Optical information recording medium

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an optical information recording medium (optical disc) in which information is recorded and erased by changing the arrangement of atoms constituting the recording layer by irradiation with light.

【0002】

[Conventional technology]

As one of the optical memory media that can record, reproduce, and erase information by irradiating a laser beam, a so-called phase change type that utilizes the transition between crystal-amorphous or between two crystal phases of crystal 1 and crystal 2. Recording media are well known.

【0003】

A chalcogen-based alloy thin film is often used as the recording layer material used in the phase change recording method. Among them, Ge-Sb-Te-based and Ag-In-Sb-Te-based alloy thin films have been put into practical use as rewritable optical discs.

【0004】

The recording principle is as follows. The recording layer immediately after film formation is in an amorphous state and has low reflectance. First, the recording layer is heated by irradiating a laser beam to make the entire surface of the disk into a crystal state with high reflectance. That is, initialization is performed. Usually, this initialization is performed by irradiating a rotating medium with a laser beam focused to about several tens to several hundreds of μm.

【0005】

The initialized optical disc is locally irradiated with laser light to melt and quench the recording layer to change the phase to an amorphous state. The optical properties (reflectance, transmittance, complex refractive index, etc.) of the recording layer change with the phase change, and information is recorded.

【0006】

The reproduction is performed by irradiating a laser beam weaker than that at the time of recording to detect the reflectance difference or the phase difference between the crystal and the amorphous. In rewriting, the recording peak power superimposed on the low-energy erasing power that causes crystallization is applied to the recording layer, thereby overwriting on the already recorded recording mark without going through the erasing process.

【0007】

It is known that in the above-mentioned Ge-Sb-Te system, in a system other than the materials that have been put into practical use, the crystalline-non-crystalline state is transferred even with the eutectic composition of Sb and Te.

【0008】

By the way, as publicly known materials including the composition range in which the third element, particularly Ge, is added to Sb70 and Te30, JP-A-1-15685, JP-A No. 1-251342, JP-A-1-303643 and the like can be mentioned. be able to.

【0009】

However, according to the contents of the publicly known publication, even if there is a part that overlaps with the present invention as its composition range, the specific configuration thereof is different as described later. the technical content, sufficient contrast, long-term stability intended by the present invention, and this low environmental load are those which can not be obtained the seeds of the optical information recording medium.

【0010】

On the other hand, the recording method of an optical disc using a phase change material has been performed by using a red laser light having a wavelength of around 650 nm or a laser light having a longer wavelength than that used in DVD-ROMs. However, in recent years, semiconductor lasers that emit light at a wavelength of around 400 nm have appeared on the market. This is because if a laser having a shorter wavelength can be used, the beam spot diameter becomes smaller and the recording density of the optical disc can be increased accordingly. Therefore, each company is studying an optical disk system using a blue laser.

【0011】

[Problems to be Solved by the Invention]

When an alloy used in a red laser such as the Ge-Sb-Te system and Ag-In-Sb-Te system described above is made compatible with a blue laser system as a recording material, it has a beam compared to a red laser. Due to the small diameter, the energy density in the beam spot is high, so if a signal is recorded on a disk with a guide groove and the recorded track is played back for a while, the playback light will damage the recording film. However, there is a problem that the recorded signal is deteriorated.

【0012】

Therefore, if the reproduced light intensity is lowered to the extent that the recorded signal is not deteriorated, the signal intensity and C / N are lowered, and a sufficient reproduced signal cannot be obtained. Further, when a recording material that is weak against reproduced light is used, there is a problem that the storage stability is poor with respect to the environmental load and the recorded signal is deteriorated when stored for a long period of time.

【0013】

Therefore, the present invention uses a GeSbTe-based material as a phase-changing optical recording layer, is compatible with an optical disk system using a blue laser, exhibits strong durability against reproduced light, and is also resistant to environmental load. The purpose is to provide an optical disc.

【0014】

[Means for solving problems]

The present invention has been made to achieve the above object, and at least the reflective layer 2, the first protective layer 3, the phase change type optical recording layer 4, and the second protective layer 5 are laminated on the substrate 1 in this order. The optical information recording medium 10 is an optical information recording medium 10 in which information is recorded and erased by changing the arrangement of atoms by irradiation with light. The phase change type optical recording layer 4 is composed of GexSbyTez. 3 x 15 (atomic ratio) x + y + z = 100 It is characterized in that 2 y / z 4.

【0015】

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings. Since the examples described below are suitable specific examples of the present invention, various technically preferable limitations are added, but the scope of the present invention is intended to particularly limit the present invention in the following description. Unless otherwise stated, the present invention is not limited to these aspects.

【0016】

First, in order to have a better understanding of the optical disc used in this embodiment, the background thereof will be described. As can be understood from the above-mentioned public publications and the like, a laser having a considerably high output is required for initialization. In a high-power laser, the beam diameter is narrowed, so the density of the beam light increases even with a small laser power, but initialization by scanning a beam diameter of several microns takes a very long time. It was what I needed.

【0017】

Therefore, GeTe and Ge, which are not eutectic systems that can be initialized with lower power.₂Sb₃GeSbTe-based materials made by combining the above were developed, and the current DVD-RAM-based products were born. Then, a little later than this material, AgInSbTe-based materials were developed, which was the birth of CD-RW and DVD-RW.

【0018】

This AgInSbTe-based material requires stronger laser power than GeSbTe used in RAM. From this point onward, lasers have become shorter in wavelength and higher in output, and those equipped with a high-power laser as an initialization device will appear.

【0019】

With the advent of such an initialization device equipped with a high-power laser, the development of eutectic GeSbTe materials, which was difficult to initialize in the past, has progressed to the present.

【0020】

Hereinafter, a preferred embodiment of the optical disc according to the present invention will be described with reference to FIG. The present invention is not limited to the structures and substances used in the examples described below as described above.

【0021】

FIG. 1 is a cross-sectional view showing an embodiment of a basic configuration of an optical disc according to the present embodiment, FIG. 2 is a diagram showing a strategy pattern at the time of recording, and FIG. 3 is a C / N for the reproduction power of the first embodiment. FIG. 4 is a diagram showing the relationship between the reproduction deterioration and the environmental load of the recording layer composition, and FIG. 5 is a diagram showing the C / N with respect to the reproduction power of Comparative Example 1.

【0022】

The optical disc 10 according to this embodiment has a reflective layer 2 on the substrate 1, a first protective layer 3 on the reflective layer 2, a recording layer 4 on the first protective layer 3, and a recording layer 4 on the recording layer 4. The second protective layer 5 is configured by providing a cover sheet 7 on the second protective layer 5 via an adhesive layer 6. The optical disc 10 of this embodiment is premised on an optical disc having a recording layer 3 on a substrate 1 and recording and erasing information by changing the arrangement of atoms constituting the recording layer 3 by irradiation with light. Is.

【0023】

Here, the laser beam is incident from the cover sheet 7 side, but the laser beam may be incident from the substrate 1 side without providing the cover sheet 7. Further, if sufficient reflectance can be obtained, the above-mentioned reflective layer 2 may not be provided.

【0024】

The substrate 1 of the optical disk 10 in this embodiment may be glass, plastic, a glass on which a photocurable resin is provided, or the like, but plastic is preferable in terms of productivity including cost. Polycarbonate resin is preferred.

【0025】

The thickness of the recording layer 4 is not particularly limited, but is 3 to 100 nm. In particular, since the recording and erasing sensitivity is high and recording and erasing can be performed many times, it is preferably 3 nm or more and 30 nm or less.

【0026】

By arranging the first and second protective layers 3 and 5 to be the dielectric layers in this way, the substrate 1, the recording layer 4 and the like described above are deformed by the irradiation heat of the laser beam at the time of recording, and the recording is performed. It has the effect of protecting the substrate 1 and the recording layer 4 from heat, such as preventing deterioration of the characteristics, and the effect of improving the signal contrast during reproduction by the optical interference effect. Furthermore, it also has the effect of promoting the crystallization of the recording layer 4 and improving the erasure rate. The first and second protective layers 3 and 5 are ZnS-SiO.₂ , Si₃N₄, Al₂O₃There are inorganic thin films such as.

【0027】

In particular, metals such as Si, Ge, Al, Ti, Zr, Ta, thin films of semiconductor oxides, metals such as Si, Ge, Al, thin films of semiconductor nitrides, Ti, Zr, Hf, Si, etc. Metal or semiconductor carbide thin film, ZnS, In₂S₃, TaS₄, GeS₂A thin film of a sulfide of a metal such as, or a semiconductor, and a film of a mixture of two or more of these compounds are preferable because they have high heat resistance and are chemically stable.

【0028】

Further, as the first and second protective layers 3 and 5 constituting the protective layer to the recording layer 4, those having no atomic diffusion are preferable. These oxides, sulfides, nitrides, and carbides do not necessarily have a stoichiometric composition, and it is also effective to control the composition or mix them for controlling the refractive index and the like.

【0029】

Also, these are MgF₂The first and second protective layers 3 and 5 formed by mixing fluorides such as the above are also preferable because the residual stress of the film (layer) is small. Especially ZnS and SiO₂This mixed film is preferable because deterioration of recording sensitivity, C / N, erasing rate, etc. is unlikely to occur even after repeated recording and erasing. The thickness of the first and second protective layers 3 and 5 is about 5 to 200 nm.

【0030】

The thickness of the first protective layer 3 is preferably 5 to 30 nm because of recording characteristics such as C / N and erasure rate and stable rewriting many times. The second protective layer 5 is preferably 30 to 200 nm because it is difficult to peel off from the recording layer 4 and the adhesive layer 6 and defects such as cracks are unlikely to occur. The first and second protective layers 3 and 5 may be composed of different compounds rather than the same.

【0031】

The material of the reflective layer 2 includes metals such as Al, Au, and Ag having light reflectivity, alloys containing these as main components and containing additive elements such as Ti, Cr, Pd, and Cu, and Al, Au, and Ag. Examples thereof include a mixture of a metal such as Al and Si with a metal nitride such as Al and Si, a metal oxide, and a metal compound such as a metal chalcogenide. Metals such as Al, Au, and Ag, and alloys containing these as main components are preferable because they have high light reflectivity and high thermal conductivity. The thickness of the reflective layer 5 described above is approximately 5 nm or more and 300 nm or less.

【0032】

As the light source used for recording the optical disk 10 of this embodiment, it is preferable to use a laser beam (laser beam), which is mainly a laser beam having a wavelength in the near infrared region of 830 nm to an ultraviolet region of 300 nm. It is also possible to use a light source in which the wavelength of the primary light is shortened by using a second harmonic generation element (SHG element).

【0033】

(Example) An embodiment of the optical disc 10 according to the present invention will be described below. FIG. 2 is an explanatory diagram showing a strategy at the time of recording on the optical disc 10 according to the present invention. The recording of 10 on the optical disc according to the present invention is performed by irradiating the crystalline recording layer 4 with a laser beam pulse or the like to heat it, quenching it, and then forming an amorphous recording mark. Practically, by applying the recording peak power (P1) superimposed on the low-energy erasing power (P2) that causes crystallization to the recording layer 4, the recording mark already recorded without going through the erasing process Overwrite to. The recording laser pulse at this time is divided into a plurality of pulses shorter than the recording mark length.

【0034】

Specific examples will be shown below, but as described above, the present invention is not limited to this example. In this example, recording (1 beam overwrite) was performed using a Shibasoku optical disk drive tester (LM330A) equipped with a laser diode having a wavelength of 405 nm and an optical lens (objective lens) having a numerical aperture of NA = 0.65. The initializer used was an initializer (LK201A) manufactured by ShibaSoku Co., Ltd.

【0035】

(Example 1) On a polycarbonate substrate 1 having a diameter of 120 mm, first, Ag alloy is used as the reflective layer 2, and ZnS-SiO is used as the first protective layer 3.₂Furthermore, GeSbTe as the recording layer 4 and ZnS-SiO as the second protective layer 5.₂Was formed in this order by the sputtering method. Then, the cover sheet 7 was attached with the UV curable resin as the adhesive layer 6. At this time, the film thickness of each layer was 50 nm for the reflective layer 2, 10 nm for the first protective layer 3, 18 nm for the recording layer 4, and 50 nm for the second protective layer 5.

【0036】

The composition of the recording layer 3 was Ge5.4%, Sb72.0%, and Te22.6% in atomic ratio. After bonding, UV irradiation was performed to sufficiently cure the adhesive layer 6. After that, the initialization conditions were fixed at a linear velocity of 2 m / s and a feed pitch of 30 μm with an initializer with a laser beam spot diameter of 120 μm, and initialization was performed with a laser output of 400 mW.

【0037】

After that, the 8-16 modulated information signal is set to 5 m / s and 1T = 17.15 nsec according to the strategy shown in Fig. 2, P1 = 9 mW, P2 = 2 mW, P3 = 0.4 mW, P4 = 0.4 mW, T1 = 0.5T. , T2 = 0.3T, T3 = 0.7T, T4 = 0.8T, recorded in the groove, sliced at the center of the amplitude of the reproduced signal, and the clock to data jitter was measured.

【0038】

Jitter was measured with a time interval analyzer (model TA520: manufactured by Yokogawa Electric Corporation). The jitter after the first recording was 8.9% at the beginning of the recording mark and 8.7% at the rear end of the recording mark, and good recording was achieved.

【0039】

In addition, a single signal with a length of 3T was recorded on the same disc using the above-mentioned strategy. The recorded track was still played back and the C / N was measured. At this time, the reproduction power was changed from 0.35 mW to 0.58 mW, and the C / N was measured immediately after the start of still reproduction and after 1 minute had passed. The results are shown in Figure 3. With the reproduced light intensity in this range, the C / N difference before and after still reproduction was within 0.2 dB. Still reproduction was continued for 1 hour with a reproduction power of 0.58 mW, but there was no deterioration in C / N. From this, it can be understood that the optical disc 10 of the present embodiment exhibits strong durability against reproduced light.

【0040】

In addition, a single signal with a length of 3T was continuously recorded with a disc diameter of about 1 mm using the above-mentioned strategy on the same disc, and the C / N was measured. After the measurement, the disc was placed in an oven and left in the air at 90 ° C for 24 hours to perform an accelerated test of the environmental load. Then, after loading, the C / N of the recorded area was measured. The reproduction power was 0.58 mW. At this time, the C / N before the environmental load was 54.2 dB, and after the environmental load was also 54.2 dB. From this, it can be understood that the optical disc 10 of the present embodiment is strong against the environmental load.

【0041】

In addition, a composition other than the composition of the recording layer 4 described above was examined. The examined composition is shown in Fig. 4. In FIG. 4, the thickness of the recording layer 4, the thickness of the first and second protective layers 3 and 5, and the thickness of the reflective layer 2 are the same as in Example 1 described above, and the amounts of Ge, Sb, and Te are set to the same. It is the result of the experiment performed by changing sequentially.

【0042】

As is clear from FIGS. 3 and 4 described above, a GeSbTe-based material is used as the phase change type optical recording layer 4, and it is compatible with an optical disk system using a blue laser and exhibits strong durability against reproduced light. Moreover, as an optical disc 10 that is resistant to environmental load, the composition range of Ge, Sb, and Te is Ge 3% or more and 15% or less in atomic ratio, Sb / Te is 2 or more and 4 or less, and the reproduction power is 0.58. It can be understood that the C / N deterioration is within 0.2 dB in the still reproduction by mW, the initial C / N is 50 dB or more, and the C / N deterioration is within 0.2 dB due to the environmental load.

【0043】

It has been found as a result of various experiments that this optimum range is in the early stage when deterioration starts. This point will be described in detail below. First, the range of Ge will be described.

【0044】

Increasing the amount of Ge has the effect of improving contrast and increasing resistance to environmental loads. The minimum value is 3% (atomic ratio), but this is in consideration of measurement error. In addition, when the amount of Ge is small, experimental results have shown that C / N cannot be obtained sufficiently. However, the higher the amount of Ge, the better.

【0045】

That is, when the amount of Ge increases, the crystallization rate slows down because the amount of Sb decreases relatively. That is, as will be described later, it leads to the inability to record and rewrite at a high linear speed. In addition, as will be described later, even with the same Sb / Te ratio, experimental results have shown that the smaller the atomic ratio (amount) of Sb, the slower the crystallization rate. Therefore, in this case, the unerased part is created by rewriting.

【0046】

On the other hand, increasing the amount of Ge increases the crystallization rate. A recording film crystallized at a high temperature exhibits high durability with very little reproduction deterioration even when recorded, but if the crystallization temperature is raised too much, initialization itself becomes difficult. In the experimental range, the upper limit was 15% (atomic ratio).

【0047】

Next, the Sb / Te ratio will be described. As mentioned above, the Sb / Te ratio affects the crystallization rate. When this ratio is large, the crystallization rate becomes high, and recording and rewriting become possible at a higher linear speed. On the contrary, if this ratio is small, the crystallization rate becomes slow. In this example, the slow limit was set to 2, because it became difficult to crystallize the initialization step around this limit. In addition, when the value is less than 2, the crystallization state may be unstable, which may cause adverse effects such as poor contrast during recording and the inability to overwrite.

【0048】

On the other hand, the fast limit was set to 4, because the environmental load worsened as this ratio increased. In addition, a high Sb / Te ratio means that the recorded amorphous marks are deteriorated and disappear because they are easily crystallized. Furthermore, probably because it is sensitive to heat, the intensity to the reproduced light also decreases, and when the recorded part is still reproduced, the recorded mark will disappear again.

【0049】

One way to suppress such deterioration is to increase the amount of Ge, but if the Sb / Te ratio exceeds 4, even if still regeneration can withstand to some extent, the environmental load will accelerate. In the test (high temperature test), deterioration occurred and it could not be put into practical use.

【0050】

(Comparative Example 1) First, on a polycarbonate substrate 1 having a diameter of 120 mm, Ag alloy is used as the reflective layer 2, and ZnS-SiO is used as the first protective layer 3.₂In addition, AgInSbTe as the recording layer 4 and ZnS-SiO as the second protective layer 5.₂Were formed in order by the sputtering method. Then, the cover sheet 7 was attached with the UV curable resin as the adhesive layer 6. At this time, the film thickness of each layer was 50 nm for the reflective layer 2, 10 nm for the first protective layer 3, 18 nm for the recording layer 4, and 50 nm for the second protective layer 5.

【0051】

The composition of the recording layer 3 was Ag3.0%, In7.0%, Sb63.0%, and Te27.0% in atomic ratio. After bonding, UV irradiation was performed to sufficiently cure the adhesive layer. After that, the initialization conditions were fixed at a linear velocity of 2 m / s and a feed pitch of 30 μm with an initializer with a laser beam spot diameter of 120 μm, and initialization was performed with a laser output of 350 mW.

【0052】

Here, the laser output for initialization is different from the example using GeSbTe, but the power is set to be optimized for AgInSbTe. After that, the 8-16 modulated information signal is set to 5 m / s and 1T = 17.15 nsec according to the strategy shown in Fig. 2, P1 = 9 mW, P2 = 2 mW, P3 = 0.4 mW, P4 = 0.4 mW, T1 = 0.5T. , T2 = 0.3T, T3 = 0.7T, T4 = 0.8T, recorded in the groove, sliced at the center of the amplitude of the reproduced signal, and the clock to data jitter was measured. Jitter was measured with a time interval analyzer (model TA520: manufactured by Yokogawa Electric Corporation).

【0053】

The jitter after the first recording was 9.0% at the beginning of the recording mark and 8.5% at the rear end of the recording mark, and good recording was achieved.

【0054】

In addition, a single signal with a length of 3T was recorded on the same disc using the above-mentioned strategy. The recorded track was still played back and the C / N was measured. At this time, the reproduction power was changed from 0.35 mW to 0.58 mW, and the C / N was measured immediately after the start of still reproduction and after 1 minute had passed. The results are shown in Fig. 5.

【0055】

As is clear from FIG. 5, there was no deterioration when the reproduction power was 0.4 mW or less, but it can be seen that the deterioration was remarkable when the reproduction light was stronger than that. In particular, at 0.53 mW or higher, deterioration starts immediately after recording, and it can be seen that the C / N has deteriorated significantly in 1 minute. As described above, according to the AgInSbTe-based optical disc, it is not possible to demand strong durability against reproduced light.

【0056】

In addition, the same disc was continuously recorded with a single signal having a length of 3T by the above-mentioned strategy with a disc diameter of about 1 mm, and the C / N was measured. After the measurement, the disc was placed in an oven and left in the air at 90 ° C for 24 hours to perform an accelerated test of the environmental load. Then, the C / N of the recorded area was measured after the load. The reproduction power was 0.40 mW. At this time, the C / N before the environmental load was 50.4 dB, and after the environmental load, it was also 50.4 dB.

【0057】

AgInSbTe, which was given as a comparative example, showed sufficient characteristics for recording and playback at a linear velocity of 3.5 m / s to 7.0 m / s in an optical disc recording / playback system using red laser light with a wavelength of around 650 nm. However, in the system using the blue laser, the C / N could not be increased because the intensity with respect to the reproduced light was weak.

【0058】

[Effect of the invention]

According to the claimed invention, at least a reflective layer, a first protective layer, a phase-changing optical recording layer, and a second protective layer are laminated in this order on a substrate, and the arrangement of atoms is changed by irradiation with light. An optical information recording medium on which information is recorded and erased. The phase-changing optical recording layer is composed of GexSbyTez, and has 3 x 15 (atomic ratio), x + y + z = 100, 2 . By configuring y / z 4, it is possible to withstand high-power regenerated light that cannot be withstood by conventional phase change materials, and optics that can obtain higher C / N. An information recording medium can be obtained. Further, the optical information recording medium as the claimed invention has a practical feature that it is extremely durable against an environmental load.

[Simple explanation of drawings]

[Figure 1]

It is sectional drawing which shows one Example of the basic structure of the optical disk which concerns on this invention.

[Figure 2]

It is a figure which shows the strategy pattern at the time of recording.

[Fig. 3]

It is a figure which shows the C / N with respect to the reproduction power of Example 1. FIG.

[Fig. 4]

It is a figure which shows the relationship with the reproduction deterioration, the environmental load, etc. with respect to the recording layer composition.

[Fig. 5]

It is a figure which shows the C / N with respect to the reproduction power of the comparative example 1. FIG.

[Explanation of symbols]

1 board 2 Reflective layer 3 First protective layer 4 Recording layer 5th protective layer 6 Adhesive layer 7 Cover sheet 10 Optical information recording medium