JP4332483B2 - Information recording medium - Google Patents

Description

  The present invention relates to an information recording medium capable of optically recording information, and more particularly to an information recording medium having a plurality of information recording layers.

  Conventionally, CD (Compact Disc) has been widely used as a large-capacity information recording medium. In recent years, DVD (Digital Video Disc or Digital Versatile Disc) has attracted attention as a further large-capacity information recording medium. A CD has a maximum recording capacity of about 650 MB (megabytes), whereas a DVD can realize a recording capacity of several GB (gigabytes) or more due to its structural characteristics. According to the specifications of a single-sided single-layer DVD having only one recording layer currently commercialized and a single-sided dual-layer DVD having two recording layers on one side, the maximum recording capacity of each is about 4. 7GB, about 8.7GB.

  By the way, in a DVD-R (recordable DVD) capable of additionally recording information, it is necessary to perform high-density recording, and information is recorded or reproduced with high reproducibility, that is, a highly reliable and high quality DVD. Providing -R is an important issue.

  In particular, in order to realize a single-sided dual-layer DVD-R capable of recording a large amount of information at high density, beam light is made incident on each recording layer that is opposed to each other and is applied to each recording layer. It is necessary to write information exclusively, and its structure is extremely important.

  When a single-sided dual-layer DVD-R is realized with a laminated structure of two recording layers, in order to obtain the same recording signal polarity as that of the first recording layer, the second recording layer is formed with a shallow groove on-groove (On-Groove ) A method of creating a structure is known. The on-groove structure means that the groove corresponding to the information recording portion has a convex shape and the land has a concave shape with respect to the spin coating direction when the recording layer is formed by spin coating of a dye material. On the other hand, a groove having a concave groove and a land convex shape with respect to the spin coat direction is referred to as an in-groove.

  When an on-groove structure with a shallow groove is employed, the dye material may accumulate more than the thickness of the groove between the grooves (positions corresponding to lands) due to the characteristics of spin coating. In this case, there is a problem in that the recording operation deteriorates the coloring matter between the grooves, and the recording quality is remarkably deteriorated.

  In view of such a problem, Patent Document 1 discloses a method of forming the second recording layer with a deep groove in-groove structure. However, if the second recording layer is formed with a deep groove in-groove structure as in Patent Document 1, the optical phase difference between the groove and the land becomes remarkably large, so that incident light is scattered on the inclined surface of the deep groove. As a result, there is a problem that the reflectivity of the disk is significantly reduced.

Japanese Patent Laid-Open No. 2001-23237

  The present invention has been made in view of the above points, and an object of the present invention is to provide a two-layer information recording medium having a highly reliable structure.

The invention according to claim 1 is an information recording medium, wherein a first information recording / reproducing unit in which a first transparent substrate, a first recording layer, and a semi-transmissive film layer are sequentially laminated, and a second transparent A second information recording / reproducing unit in which a substrate, a reflective film layer, and a second recording layer are sequentially laminated, and a transparent adhesive layer that bonds the semi-transmissive film layer and the second recording layer facing each other, Each of the first recording layer and the second recording layer has a groove part for writing information and a land part adjacent to the groove part, and the thickness of the groove part of the second recording layer is the first recording layer. rather thin than the thickness of the groove portion of the first recording layer, the depth of the groove of the second transparent substrate is characterized in that less than the depth of the groove of the first transparent substrate.

In one aspect of the present invention, an information recording medium includes a first information recording / reproducing unit in which a first transparent substrate, a first recording layer, and a semi-transmissive film layer are sequentially laminated, a second transparent substrate, A first information recording / reproducing unit in which a film layer and a second recording layer are sequentially laminated; and a transparent adhesive layer that faces and bonds the semi-transmissive film layer and the second recording layer. Each of the layer and the second recording layer has a groove portion for writing information and a land portion adjacent to the groove portion, and the thickness of the groove portion of the second recording layer is the first recording layer in most thin than the thickness of the groove portion, the depth of the groove of the second transparent substrate is smaller than the depth of the groove of the first transparent substrate.

The information recording medium can be configured as, for example, a DVD-R, DVD-RW, or other two-layer disc-shaped recording medium. By forming the first information recording / reproducing unit and the second information recording / reproducing unit separately, and integrating the first information recording / reproducing unit and the second information recording / reproducing unit with the transparent adhesive layer, An information recording medium having two recording layers can be easily manufactured. Each information recording / reproducing unit has a groove as a region where information is recorded and a land portion adjacent thereto. The thickness of the groove portion of the second recording layer is thinner than the thickness of the groove portion of the first recording layer, the depth of the second transparent substrate groove is minor than the depth of the groove of the first transparent substrate structure Is done. As a result, the optical phase difference between the groove portion and the land portion of the second recording layer can be reduced, and scattering of incident light on the inclined surface of the groove portion can be prevented, and the reflectance of the recording medium can be reduced. Can be prevented.

  In one aspect of the above information recording medium, the optical phase difference between the unrecorded groove portion in the first recording layer and the land portion in the first recording layer is the recorded groove in the second recording layer. Is equal to the optical phase difference between the portion and the land portion in the second recording layer, and the optical phase difference between the unrecorded groove portion in the second recording layer and the land portion in the second recording layer is It is equal to the optical phase difference between the recorded groove portion in the first recording layer and the land portion in the first recording layer. Thereby, the amplitude of the reproduction signal obtained by reading the recording information of the first recording layer can be matched with the amplitude of the reproduction signal obtained by reading the recording information of the second recording layer. Therefore, the recording information of the first recording layer and the second recording layer can be processed by the same reproduction processing circuit or the like. This also ensures compatibility with the single-layer information recording medium in the playback apparatus.

  In a preferred example, the groove portion of the first recording layer has a concave shape on the first transparent substrate side than the land portion of the first recording layer, and the groove portion of the second recording layer is the second portion. A convex shape is formed on the first transparent substrate side from the land portion of the recording layer. In another preferred example, the groove portion of the first recording layer has a shape protruding from the land portion of the first recording layer toward the first transparent substrate, and the groove portion of the second recording layer is A concave shape is formed on the first transparent substrate side from the land portion of the second recording layer.

  Preferred embodiments of the present invention will be described below with reference to the drawings. In the following description, as an embodiment of the information recording medium according to the present invention, a write-once DVD (hereinafter referred to as DVD-R) capable of information recording (information writing) in addition to information reproduction (information reading) will be described. To do.

  FIG. 1 is a longitudinal sectional view showing the main structure of a DVD-R according to this embodiment. More specifically, a cross-sectional structure when a disc-shaped DVD-R is cut in the thickness direction along the radial direction is shown.

  In FIG. 1, a DVD-R has a first recording layer 2, a semi-transmissive film layer 3, an adhesive layer 4, a second recording layer 5, a reflective film on a first transparent substrate 1 on which beam light described later is incident. It has an integrated structure in which the layer 6 and the second transparent substrate 7 are laminated, and has a thickness of about 1.2 mm as a whole.

  The transparent substrate 1 has a thickness of about 0.55 mm, and the recording beam light or the reading beam light 11 and 12 (through the objective lenses 9 and 10 provided in the optical pickup (not shown) are incident. Hereinafter, these lights are simply referred to as “beam light”) and are made of a hard material such as hard plastic that is transparent.

  In FIG. 1, for convenience of explanation, the beam lights 11 and 12 are individually incident by the two objective lenses 9 and 10, respectively. However, in the actual optical pickup, the first recording is performed by one objective lens. By adjusting the focus on the layer 2 and the second recording layer 6, the light beam is incident.

  The first recording layer 2 is formed of an organic dye material and is laminated on the transparent substrate 1 integrally. The semi-transmissive film layer 3 is formed of a dielectric thin film such as SiC (silicon carbide) or Au (gold) having translucency with respect to the beam lights 11 and 12 and is integrally formed with the first recording layer 2. Are stacked. The transparent substrate 1, the first recording layer 2 and the semi-transmissive film layer 3 constitute a first information recording / reproducing unit (reference numeral omitted).

  The transparent substrate 7 has a thickness of about 0.6 mm, and is formed of a hard material such as a hard plastic like the transparent substrate 1. The reflective film layer 6 is formed of Al (aluminum) or the like that totally reflects the beam lights 11 and 12 incident through the objective lenses 9 and 10. The second recording layer 5 is formed of an organic dye material in the same manner as the first recording layer 2 and is laminated integrally with the reflective film layer 6. The transparent substrate 7, the reflective film layer 6 and the second recording layer 5 constitute a second information recording / reproducing unit (reference numeral omitted).

  The first and second information recording / reproducing parts are bonded together by an adhesive layer 4 having a predetermined thickness so that the semi-transmissive film layer 3 and the second recording layer 5 are opposed to each other.

  For the adhesive layer 4, a resin transparent to the beam lights 11 and 12, for example, a two-component mixed ultraviolet curing resin is used. Also, a so-called pressure-sensitive adhesive sheet is produced by applying an acrylic pressure-sensitive adhesive material impregnated with a solvent on both surfaces of a thin film-like transparent sheet. The film layer 3 and the second recording layer 5 are adhered.

  The thickness from the first recording layer 2 to the reflective film layer 6 is set to about 50 μm. Here, the first recording layer 2 includes a groove G and a land L that spirally extend along a direction (so-called track direction) scanned by the light beam 11 during information recording or information reproduction. Is formed. The grooves G in the first recording layer 2 are arranged along the radial direction and formed in a convex shape toward the transparent substrate 1 side (lower side in the figure), and the land L is on the transparent substrate 1 side (with respect to the groove G) ( It is formed in a concave shape toward the lower side in the figure. Although not shown, a wobble for defining a physical format is formed on the side wall of the land L.

  On the other hand, the grooves G and lands L in the second recording layer 5 extend spirally along the track direction so as to face the grooves G and lands L in the first recording layer 2. The phase structure of is reversed.

  That is, the grooves G in the second recording layer 5 are arranged along the radial direction and formed in a convex shape toward the transparent substrate 7 side (upper side in the figure), and the land L is transparent to the groove G. It is formed in a concave shape toward the 7 side (upper side in the figure). A wobble for defining a physical format is also formed on the side wall of the land L in the second recording layer 5.

  As described above, as a result of the phase structures of the grooves G and lands L in the first and second recording layers 2 and 5 being reversed, the beam light 11 is emitted from the first recording layer during information recording or information reproduction. The light beam 12 is incident on the concave groove G of the second recording layer 5.

  Next, a manufacturing process of the DVD-R having such a structure will be described. First, the first information recording / reproducing unit and the second information recording / reproducing unit are formed as separate intermediate products.

  That is, in the manufacturing process of the first information recording / reproducing unit, a spiral groove for forming the groove G is formed on the surface of the transparent substrate 1 by lithography, and then the transparent substrate 1 is formed using a spin coating method. A first recording layer 2 is formed thereon. Accordingly, the groove G is formed by the organic dye-based material accumulated in the valley portion of the spiral groove, and the land L is formed by the organic dye-based material attached to the mountain portion between the spiral grooves.

  Here, the thickness dG1 of the groove G and the thickness dL1 of the land L are set to dG1> dL1, as shown in an enlarged view in FIG. 2, and the rotational speed at the time of spin coating, the organic dye-based material By adjusting the concentration and the like, the relationship dG1> dL1 is automatically obtained only by performing spin coating.

  Next, the first information recording / reproducing unit is manufactured by forming the semi-transmissive film layer 3 on the first recording layer 2 by sputtering.

  On the other hand, in the manufacturing process of the second information recording / reproducing unit, a spiral groove for forming the groove G is formed on the surface of the transparent substrate 7 by lithography.

  Next, after the reflective film layer 6 is formed on the surface of the transparent substrate 7 by sputtering, the second recording layer 5 is formed on the reflective film layer 6 by spin coating. As a result, the groove G is formed by the organic dye-based material accumulated in the valley portion of the spiral groove of the reflective film layer 6, and the land L is formed by the organic dye-based material attached to the mountain portion between the spiral grooves.

  Here, the thickness dG2 of the groove G and the thickness dL2 of the land L are set to dG2> dL2. Also in this case, the relationship of dG2> dL2 is automatically obtained only by performing the spin coating by adjusting the rotation speed at the time of spin coating, the concentration of the organic dye-based material, and the like.

  Next, by interposing an ultraviolet curable resin or an adhesive sheet as an adhesive layer between the semi-transmissive film layer 3 and the second recording layer 5 of the first and second information recording / reproducing parts thus manufactured, The DVD-R is manufactured by integrating the first and second information recording / reproducing units.

  Thus, in this embodiment, both the first recording layer 2 and the second recording layer are configured to have an in-groove structure. Therefore, the thickness of the land L between the grooves G can be reduced, and the deterioration of the recording quality due to the alteration of the dye of the land L during the recording operation can be prevented.

  Further, as shown in FIG. 2, the thickness dG2 of the groove G of the second recording layer 5 is set to be thinner than the thickness dG1 of the groove G of the first recording layer 2, and the land L of the second recording layer 5 The thickness dL2 is also set smaller than the thickness dL1 of the land L of the first recording layer 2. Thus, by setting the groove of the second recording layer 5 thin, the inclined surface of the groove of the second recording layer 5 (see the region 50 indicated by the broken line) can be reduced. The optical phase difference between the two can be reduced. Therefore, scattering of incident light on such an inclined surface can be suppressed, and a decrease in the reflectivity of the disk can be suppressed.

  Next, operations and characteristics of the first recording layer 2 and the second recording layer 5 will be described in detail. 3 shows a partial configuration and optical phase of the first recording layer 5, FIG. 3 (a) shows an unrecorded state, and FIG. 3 (b) shows a recorded state.

  3 shows a partial configuration and optical phase of the first recording layer 2, FIG. 3 (a) shows an unrecorded state, and FIG. 3 (b) shows a recorded state.

  As shown in FIG. 3A, when the two grooves Ga and Gb shown as representatives are not recorded, the organic dye-based material does not change optically. The optical phases La1 when reflected by the semi-transmissive film layer 3 through the grooves Ga and Gb and returned to the transparent substrate 1 through the grooves Ga and Gb are equal.

  The “optical phase” is a value obtained by converting an optical distance into a phase based on a wavelength. The “optical distance” is generally given by the product of the refractive index of an object through which light passes and the distance of light passing through the object. For example, if the refractive index of an object is N and the distance of light passing through the object is D, the optical distance is given by OD = N × D. If the wavelength of light is λ, the optical phase is given by OP = OD × 2π / λ.

  On the other hand, when the groove Ga is in an unrecorded state and the groove Gb is in a recorded state, as shown in FIG. 3B, the optical phase of the groove Gb changes to Lb1. As a result, an optical phase difference φ1 (= Lb1−La1) is generated between the grooves Ga and Gb.

  That is, the groove Gb on which information is recorded changes so that the organic dye material receives thermal energy from the beam light 11 at the time of writing information and the refractive index becomes small. As a result, an optical phase difference φ1 is generated.

  4 shows a partial configuration and optical phase of the second recording layer 5, FIG. 4 (a) shows an unrecorded state, and FIG. 4 (b) shows a recorded state.

As shown in FIG. 4A, when the two grooves Ga and Gb shown as representatives are both unrecorded, the organic dye-based material does not change optically. The optical phases -La2 when reflected by the reflective film 6 through the grooves Ga and Gb and returned to the transparent substrate 1 through the grooves Ga and Gb again become equal. Since the second recording layer 5 has a layer structure opposite to that of the first recording layer 2 with respect to the incident direction of the light beam 11, the optical phase generated by the groove has an inverse characteristic.

  On the other hand, when the groove Ga is in an unrecorded state and the groove Gb is in a recorded state, as shown in FIG. 4B, the optical phase of the groove Gb changes to -Lb2. As a result, an optical phase difference φ2 (= −Lb2 + La2) is generated between the grooves Ga and Gb.

  That is, the groove Gb on which information is recorded changes so that the organic dye material receives thermal energy from the beam light 11 at the time of writing information and the refractive index becomes small. As a result, an optical phase difference φ2 is generated.

  Next, the optical characteristics of the first recording layer 2 and the second recording layer 5 will be described. FIG. 5 is a diagram showing the optical characteristics of the first recording layer 2 and the second recording layer 5 by RF signals and push-pull signals obtained by reproducing the DVD-R.

  The reflected light when the information reading beam 11 is applied to the groove G is received by a photodetector having a light receiving area (two light receiving areas) divided into two, and detected and output in each light receiving area. The sum (S1 + S2) of the detection signals S1 and S2 is an RF signal, and the difference (S1−S2) between the detection signals S1 and S2 is a push-pull signal.

  When the wavelength of the light beam 11 is λ, the effective refractive index of the transparent substrate 1 is a constant N, and the distance in the direction of the transparent substrate 1 with respect to the lower surface position of the land L on the transparent substrate 1 side is represented by a variable D, The optical distance in the optical phase structure is N × D, and the optical phase difference φ given to the wavefront of the beam 11 by the reflection is φ = 4 × π × N × D / λ. In addition, the optical distance of reciprocation until the beam light 11 enters the groove G, is reflected, and returns is 2 × N × D.

  The RF signal and push-pull signal when the optical distance of the light beam 11 in the unrecorded groove Ga and the recorded groove Gb (the optical distance between the incident and reflected reciprocation) 2 × N × D is used as a parameter. The change in amplitude is shown in FIG. The RF signal is shown as a graph 110 and the push-pull signal is shown as a graph 120. The amplitude changes of these RF signals and push-pull signals are normalized based on the maximum amplitude value of the RF signal.

  As shown in FIG. 3, the optical phase of the unrecorded groove Ga of the first recording layer 2 is La1, and the amplitude value of the RF signal at that time is Pa1. On the other hand, the optical phase of the groove Gb in the recorded state of the first recording layer 2 is Lb1, and the amplitude value of the RF signal at that time is Pb1. Therefore, the absolute value of the difference between the amplitude values Pa1 and Pb1: δM1 (= | Pa1−Pb1 |) is the signal amplitude of the information recorded in the first recording layer 2.

  Further, as shown in FIG. 4, the optical phase of the unrecorded groove Ga of the second recording layer 5 is La2, and the amplitude value of the RF signal at that time is Pa2. On the other hand, the optical phase of the groove Gb in the recorded state of the second recording layer 5 is Lb2, and the amplitude of the RF signal at that time is Pb2. Therefore, the absolute value of the difference between the amplitude values Pa2 and Pb2: δM2 (= | Pa2-Pb2 |) is the signal amplitude of the information recorded in the second recording layer 5.

  Thus, the signal amplitude of the information recorded in the first recording layer 2 and the second recording layer 5 is defined by the optical phase differences φ1 and φ2 in the respective layers. Here, in an actual DVD-R, it is preferable that the signal amplitude obtained when information recorded on the first recording layer and the second recording layer is reproduced is equal. This is because in the DVD-R playback device, the playback signal obtained from the first recording layer and the playback signal obtained from the second recording layer are processed by the same playback processing circuit.

  From this point of view, in the present embodiment, the amplitudes δM1 and δM2 of the reproduction RF signal obtained when the recorded information is reproduced in the first recording layer 2 and the second recording layer 5 are made equal. That is, the optical phase difference φ1 of the first recording layer is made equal to the optical phase difference φ2 of the second recording layer. Therefore, in this embodiment, the magnitude (absolute value) of the optical phase La1 of the groove Ga in the unrecorded state of the first recording layer 2 is the optical value of the groove Gb in the recorded state of the second recording layer 5. To be equal to the magnitude (absolute value) of the target phase -Lb2. Further, the magnitude (absolute value) of the optical phase Lb1 of the groove Gb in the recorded state of the first recording layer 2 is the magnitude of the optical phase −La2 of the groove Ga in the unrecorded state of the second recording layer 5. To be equal to the absolute value. That is, in FIGS. 3 and 4, the thickness dG1 of the first recording layer 2 and the thickness dG2 of the second recording layer 5 are set so that La1 = Lb2 and Lb1 = La2.

  By doing so, as understood from FIG. 5, the amplitudes δM1 and δM2 of the reproduction RF information from the first recording layer and the second recording layer can be made equal, and the same reproduction provided in the reproduction apparatus Recording information can be reproduced from any recording layer using the processing circuit.

  As can be understood from FIG. 5, the reproduced RF signals from the first recording layer and the second recording layer have the same signal amplitude but the opposite polarities. Therefore, processing such as supplying one of the reproduction RF signals from the first recording layer or the second recording layer to the reproduction processing circuit in an inverted state, or inverting and outputting the reproduction signal output from the reproduction processing circuit is performed. Necessary.

(Specific configuration example)
Next, a specific configuration example of the first recording layer and the second recording layer that satisfies the above conditions will be described. FIG. 6 shows a configuration example of the first recording layer 2. The example of FIG. 6 has the same configuration as that of the single-layer DVD-R, and the values are as follows.
・ Track pitch: 0.74μm
・ Groove width: 0.3μm
・ Groove depth: 145 nm
Groove thickness (thickness of the first recording layer at the groove position): 70 nm
Land thickness (thickness of the first recording layer at the land position): 10 nm
7A to 7C show the relationship between the modulation depth, push-pull signal amplitude, and reflectance (unrecorded portion) by the first recording layer 2 having the above structure, and the groove thickness and land thickness. Show. The “modulation degree” is the ratio (I ₁₄ / I _14H ) of the difference I _14H between the peak value of the reproduction signal with respect to the maximum recording mark (14T mark) and the zero level and the amplitude I ₁₄ of the reproduction signal with respect to the maximum recording mark. ), And the DVD-R standard requires 60% or more.

  In FIG. 7A, at the point 121 corresponding to the condition of the groove thickness = 70 nm and the land thickness = 10 nm as described above, the degree of modulation is about 60%, which satisfies the requirements of the DVD-R standard. The value is shown.

  In FIG. 7B, a value of about 0.35 is obtained at a point 122 corresponding to the same condition. In FIG. 7C, a reflectance of about 0.65 is obtained at a point 123 corresponding to the same condition.

Next, as shown in FIG. 8, the second recording layer is
・ Track pitch: 0.74μm
・ Groove width: 0.3μm
・ Groove depth: 40nm
9A to 9C show the results of obtaining the modulation degree, push-pull signal amplitude, and reflectance (unrecorded portion) by changing the groove thickness and the land thickness.

  In FIG. 9A, a groove thickness of 60 nm and a land thickness of 20 nm (corresponding to the point 131) are obtained as an example of a condition that satisfies a modulation degree of about 60% as in the first recording layer 2. Under this condition, as shown in FIG. 8, the difference between the groove thickness and the land thickness of the second recording layer 5 is about 40 nm, and the reflection of incident light by the inclined surface of the groove is suppressed.

  Under this condition, the push-pull signal amplitude is about 0.30 as indicated by a point 132 in FIG. 9B, and the reflectance is about 0.60 as indicated by a point 133 in FIG. 9C. These are all acceptable.

  As described above, according to the present embodiment, the first recording layer 2 has the on-groove structure, the second recording layer 5 has the in-groove structure, and the groove depth of the second recording layer 5 is the first recording layer 2. It is configured to be smaller than the groove depth. By forming the second recording layer in an in-groove structure, it is possible to prevent the land portion from being formed thicker than necessary by spin coating during film formation, and it is possible to suppress a decrease in recording quality. Further, by reducing the groove depth of the second recording layer, it is possible to prevent scattering of incident light on the inclined surface of the groove and to suppress a decrease in reflectance.

  Furthermore, in this embodiment, the optical phase of the unrecorded groove of the first recording layer 2 is equal to the optical phase of the recorded groove of the second recording layer 5, and the first recording layer 2 The thicknesses of the first and second recording layers are set so that the optical phase of the recorded groove is equal to the optical phase of the unrecorded groove of the second recording layer 5. Thereby, the reproduction RF signal amplitude from the first recording layer and the reproduction RF signal amplitude from the second recording layer can be made equal, and the reproduction RF signals from both recording layers are processed by the same reproduction processing circuit. Recorded information can be reproduced.

(Modification)
In the above embodiment, as shown in FIG. 1, the first recording layer 2 and the second recording layer 5 have the grooves G and the lands L in the geometrical uneven structure, but the first recording layer 2 has the opposite phase. The positions of the grooves G and lands L in the radial direction of the second recording layer 5 are in phase with the incident directions of the beam lights 11 and 12. However, the present invention is not limited to such a structure. As shown in FIG. 10, the positions of the grooves G and lands L of the first recording layer 2 and the second recording layer 5 in the radial direction are set to the beam light 11, You may arrange | position 90 degrees out of phase with respect to 12 incident directions.

  Further, as shown in FIG. 11, the groove G of the first recording layer has a concave shape facing the transparent substrate 1 side, and the groove G of the second recording layer 5 has a convex shape facing the transparent substrate 1 side. Further, the grooves G of the first and second recording layers 2 and 5 may be formed in the same phase in the radial direction. Further, as shown in FIG. 12, the groove G of the first recording layer has a concave shape facing the transparent substrate 1 side, and the groove G of the second recording layer 5 has a convex shape facing the transparent substrate 1 side. Further, the grooves G of the first and second recording layers 2 and 5 may be formed with a 90 ° phase shift in the radial direction.

  In the above embodiment, the DVD-R has been described as an example of an information recording medium to which the present invention is applied. However, the present invention is also applied to a double-layer DVD-RW or DVD-RAM capable of rewriting information. Can be applied.

It is sectional drawing which shows typically the structure of DVD-R which concerns on the Example of this invention. FIG. 2 is an enlarged sectional view of a part of the DVD-R shown in FIG. 1. 2 shows a cross-sectional structure and optical phase characteristics of a first recording layer in an unrecorded state and a recorded state. The cross-sectional structure and optical phase characteristics of the second recording layer in an unrecorded state and a recorded state are shown. It is a graph which shows the relationship between the optical phase of the groove | channel in a 1st and 2nd recording layer, a reproduction | regeneration RF signal, and a push pull signal. The specific structure of the 1st recording layer by a suitable specific structural example is shown. FIG. 7 is a graph showing the relationship between the modulation depth, push-pull signal amplitude and reflectance, and the groove thickness and land thickness according to the specific configuration example shown in FIG. 6. The specific structure of the 2nd recording layer by a suitable specific structural example is shown. FIG. 9 is a graph showing the relationship between the modulation depth, push-pull signal amplitude, and reflectance, and the groove thickness and land thickness according to the specific configuration example shown in FIG. 8. It is sectional drawing which shows typically the other structure of DVD-R which concerns on the Example of this invention. It is sectional drawing which shows typically other structure of DVD-R which concerns on the Example of this invention. It is sectional drawing which shows typically other structure of DVD-R which concerns on the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st transparent substrate 2 ... 1st recording layer 3 ... Semi-transmissive film layer 4 ... Adhesive layer 5 ... 2nd recording layer 6 ... Reflective film layer 7 ... 2nd transparent substrate 9, 10 ... Objective lens 11, 12 ... beams G, Ga, Gb ... groove L ... land

Claims (4)

A first information recording / reproducing unit in which a first transparent substrate, a first recording layer, and a semi-transmissive film layer are sequentially laminated;
A second information recording / reproducing unit in which a second transparent substrate, a reflective film layer, and a second recording layer are sequentially laminated;
A transparent adhesive layer for laminating the semipermeable membrane layer and the second recording layer facing each other,
Each of the first recording layer and the second recording layer has a groove portion for writing information, and a land portion adjacent to the groove portion,
The thickness of the groove portion of the second recording layer is rather thin than the thickness of the groove portion of the first recording layer,
The information recording medium according to claim 1, wherein the groove depth of the second transparent substrate is smaller than the groove depth of the first transparent substrate .   The optical phase difference between the unrecorded groove portion in the first recording layer and the land portion in the first recording layer is the difference between the recorded groove portion in the second recording layer and the land in the second recording layer. The optical phase difference between the unrecorded groove portion in the second recording layer and the land portion in the second recording layer is equal to the optical phase difference between the recorded portion and the recorded portion in the first recording layer. The information recording medium according to claim 1, wherein the information recording medium is equal to an optical phase difference between a groove portion and a land portion in the first recording layer.   The groove portion of the first recording layer has a concave shape on the first transparent substrate side from the land portion of the first recording layer, and the groove portion of the second recording layer is a land portion of the second recording layer. The information recording medium according to claim 1, further having a convex shape on the first transparent substrate side.   The groove portion of the first recording layer has a shape protruding from the land portion of the first recording layer toward the first transparent substrate, and the groove portion of the second recording layer is a land portion of the second recording layer. The information recording medium according to claim 1, further comprising a concave shape on the first transparent substrate side.

Images