JP2008192233A - Optical recording medium and tracking method of optical pickup to optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium with which the tracking by continuous servo is possible while making high recording density and cross erasure resistance compatible with each other, and to provide a tracking method of optical pickup to the optical recording medium. <P>SOLUTION: With the optical recording medium, a recording layer does not exist between first recording tracks 20a and second recording tracks 20b and therefore, the prevention of the occurrence of the cross erasure is made possible. Also, the recording tracks are composed of the first recording tracks 20a of a broad width and the second recording tracks 20b of a narrow width and are alternately arranged at the same spaces via projecting parts (or recessed parts) of the same width and thereby the tracking of not only the first recording tracks 20a of the broad width but also the second recording tracks 20b of the arrow width by the continuous servo is enabled. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical recording medium that records and reproduces information using a laser beam, and in particular, an optical recording medium that has high recording density and excellent cross-erase resistance and can be tracked by continuous servo, and the optical recording medium. The present invention relates to an optical pickup tracking method for a recording medium.

  As a digital information signal recording medium, an optical recording medium in which information signals are recorded / reproduced by irradiating laser light from the outside in terms of recording capacity, random accessibility, portability, price, etc. is industrial. Widely used from consumer use to consumer use. These optical recording media include read-only types such as CD (Compact Disc) and DVD (Digital Versatile Disc), recordable types such as CD-R and DVD-R, CD-RW and DVD. Various types such as a rewritable type capable of recording any number of times such as RW, DVD-ROM, and DVD-RAM, and a Blu-ray Disc as a large-capacity optical recording medium have been developed.

  Of these, rewritable optical recording media generally use a phase change material for the recording layer. A recording layer using a phase change material generates heat upon irradiation with laser light, and reversibly changes to an amorphous phase or a crystalline phase having different optical characteristics depending on the temperature reached. The phase change type optical recording medium utilizes this characteristic to irradiate the recording layer with laser light having two levels according to the information signal to be recorded, and to produce an amorphous phase or crystal according to the intensity of the laser light. Information signals are recorded by continuously forming phases. When the recorded information signal is reproduced, it is determined that the intensity of the reflected light from the recording layer is different between the amorphous phase and the crystalline phase, and the recorded information signal is reproduced.

  In recent years, the amount of information recorded on an optical recording medium has been increasing year by year due to, for example, higher resolution of video, and accordingly, further increase in recording capacity has been demanded for the optical recording medium. As one of the typical methods for increasing the recording capacity of optical recording media, recording marks that can be formed on one recording surface by miniaturizing the pitch and pits of tracks for recording information signals and increasing the density There is something to increase the number of. As an example of an optical recording medium that has been increased in recording capacity by this method, the aforementioned Blu-ray Disc can be cited.

  In the above method, it is necessary to reduce the spot diameter of the laser beam to be irradiated and to improve the resolution of the optical system so as to cope with the miniaturized track pitch and pits. However, since the spot diameter of the laser beam is determined to be approximately (2NA / λ) depending on the wavelength λ of the laser beam to be irradiated and the aperture ratio NA of the objective lens to be used, in order to reduce the spot diameter, it is fundamental. The laser light used for the above is shortened and an objective lens having a higher aperture ratio is used. Thus, in the aforementioned Blu-ray Disc, the wavelength λ of the laser light to be used is shortened to 405 nm, and the objective lens having a numerical aperture NA of 0.85 is used, so that the track pitch is 320 nm, By miniaturizing the shortest pit length to 150 nm, a high recording capacity of 25 gigabytes per layer is achieved.

  However, if the numerical aperture NA of the objective lens is made larger than this, it becomes extremely difficult to cope with coma aberration that rapidly increases as the depth of focus approaches. Further, when the wavelength of the laser beam is further shortened, it is difficult to select a substrate material used for the optical recording medium because the laser beam enters the ultraviolet region. Therefore, it is difficult to increase the recording density and the capacity of the optical recording medium further by the above method at this stage.

  For this reason, attempts have been made to reduce the spot diameter by different methods for shortening the wavelength of the laser beam and increasing the aperture ratio of the objective lens. As one of them, in the invention disclosed in [Patent Document 1] below, the light transmittance temporarily changes in accordance with the intensity of the laser beam on the laser beam incident surface side of the recording layer constituting the optical recording medium. An auxiliary layer is provided. Since this auxiliary layer functions to reduce the spot diameter of the irradiated laser light, the spot diameter of the laser light reaching the recording layer is reduced even if the spot diameter of the laser light at the time of irradiation is large. Therefore, the resolution of the optical system can be improved, and the recording density of the optical recording medium can be increased by further miniaturizing the track pitch and pits.

Japanese Patent Laid-Open No. 5-28535

  However, when the invention disclosed in [Patent Document 1] is applied to produce a high recording density rewritable optical recording medium with a track pitch made smaller than 320 nm, the following problems occur.

  One is that although the spot diameter of the laser beam reaching the recording layer is reduced by the auxiliary layer, the track pitch is extremely narrow, so the heat generated during recording is conducted through the recording layer and reaches the adjacent recording track. However, a so-called cross erase may occur that alters the recording mark of the adjacent recording track. Therefore, further improvement to prevent this cross erase is desired.

  Another problem is related to the tracking of the miniaturized recording track. At present, in an optical system corresponding to a laser wavelength of 405 nm and an objective lens numerical aperture NA of 0.65, the track pitch that can be stably tracked by a general continuous servo is limited to 350 nm. Even in an optical system corresponding to a laser wavelength of 405 nm and an objective lens numerical aperture NA of 0.85, the track pitch cannot be significantly narrower than 320 nm for tracking by continuous servo. For this reason, when the track pitch is made narrower, it is necessary to use a so-called sample servo (discrete block servo) that performs tracking using embossed pits provided in the middle of the track.

  For this reason, a device corresponding to the above-described optical recording medium having a high recording density needs to include two tracking servos, a tracking servo for the optical recording medium having a high recording density and a continuous servo for the conventional optical recording medium. Arise. This leads to an increase in the scale of the apparatus and an increase in cost, and the optical system and the control system are complicated and are not preferable. Further improvement is desired.

  The present invention has been made in view of the above circumstances, and an optical recording medium capable of tracking by continuous servo while achieving both high recording density and cross erase resistance, and an optical pickup for the optical recording medium. The object is to provide a tracking method.

The present invention relates to an optical recording medium,
On the substrate
A first track having a first track width;
A second track having a second track width narrower than the first track width;
A recording layer provided independently for each of the first track and the second track;
Have
The optical recording medium 50, wherein the first track and the second track are alternately provided at equal intervals in the first track width direction and the second track width direction, respectively. The above problem is solved by providing 50a.

  Further, by providing the above-described optical recording medium 50, 50a provided with a light transmitting layer provided on the recording layer and having a light transmittance that varies depending on the intensity of the irradiated light. Solve the above problems.

In addition, an optical pickup tracking method for the optical recording media 50 and 50a described above,
When detecting the return light by irradiating the first pickup and the vicinity thereof with laser light from the optical pickup, the positions of both ends of the first track in the first track width direction are recognized and the Track the first track,
When the return light is detected by irradiating laser light from the optical pickup onto the second track and its vicinity, each of the first track adjacent to the second track on each side of the second track. The above-described problem is solved by providing a tracking method for an optical pickup that recognizes an end position and performs tracking of the second track.

Since the optical recording medium according to the present invention and the optical pickup tracking method for the optical recording medium have the above-described configuration and procedure,
(1) Even if the track density of the optical recording medium is narrowed to increase the recording density, no cross erase occurs during recording of the information signal.
(2) Even if the track density of the optical recording medium is narrowed to increase the recording density, tracking can be performed using a continuous servo. For this reason, a special tracking servo is not required, and a large-scale change or significant increase in cost does not occur in an apparatus related to tracking.

  Embodiments of an optical recording medium according to the present invention and an optical pickup tracking method for the optical recording medium will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view of an optical recording medium according to the present invention. FIG. 2 is a schematic sectional view of a second embodiment of the optical recording medium according to the present invention. 3 and 4 are diagrams for explaining the reduction of the diameter of the laser beam by the mask layer of the optical recording medium according to the present invention. FIG. 5 is a diagram for explaining the outline of the method for producing an optical recording medium according to the present invention. FIG. 6 is a diagram for explaining a tracking method for an optical recording medium according to the present invention.

  An optical recording medium 50 according to the present invention shown in FIG. 1 is sequentially formed on a substrate 11 as a base material provided with a concavity and convexity pattern formed concentrically or spirally on one side, and the concavity and convexity pattern of the substrate 11. A plurality of functional layers, and a protective layer 17 formed on the functional layers. The concavo-convex pattern of the substrate 11 includes a concave in-groove composed of a wide first track 11a and a narrow second track 11b, and a convex on-groove having the same width, and further includes a first track 11a and a second track. The tracks 11b are alternately arranged at equal intervals in the radial direction of the optical recording medium 50 via on-grooves having the same width. The functional layer on the concavo-convex pattern of the substrate 11 includes a reflective layer 12 formed on the substrate 11, a first dielectric layer 13 formed on the reflective layer 12, and a first dielectric layer 13 of the first track 11a. The first recording layer 14a formed thereon, the second recording layer 14b formed on the first dielectric layer 13 of the second track 11b, the first recording layer 14a, the second recording layer 14b, and the first dielectric It has the 2nd dielectric material layer 15 formed in the exposed part of the body layer 13, and the mask layer 16 as a light transmissive layer formed on the 2nd dielectric material layer 15. As shown in FIG. The first track 11a and each functional layer including the first recording layer 14a constitute a first recording track 20a capable of recording and reproducing information signals, and the second track 11b and the second recording layer 14b. Each of the functional layers included constitutes a second recording track 20b capable of recording and reproducing information signals in the same manner.

  At this time, the width of the first recording track 20a (width dimension E in FIG. 6 described later) is 100 nm or more that can be tracked by continuous servo, and the width of the second recording track 20b (width dimension D in FIG. 6 described later) is. The width of the on-groove which is a convex portion (width dimension C in FIG. 6 to be described later) is within the range of 50 nm to 75 nm in which recording / reproducing of an information signal is possible and the continuous servo cannot identify the unevenness, thereby preventing cross erase. It is set to 65 nm or more so that the effect is sufficiently exhibited. When all the above width dimensions have the minimum values, the pitch between the two first recording tracks 20a is 280 nm, and the track pitch between the first recording track 20a and the second recording track 20b is 140 nm, which is a half of that. This is a value less than 1/2 of 320 nm which is the track pitch of the conventional in-groove (on-groove) recording. Therefore, the optical recording medium 50 has a recording density approximately twice as high as that of the conventional recording medium and a high capacity thereby. Can be achieved.

  From the viewpoint of compatibility with conventional optical recording media, in an optical system having a laser beam wavelength of 405 nm and a numerical aperture NA of 0.85, the pitch between the first recording tracks 20a does not deviate significantly from 320 nm to 320 nm to 380 nm. In order to satisfy this, the width of the first recording track 20a is set to 100 nm to 160 nm, the width of the second recording track 20b is set to 50 nm, and the width of the on-groove which is a convex portion is set to a range of 65 nm to 85 nm. preferable. Furthermore, if the width of the first recording track 20a is 140 nm and the width of the on-groove which is a convex portion is 65 nm, the pitch between the first recording tracks 20a becomes 320 nm, and the width of the first recording track 20a Since the combined width of the second recording track 20b and the on-grooves on both sides thereof is 180 nm, and the difference between the two becomes as small as 40 nm, it is most preferable from the viewpoint of compatibility and tracking. Furthermore, in an optical system with a laser beam wavelength of 405 nm and a numerical aperture NA of 0.65, it is preferable to set the width of each track so that the pitch between the first recording tracks 20a does not deviate significantly from 400 nm.

  FIG. 1 shows an example in which the incident surface of the laser beam is on the surface of the protective layer 17 and the first recording track 20a and the second recording track 20b are on the in-groove side. In the case of the eleventh side, like the optical recording medium 50a shown in FIG. 2, the stacking order of the functional layers is reversed from that of the optical recording medium 50 of FIG. 1, and the first recording track 20a and the second recording track 20b is an on-groove side. Furthermore, in the optical recording media 50 and 50a, the example in which the first recording track 20a and the second recording track 20b are formed in the concave portion of the substrate 11 has been shown. However, the width of the convex portion of the substrate 11 is changed here. One recording track 20a and a second recording track 20b may be formed.

  As materials for the substrate 11 and the protective layer 17, various thermoplastic resins such as polycarbonate, polymethyl methacrylate, polystyrene, polycarbonate / polystyrene copolymer, polyvinyl chloride, alicyclic polyolefin, polymethylpentene, etc., thermosetting resin, ultraviolet curing Examples thereof include synthetic resins such as various light curable resins including resins and visible light curable resins, and ceramics such as soda lime glass, soda aluminosilicate glass, borosilicate glass, and quartz glass. Among these, polycarbonate is suitable as the material because it is excellent in moldability and productivity.

  When the thickness of the substrate 11 and the protective layer 17 corresponds to an optical system using a laser beam having a wavelength of 405 nm and an objective lens having a numerical aperture NA of 0.85, the substrate 11 on the incident surface side of the laser beam or the protective layer 17 is protected. The thickness of the layer 17 needs to be about 0.1 mm, and the total thickness of the optical recording media 50 and 50a needs to be about 1.2 mm. That is, in the case of the optical recording medium 50 in which the incident surface of the laser beam is on the protective layer 17 side, the thickness of the substrate 11 is about 1.1 mm and the thickness of the protective layer 17 is about 0.1 mm. At this time, it is preferable to use a synthetic resin substrate such as polycarbonate for the substrate 11 and a synthetic resin film or a photocuring resin such as an ultraviolet curable resin for the protective layer 17. On the contrary, in the case of the optical recording medium 50a in which the incident surface of the laser beam is on the substrate 11 side, the thickness of the substrate 11 is about 0.1 mm and the thickness of the protective layer 17 is about 1.1 mm. At this time, it is preferable to use a synthetic resin substrate such as polycarbonate for the protective layer 17 and a synthetic resin substrate or film for the substrate 11. Alternatively, a photocurable resin such as an ultraviolet curable resin may be cured while transferring the uneven pattern, and this may be used as the substrate 11. When the optical system uses a laser beam having a wavelength of 405 nm and an objective lens having a numerical aperture NA of 0.65, the thickness of the substrate 11 and the protective layer 17 is about 0.6 mm, and the optical recording medium 50, The total thickness of 50a is about 1.2 mm.

The first dielectric layer 13 and the second dielectric layer 15 have a function of preventing the first recording layer 14a, the second recording layer 14b, the substrate 11, the protective layer 17 and the like from being deformed by heat generated by laser light irradiation, A function as a multiple interference film, and further, when the reflective layer 12 is adjacent to each other, has a function of appropriately conducting the heat generated in the first recording layer 14a and the second recording layer 14b to the reflective layer 12 to dissipate heat. is doing. As materials for the first dielectric layer 13 and the second dielectric layer 15, SiO ₂ (silicon dioxide), SiO (silicon monoxide), ZnO (zinc oxide), TiO ₂ (titanium dioxide), Nb ₂ O ₅ (Niobium oxide), ZrO ₂ (zirconium oxide), MgO (magnesium oxide) and other oxides, ZnS (zinc sulfide), In ₂ S ₃ (indium sulfide), TaS ₄ (tantalum sulfide) and other sulfides, SiC ( Examples thereof include simple substances such as silicon carbide), TaC (tantalum carbide), WC (tungsten carbide), TiC (titanium carbide), and mixtures thereof. Among these, a mixed film of ZnS and SiO ₂ is suitable as the above-mentioned material because the recording sensitivity, C / N ratio, erasure rate and the like are hardly deteriorated even when recording and erasing are repeated.

  As the first recording layer 14a and the second recording layer 14b, Te (tellurium), Sb (ammotine), or the like that reversibly transitions between a crystalline phase and an amorphous phase depending on the power of the irradiated laser light. A known phase change material mainly composed of chalcogen can be used. Specifically, TeGeSb (tellurium / germanium / ammotine), TeSnSb (tellurium / tin / ammotin), TeGaSe (tellurium / gallium / selenium), InSb (indium / ammotin), TeAgInSb (tellurium / silver / indium / ammotin), CuAlTeSb (copper / aluminum / tellurium / ammotin) and the like can be mentioned.

  The reflective layer 12 reflects the transmitted light of the first recording layer 14a and the second recording layer 14b to the device side during the reproduction of the information signal and contributes to the improvement of the reading performance (reproduction S / N ratio). At the time of recording, it has a function of appropriately releasing and cooling the heat generated in the first recording layer 14a or the second recording layer 14b. The reflective layer 12 is made of Al (aluminum), Au (gold), Ag (silver), Cu (copper), Ti, Cr (chromium), Ni (nickel), Ta, Mo (molybdenum), Fe (iron). , Zn, Ga, As (arsenic), Pd (palladium), or the like, or an alloy composed of the metal and one or more metals including the metal, or the metal or the alloy and a metal oxide or metal nitride And a mixture of metal compounds such as metal carbide, metal sulfide, metal sulfide and metal fluoride. Among these, metals or alloys such as Al, Au, and Ag have both high reflectance and thermal conductivity, and are particularly suitable as the material for the reflective layer 12.

  As a material for the mask layer 16, a light transmittance changing material such as a cyclic organometallic complex whose phase is temporarily changed according to the intensity of irradiated light, a phase change material, or a photochromic is used. Specific examples of the light transmittance changing material using a cyclic organometallic complex include a zirconium porphyrin complex, which is a cyclic organometallic complex having two alkyl groups. When this zirconium porphyrin complex is irradiated with a laser beam having a wavelength of 400 nm or more, a zirconium polyphyrin complex having no alkyl group is generated, and the light transmittance increases according to the light intensity distribution of the laser beam. Then, when the laser beam is no longer irradiated, the alkyl group recombines and returns to the original light transmittance.

  It is also possible to use a phase change material as the light transmittance changing material. As described above, the phase change material reversibly transitions between a crystalline state having a low light transmittance and an amorphous state having a high transmittance by heat generated by laser light irradiation. Therefore, the phase change material is previously set in a crystalline state having a low light transmittance, and at the time of laser light irradiation, only a portion where the intensity of the laser light is high is set to a predetermined temperature or more to cause a phase transition. When the laser beam is no longer irradiated, the amorphous state portion is cooled and re-transformed into a crystalline state, and its transmittance returns to a low state. In this way, the phase change material can be used as a light transmittance changing material whose light transmittance temporarily changes according to the light intensity of the laser light. Since the change in light transmittance by this phase change material is made by heat, the dependence on the wavelength of light is low, and the same change can be obtained for laser light having a wavelength ranging from ultraviolet to infrared. Can do. Furthermore, since the phase change material can be formed by sputtering or vapor deposition, the mask layer 16 can be formed continuously during the formation of other functional layers, and the production efficiency is high.

  Next, the diameter reduction of the laser beam by the mask layer 16 will be described in more detail with reference to FIGS. A laser beam used for recording / reproducing of an optical recording medium usually has a light intensity distribution (for example, Gaussian distribution) as indicated by a solid line X in FIG. When such laser light is incident on the mask layer 16, the light transmittance of the mask layer 16 is greatly increased at the central portion of the laser light having a high light intensity, so that the light transmittance of the mask layer 16 is greatly increased. Since the temperature rise due to heat generation is small in the peripheral portion, the light transmittance does not change much. As a result, as shown by the broken line Y in FIG. 3, the light intensity of the transmitted light that has passed through the mask layer 16 decreases as the light intensity in the peripheral portion of the laser light is lower than that of the incident laser light. The distribution becomes sharper. Here, assuming that the light intensity capable of forming the recording mark on the recording layer is equal to or greater than the value Z in FIG. 3, the spot diameter of the laser beam having sufficient intensity for recording the information signal is the laser at the time of incidence. In light, it is in the range of x in FIG. 3, but after passing through the mask layer 16, it is reduced to the range of y in FIG.

  The change in the spot diameter due to the mask layer 16 described above is based on the assumption that the light transmittance characteristics of the light transmittance changing material used for the mask layer 16 are in a proportional relationship as shown by the broken line in FIG. This is about 3/4 of the laser beam. However, since the light transmittance characteristic of the actual light transmittance changing material has a curve like the solid line in FIG. 4, the spot diameter is substantially about 3/5 at the time of irradiation, and the mask layer 16 is reciprocated twice. The laser beam at the time of reproduction passing through is reduced in diameter to 1/3 to 1/2 of the irradiation time. For these reasons, by passing laser light through the mask layer 16, the spot diameter reaching the recording layer is reduced, and the track pitch, recording marks, and the like can be further miniaturized.

  The reflective layer 12, the first dielectric layer 13, and the second dielectric layer 15 constituting the optical recording media 50 and 50a are not essential, and the spot diameter is reduced to the above level by another method. The mask layer 16 may be omitted as long as it can be realized. Furthermore, other layers such as a heat diffusion layer and a transmittance adjusting layer can be appropriately added to the functional layers of the optical recording media 50 and 50a as necessary.

  Next, an outline of a method for manufacturing an optical recording medium according to the present invention is shown in FIG. First, as a substrate manufacturing process, as shown in FIG. 5A, the concave portions formed of the wide first tracks 11a and the narrow second tracks 11b are alternately continued through the convex portions having the same width. A substrate 11 having such a concavo-convex pattern is prepared. The substrate 11 is produced mainly by injection molding when the substrate 11 is made of synthetic resin and mainly by the photopolymer method when the substrate 11 is made of ceramic. When the thickness of the substrate 11 is thin, after applying a photo-curing resin such as an ultraviolet curable resin to a predetermined thickness, a stamper having a concave-convex pattern matrix is closely attached, and light in a predetermined wavelength region is directly applied. The substrate 11 may be cured by irradiation.

  Next, as a first film formation step, as shown in FIG. 5B, the reflective layer 12, the first dielectric layer 13, and the recording layer 14 having a predetermined layer thickness are sputtered on the uneven pattern of the substrate 11. The films are sequentially formed by a known film forming method such as a vapor deposition method or a vapor deposition method.

  Next, as a removing step after the formation of the recording layer 14, the recording layer 14 formed in the region other than the first track 11a and the second track 11b is removed, and as shown in FIG. The recording layer 14 is divided into a first recording layer 14a and a second recording layer 14b. As a selective removal method of the recording layer 14, ions that remove the recording layer 14 in a predetermined region by colliding krypton ions, argon ions, etc. accelerated by application of voltage with the recording layer 14 at an appropriate irradiation angle. In addition to the milling method, a reactive ion etching method or the like can be used. In particular, if the ion milling method is used, the apparatus can be installed in the sputtering apparatus, so that the first film forming process, the removing process, and the second film forming process described later can be performed continuously. Very high efficiency.

  Next, as a second film forming step, as shown in FIG. 5D, the first recording layer 14a, the second recording layer 14b, and the recording layer 14 are removed and exposed on the first dielectric layer 13. The second dielectric layer 15 is formed by a known film formation method such as sputtering or vapor deposition. When the mask layer 16 is a phase change material, the mask layer 16 is continuously formed on the second dielectric layer 15 after the second dielectric layer 15 is formed. When the mask layer 16 is a cyclic organometallic complex, photochromic, or the like, the substrate 11 is taken out after the second dielectric layer 15 is formed, and the mask is formed on the second dielectric layer 15 by a known method such as a spin coating method. Layer 16 is formed.

  Thereby, each functional layer including the first recording layer 14a is formed on the first track 11a of the substrate 11 to form the first recording track 20a. Each functional layer including the second recording layer 14b is formed on the second track 11b of the substrate 11 to form the second recording track 20b.

  Finally, as a protective layer forming step, a protective layer 17 is formed on the mask layer 16 as shown in FIG. The protective layer 17 can be formed by applying a photo-curing resin such as an ultraviolet-curing resin to a predetermined thickness by a spin coating method or the like and then curing. Further, the protective layer 17 may be formed by adhering a substrate, a film, or the like on the functional layer using an adhesive or a photo-curing resin.

  By the above procedure, the optical recording medium 50 in which the first recording track 20a and the second recording track 20b having two different widths are alternately arranged is manufactured.

  When an information signal is recorded on the optical recording medium 50 and the optical recording medium 50a, laser light whose intensity changes in two steps according to the information signal to be recorded is emitted from the protective layer 17 side in the optical recording medium 50. In the recording medium 50a, irradiation is performed from the substrate 11 side toward the first recording track 20a or the second recording track 20b. The irradiated laser light passes through the protective layer 17 or the substrate 11 and reaches the mask layer 16. The laser light reaching the mask layer 16 is reduced in diameter by the effect of the light transmittance change described above when passing through the mask layer 16, and then reaches the first recording layer 14a or the second recording layer 14b and reaches a predetermined level. A recording mark is formed. Therefore, the optical recording media 50 and 50a can satisfactorily form minute recording marks not only on the wide first recording track 20a but also on the narrow second recording track 20b. Similarly, since the spot diameter is reduced due to the light transmittance change effect of the mask layer 16 during reproduction, it is not affected by crosstalk from the adjacent recording track, and fine recording marks can be satisfactorily obtained. Can be played.

  Further, in the optical recording media 50 and 50a, the recording layer between the first recording track 20a and the second recording track 20b is removed by a removing process performed after the recording layer 14 is formed. For this reason, the heat generated in the first recording layer 14a or the second recording layer 14b during recording is not conducted to the adjacent recording track through the recording layer, thereby preventing the occurrence of cross erase.

  Here, in order to verify the recording / reproducing characteristics of the optical recording medium according to the present invention, the information signal is recorded on the optical recording medium 50 and the conventional optical recording medium having a track pitch of 320 nm by changing the length of the recording mark. Then, the jitter values of these reproduced signals were measured. The measurement results are shown in Table 1. In the verification, in order to investigate the influence of the cross erase, the measurement was performed after recording the information signal on the recording tracks adjacent to the recording track used for the measurement. In addition, the formation of a recording mark of 100 nm or less on a conventional optical recording medium was performed under special conditions using experimental equipment.

表１より、本発明の光記録媒体５０である試験ディスクＡは、記録マークの長さが１５０ｎｍから従来の記録マーク半分以下の長さである７０ｎｍまで、その再生信号のジッタ値は１０％以下という良好な値を示した。これに対して、従来の光記録媒体である試験ディスクＢは、記録マークの長さが１００ｎｍで、その再生信号のジッタ値は良否判定基準の１０％を大きく超えた１８．８％に悪化した。このことから、光記録媒体５０は従来よりも微細な記録マークによる情報信号の記録及び再生を、良好に行えることがわかる。このことは、光記録媒体５０のマスク層１６によるスポット径の小径化と記録層の分断による熱伝導の低減による、記録時のクロスイレースと再生時のクロストークの防止効果によるものと考えられる。

From Table 1, the test disk A, which is the optical recording medium 50 of the present invention, has a recording mark length of 150 nm to 70 nm, which is half the length of the conventional recording mark, and the jitter value of the reproduced signal is 10% or less. A good value was shown. On the other hand, the test disc B, which is a conventional optical recording medium, has a recording mark length of 100 nm, and the jitter value of the reproduced signal has deteriorated to 18.8%, which greatly exceeds 10% of the pass / fail criterion. . From this, it can be seen that the optical recording medium 50 can record and reproduce information signals with finer recording marks than before. This is considered to be due to the effect of preventing the cross erase at the time of recording and the crosstalk at the time of reproduction by reducing the spot diameter by the mask layer 16 of the optical recording medium 50 and reducing the heat conduction by dividing the recording layer.

  Next, the tracking method of the optical recording medium according to the present invention will be described with reference to FIG. In FIG. 6, the description of each functional layer and protective layer 17 is omitted for the sake of explanation.

  First, the width dimension E of the wide first recording track 20a has a value of 100 nm or more that can be tracked by continuous servo. Therefore, the tracking of the laser beam L1 applied to the first recording track 20a is performed based on the return light signals from the side wall portions S1 and S2 on both sides of the first recording track 20a, as in the case of the normal continuous servo tracking. . At this time, even if the laser beam used for tracking is applied to the second recording track 20b, the width D of the second recording track 20b is in the range of 50 nm to 75 nm where the unevenness cannot be identified by continuous servo. It does not affect the tracking of one recording track 20a.

  The tracking of the second recording track 20b having a narrow width reverses the polarity of the unevenness as that of the tracking of the first recording track 20a, and the convex portions (on grooves) on both sides of the second recording track 20b and the first recording track 20a. This is performed based on the return light signal from the side walls S1 and S3. That is, the continuous servo that cannot recognize the narrow second recording track 20b recognizes the second recording track 20b and the convex portions on both sides as if it were one on-groove, and uses this virtual on-groove. Tracking is performed. This means that tracking is performed with respect to the center of the virtual on-groove, that is, the second recording track 20b sandwiched between the convex portions having the same width C. As a result, the second recording track 20b having a narrow width can be tracked by continuous servo, and the center of the laser beam L2 can be stably irradiated.

  The tracking of the optical recording medium of the present invention is performed as if it were an optical recording medium for land-and-groove recording. However, since the recording track is either in-groove or on-groove, the information signal recording / reproducing system is a recording track. There is no need to switch every time. For this reason, the apparatus involved in the information signal recording / reproducing system and the control thereof are not complicated while having a recording capacity equivalent to that of land and groove recording.

  From the above, according to the optical recording medium according to the present invention, since there is no recording layer between the first recording track 20a and the second recording track 20b, the first recording layer 14a or the second recording layer is recorded during recording. The heat generated in 14b is not conducted to the adjacent recording track through the recording layer. For this reason, the occurrence of cross erase can be prevented, and an optical recording medium excellent in cross erase resistance can be obtained.

  Further, according to the optical recording medium and the optical recording medium tracking method of the present invention, the recording track is composed of the wide first recording track 20a and the narrow second recording track 20b, which have the same width. Are alternately arranged at the same interval via the convex portions (or concave portions) of the recording medium, and by optimizing the width of each track, not only the wide first recording track 20a but also the narrow second recording track 20b. Can also be tracked by continuous servo.

  Also, the method for manufacturing an optical recording medium according to the present invention forms two layers of the first recording track 20a and the second recording track having different widths by forming a functional layer on the substrate 11 having a concavo-convex pattern having a predetermined dimension. An optical recording medium in which 20b is alternately arranged can be manufactured. Further, by providing a removal step after the formation of the recording layer 14 constituting the optical recording medium, the recording layer between the first recording track 20a and the second recording track 20b can be selectively removed. As a result, it is possible to produce an optical recording medium with high recording density that is excellent in cross erase resistance and capable of tracking by continuous servo.

  In this example, the rewritable optical recording medium has been described as an example. However, the present invention can be applied to a write-once optical recording medium, and the present invention does not depart from the gist of the present invention. It is possible to carry out by changing the range.

1 is a schematic cross-sectional view of an optical recording medium according to the present invention. It is a schematic cross section of the 2nd form of the optical recording medium based on this invention. It is a figure explaining diameter reduction of the laser beam by the mask layer of the optical recording medium based on this invention. It is a figure explaining diameter reduction of the laser beam by the mask layer of the optical recording medium based on this invention. It is a figure explaining the outline of the manufacturing method of the optical recording medium based on this invention. It is a figure explaining the tracking method of the optical recording medium based on this invention.

Explanation of symbols

11 Substrate
11a First track
11b Second track
14a First recording layer
14b Second recording layer
20a First recording track
20b Second recording track
50, 50a Optical recording medium
S1, S2, S3 Side walls of the first recording track

Claims (3)

In optical recording media,
On the substrate
A first track having a first track width;
A second track having a second track width narrower than the first track width;
A recording layer provided independently for each of the first track and the second track;
Have
The optical recording medium, wherein the first track and the second track are alternately provided at equal intervals in the first track width direction and the second track width direction, respectively. The optical recording medium according to claim 1, further comprising: a light transmission layer provided on the recording layer and having a light transmittance that changes in accordance with the intensity of the irradiated light. An optical pickup tracking method for the optical recording medium according to claim 1 or 2,
When detecting the return light by irradiating the first pickup and the vicinity thereof with laser light from the optical pickup, the positions of both ends of the first track in the first track width direction are recognized and the Track the first track,
When the return light is detected by irradiating laser light from the optical pickup onto the second track and its vicinity, each of the first track adjacent to the second track on each side of the second track. A tracking method for an optical pickup, characterized in that the second track is tracked by recognizing an end position.

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