternately applied by irradiating the heating pulse m times and the cooling pulse m−1 times, and the following equation m ≦ (n / 2 + 1) And an irradiation time of the leading cooling pulse is set to be 0.2T to 0.4T. The optical recording apparatus according to claim 7, wherein the recording strategy is set so that the irradiation time of the second cooling pulse is 1.0T to 2.5T when m ≧ 3.