Patent Publication Number: US-6905750-B2

Title: Metal alloys for the reflective or the semi-reflective layer of an optical storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This patent application is a continuation-in-part of patent application Ser. No. 10/457,935 filed Jun. 10, 2003 which is a continuation-in-part of application Ser. No. 10/342,649, filed Jan. 15, 2003, now U.S. Pat. No. 6,790,503, which is a continuation-in-part of application Ser. No. 10/090,855, filed Mar. 4, 2002, now U.S. Pat. No. 6,764,735, which is a continuation-in-part of application Ser. No. 09/661,062, filed Sep. 13, 2000, now U.S. Pat. No. 6,451,402, issued on Sep. 17, 2002, which is a continuation-in-part of application Ser. No. 09/557,135, filed Apr. 25, 2000, now abandoned, which is a continuation-in-part of application Ser. No. 09/438,864, filed Nov. 12, 1999, now U.S. Pat. No. 6,280,811, issued on Aug. 28, 2001, which is a continuation-in-part of application Ser. No. 09/102,163, filed Jun. 22, 1998, now U.S. Pat. No. 6,007,889, issued on Oct. 28, 1999, and is also a continuation-in-part of application Ser. No. 10/409,037, filed on Apr. 8, 2003, now abandoned, which is a continuation of application Ser. No. 09/834,775 filed on Apr. 13, 2001, now U.S. Pat. No. 6,544,616, issued on Apr. 8, 2003, which claims the benefit of U.S. Provisional Application No. 60/219,843, filed Jul. 21, 2000. 

   FIELD OF THE INVENTION 
   This invention relates to reflective layers or semi-reflective layers used in optical storage media that are made of silver-based alloys. 
   BACKGROUND OF THE INVENTION 
   Four layers are generally present in the construction of a conventional, prerecorded, optical disc such as compact audio disc. A first layer is usually made from optical grade, polycarbonate resin. This layer is manufactured by well-known techniques that usually begin by injection or compression molding the resin into a disc. The surface of the disc is molded or stamped with extremely small and precisely located pits and lands. These pits and lands have a predetermined size and, as explained below, are ultimately the vehicles for storing information on the disc. 
   After stamping, an optically reflective layer is placed over the information pits and lands. The reflective layer is usually made of aluminum or an aluminum alloy and is typically between about 40 to about 100 nanometers (nm) thick. The reflective layer is usually deposited by one of many well-known vapor deposition techniques such as sputtering or thermal evaporation.  Kirk - Othmer, Encyclopedia of Chemical Technology , 3 rd  ed. Vol. 10, pp. 247 to 283, offers a detailed explanation of these and other deposition techniques such as glow discharge, ion plating, and chemical vapor deposition, and this specification hereby incorporates that disclosure by reference. 
   Next, a solvent-based or an UV (ultraviolet) curing-type resin is applied over the reflective layer, which is usually followed by a label. The third layer protects the reflective layer from handling and the ambient environment. And the label identifies the particular information that is stored on the disc, and sometimes, may include artwork. 
   The information pits residing between the polycarbonate resin and the reflective layer usually take the form of a continuous spiral. The spiral typically begins at an inside radius and ends at an outside radius. The distance between any 2 spirals is called the “track pitch” and is usually about 1.6 microns for compact audio disc. The length of one pit or land in the direction of the track is from about 0.9 to about 3.3 microns. All of these details are commonly known for compact audio discs and reside in a series of specifications that were first proposed by Philips NV of Holland and Sony of Japan as standards for the industry. 
   The disc is read by pointing a laser beam through the optical grade polycarbonate substrate and onto the reflective layer with sufficiently small resolution to focus on the information pits. The pits have a depth of about ¼ of the wavelength of the laser light, and the light generally has a wavelength in the range of about 780 to 820 nanometers. Destructive (dark) or constructive (bright) interference of the laser light is then produced as the laser travels along the spiral track, focusing on an alternating stream of pits and lands in its path. 
   This on and off change of light intensity from dark to bright or from bright to dark forms the basis of a digital data stream of 1 and 0&#39;s. When there is no light intensity change in a fixed time interval, the digital signal is “0,” and when there is light intensity change from either dark to bright or bright to dark, the digital signal is “1.” The continuous stream of ones and zeros that results is then electronically decoded and presented in a format that is meaningful to the user such as music or computer programming data. 
   As a result, it is important to have a highly reflective coating on the disc to reflect the laser light from the disc and onto a detector in order to read the presence of an intensity change. In general, the reflective layer is usually aluminum, copper, silver, or gold, all of which have a high optical reflectivity of more than 80 percent from 650 nm to 820 nm wavelength. Aluminum and aluminum alloys are commonly used because they have a comparatively lower cost, adequate corrosion resistance, and are easily placed onto the polycarbonate disc. 
   Occasionally and usually for cosmetic reason, a gold or copper based alloy is used to offer the consumer a “gold” colored disc. Although gold naturally offers a rich color and satisfies all the functional requirements of a highly reflective layer, it is comparatively much more expensive than aluminum. Therefore, a copper-based alloy that contains zinc or tin is sometimes used to produce the gold colored layer. But unfortunately, the exchange is not truly satisfactory because the copper alloy&#39;s corrosion resistance, in general, is considered worse than aluminum, which results in a disc that has a shorter life span than one with an aluminum reflective layer. 
   For the convenience of the reader, additional details in the manufacture and operation of an optically readable storage system can be found in U.S. Pat. No. 4,998,239 to Strandjord et al. and U.S. Pat. No. 4,709,363 to Dirks et al., the disclosures of which are hereby incorporated by reference. 
   Another type of disc in the compact disc family that has become popular is the recordable compact disc or “CD-R.” This disc is similar to the CD described earlier, but it has a few changes. The recordable compact disc begins with a continuous spiral groove instead of a continuous spiral of pits and has a layer of organic dye between the polycarbonate substrate and the reflective layer. The disc is recorded by periodically focusing a laser beam into the grooves as the laser travels along the spiral track. The laser heats the dye to a high temperature, which in turn places pits in the groove that coincide with an input data stream of ones and zeros by periodically deforming and decomposing the dye. 
   For the convenience of the reader, additional details regarding the operation and construction of these recordable discs can be found in U.S. Pat. No. 5,325,351 to Uchiyama et al., and U.S. Pat. Nos. 5,391,462; 5,415,914; and 5,419,939 to Arioka et al., and U.S. Pat. No. 5,620,767 to Harigaya et al., the disclosures of which are hereby incorporated into this specification by reference. 
   The key component of a CD-R disc is the organic dye, which is made from solvent and one or more organic compounds from the cyanine, phthalocyanine or azo family. The disc is normally produced by spin coating the dye onto the disc and sputtering the reflective layer over the dye after the dye is sufficiently dry. But because the dye may contain halogen ions or other chemicals that can corrode the reflective layer, many commonly used reflective layer materials such as aluminum may not be suitable to give the CD-R disc a reasonable life span. So being, frequently gold must be used to manufacture a recordable CD. But while gold satisfies all the functional requirements of CD-R discs, it is a very expensive solution. 
   Recently, other types of recordable optical disks have been developed. These optical disks use a phase-change or magneto-optic material as the recording medium. An optical laser is used to change the phase or magnetic state (microstructural change) of the recording layer by modulating a beam focused on the recording medium while the medium is rotated to produce microstructural changes in the recording layer. During playback, changes in the intensity of light from the optical beam reflected through the recording medium are sensed by a detector. These modulations in light intensity are due to variations in the microstructure of the recording medium produced during the recording process. Some phase-change and/or magneto-optic materials may be readily and repeatedly transformed from a first state to a second state and back again with substantially no degradation. These materials may be used as the recording media for a compact disc-rewritable disc, or commonly known as CD-RW. 
   To record and read information, phase change discs utilize the recording layer&#39;s ability to change from a first dark to a second light phase and back again. Recording on these materials produces a series of alternating dark and light spots according to digital input data introduced as modulations in the recording laser beam. These light and dark spots on the recording medium correspond to 0&#39;s and 1&#39;s in terms of digital data. The digitized data is read using a low laser power focused along the track of the disc to play back the recorded information. The laser power is low enough such that it does not further change the state of the recording media but is powerful enough such that the variations in reflectivity of the recording medium may be easily distinguished by a detector. The recording medium may be erased for re-recording by focussing a laser of intermediate power on the recording medium. This returns the recording medium layer to its original or erased state. A more detailed discussion of the recording mechanism of optically recordable media can be found in U.S. Pat. Nos. 5,741,603; 5,498,507; and 5,719,006 assigned to the Sony Corporation, the TDK Corporation, and the NEC Corporation, all of Tokyo, Japan, respectively, the disclosures of which are incorporated herein by reference in their entirety. 
   Still another type of disc in the optical disc family that has become popular is a prerecorded optical disc called the digital videodisc or “DVD.” This disc has two halves. Each half is made of polycarbonate resin that has been injection or compression molded with pit information and then sputter coated with a reflective layer, as described earlier. These two halves are then bonded or glued together with an UV curing resin or a hot melt adhesive to form the whole disc. The disc can then be played from both sides as contrasted from the compact disc or CD where information is usually obtained only from one side. The size of a DVD is about the same as a CD, but the information density is considerably higher. The track pitch is about 0.7 micron and the length of the pits and lands is from approximately 0.3 to 1.4 microns. 
   One variation of the DVD family of discs is the DVD-dual layer disc. This disc also has two information layers; however, both layers are played back from one side. In this arrangement, the highly reflectivity layer is usually the same as that previously described. But the second layer is only semi-reflective with a reflectivity in the range of approximately 18 to 30 percent at 650 nm wavelength. In addition to reflecting light, this second layer must also pass a substantial amount of light so that the laser beam can reach the highly reflective layer underneath and then reflect back through the semi-reflective layer to the signal detector. 
   In a continued attempt to increase the storage capacity of optical discs, a multi-layer disc can be constructed as indicated in the publication “SPIE Conference Proceeding Vol. 2890, page 2-9, November, 1996” where a tri-layer or a quadri-layer optical disc was revealed. All the data layers were played back from one side of the disc using laser light at 650 nm wavelength. A double-sided tri-layered read-only-disc that included a total of six layers can have a storage capacity of about 26 gigabytes of information. 
   More recently, a blue light emitting laser diode with wavelength of 400 nm has been made commercially available. The new laser will enable much denser digital videodisc data storage. While current DVD using 650 nm red laser can store 4.7 GB per side, the new blue laser will enable 12 GB per side, enough storage space for about 6 hours of standard-resolution video and sound. With a multi-layer disc, there is enough capacity for a featured movie in the high-definition digital video format. Silver alloys of the present invention can be used for any one layer of the multi-layer optical disc. 
   Recent advances in the development of thin silver alloy films for use as both semi-reflective and highly reflective layers in DVD-9s has made it feasible to create tri-layer and even quadruple-layer optical discs with all playback information layers on the same side of the disc. See for example, U.S. Pat. Nos. 6,007,889, and 6,280,811. Thus multiple-layer disc can be constructed and manufactured at low cost. Combined with objective lens having a numerical aperture (NA) of 0.60, and playback lasers having a wavelength of about 650 nm, multiple-layer optical storage devices with the capacity to store 14 gigabytes of information (DVD-14) or 18 gigabytes (DVD-18) of information storage capacity can be made. 
   Various formats for the next generation optical discs have been proposed. One of these is referred to so as a “Blu-ray” disc. The Blu-ray disc system is characterized by a playback laser operating at a wavelength of about 405 nm (blue light) and an objective lens with a numerical aperture of 0.85. The storage capacity of this device, used with one information layer, is estimated to be about 25 gigabytes for the prerecorded format. Such devices have track pitch values in the 0.32 μm range and channel bit length on the order of 0.05 μm. 
   Because the focal depth of an objective lens with a NA of 0.85 is typically less than one micron, the tolerance of the optical path length variation is drastically reduced relative to currently used systems. Thus a cover layer about 100 microns thick (the distance is measured from the surface of the disc to the information layer) has been proposed. The variation of the thickness of this cover layer is extremely critical to the success of this system. For example, a 2 or 3 micron thickness variation in the cover layer will introduce very high spherical aberration in the playback signal, potentially degrading the signal to an unacceptable low level. 
   Another major problem with the Blu-ray format is that the current generation of production equipment used for DVDs can not be used to produce discs with the Blu-ray format, because the proposed format is too different from currently used DVD format. The need to invest in new equipment to manufacture Blu-ray discs substantially increases the cost of making the Blu-ray disc, and presents another obstacle to adopting the Blu-ray disc system as the standard for the next generation of DVD. 
   In part, because of the aforementioned problems associated with the Blu-ray disc, another format for the next generation of DVD has been proposed. This proposed format is sometimes referred to as the Advanced Optical Disc” (AOD). 
   The AOD format preserves some of the features of the currently used DVD, for example, an AOD comprises two 0.6 mm thick half-discs glued together to create a symmetrical structure. The proposed AOD system uses a playback laser with a wavelength of 405 nm and an objective lens with a NA of about 0.65. The storage capacity of the prerecorded type of AOD disc with one information layer is about 15 gigabytes. Although manufacturing a AOD disc is less complicated and less challenging than manufacturing a Blu-ray disc, AOD suffers one drawback. The playback signal quality of an AOD disc is strongly dependant upon the flatness of the disc. In order to deal with the variation of disc flatness introduced in the mass production of AOD discs, a tilt servo mechanism in the player is most likely required. The need for this mechanism will increase the cost of players designed to read AOD discs. 
   Currently, there is an interest in adapting CD-RW techniques to the DVD field to produce a rewritable DVD (DVD−RW) and next generation phase-change rewritable discs such as Blu-ray or AOD. Some difficulties in the production of a DVD−RW have arisen due to the higher information density requirements of the DVD format. For example, the reflectivity of the reflective layer must be increased relative that of the standard DVD reflective layer to accommodate the reading, writing, and erasing requirements of the DVD−RW format. Also, the thermal conductivity of the reflective layer must also be increased to adequately dissipate the heat generated by both the higher laser power requirements to write and erase information and the microstructural changes occurring during the information transfer process. The potential choice of the reflective layer is currently pure gold, pure silver and aluminum alloys. Gold seems to have sufficient reflectivity, thermal conductivity, and corrosion resistance properties to work in a DVD−RW disk. Additionally, gold is relatively easy to sputter into a coating of uniform thickness. But once again, gold is also comparatively more expensive than other metals, making the DVD−RW format prohibitively expensive. Pure silver has higher reflectivity and thermal conductivity than gold, but its corrosion resistance is relatively poor as compared to gold. Aluminum alloy&#39;s reflectivity and thermal conductivity is considerably lower than either gold or silver, and therefore is not necessarily a good choice for the reflective layer in DVD−RW or DVD+RW. 
   For the convenience of the reader, additional details regarding the manufacture and construction of DVD discs can be found in U.S. Pat. No. 5,640,382 to Florczak et al. the disclosure of which is hereby incorporated by reference. 
   Therefore, what is needed are some new alloys that have the advantages of gold when used as a reflective layer or as a semi-reflective layer in an optical storage medium, but are not as expensive as gold. These new alloys also have better corrosion resistance than pure silver. The current invention addresses that need. 
   SUMMARY OF THE INVENTION 
   It is an objective of this invention to provide new metallic alloys for thin film reflective layers that has high reflectivity and similar sputtering characteristics as gold, and is corrosion resistant yet inexpensive. When a layer of this invention is made thin enough, it can be semi-reflective and transmissive to laser light and used in applications such as a DVD-dual layer. 
   It is another objective of this invention to provide a lower cost alternative to the gold reflective layer in a recordable compact disc and still satisfy other functional requirements of the disc such as, high reflectivity and corrosion resistance. 
   It is a further objective of this invention to provide a silver-based alloy with chemical, thermal, and optical properties that satisfy the functional requirements of the reflective layer in a DVD−RW or DVD+RW disc, and other current or future generations of optical discs in which reflectivity, corrosion resistance, and ease of application are all important requirements for a low cost and high performance product. 
   In one aspect, this invention is an optical storage medium, comprising: a first layer having a pattern of features in at least one major surface; and a first coating adjacent the first layer, the first coating includes a first metal alloy; wherein the first metal alloy comprises: silver; and at least one other element, selected from the group consisting of copper, zinc, silicon, cadmium, tin, lithium, nickel, cobalt, indium, chromium, antimony, gallium, boron, molybdenum, zirconium, beryllium, germanium, aluminum, manganese, and titanium, wherein said other elements are present from 0.01 a/o percent to 10.0 a/o percent of the amount of silver present. In another aspect of the invention, the aforementioned elements alloyed with silver are present in the amount of 0.1 a/o percent to 5.0 a/o percent. The first coating of the optical storage medium may directly contact the first metal layer of the medium. 
   In another aspect of the invention, the medium may further comprise a second layer having a pattern of features in at least one major surface and a second coating adjacent to the second layer. The second layer may include a dielectric material. Additionally, the medium may include a third layer having a pattern of features in at least one major surface, the third layer including an optically recordable material and a forth layer having a pattern of features in at least one major surface, the forth layer may include a dielectric material. 
   In another aspect, this invention is an optical storage medium. The optical storage medium has a substrate with a pattern of features in at least one major surface and a recording layer adjacent the feature pattern. A semi-reflective layer then resides adjacent the recording layer. The optical storage medium may also have a second substrate with a pattern of features in at least one major surface, a second recording layer adjacent the feature pattern, and a second reflective layer adjacent the recording layer. A space layer is then located between the first and second substrates. At least one of the reflective or semi-reflective coatings are made of silver and copper wherein the relationship between the amounts of silver and copper is defined by Ag x Cu t  where 0.90&lt;x&lt;0.999 and 0.001&lt;t&lt;0.10. 
   In still another aspect this invention is an optical storage medium comprising a first layer having a pattern of features in at least one major surface and a semi-reflective layer adjacent to the first feature pattern. The semi-reflective layer or coating can be comprised of any of the metal alloys of the invention suitable for use in a semi-reflective layer and compatible for use with a laser in the range of 405 nm. The storage medium further includes a second layer having a pattern of features in at least one major surface and a highly reflective layer or coating adjacent to the second pattern of features. In one embodiment of the invention the first pattern of features includes a spiral groove. 
   In yet another aspect the invention provides an optical storage device including, in addition to a first layer and second layer each having feature patterns, a forth layer including an optically recordable material positioned between a third layer including a dielectric material and a fifth layer including a dielectric material. Optical recording layer  4  and dielectric layers  3  and  5  are positioned between the first layer and the second layer. In one embodiment of the invention the feature pattern in either, or both, the first and second layers comprise a spiral groove either with or without data pits. 
   In one embodiment of the invention the recordable material in layer  4  is a phase changeable material. 
   In still another embodiment of the invention the recordable material in layer  4  is magnetic optical recordable material. 
   In yet another embodiment of the invention the recordable material in layer  4  is a optically active dye. 
   In another aspect of the invention, the optically recordable material is a phase-changeable material. The optically recordable material may comprise a phase changeable materials selected from the group consisting of Ge—Sb—Te, As—In—Sb—Te, Cr—Ge—Sb—Te, As—Te—Ge, Te—Ge—Sn, Te—Ge—Sn—O, Te—Se, Sn—Te—Se, Te—Ge—Sn—Au, Ge—Sb—Te, Sb—Te—Se, In—Se—Tl, In Sb, In—Sb—Se, In—Se—Tl—Co, Bi—Ge, Bi—Ge—Sb, Bi—Ge—Te, and Si—Te—Sn. The optically recordable material may be a magneto-optic material selected for example from the group consisting of Tb—Fe—Co and Gd—Tb—Fe. 
   In another aspect of the invention, the first metal alloy in the a layer of an optical recording medium may comprise copper, zinc, and silver wherein copper is present from about 0.01 a/o percent to about 10.0 a/o percent, zinc is present from about 0.01 a/o percent to 10.0 a/o, and the remainder is silver. 
   In another aspect of the invention, a metal alloy in a layer of an optical recording medium may comprise copper, titanium, and silver, wherein copper is present in about 0.01 a/o percent to about 10.0 a/o percent of the amount of silver present, and titanium is present from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present in the alloy. 
   In another aspect of the invention, a metal alloy in a layer of an optical recording medium may comprise silver; and at least one other metal selected from the group consisting of gold, rhodium, ruthenium, osmium, iridium, platinum, palladium, and mixtures thereof, wherein at least one of these metals is present from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In another aspect of the invention, the metal alloy in a layer of an optical recording medium may comprise silver, copper, and silicon, wherein copper is present from about 0.01 a/o percent to about 10.0 a/o percent of the amount of silver present, and silicon is present from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In still another aspect this invention is an optical information recording medium, comprising: a first substrate having a pattern of features in at least one major surface; a first recording layer adjacent the feature pattern; and a first reflective layer adjacent to the first recording layer. The reflective layer includes a first metal alloy; wherein the first metal alloy comprises: silver; and at least one other element selected from the group consisting of copper, zinc, titanium, cadmium, lithium, nickel, cobalt, indium, aluminum, germanium, chromium, germanium, tin, beryllium, magnesium, manganese, antimony, gallium, silicon, boron, zirconium, molybdenum, and mixtures thereof, wherein said other elements are present from 0.01 a/o percent to 10.0 a/o percent of the amount of silver present. In another aspect of the invention, the other elements of the aforementioned metal alloy are present from about 0.1 a/o percent to 5.0 a/o percent of the amount of silver present in the alloy. 
   In one aspect of the invention, the first recording layer of an optical information recording medium may directly contact the first metal layer. 
   In another aspect of the invention, a metal alloy of an optical recording medium, may comprise silver, copper, and zinc wherein copper is present from about 0.01 a/o percent to 10.0 a/o percent of the amount of silver present, and zinc is present from about 0.01 a/o percent to 10.0 a/o percent of the amount of silver present. 
   In another aspect of the invention, a metal alloy of a layer of an optical recording medium is comprised of silver and at least one element selected from the group consisting of gold, rhodium, ruthenium, osmium, iridium, platinum, palladium, and mixtures thereof, wherein the element is present from about 0.01 a/o percent to 5.0 a/o percent of the amount of silver present. 
   In yet another aspect, the invention is an optical storage medium, comprising: a first substrate having a pattern of features in at least one major surface; a semi-reflective layer adjacent a feature pattern, the semi-reflective layer including a metal alloy; the metal alloy comprising: silver; and copper; wherein the relationship between the amounts of silver and copper is defined by Ag x Cu y , where 0.90&lt;x&lt;0.999, 0.001&lt;y&lt;0.10; a second substrate having a pattern of features in at least one major surface; a high reflective layer adjacent the feature pattern of the second substrate; and at least one spacer layer, located between said first and second substrates. 
   The aforementioned medium may further include a second substrate having a pattern of features in at least one major surface and a second reflective layer adjacent the second substrate. The metal alloy may also be comprised of at least one additional element selected from the group consisting of silicon, cadmium, tin, lithium, nickel, cobalt, indium, chromium, antimony, gallium, boron, molybdenum, zirconium, beryllium, titanium, magnesium, wherein the elements are present from about 0.01 a/o percent to 10.0 a/o percent of the amount of silver present. 
   In still another aspect of the invention, the first metal alloy in an optical storage medium with both reflective and semi-reflective layers, comprising Ag x Cu y , where 0.90&lt;x&lt;0.999, 0.001&lt;y&lt;0.10 , includes manganese present from about 0.01 a/o percent to about 7.5 a/o percent of the amount of silver present. 
   In still another aspect of the invention, the metal alloy in an optical storage medium with both reflective and semi-reflective layers, comprising Ag x Cu y , where 0.90&lt;x&lt;0.999, 0.001&lt;y&lt;0.10, includes manganese present from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In still another aspect of the invention, the metal alloy in an optical storage medium with both reflective and semi-reflective layers, comprising Ag x Cu y , where 0.90&lt;x&lt;0.999, 0.001&lt;y&lt;0.10, includes titanium present from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In still another aspect of the invention, the metal alloy in an optical storage medium with both reflective and semi-reflective layers, comprising Ag x Cu y  where 0.90&lt;x&lt;0.999, 0.001&lt;y&lt;0.10, includes silicon present from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In another aspect of the invention, the semi-reflective layer of optical storage medium includes a metal alloy comprising Ag x Cu y , wherein 0.95&lt;x&lt;0.999, 0.001&lt;y&lt;0.050. 
   In another aspect of the invention, an optical storage medium has at least one semi-reflective layer comprising a metal alloy including Ag x Cu y , wherein 0.95&lt;x&lt;0.999, 0.001&lt;y&lt;0.050. 
   In another aspect of the invention, the semi-reflective layer of an optical storage medium directly contacts the first metal alloy of the medium. 
   In another aspect of the invention, an optical information recording medium, may further include a second substrate having a pattern of features in at least one major surface and spacer layer located between the first and second substrates. 
   In one aspect, this invention is an optical storage medium with a first substrate having a pattern of features in at least one major surface and a first reflective layer adjacent the feature pattern. The reflective layer is made of a silver and zinc alloy wherein the relationship between the amount of silver and the amount of zinc is defined by Ag x Zn y , where 0.85&lt;x&lt;0.9999 and 0.0001&lt;y&lt;0.15. 
   In another aspect, this invention is an optical storage medium with a first substrate having a pattern of features in at least one major surface and a first reflective layer adjacent the feature pattern. The reflective layer is made of a silver and aluminum alloy where the relationship between the amount of silver and the amount of aluminum is defined by Ag x Al z , where 0.95&lt;x&lt;0.9999 and 0.0001&lt;z&lt;0.05. 
   In another aspect, this invention is an optical storage medium with a first substrate having a pattern of features in at least one major surface and a first reflective layer adjacent the feature pattern. The reflective layer is made of a silver and zinc and aluminum alloy where the relationship between the amount of silver and the amount of zinc and the amount of aluminum is defined by Ag x Zn y Al z , where 0.80&lt;x&lt;0.998 and 0.001&lt;y&lt;0.15, and 0.001&lt;z&lt;0.05. 
   In another aspect, this invention is an optical storage medium with a first substrate having a pattern of features in at least one major surface and a first reflective layer adjacent the feature pattern. The reflective layer is made of a silver and manganese alloy where the relationship between the amount of silver and manganese is defined by Ag x Mn t , where 0.925&lt;x&lt;0.9999 and 0.0001&lt;t&lt;0.075. 
   In another aspect, this invention is an optical storage medium with a first substrate having a pattern of features in at least one major surface and a first reflective layer adjacent the feature pattern. The reflective layer is made of a silver and germanium alloy wherein the relationship between the amount of silver and the amount of germanium is defined by Ag x Ge q , where 0.97&lt;x&lt;0.9999 and 0.0001&lt;q&lt;0.03. 
   In another aspect, this invention is an optical storage medium with a first substrate having a pattern of features in at least one major surface and a first reflective layer adjacent the feature pattern. The reflective layer is made of a silver and copper and manganese alloy wherein the relationship between the amount of silver and the amount of copper and the amount of manganese is defined by Ag x Cu p Mn t , where 0.825&lt;x&lt;0.9998 and 0.0001&lt;p&lt;0.10, and 0.0001&lt;t&lt;0.075. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an optical storage system according to one embodiment of this invention. 
       FIG. 2  is an optical storage system according to another embodiment of this invention where an organic dye is used as a recording layer. 
       FIG. 3  is an optical storage system according to another embodiment of this invention with two layers of information pits where the playback of both layers is from one side. 
       FIG. 4  is an optical storage system according to another embodiment of this invention with three layers of information pits where the playback of all three layers is from one side. 
       FIG. 5  is an optical storage system according to another embodiment of this invention where the system contains a rewritable information layer. 
       FIG. 6  is an optical storage system according to another embodiment of this invention where the system contains a rewritable information layer. 
       FIG. 7  is an optical storage system according to another embodiment of this invention for example a DVD-14. 
       FIG. 8  is an optical storage system according to another embodiment of this invention the for example a DVD-18. 
       FIG. 9  is an optical storage system according to another embodiment of the invention, an optical storage system of the Blu-ray type with layers suitable for high density digital information storage readable from one side. 
       FIG. 10  is an optical storage system according to another embodiment of the invention, an optical storage system of the Blu-ray type including two re-writable high density digital information storage layers readable and re-recordable from one side. 
       FIG. 11  is an optical storage system according to another embodiment of the invention, an optical storage system of the Advanced Optical Disc (AOD) type including two high density digital information storage layers readable from one side. 
       FIG. 12  is an optical storage system according to another embodiment of the invention, an optical storage system of the Advanced Optical Disc (AOD) type including two re-writable high density digital information storage layers readable and re-recordable from one side. 
       FIG. 13  is an optical storage system according to still another embodiment of the invention including two readable and recordable layers readable and recordable from one side. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Specific language is used in the following description and examples to publicly disclose the invention and to convey its principles to others. No limits on the breadth of the patent rights based simply on using specific language are intended. Also included are any alterations and modifications to the descriptions that should normally occur to one of average skill in this technology. 
   As used in this specification the term “atomic percent” or “a/o percent” refers to the ratio of atoms of a particular element or group of elements to the total number of atoms that are identified to be present in a particular alloy. For example, an alloy that is 15 atomic percent element “A” and 85 atomic percent element “B” could also be referenced by a formula for that particular alloy: A 0.15 B 0.85 . 
   As used herein the term “of the amount of silver present” is used to describe the amount of a particular additive that is included in the alloy. Used in this fashion, the term means that the amount of silver present, without consideration of the additive, is reduced by the amount of the additive that is present to account for the presence of the additive in a ratio. For example, if the relationship between Ag and an element “X” is Ag 0.85  X 0.15  (respectively 85 a/o percent and 15 a/o percent) without the considering the amount of the additive that is present, and if an additive “B” is present at a level 5 atomic percent “of the amount of silver present”; then the relationship between Ag, X, and B is found by subtracting 5 atomic percent from the atomic percent of silver, or the relationship between Ag, X, and B is Ag 0.80  X 0.15  B 0.05  (respectively 80 a/o percent silver, 15 a/o percent “X”, and 5 a/o percent “B”). 
   As used in this specification the term “adjacent”refers to a spatial relationship and means “nearby” or “not distant.” Accordingly, the term “adjacent” as used in this specification does not require that items so identified are in contact with one another and that they may be separated by other structures. For example, referring to  FIG. 5 , layer  424  is “adjacent” or “nearby” layer  422 , just as layer  414  is “adjacent” or “nearby” layer  422 . 
   Metal alloys for use in optical recording devices have been disclosed in U.S. Pat. Nos. 6,007,889, 6,280,811, 6,451,402 B1 and 6,544,616 B2, and these patents are hereby incorporated by reference in their entirety. 
   This invention comprises multi-layer metal/substrate compositions that are used as optical data storage media. One embodiment of this invention is shown in  FIG. 1  as optical data storage system  10 . Optical storage medium  12  comprises a transparent substrate  14 , and a highly reflective thin film layer or coating  20  on a first data pit pattern  19 . An optical laser  30  emits an optical beam toward medium  12 , as shown in FIG.  1 . Light from the optical beam that is reflected by thin film layer  20  is sensed by detector  32 , which senses modulations in light intensity based on the presence or absence of a pit or land in a particular spot on the thin film layer. The disc is unique in that one of the alloys presented below is deposited upon the information pits and lands and is used as the highly reflective thin film  20 . In one alternative (not shown), the disc may be varied by attaching two optical storage media  12  back-to-back, that is, with each transparent substrate  14  facing outward. 
   Another embodiment of this invention is shown in  FIG. 2  as optical data storage system  110 . Optical storage medium  112  comprises a transparent substrate  114 , and a highly reflective thin film layer  120 , over a layer of dye  122 , placed over a first pattern  119 . An optical laser  130  emits an optical beam toward medium  112 , as shown in FIG.  2 . As discussed earlier, data is placed upon the disc by deforming portions of the dye layer with a laser. Thereafter, the disc is played by light from the optical beam, which is reflected by thin film layer  120  and sensed by detector  132 . Detector  132  senses modulations in light intensity based on the presence or absence of a deformation in the dye layer. The disc is unique in that one of the alloys presented below is deposited over the dye layer  122  and is used as the highly reflective thin film or coating  120 . In one alternative (not shown), the disc may be varied by attaching two optical storage media  112  back-to-back, that is, with each transparent substrate  114  facing outward. 
   Another embodiment of this invention is shown in  FIG. 3  as optical data storage system  210 . Optical storage medium  212  comprises a transparent substrate  214 , a partially reflective thin film layer or coating  216  on a first data pit pattern  215 , a transparent spacer layer  218 , and a highly reflective thin film layer or coating  220  on a second data pit pattern  219 . An optical laser  230  emits an optical beam toward medium  212 , as shown in FIG.  3 . Light from the optical beam that is reflected by either thin film layer  216  or  220  is sensed by detector  232 , which senses modulations in light intensity based on the presence or absence of a pit in a particular spot on the thin film layers. The disc is unique in that one of the alloys presented below is deposited upon the information pits and lands and used as the highly reflective thin film  220  or semi-reflective layer  216 . In another alternative (not shown), the disc may be varied by attaching two optical storage media  212  back-to-back, that is, with each transparent substrate  214  facing outward. The attachment method could be by UV cured adhesive, hot melt adhesive or other type of adhesives. 
   Another embodiment of this invention is shown in  FIG. 4  as optical data storage system  310 . Optical storage medium  312  comprises a transparent substrate  314 , a partially reflective thin film layer or coating  316  or layer “zero” on a first data pit pattern  315 , a transparent spacer layer  318 , another partially reflective thin film layer or coating  320  or layer “one” on a second data pit pattern  319 , a second transparent spacer layer  322 , and a highly reflective thin film layer or coating  324  or layer“two” on a third pit pattern  323 . An optical laser  330  emits an optical beam toward medium  312 , as shown in FIG.  4 . Light from the optical beam that is reflected by thin film layer  316 ,  320  or  324  is detected by detector  332 , which senses modulation in light intensity based on the presence or absence of a pit in a particular spot on the thin film layers. The disc is unique in that any or all of the alloys presented below can be deposited upon the information pits and lands and used as the highly reflective thin film or coating  324  or the semi-reflective layer or coating  316  and  320 . To playback the information on Layer  2 , the light beam from laser diode  330  is going through the transparent polycarbonate substrate, passing through the first semi-reflective Layer  0 , and the second semi-reflective Layer  1  and then reflected back from layer  2  to the detector  332 . In another alternative (not shown), the disc may be varied by attaching two optical storage media  312  back-to-back, that is, with each transparent substrate  314  facing outward. The attachment method could be by UV cured adhesive, hot melt adhesive or other type of adhesives. 
   Still another embodiment of this invention is shown in  FIG. 5  as optical data storage system  410 . Optical storage medium  412  comprises a transparent substrate or a transparent layer  414 , a dielectric layer  416  on a first data pit pattern  415 , a recording layer  418  made of a material having a microstructure including domains or portions capable of repeatedly undergoing laser-induced transitions from a first state to a second state and back again (i.e., an optically re-recordable or rewritable layer), such as a phase change material or a magneto-optic material, another dielectric material  420 , a highly reflective thin film layer  422 , and a transparent substrate or layer  424 . As used in this specification, a dielectric material is a material that is an electrical insulator or in which an electric field can be sustained with a minimum dissipation of power. The different layers  414 ,  416 ,  418 ,  420  and  422  of the optical storage medium  410  are preferably oriented so as to be adjacent with one another. 
   The optical recordable material may be for example, a magneto-optic material selected from the group consisting of Tb—Fe—Co and Gd—Tb—Fe. 
   Commonly used phase change materials for the recording layer  418  include germanium-antimony-tellurium (Ge—Sb—Te), silver-indium-antimony-tellurium (Ag—In—Sb—Te), chromium-germanium-antimony-tellurium (Cr—Ge—Sb—Te) and the like. Commonly used materials for the dielectric Layer  416  or  420  include zinc sulfide-silica compound (ZnS.SiO 2 ), silicon nitride (SiN), aluminum nitride (AlN) and the like. Commonly used magneto-optic materials for the recording layer  418  include terbium-iron-cobalt (Tb—Fe—Co) or gadolinium-terbium-iron (Gd—Tb—Fe). An optical laser  430  emits an optical beam toward medium  412 , as shown in FIG.  5 . In the recording mode for the phase change recordable optical medium, light from the optical beam is modulated or turned on and off according to the input digital data and focused on the recording layer  418  with suitable objective while the medium is rotated in a suitable speed to effect microstructural or phase change in the recording layer. In the playback mode, the light from the optical beam that is reflected by the thin film layer  422  through the medium  412  is sensed by the detector  432 , which senses modulations in light intensity based on the crystalline or amorphous state of a particular spot in the recording layers. The disc is unique in that one of the alloys presented below is deposited upon the medium and used as the highly reflective thin film  422 . In another alternative (not shown), the disc may be varied by attaching two optical storage media  412  back-to-back, that is, with each transparent substrate or coating  414  facing outward. The attachment method could be by UV cured adhesive, hot melt adhesive or other type of adhesives. 
   As shown in  FIG. 5 , if transparent substrate  414  is about 1.2 mm thick made of injection molded polycarbonate with continuous spirals of grooves and lands,  424  is a UV cured acrylic resin 3 to 15 micron thick acting as a protective layer with the playback laser  430  at 780 to 820 nanometer, and rewritable layer  418  is a phase change material of a typical composition such as Ag—In—Sb—Te, it is a compact disc-rewritable disc structure, commonly known as a CD-RW. To record and read information, phase change discs utilize the recording layer&#39;s ability to change from an amorphous phase with low reflectivity (dark) to a crystalline phase with high reflectivity (bright). Before recording, the phase change layer is in a crystalline state. During recording, a laser beam with high power focused on the recording layer will heat the phase change material to high temperature and when the laser is turned off, the heated spot will cool off very quickly to create an amorphous state. Thus a series of dark spots of amorphous states are created according to the input data of turning the focused laser beam on and off. These on and off correspond to “0” and “1” of a digital data stream. 
   In reading, a low laser power is used to focus on and read the dark or bright spots along the track of the disc to play back the recorded information. To erase, an intermediate laser power is used to focus on the grooves or tracks with the disc spinning so that an intermediate temperature of the focused spots is reached. After the laser is moved to another location, the spots cool to room temperature forming a crystalline structure of high reflectivity. This returns the recording layer to its original or erased state. The change of the spots&#39; state from amorphous to crystalline is very reversible, thus many record and erase cycles can be accomplished and different data can be repeatedly recorded and read back without difficulty. 
   If transparent substrate  414  is about 0.5 to 0.6 mm thick made of injection molded polycarbonate with continuous spirals of grooves and lands,  416  and  420  are dielectric layers typically made of ZnS.SiO 2 ,  418  is made of a phase change material such as Ag—In—Sb—Te or Ge—Sb—Te,  422  is made of a silver alloy of the current invention, and  424  is a UV cured resin bonding another half of the same structure as depicted in  FIG. 5. , and the structure is used with a read and write laser  430  at 630 to 650 nanometer wavelength, then it is a digital versatile disc with rewritable capability, commonly referred to as DVD+RW. Some preferred phase-changeable materials include materials from the following series: As—Te—Ge, As—In—Sb—Te, Te—Ge—Sn, Te—Ge—Sn—O, Bi—Ge, Bi—Ge—Sb, Bi—Ge—Te, Te—Se, Sn—Te—Se, Te—Ge—Sn—Au, Ge—Sb—Te, Sb—Te—Se, In—Se—Tl, In—Sb, In—Sb—Se, In—Se—Tl—Co, Cr—Ge—Sb—Te and Si—Te—Sn, where As is arsenic, Bi is Bismuth, Te is tellurium, Ge is germanium, Sn is tin, O is oxygen, Se is selenium, Au is gold, Sb is antimony, In is indium, Tl is thallium, Co is cobalt, and Cr is chromium. In this disc configuration, the highly reflective layer  422  needs not only high reflectivity at 650 nanometer wavelength and high thermal conductivity, but also high corrosion resistance in the presence of ZnS.SiO 2 . Conventional aluminum alloy does not have high enough reflectivity nor high enough thermal conductivity. Pure silver or other conventional silver alloys do not have either high corrosion resistance or high reflectivity and high thermal conductivity. Thus it is another objective of the current invention to provide a series of silver alloys that can meet the requirements for this application. 
   Another embodiment of the current invention is shown in  FIG. 6 , a rewritable type optical information storage system  510 . Transparent cover layer  514  is approximately 0.1 mm thick. Dielectric layers  516  and  520  are preferably made of ZnS.SiO 2  and serve as a protective layer for the rewritable layer or phase change layer  518 . Rewritable layer  518  is preferably formed from Ag—In—Sb—Te or the like. Highly reflective layer  522  is preferably formed from a silver alloy, such as disclosed herein. Transparent substrate  524  is preferably approximately 1.1 mm in thickness with continuous spiral tracks of grooves and lands usually made with polycarbonate resin. Laser  530  preferably has a wavelength of about 400 nm with associated optics to focus the laser beam onto recording layer  518 . The reflected laser beam is received by the detector  532 , which preferably includes associated data processing capability to read back the recorded information. System  510  is sometimes called a “Digital Video Recording System”or DVR, and it is designed to record high definition TV signal. The principle of operation of optical information storage system  510  is similar to that of a CD-RW disc except that the recording density is considerably higher, the storage capacity of a 5 inch diameter disc is approximately 20 gigabytes. Again the performance of the disc stack depends on a layer  522 , that is highly reflective at 400 nm wavelength, with high corrosion resistance and very high thermal conductivity. Conventional reflective layers such as aluminum, gold or copper all have difficulty meeting these requirements. Thus it is another objective of the current invention to provide a silver alloy reflective layer that is capable of meeting these demanding requirements. 
   Other optical recording media which can be used to practice this invention include for example optical storage devices readable and in some embodiments also rewritable from both sides of the device. 
   One embodiment of this invention is illustrated in  FIG. 7  optical data storage system  610 . Optical storage system  610  is sometimes referred to as DVD-14 and is illustrative of devices that have the capacity to store accessible data on both sides of the structure. 
   Optical storage system  610  comprises a 0.6 mm thick transparent polycarbonate substrate (PC), adjacent to the PC layer or a part of the PC layer is a first data pit pattern  614  comprising a series of pits and lands. Adjacent to layer  614  and conforming to the contour of layer  614  is a semi-reflective layer or coating  618 . Adjacent to the layer or coating  618  is a spacer  622  comprised of a transparent material adjacent to or a part of spacer layer  622  is a second data pit pattern  626  comprising a series of pits and lands. Adjacent to and conforming to the contour of second data pit pattern  626  is a reflective layer or coating  630 . Both semi-reflective layer or coating  618  and highly reflective layers  630  can be read from the same side of structure  610 . 
   Adjacent to layer or coating  634  is a second reflective layer or coating  638 . Layer or coating  638  is adjacent to and conforms to the contours of a third data pit pattern  642  comprising a series of pits and lands. Third data pit pattern  642  and highly reflective layer or coating  638  are readable from the side of the device opposite to the side of the device from which data pit patterns  618 ,  626  are read. Adjacent to or comprising data pit pattern  642  is a second 0.6 mm thick polycarbonate layer. 
   An optical laser  660  emits an optical beam towards second polycarbonate layer PC, the beam is reflected by highly reflective layer or coating  638  and sensed by detector  662  modulations in light intensity based on the presence or absence of a pit in a particular spot on the highly reflective coating or layer. 
   As illustrated in  FIG. 7 , from the side of device  610  opposite of laser  660 , a second optical beam from laser  650  is directed towards first polycarbonate substrate layer PC towards data pit pattern  614 . As illustrated in  FIG. 7 , the second laser  650  emits an optical beam towards semi-reflective layer or coating  618  and highly reflective layer  630 . At least a portion of the optical beam emitted by laser  650  passes through semi-reflective layer  618  to reach reflective layer  626 . Light from the optical beam that is reflected by layer or coating  626  is sensed by detector  652 , which senses modulations in light intensity based on the presence or absence of a pit or land in a particular spot on the highly reflective layer. 
   While the optical storage device illustrated in  FIG. 7  comprises multiple laser sources  650 ,  660  and multiple detectors  652 ,  662 , the same could be accomplished using a single laser source and detector configured such that the same optical beam source and detector can be used to collect signal from all sets of information pits and lands comprising the device, for example set  618 ,  626 ,  642 . 
   In still another embodiment the invention may be practiced using the optical storage system  710  as illustrated in FIG.  8 . Optical storage medium  710  is illustrative of a DVD-18 and is representative of optical storage systems that have multiple information layers readable from both sides of the optical storage medium. 
   Optical storage system  710  comprises a 0.6 mm thick transparent substrate  712  adjacent to, or comprising a first data pit pattern  714 . Data pit pattern  714  comprises a series of pits and lands and is adjacent to a semi-reflective layer or coating  716 . The device further includes a transparent spacer layer  718  about 50 microns thick, and a second data pit pattern  720  adjacent to a highly reflective film or coating  722 . Both semi-reflective layer or coating  716  and highly reflective layer or coating  722  can be read from the same side of  710 . 
   An optical laser  770  emits an optical beam towards transparent layer  712 . As illustrated in  FIG. 7  at least a portion of the optical beam emitted by laser source  770  passes through semi-reflective layer  716  to reach highly reflective layer  722 . Light from the optical beam that is reflected by semi-reflective layer or coating  716  and highly reflective layer  722  is sensed by detector  772 , which senses modulations in light intensity based on the presence or absence of a pit or land in a particular spot on the highly reflective layer or the semi-reflective layer. 
   The optical storage device illustrated in  FIG. 8  further includes the spacer layer  724 , which connects the portion of the device comprising the first two information layers  714 ,  720  with the portion of the device comprising the third and forth information layers  728 ,  734 . Substrate layer  724  is adjacent to and separates highly reflective layer or coating  728  and highly reflective layer or coating  722 . 
   Highly reflective layer or coating  724  is adjacent to, and conforms to the contours of the pit and lands or data pit pattern layer  728 . Layer  728  is adjacent to spacer layer  726 , spacer layer  726  is adjacent to semi-reflective layer  732 , which is adjacent to, and conforms to the contours of data pit pattern layer  734 . Data pit pattern layer  734  is contiguous with, or adjacent to, 0.6 mm thick substrate layer  736 . 
   In the embodiment illustrated in  FIG. 8  an optional second optical laser  780  is provided which emits an optical beam towards layer  736 . A portion of the light emitted by laser  780  passes through semi-reflective layer or coating  732  and is reflected by highly reflective layer or coating  724  light reflected by semi-reflective layer or coating  732  and highly reflective layer  724  is sensed by detector  782 , which senses modulations in light intensity based on the presence or absence of a pit or land in a particular spot on the highly reflective layer. 
   While the optical storage device illustrated in  FIG. 8  includes multiple laser sources  770 ,  780  and multiple detectors  752 ,  772 , the same could be accomplished using a single laser source and detector configured such that the same optical beam source and detector can be used to collect signal from all sets of information pits and lands comprising the device. 
   Yet another embodiment of the inventions includes the proposed next generation optical storage device sometimes referred to as “Blu-ray.” Blu-ray devices incorporate lasers, which operate at a wavelength of 405 nm and lenses, with a numerical aperture of 0.85. 
   As illustrated in  FIG. 9  optical storage system  810  of the prerecorded type of “Blu-Ray” disc comprises two sets of information pits and lands  818  and  830  readable from the same side of the device. Device  810  comprises transparent cover layer  814  about 0.1 mm in thickness, and a substrate layer  838  about 1.1 mm thickness with an adjacent highly reflective layer or coating  834 . Highly reflective layer or coating  834  is adjacent to, and conforms to the second data pit pattern  830  injection molded onto the substrate  838 . Data pit pattern  830  comprising a set of pits and lands is adjacent to, or a part of, substrate  838 . Layer  826  is adjacent to the semi-reflective layer  822 . Semi-reflective layer or coating  822  is adjacent and conforms to first data pit pattern  818  comprising a set of pits and lands. Data pit  818  is adjacent to or a part of the transparent cover layer  814 . 
   As illustrated in  FIG. 9 , an optical beam source laser  850  is provided, as is detector  852 . Optical laser  850  emits an optical beam towards layer  814  through an objective lens (not shown in FIG.  9 ). A portion of the light emitted by laser  850  passes through a lens (not shown), the semi-reflective layer, or coating,  822  and is reflected by highly reflective layer, or coating,  834  and sensed by detector  852 , which senses modulations in light intensity based on the presence or absence of a pit or land in a particular spot on the highly reflective layer or coating  822 . 
   A portion of the optical beam emitted by optical laser  850  is partially reflected by semi-reflective layer or coating  822  is sensed by detector  852 , which senses modulations in light intensity based on the presence or absence of a pit or land in a particular spot on semi-reflective layer or coating  822 . 
   In one embodiment of the invention as illustrated in  FIG. 10 , an optical storage device  910  of the Blu-ray rewritable type further comprises two read and rewritable layers  926 ,  954 . Optical storage device  910  comprises a substrate layer  972  about 1.1 mm thick, adjacent to highly reflective layer or coating  968 . Adjacent to layer or coating  968  is a first dielectric layer  964  comprising ZnS—SiO 2 , adjacent to layer  964  is a first interface layer  960  such as Ge—N or others. Adjacent to layer  960  is a phase-change type recording layer such as Ge—Sb—Te  954  and the like with thickness about 10 to 15 nm, adjacent to layer  954  is layer  950  a second layer such as Ge—N and the like. Adjacent to layer  950  is layer  946  a second dielectric layer of ZnS—SiO 2 . 
   Optical storage device  910  further includes an intermediate layer  942  sandwiched between the dielectric layer  946  approximately 20 to 40 microns thick and a semi-reflective layer or coating  938  about 10 nm thick. A third dielectric layer  934  comprised of ZnS—SiO 2  is adjacent to layer or coating  938 . Adjacent to layer  934  is a third Interface layer  930  made with Ge—N or others, a recording layer  926  6-10 nm thick comprised of Ge—Sn—Sb—Te or other phase-change material is sandwiched between layers  930  and a forth interface layer  922  made of Ge—N and the like. Adjacent to layer  922  is a forth layer of dielectric material layer  918  comprised of ZnS—SiO 2  Adjacent to layer  918  is a transparent cover layer  914  about 80 to 100 microns thick. 
   As illustrated in  FIG. 10  an optical beam emitted by laser  970  passes through layers  914 ,  918 ,  922 ,  926 ,  930 ,  934  and is reflected by layer  938  and sensed by detector  972 . A portion of an optical beam emitted by laser  970  passes through layers  914 ,  918 ,  922 ,  926 ,  930 ,  934 ,  938 ,  942 ,  946 .  950 ,  954 ,  960 ,  964 , and is reflected by layer  968  to and sensed by detector  972 . All the silver alloy compositions disclosed in this invention can be used for the semi-reflective layer  938  or the highly reflective layer  968 . In the recording mode, the laser beam from laser  970  will be focused on the phase-change layer  926  or  954  to change its reflectivity properties similar to a conventional CD-RW, DVD−RW, DVD+RW or next generation of optical discs with playback laser wavelength at around 400 nm as disclosed in prior art such as U.S. Pat. Nos. 6,544,616, 6,652,948, 6,649,241 and others. 
   It is understood that the disc structure as described in  FIG. 11  can be modified that both  1014  and  1060  can be of approximately of the same thickness or around 0.6 mm and with similar phase-change material recording stack, the disc structure could be a rewritable optical disc of the “Advanced Optical Disc” or AOD type wherein the recording and playback laser wavelength is around 400 nm. 
   It is further understood that all the optical disc structure as described in  FIG. 7 ,  8  ,  9 ,  12  contain a dual layer disc structure of the prerecorded type wherein the playback laser beam has a wavelength of around 635 to 650 nm as in  FIG.7 and 8 , or contain a dual layer HD-DVD disc structure wherein the playback laser has a wavelength around 400 nm or any other optical disc structure with two or more layers of information all recorded or played back from one side of the disc in which a semi-reflective layer or layers of silver alloy as disclosed in this invention is made useful. 
   One embodiment of the invention as illustrated in  FIG. 11  is an optical storage device  1010  of the ‘Blu-ray’ configuration further comprising two write once layers  1048  and  1024 . Optical storage device  1010  is a dual-layer write once recording medium comprised of 1.1 mm thick substrate layer  1060 , adjacent to a highly reflective layer  1056  about 30 to 60 nm thick usually made with silver alloy of the current invention or an aluminum alloy. Layer  1056  is adjacent to protective layer  1052 , layer  1052  is adjacent to a recordable layer  1048 , 15 to 25 nm thick comprised of Te—O—Pd based material or others. Layer  1048  is adjacent to protective film layer  1044 . 
   Layer  1044  is adjacent to a separation layer or spacer layer  1040  which is adjacent to a 10 nm thick semi-reflective layer or coating  1034  made with silver alloy of the current invention. Layer or coating  1034  is adjacent to protective film layer  1030  which is adjacent to a second 10 nm thick recording layer  1024  comprising Te—O—Pd based material or others. Layer  1024  is adjacent to protective film  1020  which is adjacent to a 0.075 mm thick cover layer  1014 . 
   As illustrated in  FIG. 11 , an optical beam emitted by laser  1070  passes a lens system with NA 0.85 (not shown in FIG.  11  through layers  1014 ,  1020 ,  1024 ,  1030  and is reflected by the semi-reflective layer  1034  and sensed by detector  1072 . A portion of an optical beam emitted by laser  1070  passes through layers  1014 ,  1020 ,  1024 ,  1030 ,  1034 ,  1040 ,  1044 ,  1048 ,  1052 , and is reflected by highly reflective layer  1056  and sensed by detector  1072 . Detector  1072  senses modulations in light intensity based on the amorphous or the crystalline state of the layer  1024  or  1048  in a particular spot on semi-reflective layer or coating  1034  and on the highly reflective layer  1056  and reads the stored information back by focusing laser light from  1070  laser on the write-once layer  1024  or  1048 . The spacer layer  1040  should be thick enough so that when the read beam is focused on the recordable layer  1024 , the read beam is sufficiently defocused on the next recordable layer  1048  and only the modulation of light information from  1024  is reflected back to the detector  1072 . Conversely, when the read beam is focused on the recordable layer  1048 , the read beam is sufficiently defocused on the other recording layer  1024  and only the modulation from  1048  is reflected to the detector  1072  and read. 
   It is also understood that as described in  FIG. 10 and 11 , a dual layer disc of the write-once or a rewritable type with a phase change recording layer or other types of recording layers can be constructed that at least two recording layers can be recorded and read from one side or the same side of the disc wherein a semi-reflective layer made with silver alloy of the current invention can be utilized and made useful. 
   Another embodiment the invention, as illustrated in  FIG. 12  is optical storage device  1110  of a prerecorded type is the proposed next generation optical storage device sometimes referred to as an Advanced Optical Device (AOD). AOD is a system that uses a 405 nm wavelength laser beam and a lens system with a NA of 0.65 to record and retrieve information for both faces of an optical storage device wherein the transparent substrates  1120  and  1140  made typically with injection molded polycarbonate are approximately 0.6 mm thick. 
   Device  1110  comprises a transparent substrate layer  1140  adjacent to a highly-reflective layer or coating  1136  which is adjacent to and conforms to the contours of a first data pit pattern  1138  comprising a set of pits and lands. High reflectivity layer  1136  is adjacent to spacer layer  1132  which is adjacent to a semi-reflective layer or coating  1124  of the current invention which is adjacent to and conforms to the contours of a second data pit pattern  1128  comprising a series of pits and lands. Layer  1124  is adjacent to a second substrate or layer  1120 . 
   As illustrated in  FIG. 12 , a portion of an optical beam emitted by laser  1150  passes through layers  1120 ,  1124 ,  1128 ,  1132 , and is reflected by the highly reflective layer  1136  and sensed by detector  1152 . A portion of an optical beam emitted by laser  1150  passes through layers  1120 , and is reflected by semi-reflective layer or coating  1124  and sensed by detector  1152 . Detector  1152  senses modulations in light intensity based on the presence or absence of a pit or land in a particular spot on semi-reflective layer or coating  1124  and the highly reflective layer or coating  1136  by focusing on layer  1124  or  1136 . 
   In another embodiment the invention, illustrated in  FIG. 13  an optical storage device  1210  of the organic dye recordable-dual-layer type comprises two layers which are both readable and recordable from the same side of the device. Device  1210  comprises a transparent substrate layer  1214  adjacent to first recordable dye layer  1218 . Dye layer  1218  is adjacent to semi-reflective layer or coating  1222  of the current invention. Layer or coating  1222 , sometimes called “Layer zero” or L 0 , is adjacent to spacer layer  1226 . Spacer layer  1226  is adjacent to a second dye recording layer  1230 . Layer  1230  is adjacent to highly reflective layer or coating  1234 . Reflective layer or coating  1234 , sometimes called “layer one” or L 1 , is adjacent to polycarbonate substrate or layer  1238 . 
   In write mode, as illustrated in  FIG. 13 , optical beam source  1250  emits a laser beam which passes through layers  1214 , and is focused on dye layer  1218 . When laser  1250  is operating at high intensity the optical beam focused on layer  1218  decomposes the dye in layer  1218  creating a data pit pattern comprising the equivalent of a series of pits and lands. A portion of an optical beam emitted by laser  1250  passes through layers  1214 ,  1218 ,  1222 ,  1226  and is focused on dye layer  1230 . When laser  1250  is operating at high intensity, the optical beam focused on layer  1230  decomposes the dye in layer  1230  to create a data pit pattern comprising a series of pits and lands. 
   In read mode a portion of an optical beam emitted by laser  1250  passes through transparent polycarbonate layer  1214  and dye layer  1218 , is reflected by the semi-reflective layer or coating  1222  and sensed by detector  1252 . A portion of the optical beam also passes through layers  1214 ,  1218 ,  1222 ,  1226 ,  1230  and is reflected by highly reflective layer  1234  and sensed by detector  1252 . Detector  1252  senses modulations in light intensity based on the presence or absence of a pit or land in a particular spot on the reflective layer or coating  1234  or by the semi-reflective layer or coating  1222  depending on whether the laser light  1250  is focused on the semi-reflective layer  1222  or the highly reflective layer  1234 . For the general operation of an organic dye-based optical recording medium, the reader can refer to U.S. Pat. Nos. 6,641,889, 6,551,682, etc. 
   It is further understood that the optical disc structure as described in  FIG. 13  can be a dual layer DVD−R or DVD+R disc wherein the playback laser beam has a wavelength of around 635 to 650 nm, or the structure can be a dual layer HD-DVD−R disc wherein the playback laser has a wavelength around 400 nm or any other optical disc structure wherein two or more layers of information can all be recorded or played back from one side of the disc in which a semi-reflective layer or layers of silver alloy as disclosed in this invention is made useful. 
   As used herein, the term “reflectivity” refers to the fraction of optical power incident upon transparent substrate  14 ,  114 ,  214 ,  314 ,  414  or  514  which, when focused to a spot on a region of layer  20 ,  120 ,  216 ,  220 ,  316 ,  320 ,  324 ,  422  or  522  could in principle, be sensed by a photodetector in an optical readout device. It is assumed that the readout device includes a laser, an appropriately designed optical path, and a photodetector, or the functional equivalents thereof. 
   This invention is based on the inventor&#39;s discovery that, a particular silver-based alloy provides sufficient reflectivity and corrosion resistance to be used as the reflective or the semi-reflective layer in an optical storage medium, without the inherent cost of a gold-based alloy or the process complication of a silicon-based material. In one embodiment, silver is alloyed with a comparatively small amount of zinc. In this embodiment, the relationship between the amounts of zinc and silver ranges from about 0.01 a/o percent (atomic percent) to about 15 a/o percent zinc and from about 85 a/o percent to about 99.99 a/o percent silver. But preferably in respect to each metal, the alloy has from about 0.1 a/o percent to about 10.0 a/o percent zinc and from about 90.0 a/o percent to about 99.9 a/o percent silver. 
   In another embodiment, the silver is alloyed with a comparatively small amount of aluminum. In this embodiment, the relationship between the amounts of aluminum and silver ranges from about 0.01 a/o percent (atomic percent) to about 5 a/o percent aluminum and from about 95 a/o percent to about 99.99 a/o percent silver. But preferably in respect to each metal, the alloy has from about 0.1 a/o percent to about 3.0a/o percent aluminum and from about 97 a/o percent to about 99.9a/o percent silver. 
   In another embodiment of the present invention, the silver-based, binary alloy systems as mentioned above are further alloyed with cadmium (Cd), lithium (Li), or manganese (Mn). If one or more of these metals replaces a portion of the silver in the alloy, the corrosion resistance of the resultant thin film will likely increase; however, the reflectivity will also likely decrease. The amount of cadmium, lithium, or manganese that may favorably replace some of the silver in the binary alloy ranges from; about 0.01 a/o percent to about 20 a/o percent of the amount of silver present for cadmium; from about 0.01 a/o percent to about 10 a/o percent, or even, to about 15 a/o percent of the amount of silver present for lithium; and from about 0.01 a/o percent to about 7.5 a/o percent of the amount of silver present for manganese. 
   In still another embodiment of the present invention, the silver-based, zinc and aluminum binary alloy systems as mentioned above are further alloyed with a precious metal such as gold (Au), rhodium (Rh), copper (Cu), ruthenium (Ru), osmium (Os), iridium (Ir), platinum (Pt), palladium (Pd), and mixtures thereof, which may be added to the above binary alloys with the preferable range of precious metal to be about 0.01 a/o to 5.0 a/o percent of the amount of silver present. In addition to precious metals, the above alloys may be still further alloyed with a metal such as titanium (Ti), nickel (Ni), indium (In), chromium (Cr), germanium (Ge), tin (Sn), antimony (Sb), gallium (Ga), silicon (Si), boron (B), zirconium (Zr), molybdenum (Mo), and mixtures thereof. In relation to the amount of silver that is present in the aforementioned silver alloys, the amount of these metals that may preferably be added ranges from about 0.01 a/o percent to about 5.0 a/o of the amount of silver present. 
   In another embodiment, silver is alloyed with at least one other element, selected from the group of elements including copper, silicon, cadmium, tin, lithium, nickel, cobalt, indium, chromium, antimony, gallium, boron, molybdenum, zirconium, beryllium, titanium and magnesium, wherein said other elements are present from about 0.01 a/o percent to 10.0 a/o percent of the amount of silver present. In one preferred embodiment, the non-silver element is present in the alloy in the amount of about 0.1 a/o percent to 5.0 a/o percent. 
   In still another embodiment, the silver is alloyed with a comparatively small amount of both zinc and aluminum. In this embodiment, the relationship between the amounts of zinc, aluminum and silver ranges from about 0.1 a/o percent to about 15 a/o percent zinc, from about 0.1 a/o percent to about 5 a/o percent aluminum, and from about 80 a/o percent to about 99.8 a/o percent silver. But preferably with respect to each metal, the alloy has from about 0.1 a/o percent to about 5.0 a/o percent zinc, from about 0.1 a/o percent to about 3.0 a/o percent aluminum, and from about 92.0 a/o percent to about 99.8 a/o percent silver. 
   In yet another embodiment of the present invention, the silver-based zinc-aluminum ternary alloy system as mentioned above is further alloyed with a fourth metal. The fourth metal may include manganese or nickel. If one or a mixture of these metals replaces a portion of the silver in the alloy, the corrosion resistance of the resultant thin film will likely increase; however, the reflectivity will also likely decrease. The amount of manganese or nickel that may favorably replace some of the silver in the above ternary alloys ranges from, about 0.01 a/o percent to about 7.5 a/o percent of the amount of silver present for manganese, with a preferable range being between about 0.01 a/o percent and about 5.0 a/o percent of the amount of silver present. The amount of nickel may range from between about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present with a preferable range being between from about 0.01 a/o percent and about 3.0 a/o percent of the amount of silver present. 
   In still another embodiment of the present invention, the silver-based zinc-aluminum ternary alloy system as mentioned above is further alloyed with a precious metal such as gold, rhodium, copper, ruthenium, osmium, iridium, platinum, palladium, and mixtures thereof, which may be added to the above ternary alloys with the preferable range of precious metal to be about 0.01 a/o to 5.0 a/o percent of the amount of silver present. In addition to the precious metals, the above alloys may also be alloyed with a metal such as titanium, nickel, indium, chromium, germanium, tin, antimony, gallium, silicon, boron, zirconium, molybdenum, and mixtures thereof. In relation to the amount of silver that is present in the above silver alloy system, the amount of such metals that may be preferably added ranges from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In another embodiment, the silver is alloyed with a comparatively small amount of manganese. In this embodiment, the relationship between the amounts of manganese and silver ranges from about 0.01 a/o percent to about 7.5 a/o percent manganese and from about 92.5 a/o percent to about 99.99 a/o percent silver. But preferably, in respect to each metal, the alloy has from about 0.1 a/o percent to about 5 a/o percent manganese and from about 95 a/o percent to about 99.9 a/o percent silver. 
   In yet another embodiment of the present invention, the silver-based binary manganese alloy system as mentioned above is further alloyed with a third metal. The third metal may include cadmium, nickel, lithium and mixtures thereof. If one or a mixture of these metals replaces a portion of the silver in the alloy, the corrosion resistance of the resultant thin film will likely increase; however, the reflectivity will also likely decrease. In relation to the amount of silver that is present in the above binary alloy systems, the amount of cadmium may be range from about 0.01 a/o percent to about 20 a/o percent of the alloy of the amount of silver present, the amount of nickel may range from between about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present, and the amount of lithium may range from about 0.01 a/o percent to about 10.0 a/o percent of the amount of silver present. 
   In still another embodiment of the present invention, the aforementioned silver-based manganese alloy system is further alloyed with a precious metal such as gold, rhodium, copper, ruthenium, osmium, iridium, platinum, palladium, and mixtures thereof, which may be added to these binary alloys, the preferred range of precious metal added is about 0.01 a/o to 5.0 a/o percent of the amount of silver present. In addition to the precious metals, the aforementioned alloys may also be alloyed with a metal such as titanium, indium, chromium, germanium, tin, antimony, gallium, silicon, boron, zirconium, molybdenum, and mixtures thereof. In relation to the amount of silver that is present in the above silver alloy system, the amount of the latter metal(s) that may preferably be added ranges from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In still another embodiment, silver is alloyed with a comparatively small amount of germanium. In this embodiment, the relationship between the amounts of germanium and silver ranges from about 0.01 a/o percent to about 3.0 a/o percent germanium and from about 97.0 a/o percent to about 99.99 a/o percent silver. But preferably in respect to each metal, the alloy has from about 0.1 a/o percent to about 1.5 a/o percent germanium and from about 98.5 a/o percent to about 99.9 a/o percent silver. 
   In yet another embodiment of the present invention, the silver-based germanium alloy system as mentioned above is further alloyed with a third metal. The third metal may include manganese or aluminum. If one or a mixture of these metals replaces a portion of the silver in the alloy, the corrosion resistance of the resultant thin film will likely increase; however, the reflectivity will also likely drop. In relation to the amount of silver that is present in the above binary alloy system, the amount of manganese may be range from about 0.01 a/o percent to about 7.5 a/o percent of the amount of silver present and the amount of aluminum may range from between about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In still another embodiment of the present invention, the aforementioned silver-based germanium alloy system is further alloyed with a precious metal such as gold, rhodium, copper, ruthenium, osmium, iridium, platinum, palladium, and mixtures thereof, which may be added to the above binary alloys, the preferable range of precious metals added is about 0.01 a/o to 5.0 a/o percent of the amount of silver present. In addition to the precious metals, the alloys may also be alloyed with a metal such as zinc, cadmium, lithium, nickel, titanium, zirconium, indium, chromium, tin, antimony, gallium, silicon, boron, molybdenum, and mixtures thereof. In relation to the amount of silver present in the above silver alloy system, the amount of these metals that may be preferably added ranges from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In still another embodiment, the silver is alloyed with a comparatively small amount of both copper and manganese. In this embodiment, the relationship between the amounts of copper, manganese and silver ranges from about 0.01 a/o percent to about 10 a/o percent copper, from about 0.01 a/o percent to about 7.5 a/o percent manganese, and from about 82.5 a/o percent to about 99.98 a/o percent silver. But preferably in respect to each metal, the alloy has from about 0.1 a/o percent to about 5.0 a/o percent copper, from about 0.1 a/o percent to about 3.0 a/o percent manganese, and from about 92.0 a/o percent to about 99.8 a/o percent silver. 
   In yet another embodiment of the present invention, the silver-based copper-manganese alloy system as mentioned above is further alloyed a fourth metal. The fourth metal such as aluminum, titanium, zirconium, nickel, indium, chromium, germanium, tin, antimony, gallium, silicon, boron, molybdenum, and mixtures thereof. In relation to the amount of silver that is present in the above silver alloy system, the amount of fourth metal that may be preferably added ranges from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   The optical properties of these silver alloys as thin film, with a thickness in the range of 8 to 12 nanometers, for the semi reflective layer of DVD-9 dual layer discs are illustrated in Table I in the following. As mentioned in U.S. Pat. No. 5,464,619 assigned to Matsushita Electric and U.S. Pat. No. 5,726,970 assigned to Sony, in a dual layer optical disc structure (as illustrated in FIG.  3  and in Table I), the relationship between R 0  the reflectivity of Layer “0”or 216 and R 1  the reflectivity of Layer “1” or 220 is given by R 0 =R 1 T 0   2 . Where the reflectivity of Layer “1” or 220 is measured from outside the disc, and the transmission of Layer “0” is given as T 0 . When the thickness of layer “0”is optimized for balanced signal and reflectivity, and Layer “1” is an conventional aluminum alloy, at 50 to 60 nanometers, the balanced reflectivity of various silver alloys is shown in Table I. In Table I, R is the reflectivity of the thin film achievable at a thickness of 60 nanometer or greater, at a wavelength of 650 nanometer if used as Layer “1” or the high reflectivity layer of DVD-9 or any other high reflectivity application in an optical information storage medium. All compositions in the table I are given in atomic percent. 
   
     
       
         
             
           
             
               TABLE I 
             
           
          
             
                 
             
             
               Balance of reflectivity of Layer 0 and 
             
             
               Layer 1 of DVD-9 dual layer disc for various 
             
             
               silver alloy Layer 0 and typical aluminum alloy 
             
             
               Layer 1. 
             
          
         
         
             
             
             
             
             
          
             
               Composition 
               T 0   
               R 0   
               R 1 ′ 
               R 
             
             
                 
             
             
               Ag-13.0% Zn 
               0.47 
               0.185 
               0.183 
               0.80 
             
             
               Ag-6.0% Zn 
               0.52 
               0.22 
               0.224 
               0.92 
             
             
               Ag-4.0% Zn 
               0.53 
               0.23 
               0.233 
               0.93 
             
             
               Ag-10.3% Cd 
               0.51 
               0.22 
               0.216 
               0.91 
             
             
               Ag-14.5% Li 
               0.53 
               0.23 
               0.232 
               0.93 
             
             
               Ag-4.3% Al 
               0.47 
               0.18 
               0.183 
               0.80 
             
             
               Ag-1.5% Al 
               0.53 
               0.23 
               0.234 
               0.93 
             
             
               Ag-2.0% Ni 
               0.54 
               0.241 
               0.241 
               0.94 
             
             
               Ag-1.0% Ni 
               0.545 
               0.247 
               0.246 
               0.95 
             
             
               Ag-3.1% Mn 
               0.51 
               0.216 
               0.214 
               0.91 
             
             
               Ag-1.5% Mn 
               0.54 
               0.243 
               0.242 
               0.94 
             
             
               Ag-0.4% Ti 
               0.49 
               0.198 
               0.197 
               0.88 
             
             
               Ag-1.0% Zr 
               0.52 
               0.229 
               0.224 
               0.93 
             
             
                 
             
          
         
       
     
   
   In still another embodiment of the present invention, the sputtering target and the thin film on the optical information storage medium is a silver alloy with a comparatively small addition of aluminum as an alloying element. In this embodiment, the relationship between the amounts of silver and aluminum ranges from about 0.01 a/o percent to about 5.0 a/o percent aluminum and from about 95.0 a/o percent to about 99.99 a/o percent silver. But preferably from about 0.1 a/o percent to about 3.0 a/o percent aluminum, and from about 97.0 a/o percent to about 99.9 a/o percent silver. This silver and aluminum binary alloy can be further alloyed with zinc, cadmium, lithium, manganese, nickel, titanium and zirconium or mixtures of these metals. In relation to the amount of silver that is present in the above silver and aluminum binary alloy, the amount of the above-identified metal that may be preferably added ranges from 0.01 a/o percent to about 5.0 a/o percent of the silver content. 
   For the convenience of the reader, the following are some combinations of silver alloys, wherein the alloying elements, which may be preferably alloyed with silver, are identified by their periodic table symbols: Ag+Zn, or Ag+Cd, or Ag+Li, or Ag+Al, or Ag+Ni, or Ag+Mn, or Ag+Ti, or Ag+Zr, or Ag+Pd+Zn, or Ag+Pt+Zn, or Ag+Pd+Mn, or Ag+Pt+Mn, or Ag+Zn+Li, or Ag+Pt+Li, or Ag+Li+Mn, or Ag+Li+Al, or Ag+Ti+Zn, or Ag+Zr+Ni, or Ag+Al+Ti, or Ag+Pd+Ti or Ag+Pt+Ti, or Ag+Ni+Al, or Ag+Mn+Ti, or Ag+Zn+Zr, or Ag+Li+Zr, or Ag+Mn+Zn, or Ag+Mn+Cu, or Ag+Pd+Pt+Zn or Ag+Pd+Zn+Mn, or Ag+Zn+Mn+Li, or Ag+Cd+Mn+Li, or Ag+Pt+Zn+Li, or Ag+Al+Ni+Zn, or Ag+Al+Ni+Ti, or Ag+Zr+Ti+Cd, or Ag+Zr+Ni+Li, or Ag+Zr+Ni+Al, or Ag+Pt+Al+Ni, or Ag+Pd+Zn+Al, or Ag+Zr+Zn+Ti, or Ag+Ti+Ni+Al. 
   In another embodiment of the present invention, silver can be alloyed additionally with indium, chromium, nickel, germanium, tin, antimony, gallium, silicon, boron, zirconium, and molybdenum or mixture of these elements. In relation to the amount of silver that is present in the alloy systems, the amount of the above-identified elements that may be added ranges from about 0.01 a/o percent to about 5.0 a/o percent of the silver content. But more preferably, the amount of alloying elements added to silver may range from about 0.1 a/o percent to about 3.0 a/o percent. This is further illustrated in Table II for an optical information storage medium as presented in FIG.  3 . All the optical property symbols in Table II have the same meaning as the same symbols as those used in Table I. 
   
     
       
         
             
           
             
               TABLE II 
             
           
          
             
                 
             
             
               Balance of reflectivity of Layer 0 and 
             
             
               Layer 1 of DVD-9 dual layer disc for various 
             
             
               silver alloy Layer 0 and typical aluminum alloy 
             
             
               Layer 1. 
             
          
         
         
             
             
             
             
             
             
          
             
                 
               Composition 
               T 0   
               R 0   
               R 1 ′ 
               R 
             
             
                 
                 
             
             
                 
               Ag-2.5% In 
               0.500 
               0.212 
               0.208 
               0.91 
             
             
                 
               Ag-1.2% Cr 
               0.535 
               0.243 
               0.238 
               0.94 
             
             
                 
               Ag-0.7% Ge 
               0.515 
               0.220 
               0.220 
               0.92 
             
             
                 
               Ag-1.0% Sn 
               0.504 
               0.216 
               0.211 
               0.92 
             
             
                 
               Ag-0.5% Sb 
               0.520 
               0.224 
               0.224 
               0.93 
             
             
                 
               Ag-3.0% Ga 
               0.475 
               0.195 
               0.187 
               0.86 
             
             
                 
               Ag-1.5% Si 
               0.490 
               0.202 
               0.199 
               0.90 
             
             
                 
               Ag-1.2% B 
               0.513 
               0.247 
               0.218 
               0.92 
             
             
                 
               Ag-0.8% Mo 
               0.515 
               0.220 
               0.218 
               0.92 
             
             
                 
                 
             
          
         
       
     
   
   It is well understood in the art, that the compositions listed in Table I and Table II can also be used as the high reflectivity layer (Layer  1 ) in prerecorded dual layer optical disc structures such as DVD-9, DVD-14 or DVD-18, in a tri-layer optical disc structure as illustrated in  FIG. 4 , in a recordable optical disc such as DVD−R, in a rewritable optical disc such as DVD−RAM, or DVD−RW, or as the one illustrated in FIG.  5 . 
   For the convenience of the reader, the following are some silver alloys, where the alloying elements, that may preferably be alloyed with silver are identified by their periodic table symbols; Ag+In, or Ag+Cr, or Ag+Ge, or Ag+Sn, or Ag+Sb, or Ag+Ga, or Ag+Si, or Ag+B, or Ag+Mo, or Ag+In+Cr, or Ag+Cr+Ge, or Ag+Cr+Sn, or Ag+Cr+Sb, or Ag+Cr+Si, or Ag+Si+In, or Ag+Si+Sb, or Ag+Si+B, or Ag+Si+Mo, or Ag+Mo+In, or Ag+Mo+Sn, or Ag+Mo+B, or Ag+Mo+Sb, or Ag+Ge+B, or Ag+In+Cr+Ge, or Ag+Cr+Sn+Sb, or Ag+Ga+Si+Mo, or Ag+Cr+Si+Mo, or Ag+B+Mo+Cr, or Ag+In+Sb+B, or Ag+Cr+Si+B, Ag+Ga+Ge+Cr, or Ag+Si+Ge+Mo or Ag+Sb+Si+B, or Ag+Cr+Si+In, or Ag+Si+Cr+Sn. 
   The optical properties of a few of the ternary silver alloys of the present invention are further illustrated in Table III. In Table III, which shows the reflectivity and transmission of a thin film, layer zero, with a thickness of about 8 to 12 nm, in a DVD-9 dual layer disc construction. The meaning of each symbol is the same as in Table I. 
   
     
       
         
             
           
             
               TABLE III 
             
           
          
             
                 
             
             
               Balance of reflectivity of Layer 0 and 
             
             
               Layer 1 of DVD-9 dual layer disc for various 
             
             
               ternary silver alloy layer 0 and typical aluminum 
             
             
               alloy Layer 1. 
             
          
         
         
             
             
             
             
             
             
          
             
                 
               Composition 
               T 0   
               R 0   
               R 1 ′ 
               R 
             
             
                 
                 
             
             
                 
               Ag-1.2% Pd-1.4% Zn 
               0.54 
               0.245 
               0.242 
               0.95 
             
             
                 
               Ag-0.8% Cu-1.5% Mn 
               0.535 
               0.240 
               0.238 
               0.94 
             
             
                 
               Ag-1.5% Al-1.0% Mn 
               0.50 
               0.213 
               0.208 
               0.91 
             
             
                 
               Ag-1.0% Cu-0.3% Ti 
               0.50 
               0.210 
               0.207 
               0.90 
             
             
                 
               Ag-1.2% Al-1.3% Zn 
               0.53 
               0.224 
               0.233 
               0.93 
             
             
                 
               Ag-1.0% Ge-0.7% Al 
               0.49 
               0.203 
               0.201 
               0.89 
             
             
                 
               Ag-1.2% Sb-0.3% Li 
               0.47 
               0.187 
               0.183 
               0.83 
             
             
                 
                 
             
          
         
       
     
   
   In another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with a comparatively small amount of at least one other element selected from the group consisting of copper, silicon, cadmium, tin, lithium, nickel, cobalt, indium, chromium, antimony, gallium, boron, molybdenum, zirconium, beryllium, titanium and magnesium. The amount of other elements that may be alloyed with silver ranges from about 0.01 a/o percent to about 10.0 a/o percent. And more preferably, the amount of the other element present in the silver based alloy ranges from about 0.1 a/o percent to about 5.0 a/o percent, of the amount of silver present. 
   In another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with copper and zinc. The amount of Cu present in the alloy ranges from about 0.01 a/o percent to about 10.0 a/o percent; and the amount of zinc present ranges from about 0.01 a/o percent to about 10.0 a/o percent, of the silver present in the alloy. 
   In another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with copper and titanium. The amount of Cu present in the alloy ranges from about 0.01 a/o percent to about 10.0 a/o percent; and the amount of titanium present in the alloy ranges from about 0.01 a/o percent to about 5.0 a/o percent, of the amount of silver present. 
   In another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with at least one other metal selected from the group including gold, rhodium, ruthenium, osmium, iridium, platinum, palladium, and mixtures thereof. The amount of the other metal present in the silver based alloy ranges from about 0.01 a/o percent to about 5.0 a/o percent of the amount of silver present. 
   In another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with copper, and silicon. The amount of copper in the alloy ranges from about 0.01 a/o to about 10.0 a/o percent, of the amount of silver present in the alloy. The amount of silicon present in the alloy ranges from about 0.01 a/o to about 5.0 a/o percent of the amount of silver present. 
   In still another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with at least one of the following elements selected from the group including; copper, zinc, titanium, cadmium, lithium, nickel, cobalt, indium, aluminum, germanium, chromium, germanium, tin, beryllium, magnesium, manganese, antimony, gallium, silicon, boron, zirconium, molybdenum, and mixtures thereof. The amount of the elements alloyed with silver ranges from about, 0.01 a/o percent to about 10.0 a/o percent of the amount of silver present. In one preferred embodiment the amount of the other element alloyed with silver ranges from about 0.1 a/o to about 5.0 a/o percent of the amount of silver present. 
   In another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with copper and zinc. The amount of copper in the alloy ranges from about 0.01 a/o to about 10.0 a/o percent, of the amount of silver present in the alloy. And the amount of zinc in the alloy ranges from about 0.01 a/o to about 10.0 a/o percent, of the amount of silver present in the alloy. 
   In still another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with at least one element selected from the group including gold, rhodium, ruthenium, osmium, iridium, platinum, palladium, and mixtures thereof. The amount of the element present in the alloy ranges from about 0.01 a/o to about 5.0 a/o percent, of the amount of silver present in the alloy. 
   In yet another embodiment of invention, the thin film on an optical information storage medium is a silver copper alloy defined by Ag x Cu y . The amount of silver present in the alloy is given by a value of x, where x is in the range of about 0.90 to about 0.999. And the amount of Cu in the alloy is given by a value of y, and y is in the range of about 0.001 to about 0.01. 
   In one preferred embodiment of the invention, the amount of silver in the alloy is given by a value of x in the range of about 0.95 to about 0.999, and the amount of Cu in the alloy is given by a value of y, in the range of about 0.001 to about 0.050. 
   In yet another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with copper, and at least one other element selected from the group including silicon, cadmium, tin, lithium, nickel, cobalt, indium, chromium, antimony, gallium, boron, molybdenum, zirconium, beryllium, titanium, magnesium. The amount of the other elements present in the alloy ranges from 0.01 a/o percent to about 10.0 a/o percent, of the amount of silver present. 
   In still another embodiment of the current invention, the thin film on an optical information storage medium is silver alloyed with copper and manganese. The amount of copper in the alloy ranges from about 0.001 to about 0.01 a/o; the amount of manganese present in the alloy ranges from about 0.01 a/o to about 7.5 a/o percent, of the amount of silver present. In another preferred embodiment of the invention the amount of manganese present in the alloy ranges from about 1.01 a/o to about 5.0 a/o percent, of the amount of silver present. 
   In another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with copper and titanium. The amount of copper present in the alloy ranges from about 0.001 to about 0.01 a/o, and the amount of titanium present in the alloy ranges from about 0.01 a/o to about 5.0 a/o percent, of the amount of silver present. 
   In still another embodiment of the current invention, the thin film on an optical information storage medium is, silver alloyed with copper and silicon. The amount of copper in the alloy is in the range of about 0.001 to about 0.01 a/o, and the amount of silicon in the alloy ranges from about 0.01 a/o to about 5.0 a/o percent, of the amount of silver present. 
   In still another embodiment of the current invention, the sputtering target and the thin film on an optical information storage medium is, silver alloyed with a comparatively, small amount of copper and other elements selected from the group consisting of: aluminum, nickel, manganese, titanium, zirconium, indium, chromium, germanium, tin, antimony, gallium, silicon, boron, molybdenum and mixtures thereof. In this embodiment, the relationship between the amounts of silver and copper ranges from about 0.01 a/o percent to about 5.0 a/o percent copper and from about 95.0 a/o percent to about 99.99 a/o percent silver. But preferably from about 0.1 a/o percent to about 3.0 a/o percent copper, and from about 97.0 a/o percent to about 99.9 a/o percent silver. In relationship to the amount of silver that is present in the alloy system, the amount of the above-identified elements that may be added ranges from 0.01 a/o percent to about 5.0% of the silver content. But more preferably, the amount of alloying elements added to silver may ranges from about 0.1 a/o percent to about 3.0 a/o percent. As data presented in Table I, II and III indicated, if the individual alloy addition to silver is more than 5.0 a/o percent, the balanced reflectivity between layer zero and layer one in the DVD-9 dual layer disc structure is likely to be lower than the DVD specification of 18 percent, therefore not composition with utility. 
   Having presented the preceding compositions for the thin film materials, it is important to recognize that both the manufacturing process of the sputtering target and the process to deposit the target material into a thin film play important roles in determining the final properties of the film. To this end, a preferred method of making the sputtering target will now be described. In general, vacuum melting and casting of the alloys or melting and casting under protective atmosphere, are preferred to minimize the introduction of other unwanted impurities. 
   Afterwards, the as-cast ingot should undergo a cold or hot working process to break down the segregated and the nonuniform as-cast microstructure. One preferred method is cold or hot forging or cold or hot uniaxial compression with a more than 50 percent of size reduction, followed by annealing to recrystallize the deformed material into fine equi-axed grain structure with preferred texture of&lt;1,1,0&gt;orientation. This texture promotes directional sputtering in a sputtering apparatus so that more of the atoms from the sputtering target will be deposited onto the disc substrates for more efficient use of the target material. 
   Alternatively, a cold or hot multi-directional rolling process with more than a 50 percent size reduction can be employed, followed by annealing, to promote a random oriented microstructure in the target followed by machining the target to a final shape and size suitable for a given sputtering apparatus. A target, with a more random crystal orientation, will ejection atoms more randomly during sputtering, and will produce a disc substrate with a more uniform distribution and thickness. 
   Depending on the application, different discs&#39; optical and other system requirements, either a cold or hot forging or a cold or hot multi-directional rolling process can be employed in the target manufacturing process to optimize, the optical and other performance requirements of, the thin film for use in a given application. 
   The alloys of this invention can be deposited using the well-known methods described earlier including, for example sputtering, thermal evaporation or physical vapor deposition, and possibly electrolytic or electroless plating processes. The thin film alloy&#39;s reflectivity can vary depending on the method of application. Any application method that adds impurities to, or changes the surface morphology of, the thin film layer on the disc could conceivably, lower the reflectivity of the layer. But to a first order of approximation, the reflectivity of the thin film layer on the optical disc is primarily determined by the starting material of the sputtering target, evaporation source material, or the purity and composition of the electrolytic and electroless plating chemicals used. 
   It should be understood that the reflective layer of this invention can be used for future generations of optical discs that use a reading laser of a shorter wavelength, for example, a reading laser with a wavelength of 650 nanometers or shorter. 
   It should also be understood that, if the reflective film is reduced to a thickness of approximately 5 to 20 nanometers, a semi-reflective film layer can be formed from the alloys of this invention that have sufficient light transmittance for use in dual-layer DVD or dual layer blue-ray optical disc applications. 
   EXAMPLES 
   Example 1 
   A silver based alloy with about 1.2 atomic percent chromium and approximately 1.0 atomic percent zinc, at a thickness of about 60-100 nanometers, will have a reflectivity of approximately 94 to 95 percent at a wavelength of 800 nanometers and a reflectivity of approximately 93 to 94 percent at a wavelength of 650 nanometers and a reflectivity of approximately 86 to 88 percent at a wavelength of 400 nanometers. 
   Example 2 
   A silver-rich alloy with 1.5 a/o percent of manganese, and 0.8 a/o percent of copper will have a reflectivity of approximately 94 to 95 percent at 650 nanometers wavelength. If the thickness of the thin film is reduced to the 8 to 12 nanometers range, the reflectivity will be reduced to the range of 18 to 30 percent applicable for use as a DVD-9&#39;s semi-reflective layer. Adding a low concentration of deoxidizer such as lithium can further simplify the manufacturing process of the starting material of the thin film. As silver has a tendency to dissolve some oxygen in the solid state, which tends to lower the reflectivity of the alloy, the added lithium will react with the oxygen and lessen the degree of oxygen&#39;s impact to reflectivity. The desirable range of lithium is in the approximate range of 0.01 percent to 5.0 atomic percent, with the preferred range from about 0.1 to 1.0 a/o percent. 
   Example 3 
   A silver based alloy with about 0.5 a/o percent of nickel and about 0.5 a/o percent of zinc, about 60-70 nanometers thick, will have a reflectivity of approximately 95 percent at a wavelength of about 650 nanometers. It is suitable for any high reflectivity application in an optical information storage medium. 
   Example 4 
   A silver based alloy. sputtering target with a composition of about 1.0 a/o percent manganese, 0.3 a/o percent titanium and the balance silver is employed to produce the semi-reflective layer of a DVD-9 dual layer disc using the following procedure. On top of a transparent polycarbonate half disc approximately 0.6 millimeters thick and 12 centimeter in diameter with information pits injection molded from a suitable stamper, a semi-reflective thin film or layer “zero” of silver based alloy approximately 10 to 11 nanometers thick is deposited or coated, in a magnetron sputtering machine. On top of another transparent polycarbonate half disc approximately 0.6 millimeter thick with information pits injection molded from a suitable stamper, a high reflectivity thin film or layer “one” of and aluminum based alloy approximately 55 nanometers thick is deposited using a suitable aluminum sputtering target in a sputtering machine. These two half discs are then separately spin-coated with suitable liquid organic resins, bonded together with layer “zero” and layer “one” facing each other and the resin is cured with ultraviolet light. The distance within the disc between the layer “zero” and the layer “one” is kept at about 55+/−5 microns. 
   The reflectivity of the two information layers is measured from the same side of the disc and found to be about the same 21 percent using a 650 nanometers wavelength laser light. Electronic signals such as jitter and PI error are measured and found to be within published DVD specifications. Subsequently, an accelerated aging test at 80 degrees C and 85 percent relative humidity for 4 days is conducted on the disc. Afterwards, the reflectivity and the electronic signals are measured again and no significant changes are observed as compared to the same measurements made before the aging test. 
   Example 5 
   A silver alloy sputtering target with the composition in atomic percent of about 0.2 percent lithium, 1.0 percent manganese, 0.3 percent germanium and the balance silver is employed to produced the semi-reflective layer of a DVD-9 dual layer disc. The procedure used to make the discs is the same as the procedure used in the aforementioned example 4. The reflectivity of the two information layers in the finished disc is measured from the same side of the disc and found to be about the same, about 22.5 percent using a 650 nanometers wavelength laser light. Electronic signals such as jitter and PI error are also measured and found to be within published DVD specifications. Subsequently, an accelerated aging test at 70 degrees C. and 50 percent relative humidity for 96 hours is conducted on the disc. Afterwards, the reflectivity and the electronic signals are measured again and no significant changes are observed compared to the same measurements made before the aging test. 
   It is understood that the same silver alloy thin film in this example, deposited on the disc with a thickness ranging from about 30 to about 200 nanometers range can serve as the high reflectivity layer, such as Layer “one”in DVD-9 or Layer “two” in a tri-layer optical disc, as illustrated in FIG.  4 . The same silver alloy can serve in other high reflectivity applications such as a rewritable optical disc such as DVD−RW, DVD−RAM in a general structure as illustrated in  FIG. 5  at 650 nanometers wavelength or any other future optical information storage medium played back at around 400 nanometers wavelength. 
   Example 6 
   A silver based alloy sputtering target with a composition in a/o % of approximately 1.0% copper, 1.0% zinc, and the balance silver is used to produce the reflective layer of another type of recordable disc a DVD−R disc or a DVD+R disc using the following procedure. Referring now to FIG.  2 . An azo based recording dye is spin-coated on top of a transparent polycarbonate half disc about 0.6 mm thick and 12 cm in diameter with pregrooves suitable for DVD−R or DVD+R injection molded by a suitable stamper, and, dried. Subsequently, a reflective layer of silver based alloy approximately 150 nm in thickness is deposited or coated on the recording dye using the sputtering target with the aforementioned composition in a magnetron sputtering machine. Afterwards, this half disc is bonded to another 0.6 mm thickness half disc using a UV cured resin. Information is recorded onto the disc in a DVD−R or DVD+R recorder and the quality of the electronic signal is measured. 
   The disc is then subjected to an accelerated aging test. The disc is held at 80 degrees C. and 85% RH for 96 hours. Afterwards, the reflectivity and the electronic signals are measured again and no significant changes are observed as compared to the same measurements before aging test. 
   Example 7 
   A process to make the sputtering target with the composition as indicated in example 6 is described hereafter. Suitable charges of silver, manganese and aluminum are put into the crucible of a suitable vacuum induction furnace. The vacuum furnace is pumped down to vacuum pressure of approximately 1 milli-torr and then induction heating is used to heat the charge. While the charge is heating up and the out-gassing finished, the furnace can be back filled with argon gas to a pressure of about 0.2 to 0.4 atmosphere. Casting of the liquid melt can be accomplished at a temperature approximately 10% above the melting point of the charge. The graphite crucible holding the melt can be equipped with a graphite stopper at the bottom of the crucible. 
   Pouring of the molten metal into individual molds of each sputtering target can be accomplished by opening, and closing, the graphite stopper in synchrony with mechanically placing each mold into position just underneath the melting crucible to that the proper amount of melt is poured and cast into each mold. Afterwards, additional argon flow into the vacuum furnace can be introduced to cool and quench the casting. Subsequently, a cold or warm multi-directional rolling process that causes a more than 50% reduction in thickness can be used to break up any nonuniform casting microstructure. 
   Then the final anneal is done at 550 to 600 degrees C. in a protective atmosphere for 15 to 30 minutes. After being machined into the right shape and size, cleaned in detergent and properly dried, the finished sputtering target is ready to be put into a magnetron sputtering apparatus to coat optical discs. Approximate sputtering parameters sufficient to make the semi-reflective layer of an ultra high density optical disc suitable for use with a playback laser with a wavelength of 400 nanometers as mentioned in example 9 are as follows: 1 kilowatt of sputtering power, 1 second of sputtering time, an argon partial pressure of 1 to 3 milli-torr, with a target to disc distance of approximately 4 to 6 centimeters, giving a deposition rate of 10 nanometers per second. Using the same sputtering target and sputtering apparatus, the high reflectivity layer can be made with about the same sputtering parameters as the semi-reflective layer, except that to deposit the high reflectivity layer the sputtering power needs to be increased to 4 to 5 kilowatts. Thus an ultra high density read-only optical disc, 5 inches in diameter, with user storage capacity of about 20 to 25 giga bytes or higher per side can be made in this manner. A dual layer disc with the structure, illustrated in  FIG. 3 , has the capacity to store approximately 40 to 50 giga bytes of information, more than enough storage capacity for a full-length motion picture in the high-definition digital television format. 
   Example 8 
   The feasibility of using the same silver alloy thin film for both the reflective layer and the semi-reflective layer of a dual layer ultra high density read-only optical disc with a playback laser at a wavelength of 400 nanomaters is investigated. 
   A silver alloy sputtering target with a composition given in a/o %: of Pd, 1.2%, Zn, 1.4% and balance silver was used to produce a dual layer optical information storage medium as depicted in  FIG. 3. A  thin film about 10 nanometers thick of this silver alloy was deposited on a suitable polycarbonate substrate by using a magnetron sputtering machine. Referring now to  FIG. 3 , the indices of refraction (n) of the transparent substrate  214 , the semi-reflective layer  216 , the spacer layer  218  and the high reflectivity layer are 1.605, 0.035, 1.52, 0.035, respectively. The extinction coefficient (k) for the semi-reflective layer and the high reflectivity layer is 2.0. 
   Calculations show that with a thickness of 24 nm, the semi-reflective layer will have a reflectivity R 0  of 0.242 and a transmission T 0  of 0.600 in the disc at a wavelength of 400 nm. At a thickness of 55 nm, the high reflectivity layer will have a reflectivity R 1  of 0.685. The reflectivity of the high reflectivity layer measured from outside the disc through the semi-reflective layer will be R 0 =R 1 T 0   2  or 0.247. In other words, to the detector outside the disc, the reflectivity from both the semi-reflective layer and the high reflectivity layer will be approximately the same. This fulfills one important requirement for a dual layered optical information storage medium, that the reflectivity from these 2 information layers be approximately equal, the relationship between the optical properties of these two layers is R 0 =R 1 T 0   2 . 
   Example 9 
   The same silver alloy used in example 8 can also be used as the high reflectivity layer and the two semi-reflective layers in a tri-layer optical information storage medium for at playback using a laser with a wavelength of 400 nm. Referring now to FIG.  4 . Calculations show that, at a thickness of 16 nm for the first semi-reflective layer  316 , a thickness of 24 nm for the second semi-reflective layer  320 , and a thickness of 50 nm for the high reflectivity layer  324 , the reflectivity, measured at the detector  332 , will be 0.132, 0.137, 0.131, respectively. This shows that approximately the same reflectivity can be achieved from all three layers. Balance of reflectivity from all three, information layers can be achieved, using the same silver alloy. Additionally, one sputtering machine and one silver alloy sputtering target can be used to manufacture all three layers of an ultra high density tri-layer optical information storage medium suitable for use with playback laser at wavelength 400 nm in a production environment. It will also be obvious, that aluminum alloys can also be used for the high reflectivity layer of this tri-layer medium. 
   Example 10 
   A silver alloy sputtering target having the composition given in a/o % of: Pd, 0.4%; Cu, 1.5%; and balance silver was used to produce the reflective layer in a rewritable phase change disc structure such as DVD+RW, DVD−RW or DVD−RAM. Referring to FIG.  5 . Successive layers of ZnO.SiO 2 , Ag—In—Sb—Te, and ZnO.SiO 2  of suitable thickness are coated on a 0.6 mm thick polycarbonate substrate which has continuous spiral tracks of grooves and lands made by injection molding from a suitable stamper. Next, a sputtering target with the aforementioned composition is used in a magnetron sputtering apparatus to deposit a silver alloy film about 150 nm thick on top of the ZnO.SiO 2  film. Subsequently, the half disc is bonded with a suitable adhesive to the another 0.6 mm thick half disc of the same construction as the aforementioned half disc to form a complete disc. 
   Repeated record and erase cycles are performed in a suitable DVD+RW, DVD−RW or DVD−RAM drive. The disc meets the performance requirements imposed on the recording medium. The disc further under goes an accelerated environmental test at 80 degrees C., 85% relative humidity for 4 days. Afterwards, disc performance is checked again, no significant change in the disc property is observed as compared to the disc&#39;s performance before the environmental test. 
   Example 11 
   A silver alloy sputtering target having the composition given in a/o % of: Mn,0.7%; Cu, 1.5%; Ti,0.2% and balance silver was used to produce the semi-reflective layer  938  approximately 10 nm in thickness in a Blu-Ray rewritable phase change dual-layer disc structure such as the one described in FIG.  10 . Successive layers of silver alloy 60 nm in thickness, dielectric layer of ZnO.SiO 2 , interface layer, recording layer such as Ge—Sb—Te, another interface layer and dielectric layer ZnO.SiO 2  of suitable thickness are coated on a 1.1 mm thick polycarbonate substrate which has continuous spiral tracks of grooves and lands made by injection molding from a suitable stamper. Afterwards, an organic resin about 50 microns in thickness as a spacer layer is spin-coated on the 1.1 mm thick substrate and cured by UV light. Next, another sputtering target with the aforementioned composition is used in a magnetron sputtering apparatus to deposit the semi-reflective silver alloy film about 10 nm thick on top of the spacer layer, followed by sputtered coating of ZnO.Sio 2  dielectric film, interface layer, phase change recording layer, interface layer and dielectric layer. Subsequently, the film or layer stacks on the 1.1 mm thickness substrate is spin-coated and UV cured a cover layer about 100 microns in thickness to form a complete disc. 
   Repeated record and erase cycles are performed in a suitable Blu-Ray recorder drive with playback lens NA of 0.85 and focused laser beam of 405 nm wavelength. The disc meets the performance requirements imposed on the recording medium. The disc further under goes an accelerated environmental test at 75 degrees C., 85% relative humidity for 10 days. Afterwards, disc performance is checked again, no significant change in the disc property is observed as compared to the disc&#39;s performance before the environmental test. 
   Example 12 
   A silver alloy sputtering target having a composition given in a/o % of: Cu, 1.0%; Ag, 99.0% was used to produce the highly reflective layer in a rewritable phase change disc structure or “DVR” as shown in FIG.  6 . In this DVR structure, between dielectric layer  520  and highly reflective layer  522 , there is an interface layer of SiC (not shown). The layers in this example are deposited in the reverse order from the order of layer addition used in Example 10. The transparent substrate  524  was made of polycarbonate and injection molded from a suitable stamper, then the silver alloy reflective layer was deposited on the transparent substrate using the above-mentioned sputtering target in a magnetron sputtering apparatus. Dielectric layer  520  (preferably ZnO.SiO 2 ), recording layer  518  (preferably Ag—In—Sb—Te), another dielectric layer  516  (preferably ZnO.SiO 2 ) and an interface layer (preferably SiC) were then vacuum coated, in sequence. Finally, the disc was covered with a layer of UV cured resin  514 , about 100 microns thick. 
   The performance of the disc is verified with a DVR type recording and play back system using a 405 nm wavelength laser beam. Repeated record and erase cycles are conducted satisfactorily. The disc is subjected to an accelerated environmental test at 80 degrees C. and 85% relative humidity for 4 days. The performance of the disc is again checked and verified. No significant degradation of the disc&#39;s property is observed. 
   Example 13 
   A silver based alloy sputtering target with a composition in a/o % of approximately 2.2% copper, 0.5% zinc, and the balance silver is used to produce the semi-reflective layer or L 0  of another type of recordable disc such as a DVD−R dual-layer disc or a DVD+R dual-layer disc as shown in  FIG. 13  using the following procedure. An azo based recording dye is spin-coated on top of a transparent polycarbonate half disc about 0.6 mm thick and 12 cm in diameter with pregrooves suitable for DVD−R dual-layer or DVD+R dual-layer injection molded by a suitable stamper, and, dried. Subsequently, a semi-reflective layer of silver based alloy approximately 10 nm in thickness is deposited or coated on the recording dye using the sputtering target with the aforementioned composition in a magnetron sputtering machine. Afterwards, this half disc is bonded to the other 0.6 mm thickness half disc using a UV cured resin. The other half disc contains 150 nm thickness of silver alloy sputtered from another sputtering target of the composition: 1.7 a/o % Cu, 1.0 a/o % Zn and 97.3 a/o % Ag on the clear polycarbonate substrate and subsequently coated with another Azo based recording dye and dried by hot circulating air. Information is recorded onto both layers of the disc in a DVD−R dual-layer or DVD+R dual-layer recorder and the quality of the electronic signal is measured. The disc is then subjected to an accelerated aging test at 80 degrees C. and 85% RH for 2 days. Afterwards, the reflectivity and the electronic signals of the disc are measured again and no significant changes are observed as compared to the same measurements before the aging test. 
   THE CLAIMS 
   While the invention has been illustrated and described in detail, this is to be considered as illustrative and not restrictive of the patent rights. The reader should understand that only the preferred embodiments have been presented and all changes and modifications that come within the spirit of the invention are included if the following claims or the legal equivalent of these claims describes them.