Abstract:
Improved structures of optical medium are disclosed. According to one embodiment, multiple reflective layers are used. These reflective layers are in different materials. At least one of the reflective layers allowing a significant amount of a laser beam to transmit is used to protect another reflective layer with superior reflectivity from moisture on one side. An additional reflective layer may also be used to protect the high reflective layer from moisture on the other side.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is generally related to the area of optical information recordable medium. More particularly, the present is related to structures for optical medium for carrying or recording digital information and method for making such optical medium. 
     2. The Background of Related Art 
     One of the most popular optical storage medium is DVD (Digital Versatile Disc). Technically, DVD is a relatively new generation of optical disc storage technology. It is much larger in data capacity and faster in reading than CD and can hold cinema-like video, better-than-CD audio, still photos, and computer data. DVD aims to encompass home entertainment, computers, and business information with a single digital format. It has replaced laserdisc, is well on the way to replacing videotape and video game cartridges, and could eventually replace audio CD and CD-ROM. DVD has widespread support from all major electronics companies, all major computer hardware companies, and all major movie and music studios. With this unprecedented support, DVD became the most successful storage device of all time in the history of optical storage technologies. 
     With the popularity of various multimedia applications and data, blank DVD, also called DVDR (i.e., DVD Recordable), is becoming probably the most desirable recordable medium. Users may use DVDR to preserve their own data (e.g., movies, music, and photos). In principle, a DVDR is a blank DVD with a piece of medium that is writable with a laser beam. Data on the same disk can also be read out by the laser beam. Because of the relatively low in cost, DVDR is gaining great popularity among all uses, professional or armature alike. 
       FIG. 1  shows a cross section view of a structure  100  of a traditional DVDR. As illustrated, there are six layers in a DVDR, a first substrate  10 , a dye recording layer  20 , a reflective layer  30 , an adhesive layer  40 , a second substrate  50  and a labeling layer  60 . A DVDR is essentially formed by stacking or integrating these six layers on top of each other. 
     From a user perspective, the labeling layer  60 , being a first layer, is for labeling purpose. The labeling layer  60  allows a user to write thereon or is printed to indicate the content therein or the data capacity a disk has. A second layer is the second substrate  50  made of, for example, polycarbonate. The second layer is typically relatively thick and provides the physical strength and support of the disk. The third layer is the adhesive layer  40  that is formed by, for example, UV curable glue. Besides protecting the dye recording layer  20  and the reflective layer  30 , the third layer bonds the first substrate  10  and the second substrate  50  together. The fourth layer is the reflective layer  30  to reflect a laser beam. In general, the reflective layer  30  is made out of a reflective material, such as silver with 99.99% purity. The fifth layer is the dye recording layer  20  that records and preserves data. Accordingly, the dye recording layer  20  affects substantially the quality of a disk. The sixth layer is the first substrate  10  supporting the dye recording layer  20  and the reflective layer  30 . The first substrate  10  and the second substrate  50  are bonded together to hold both the reflective layer  30  and the dye recording layer  20  therebetween to form a disc (with the labeling layer). 
     Given the structure  100  of the traditional DVDR, the manufacturing process may be summarized as follows: providing a first substrate, forming a dye recording layer on the substrate, metalizing the dye recording layer in vacuum to form a reflective layer, then applying a type of adhesive to bond with another substrate to form a disk. A printing layer is applied on top of the disk. In other words, there are five essential steps in manufacturing a DVDR disk, there are molding (to create the substrates), dyeing (to create a dye recording layer), metalizing (to form a reflective layer), bonding (to bond all together), and printing (labeling the final disk). 
     Metalizing is a very important part of the manufacturing process. It laminates a substrate with a layer of reflective material that reflects a laser beam to read data from the disc or write data into the disc. To facilitate the reading by laser, the material used as the reflective material shall have superior reflectivity, otherwise a reflected light beam would be too weak to read off the data on the disk or write data into the disk. It is known that the wavelength of a laser beam for DVDR is 650 nm. At the wavelength, silver has the highest reflectivity, approaching 98.9% while gold has a reflectivity of 95.5%, copper has a reflectivity of 96.6% and aluminum has a reflectivity of 90.5%. Accordingly, silver is more appropriate than others. 
     In manufacturing DVDR disks, there is a tremendous requirement for the dryness of the dye recording layer. Practically, it is difficult to have the dye recording layer that is completely dry. There may be a certain level of moisture in the dye material. When the dye recording layer is laminated with a reflective material (e.g., silver), the material could react to the moisture in the dye recording layer, causing bubbles, voids and undesirable results. As a result, the quality of a resultant disc is compromised. The disk may be completely inferior or downgraded, thus increasing the manufacturing cost. 
     On the other end, the moisture in the adhesive (e.g., glue) applied to bond the substrates may also cause chemical erosion to the silver, thus causing bubbles where air trapped in the bubbles can oxidize silver, leading to voids after sometime. When a disc with bubbles is being read at high spinning speed in a disk drive, the layers in the disc intend to split under the centrifugal force of the spinning. As a result, the stability and lifespan of the disk are affected, and a reading device may be ruined. 
     There thus a need for improved structures of optical medium (e.g., DVD or DVDR) that can overcome the problems commonly seen in the traditional DVDR. 
     SUMMARY OF THE INVENTION 
     This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions in this section as well as in the abstract or the title of this description may be made to avoid obscuring the purpose of this section, the abstract and the title. Such simplifications or omissions are not intended to limit the scope of the present invention. 
     In general, the present invention pertains to techniques for producing optical medium that can be read at substantially high speeds with greater stability and accuracy, and reduce manufacturing costs. According to one aspect of the present invention, multiple reflective layers are used. These reflective layers are in different materials. At least one of the reflective layers allowing a significant amount of a laser beam to transmit is used to protect another reflective layer with superior reflectivity from moisture on one side. An additional reflective layer may also be used to protect the high reflective layer from moisture on the other side. 
     According to one embodiment, there are three reflective layers in a disc. The middle reflective layer to be protected by the other two reflective layers is in silver material. The other two reflective layers may be in gold or bronze. Because all the reflective layers are in different metal materials so that resultant discs remain metallic and expensive looking. There are numerous functions, benefits and advantages in the present invention, one of them is that the present invention provides new structures of optical medium using multiple reflective layers in a disc. 
     The present invention may be implemented as method, process, or apparatus. According to one embodiment of the present invention, the present invention is a method for producing an optical disc, the method comprises providing a first substrate and a second substrate, laminating the first substrate with a dye recording layer and at least two different reflective layers, wherein the two different reflective layers are in two different materials; and bonding the laminated first substrate with the second substrate with an adhesive layer formed therebetween to produce a disk. With a labeling layer on top of the disk, the complete optical disc is produced. 
     According to another embodiment of the present invention, the present invention is an optical disc comprising: a first substrate and a second substrate, a dye recording layer, at least first and second reflective layers, wherein the dye recording layer and the at least first and second reflective layers are sandwiched between the first substrate and the second substrate via an adhesive layer. The optical disc further comprises a labeling layer. 
     Objects, features, and advantages of the present invention will become apparent upon examining the following detailed description of an embodiment thereof, taken in conjunction with the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG. 1  shows a cross section view of a structure of a traditional DVDR; 
         FIG. 2  shows a cross section view of a structure of an optical disk according to one embodiment of the present invention; 
         FIG. 3  shows a cross section view of another structure of an optical disk according to one embodiment of the present invention; and 
         FIG. 4  shows a cross section view of another structure of an optical disk according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The detailed description of the present invention is presented largely in terms of procedures, steps, logic blocks, processing, or other symbolic representations that directly or indirectly resemble the manufacturing processing and optical medium. These descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. 
     Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams or the use of sequence numbers representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention. 
     Referring now to the drawings, in which like numerals refer to like parts throughout the several views.  FIG. 2  shows a cross section view of a structure of an optical disk  200  according to one embodiment of the present invention. As illustrated, there are seven layers in the optical disk  200 , a first substrate  201 , a dye recording layer  202 , a first reflective layer  203 A, a second reflective layer  203 B, an adhesive layer  204 , a second substrate  205  and a labeling layer  206 . 
     One of the important features in the present invention is the use of multiple reflective layers in different materials. According to one embodiment, the structure of an optical disk  200  uses two reflective layers  203 A and  203 B. The first reflective layer  203 A is laminated substantially on top of the first substrate  201  that has already been laminated with a dye recording layer  202 , and the second reflective layer  203 B is laminated substantially on top of the first reflective layer  203 A. The adhesive layer  204  is essentially formed on top of the second reflective layer  203 B to bond the first substrate  201  and the second substrate  205  to sandwich all the layers therebetween. 
     In one embodiment, the first reflective layer  203 A is made of gold, and the second reflective layer  203 B is made of silver (hence a silver layer). To prevent the silver from being chemically affected by moisture (e.g., from the dye recording material), the first reflective layer  203 A is provided to isolate the second reflective layer  203 B from the dye recording layer  202  in a sense that moisture from the dye recording layer  202  is stopped by the first reflective layer  203 A, where the first reflective layer  203 A is generally from a material (e.g., gold) that is resistant to moisture. In that embodiment, the thickness of the silver layer is controlled between 10-30 nm, and the thickness of the protecting reflective layer  203 A is controlled between 50-80 nm. 
     In another embodiment, the first reflective layer  203 A is made of silver (hence a silver layer), and the second reflective layer  203 B is made of gold. To prevent the silver from being chemically affected by moisture (e.g., from the adhesive), the second reflective layer  203 B is provided to isolate the first reflective layer  203 A from the adhesive layer  204  in a sense that moisture from the adhesive layer  204  is stopped by the second reflective layer  203 B, where the second reflective layer  203 B is generally from a material (e.g., gold) that is resistant to moisture. 
     There are a lot of materials that are resistant to moisture. In one embodiment, the material to protect the silver layer is gold, bronze or copper. As a result, the final optical disk still looks metallic through the substrate  201  or  205  that is in general transparent (e.g., polycarbonate). 
       FIG. 3  shows a cross section view of another structure of an optical disk  300  using more than two reflective layers, according to one embodiment of the present invention. As illustrated, there are at least eight layers in the optical disk  300 , a first substrate  301 , a dye recording layer  302 , a first reflective layer  303 A, a second reflective layer  303 B, a third reflective layer  303 C, an adhesive layer  304 , a second substrate  305  and a labeling layer  306 . 
     As shown, the structure of an optical disk  300  uses three reflective layers  303 A,  303 B and  303 C. The first reflective layer  303 A is laminated substantially on top of the first substrate  301  that has already been laminated with a dye recording layer, the second reflective layer  303 B is laminated substantially on top of the first reflective layer  303 A, and the third reflective layer  303 C is laminated substantially on top of the second reflective layer  303 B. The adhesive layer  304  is essentially formed on top of the third reflective layer  303 C. 
     According to one embodiment, the first reflective layer  303 A is made out of gold, the second reflective layer  303 B is made out of silver, and the third reflective layer  303 C is made out of bronze or copper. In terms of area, the first reflective layer  303 A is larger than the dye recording layer so that the dye recording layer is completely protected while the second reflective layer is between the first reflective layer and the dye recording layer, and that the second reflective layer  303 B is close to the first reflective layer  303 A. In one embodiment, the thickness of the three reflective layers is collectively between 80-120 nm. 
       FIG. 4  shows a cross section view of another structure of an optical disk  400  according to one embodiment of the present invention. As illustrated, there are at least eight layers in the optical disk  400 , a first substrate  401 , a dye recording layer  402 , a first reflective layer  403 A, a second reflective layer  403 B, a third reflective layer  403 C, an adhesive layer  404 , a second substrate  405  and a labeling layer  406 . 
     As shown, the structure of an optical disk  400  uses three reflective layers  403 A,  403 B and  403 C. The first reflective layer  403 A is laminated substantially on top of the first substrate  401  that has already been laminated with a dye recording layer  402 , the second reflective layer  403 B is laminated substantially on top of the first reflective layer  403 A, and the third reflective layer  403 C is laminated substantially on back of the second substrate  405 . The adhesive layer  404  is essentially formed between the laminated first and second substrates  401  and  405  to bond the two substrates together. 
     According to one embodiment, the first reflective layer  403 A is made out of gold, the second reflective layer  403 B is made out of silver, and the third reflective layer  403 C is made out of bronze or copper. In terms of area, the first reflective layer  403 A is larger than the dye recording layer so that the dye recording layer is completely protected while the second reflective layer is between the first reflective layer and the dye recording layer, the third reflective layer is similar to the first reflective layer. In one embodiment, the thickness of the three reflective layers is collectively between 80-120 nm. 
     In operation, after a dye recording layer is laminated on the first substrate (L 0 ), the first substrate is metalized in a vacuum chamber when a pre-determined vacuum level is reached. A reflective material (e.g., silver) with desired reflectivity is evaporated and then condensed evenly on the part that needs to be metalized at a regulated rate. The thickness of the first silver reflective layer is controlled between 10-30 nm and covers completely the dye recording layer. In the case of the optical medium being a DVDR, the inner diameter of the first silver reflective layer is smaller than that of the dye recording layer. In other words, the area of the first silver reflective layer is larger than that of the dye recording layer. 
     The second reflective layer is laminated onto the laminated first substrate (now with the dye recording layer and the silver layer) by, for example, vacuum metalizing. The thickness of the second reflective layer may be controlled between 50-80 nm depending on application. The inner diameter of the second reflective layer is between that of the first reflective layer and that of the dye recording layer. In other words, the area of the second reflective layer is between the areas of the first reflective layer and that of the dye recording layer. The glue layer is formed, perhaps by a processing of spinning a certain amount of glue deposed on the second reflective layer or between the laminated first substrate and the second substrate to form a disc. After forming a printing layer on top of the disc, a complete disc is done. 
     It can be appreciated that in one embodiment the second reflective layer (i.e., the silver layer) is isolated from the dye recording layer by the first reflective layer (e.g., the gold) and isolated from the adhesive layer by the third layer (e.g., the bronze). As a result, the dye recording layer can be protected from possible moisture that may exist in the dye recording layer and the adhesive layer, thus improving the quality of a disk and still keeping the disk appear metallic. 
     The present invention has been described in sufficient details with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. For example, the present invention may be applied to non-disk like optical medium. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description of embodiments.