Patent Publication Number: US-2006019054-A1

Title: Optical information storage medium

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The invention relates to an optical information storage medium, and more particularly to a single side dual layer or dual side dual layer optical information storage medium.  
      2. Description of the Related Art  
      With the coming of the information and multimedia age, the demands of the electrical products on the storage density and capacity of the storage medium are constantly increased. The conventional storage media may be generally classified into two kinds, which are magnetic recording media and optical recording media. Currently, the optical recording media, which includes read only memory (CD-ROM), write-once CD (CD-R), rewritable CD (CD-RW), read only memory DVD (DVD-ROM), write-once DVD (DVD-R), rewritable DVD (DVD−RW, DVD+RW), and random memory DVD (DVD-RAM), gets the lager market share.  
      Increasing the data capacity of the optical disk is a target to be sought in the industry in order to meet the video information quantity that is getting larger and larger. Because the DVD has a larger data storage capacity than the CD does, it has gained a giant share of the market. There are several kinds of DVD, such as single side single layer, dual side single layer, single side dual layer, and dual side dual layer. The storage capacities of these discs range from 4.7 GB to 17 GB.  
      The 2P process (Photo-Polymerization Process) is one of the frequently used methods for manufacturing the single side dual layer DVD-R disc and the dual side dual layer DVD-R disc. The 2P process will be described with reference to the single side dual layer DVD-R disc  10  as an example.  
      As shown in  FIGS. 1A  to  1 F describing the 2P process, a first recording layer  121 , a first reflective layer  122 , and a light-cured adhesive layer  13 ′ are sequentially formed above a pre-grooved first substrate  11 . Next, a pre-grooved stamper  16  is pressed onto the light-cured adhesive layer  13 ′, and a spacer layer  13  is formed after the layer  13 ′ is cured by ultra-violet rays. After the stamper  16  is peeled off, at least one groove G is formed on the spacer layer  13 , and a second recording layer  141  and a second reflective layer  142  are formed above the spacer layer  13 . Finally, the second substrate  15  is bonded to the second reflective layer  142 , and the single side dual layer DVD-R disc  10  is thus formed.  
      Of course, in addition to the single side dual layer DVD-R disc  10 , the dual side dual layer DVD-R disc  20  also may be manufactured using the 2P process.  
      As shown in  FIGS. 2A  to  2 C, the first half of the processes for forming the dual side dual layer DVD-R disc  20  is the same as those of the single side dual layer DVD-R disc  10 . A first half disc sequentially has a first substrate  21 , a first recording layer  221 , a first reflective layer  222 , a first spacer layer  23 , a second recording layer  241 , a second reflective layer  242 , according to  FIG. 1E . The second half of the disc sequentially has a second substrate  29 , a fourth recording layer  282 , a fourth reflective layer  281 , a third spacer layer  27 , a third recording layer  262 , a third reflective layer. Next, the two half discs are adhered together using the light-cured adhesive, which forms a second spacer layer  25  after the curing process, and then the manufacturing of the dual side dual layer DVD-R disc  20  is thus completed.  
      As shown in  FIGS. 1A  to  1 F and  FIGS. 2A  to  2 C, the requirement of data access only can be achieved when the single side dual layer DVD-R disc  10  or the dual side dual layer DVD-R disc  20  has the thickness of 150 nm to 170 nm if the AZO dye serves as the material of the second recording layer  141  or the third recording layer  262  in the prior art. Taking the processes for forming the second recording layer  141  as an example, the pre-grooved stamper  16  and the spacer layer  13  are pressed together and then separated so that the grooves G having a depth of about 160 to 180 nm are formed on the spacer layer  13 . Then, the AZO dye is coated onto the grooves G so that the second recording layer  141  having the thickness ranging from 150 nm to 170 nm is formed.  
      In the prior art, however, the PMMA (Polymethyl Methacrylate) having poor mobility as the material of the stamper  16 , and it is difficult to form the stamper  16  having a groove with the depth of about 160 nm. Thus, the desired thickness of the second recording layer  141  is influenced. Hence, the process yield of the discs will be reduced. Consequently, the stamper  16  made of PMMA with poor mobility is not suitable for forming the grooves G required by the second recording layer  141  nor the third recording layer  262  made of the AZO dye. In addition, the adhesive force between the first recording layer  121  and the first reflective layer  122  are relatively weak, and they cannot withstand a large pulling force. Consequently, when the stamper  16  is being peeled off, the spacer layer  13  tends to break and peel off, or even the first recording layer  121  and the first reflective layer  122  are separated from the first substrate  11 , as shown in  FIG. 3 . Furthermore, as the depth of the groove G gets larger, a larger pulling force is required when the stamper  16  is peeled off. In this case, the stamper  16  or the spacer layer  13  tends to be broken and damaged, and the transmitting path of the laser light for accessing data is influenced. Therefore, the disc production yield is low, and the manufacturing cost is increased.  
      In view of the above-mentioned problems, it is an important subject of the invention to provide an optical information storage medium capable of solving the above-mentioned problems, in which the PMMA stamper cannot form the groove depth required by the second recording layer made of AZO dye in a dual layer digital versatile disc.  
     SUMMARY OF THE INVENTION  
      In view of the foregoing, the invention is to provide an optical information storage medium having a second recording layer made of cyanine dye.  
      In addition, the invention is to provide an optical information storage medium having a second recording layer made of cyanine dye, and a third recording layer made of cyanine dye.  
      To achieve the above, an optical information storage medium of the invention includes a first substrate, a first recording layer, a first reflective layer, a spacer layer, a second recording layer, a second reflective layer and a second substrate. The first recording layer is disposed above the first substrate. The first reflective layer is disposed above the first recording layer. The spacer layer is disposed above the first reflective layer. The second recording layer is disposed above the spacer layer. The second recording layer, which is made of cyanine dye, is disposed above the second recording layer. The second substrate is disposed above the second reflective layer.  
      The invention also provides an optical information storage medium, which includes a first substrate, a first recording layer, a first reflective layer, a first spacer layer, a second recording layer, a second reflective layer, a second spacer layer, a third reflective layer, a third recording layer, a third spacer layer, a fourth reflective layer, a fourth recording layer and a second substrate. In this case, the first recording layer is disposed above the first substrate. The first reflective layer is disposed above the first recording layer. The first spacer layer is disposed above the first reflective layer. The second recording layer is disposed above the first spacer layer, and the second recording layer is made of cyanine dye and disposed above the second recording layer. The second spacer layer is disposed above the second reflective layer. The third reflective layer is disposed above the second spacer layer. The third recording layer is disposed above the third reflective layer, and the third recording layer is made of cyanine dye and disposed above the third recording layer. The fourth reflective layer is disposed above the third spacer layer. The fourth recording layer is disposed above the fourth reflective layer. The second substrate is disposed above the fourth recording layer.  
      As mentioned above, the optical information storage medium of the invention utilizes the cyanine dye as the material of the second recording layer of the single side dual layer DVD-R disc, and as the materials of the second recording layer and the third recording layer of the dual side dual layer DVD-R disc. Compared to the prior art, because the depth of the groove of the spacer required by the recording layer made of the cyanine dye is smaller in the optical information storage medium of the invention. As a result, the depth of the groove of the stamper for pressing the spacer layer to form the groove is relatively reduced. Because the demand on the depth of the groove is reduced, a cheaper PMMA material may be used to form the stamper by way of injection molding, and the manufacturing cost of the product may be reduced accordingly. In addition, with the decrease of the required depth of the groove of the spacer layer, the pulling force for peeling off the stamper may be reduced, too. Consequently, it is possible to prevent the stamper or other corresponding spacer layer, reflective layer or even recording layer from being damaged, and the product yield may be thus increased. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will become more fully understood from the detailed description given herein below illustration only, and thus is not limitative of the present invention, and wherein:  
       FIGS. 1A  to  1 F are schematic illustrations showing the manufacturing processes of a conventional single side dual layer digital versatile disc;  
       FIGS. 2A  to  2 C are schematic illustrations showing the manufacturing processes of a conventional dual side dual layer digital video disc;  
       FIG. 3  is a schematic illustration showing the manufacturing process of a conventional single side dual layer digital versatile disc, wherein the spacer layer or stamper is damaged when the stamper is peeled off;  
       FIG. 4  is a schematic illustration showing an optical information storage medium according to a first preferred embodiment of the invention, wherein the optical information storage medium is a single side dual layer digital video disc; and  
       FIG. 5  is a schematic illustration showing an optical information storage medium according to a second preferred embodiment of the invention, wherein the optical information storage medium is a dual side dual layer digital versatile disc. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The optical information storage media according to the preferred embodiments of the invention will be described with reference to the accompanying drawings.  
      The optical information storage medium of the invention is manufactured by the 2P process (Photo-Polymerization Process). The optical information storage medium can be a write once single side dual layer digital versatile disc, or a write once dual side dual layer digital versatile disc.  
      The optical information storage medium according to the first preferred embodiment of the invention will be described with reference to  FIG. 4 .  
      Referring to  FIG. 4 , the single side dual layer DVD-R disc  30  includes a first substrate  31 , a first recording layer  321 , a first reflective layer  322 , a spacer layer  33 , a second recording layer  341 , a second reflective layer  342  and a second substrate  39 .  
      The first recording layer  321  and the first reflective layer  322  may be referred to as a first recording stack L 0 , and the second recording layer  341  and the second reflective layer  342  may be referred to as a second recording stack L 1 . The laser light enters the disc from the first recording stack L 0  side.  
      The frequently used material of the first substrate  31  and the second substrate  39  is the polycarbonate (PC), which has good optical property and good chemical stability. In this embodiment, the first substrate  31  and the second substrate  39  are made of polycarbonate and are injection molded into pre-grooved substrates.  
      The first recording layer  321  is disposed above the first substrate  31 . The material of the first recording layer  321  may be the organic dye or inorganic material. In this embodiment, the material of the first recording layer  321  is the organic dye, and the first recording layer  321  is formed by spin coating.  
      The first reflective layer  322  is disposed above the first recording layer  321  an the first reflective layer  322  is a semi-reflective layer made of the material of pure metal or the alloy thereof, such as the silver or silver alloy, the aluminum or aluminum alloy, and the gold or the gold alloy. The first reflective layer  322  is usually formed by sputtering or evaporation.  
      The spacer layer  33  is disposed above the first reflective layer  322 . During the formation of the spacer layer  33 , a liquid light-cured adhesive is coated, and then a pre-grooved soft stamper is pressed onto the light-cured adhesive. After exposed to the ultra-violet ray, the light-cured adhesive is cured into a solid spacer layer  33 , which can distinguish the light rays reflected by different recording layers. In this case, the groove depth of the soft stamper is about 100 to 150 nm.  
      Consequently, the spacer layer  33  at least has one groove pattern G facing the second recording layer  341 , and the groove pattern G has a depth of about 100 to 150 nm. In this embodiment, the material of the soft stamper for forming the groove pattern G may be the PMMA (Polymethyl Methacrylate).  
      The second recording layer  341  is disposed above the spacer layer  33  and the second recording layer  341  is made of cyanine dye by coating. The thickness of the second recording layer  341  is about 110 to 140 nm. Thus, the required depth of the groove pattern G of the spacer layer  33  is smaller than that of the AZO dye (the AZO dye needs the groove depth of about 160 nm, and the cyanine dye only needs the groove depth of about 120 nm).  
      The second reflective layer  342  is disposed above the second recording layer  341 , and the second reflective layer  342  may be made of the inorganic material. The material of the second reflective layer  342  may be a semi conductive alloy film, a conductive alloy film, or a metal film.  
      The second substrate  39  is disposed above the second reflective layer  342 , and may be adhered to the second reflective layer  342  using an adhesive.  
      The optical information storage medium according to the second preferred embodiment of the invention will be described with reference to  FIG. 5 .  
      The dual side dual layer DVD-R disc  30 ′ includes a first substrate  31 , a first recording layer  321 , a first reflective layer  322 , a first spacer layer  33 ′, a second recording layer  341 , a second reflective layer  342 , a second spacer layer  35 , a third reflective layer  361 , a third recording layer  362 , a third spacer layer  37 , a fourth reflective layer  381 , a fourth recording layer  382  and a second substrate  39 .  
      Because the laser light may enter the disc from two sides of the substrate, the first recording layer  321  and the first reflective layer  322  may be referred to as the first recording stack L 0 , and the fourth reflective layer  381  and the fourth recording layer  382  also may be referred to as the first recording stack L 0 . In addition, the second recording layer  341  and the second reflective layer  342  are referred to as the second recording stack L 1 , and the third reflective layer  361  and the third recording layer  362  also may be referred to as the second recording stack L 1 .  
      The first recording layer  321  is disposed above the first substrate  31 , the first reflective layer  322  is disposed above the first recording layer  321 , the first spacer layer  33 ′ is disposed above the first reflective layer  322 , the second recording layer  341  is disposed above the first spacer layer  33 ′, the second recording layer  341  is made of cyanine dye, and the second reflective layer  342  is disposed above the second recording layer  341 .  
      In this embodiment, the functions and features of the first substrate  31 , the first recording layer  321 , the first reflective layer  322 , the first spacer layer  33 ′, the second recording layer  341  and the second reflective layer  342  are respectively the same as the first substrate  31 , the first recording layer  321 , the first reflective layer  322 , the spacer layer  33 , the second recording layer  341  and the second reflective layer  342  of the first embodiment of the invention, and detailed descriptions thereof will not be repeated.  
      The third reflective layer  361  is disposed above the second spacer layer  35 , the third recording layer  362  is disposed above the third reflective layer  361 , and the third recording layer  362  is made of cyanine dye. In this embodiment, the third reflective layer  361  and the second reflective layer  342  may be made of the same material, and the third recording layer  362  and the second recording layer  341  may be made of the same material. Because the cyanine dye cannot withstand too much light, the second recording stack L 1  of the disc can reduce the light intensity to the cyanine dye.  
      The second spacer layer  35  is disposed above the second reflective layer  342  and the third spacer layer  37  is disposed above the third recording layer  362 . In this embodiment, each of the second spacer layer  35  and the third spacer layer  37  may be formed by curing a light-cured adhesive. The materials of the second spacer layer  35  and the third spacer layer  37  may be the same as that of the first spacer layer  33 ′, and detailed descriptions thereof will be omitted.  
      The fourth reflective layer  381  is disposed above the third spacer layer  37 , and the fourth recording layer  382  is disposed above the fourth reflective layer  381 . The material of the fourth reflective layer  381  may be the same as that of the first reflective layer  322 , and each of the fourth reflective layer  381  and the first reflective layer  322  is a semi-reflective layer.  
      The second substrate  39  is disposed above the fourth recording layer  382 . In this embodiment, the material of the second substrate  39  may be the same as that of the first substrate  31 .  
      As mentioned above, the optical information storage medium of the invention utilizes the cyanine dye as the material of the second recording layer of the single side dual layer DVD-R disc, and as the materials of the second recording layer and the third recording layer of the dual side dual layer DVD-R disc. Compared to the prior art, because the depth of the groove of the spacer required by the recording layer made of the cyanine dye is smaller in the optical information storage medium of the invention, the depth of the groove of the stamper for pressing the spacer layer to form the groove is relatively reduced. Because the demand on the depth of the groove is reduced, a cheaper PMMA material may be used to form the stamper by way of injection molding, and the manufacturing cost of the product may be reduced accordingly. In addition, with the decrease of the depth of the groove of the spacer layer, the pulling force for peeling off the stamper away may be reduced. Consequently, it is possible to prevent the stamper or other corresponding spacer layer, reflective layer or even recording layer from being damaged, and the product yield may be thus increased.  
      While the invention has been described by way of examples and in terms of preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications.