Abstract:
The invention presents systems and methods for initializing the phase-change layer of an optical medium. The method includes alternately quenching the phase-change material into amorphous states and crystallization states in a single pass of an optical head past the optical medium.

Description:
TECHNICAL FIELD  
         [0001]    The invention relates to data storage media and, more particularly, to techniques for manufacturing optical media.  
         BACKGROUND  
         [0002]    Some forms of optical recording media record digital information in a material that can assume two distinct phases. Such media are often referred to as “phase-change” media. In the amorphous phase, the molecules of the material do not exhibit any long-range structure. In the crystalline phase, by contrast, the molecules possess a long-range order. The reflectivity of the material in the amorphous phase is different from the reflectivity of the material in the crystalline phase.  
           [0003]    Phase-change material may be included in a disk as a phase-change recording layer. Digital information may be encoded in the phase-change layer by creation of regions of amorphous material and regions of crystalline material. The digital information encoded in the phase-change layer may be recovered by rotating the disk under a focused light and sensing the changes in reflectivity as the light strikes different regions of the disk.  
           [0004]    The phase-change recording layer may be deposited on a polycarbonate substrate between dielectric layers and coated with a light reflection and heat dissipation layer. Techniques such as sputtering may be used to form the phase-change layer. The phase-change layer may be a compound comprising silver (Ag), indium (In), antimony (Sb) and tellurium (Te), although other compounds may be used as well.  
           [0005]    When sufficiently heated, the material in the phase-change layer melts. Once melted, the material may be “quenched” or cooled into one of two phases: a crystalline phase or an amorphous phase. In general, heating the material to a high melting temperature followed by rapid cooling causes the material to assume the amorphous state. If cooling is more gradual, however, the molecules in the material have time to align themselves, and the material assumes the crystalline state. Although the material must be melted and cooled to cause it to become amorphous, the material may assume a crystalline phase at a lower temperature when heated for a longer time.  
           [0006]    An optical recording medium typically includes a recording zone having a vast multitude of tiny regions addressable by a laser beam. The phase-change material in each region forms a data site that may be individually changed from one state to the other, thereby allowing for storage of digital data. The data sites are typically arranged in tracks called “data tracks.” Data stored on such an optical recording medium can be erased and/or written over by new data.  
         SUMMARY  
         [0007]    The invention is directed to techniques for initializing optical media that include phase-change material. The effect of these techniques is to run the phase-change material on a medium through several phase-change cycles, before putting the medium into actual use. Initializing the medium with several phase-change cycles conditions the recording layer to reduce jitter in the recorded data.  
           [0008]    In addition, the invention is directed to techniques for initializing optical media by moving the medium surface past an optical head and performing the multi-cycle initialization in a single pass of the optical head over the medium surface. Multi-cycle initialization in a single pass of the optical head over the optical medium saves manufacturing time.  
           [0009]    Initialization is beneficial to an optical medium employing a phase-change layer, such as a rewritable compact disk, DVD-RW or DVD-RAM. Digital information recorded on a phase-change medium generally can be erased and over-recorded a thousand times or more. A high intensity spot of focused laser light is used for recording, erasing and over-recording. Recorded data may be recovered with a lower intensity spot of focused laser light, which scans the recorded regions and which is affected by the different reflectivities of the amorphous and crystalline regions.  
           [0010]    Ideally, the sensed changes in reflectivity occur in precisely separated time intervals. Actual sensed changes typically present some deviation from ideal timing, a phenomenon known as “jitter.” Jitter can be manifested in different forms in the first few media cycles of a newly manufactured phase-change disk. A “media cycle” entails changing the phase-change material from one phase to the other and back again, such as from amorphous phase to crystalline phase to amorphous phase. Sometimes a phase-change disk exhibits severe jitter during the first cycle, substantially less jitter on the second cycle, and far less on the third. In other cases, a phase-change disk exhibits little jitter after the first cycle, but substantially more jitter on the second cycle. In general, jitter generally disappears or is greatly reduced after a few media cycles, and remains relatively constant until the optical medium approaches the end of its useful life.  
           [0011]    The invention improves media performance and reduces jitter by running the phase-change material through several media cycles during the manufacturing process. The initialization takes place in a single pass of the optical head.  
           [0012]    In one embodiment, the invention comprises a system, including at least one light source such as a semiconductor laser. The light source generates at least two amorphous melt regions and at least two crystallization regions in an optical medium comprising phase-change material. The system also includes a drive that moves the optical medium relative to the light source to cause the phase-change material to assume in succession a first amorphous state, followed by a first crystalline state, followed by a second amorphous state, followed by a second crystalline state. The light source causes the phase-change material to undergo at least two media cycles in a single pass. The system further may further include a plurality of light sources.  
           [0013]    In another embodiment, the invention presents a method, comprising orienting one or more light sources relative to an optical medium comprising phase-change material and moving the optical medium relative to the light source. In one pass, the phase-change material assumes in succession a first amorphous state, followed by a first crystalline state, followed by a second amorphous state, followed by a second crystalline state. The method may also comprise arranging a plurality of light sources in a pattern and orienting the plurality of light sources relative to the optical medium.  
           [0014]    In a further embodiment, the invention comprises a method, comprising moving phase-change material relative to at least one light source that generates an amorphous melt region and a crystallization region in the phase-change material. The phase-change material makes a single pass relative to the light source, causing the phase-change material to assume a first amorphous state, a first crystalline state, a second amorphous state and a second crystalline state.  
           [0015]    The details of one or more embodiments of the present invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the present invention will be apparent from the description and drawings, and from the claims. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a plan view diagram illustrating initialization of an optical medium, including a configuration of spots from an optical head.  
         [0017]    [0017]FIGS. 2A, 2B and  2 C are diagrams illustrating initialization of an initialization track of an optical medium.  
         [0018]    [0018]FIG. 3 is a diagram illustrating initialization of an optical medium with an alternate configuration of spots from an optical head.  
         [0019]    [0019]FIG. 4 is a diagram illustrating initialization of an optical medium with another configuration of spots from an optical head.  
         [0020]    [0020]FIG. 5 is a diagram of a system for initializing an optical medium. 
     
    
     DETAILED DESCRIPTION  
       [0021]    [0021]FIG. 1 is a diagram showing a plan view of optical medium  10 , which includes a phase change layer. Optical medium  10  may be any of a number of phase-change media, such as a phase-change disk. The invention is directed to techniques for initializing the phase-change material in optical medium  10 . The manufacturer performs the initialization as part of the manufacturing process.  
         [0022]    [0022]FIG. 1 shows optical medium  10  divided into several initialization tracks  14 , which are arbitrary regions undergoing initialization. Typically, initialization tracks are oriented in the same direction as data tracks but are wider than data tracks. Each initialization track may comprise one or more data tracks, and the number of data tracks per initialization track need not be a whole number.  
         [0023]    Spots  12  from one or more light sources are projected onto optical medium  10 . The light sources are preferably one or more lasers, such as semiconductor lasers, and are organized in an optical head proximal to optical medium  10 . The light sources may emit light at visible wavelengths or at invisible wavelengths, such as infrared wavelengths. Although seven spots  12  are shown in FIG. 1, an optical head may generate more or fewer spots. Each of spots  12  may be generated by a separate light source. Alternatively, one light source may emit light that is split to form two or more spots. As shown in FIG. 1, spots  12  form a one-dimensional array. As will be discussed below, an optical head may generate spots in other patterns, and may generate initializing shapes other than round spots.  
         [0024]    Typical spot  16  includes amorphous melt spot  18  surrounded by crystallization spot  20 . Amorphous melt spot  18  and crystallization spot  20  are generated by a single focused light source. The size of amorphous melt spot  18  and crystallization spot  20  depend upon factors such as the power of the light source, the focusing of the light, the thermal characteristics of the phase-change layer of optical medium  10  and the thermal characteristics of the dielectric layers and light reflection/heat dissipation layer.  
         [0025]    In FIG. 1, amorphous melt spot  18  has been sized to a diameter of three initialization tracks  14 , and crystallization spot  20  has been sized to a diameter of nine initialization tracks  14 . These proportions are for purposes of illustration, and other spot sizes may be used as well. Furthermore, the boundaries between amorphous melt spot  18  and crystallization spot  20  need not be sharp boundaries.  
         [0026]    The quenched state of the phase-change material is a function of the energy imparted to the material, the length of time of exposure to the energy and the cooling rate. The rate of energy transfer is higher in amorphous melt spot  18  than in crystallization spot  20 . Accordingly, the temperature induced in optical medium  10  by amorphous melt spot  18  is typically much higher for a given period of time than the temperature induced by crystallization spot  20 . With a rapid cooling rate, phase-change material exposed to amorphous melt spot  18  quenches to the amorphous phase. The temperature of crystallization spot  20  is not high enough to cause the phase-change material of optical medium  10  to reach an amorphous state within the same period of time.  
         [0027]    Optical medium  10  moves relative to spots  12 . The path of optical medium  10  relative to spots  12  is shown by reference numeral  22 . In the case of an optical disk, optical medium  10  is typically rotated relative to a stationary optical head, thereby allowing spots  12  to strike initialization tracks  14 , which are spirally oriented on the disk.  
         [0028]    The optical head is typically allowed to move orthogonally to direction of motion  22  of optical medium  10 . Radial motion of the optical head allows spots  12  to strike initialization tracks in other regions of optical medium  10 . In a phase-change disk, for example, the optical head may move radially relative to the disk, bringing the optical head closer to or farther from the center of the disk.  
         [0029]    The one-dimensional array of spots  12  is oriented such that spots  12  line up slightly offset relative to direction of motion  22  of optical medium  10 . As a result, the motion of optical medium  10  causes each point in initialization tracks  14  to be struck by a plurality of spots.  
         [0030]    [0030]FIGS. 2A, 2B and  2 C demonstrate how orienting a one-dimensional array of spots slightly offset relative to direction of motion of optical medium  10  takes phase-change material in a typical initialization track  30  through several phase-change cycles in a single pass. In particular, FIGS. 2A, 2B and  2 C show the interaction of typical segment  32  of initialization track  30  with a series of spots  34 - 56 . Like spots  12  shown in FIG. 1, spots  34 - 56  are slightly offset relative to direction of motion  22  of optical medium  10 . Each of spots  34 - 56  includes an amorphous melt spot and a crystallization spot that surrounds the amorphous melt spot, like typical spot  16  shown in FIG. 1.  
         [0031]    In FIG. 2A, segment  32  moves in direction  22 , bringing the segment through the crystallization spot of spot  38 . Spots  34  and  36  do not affect initialization track  30 . Rather, spots  34  and  36  act on regions of medium  10  adjacent to initialization track  30 . The crystallization spot of spot  38  may promote crystallization of the phase-change material in initialization track  30 , but does not cause phase-change material to melt into an amorphous state. Similarly, the crystallization spot of spot  40 , which segment  32  next encounters, may promote crystallization but not melting into an amorphous state.  
         [0032]    In FIG. 2B, segment  32  interacts with spots  42 - 48 . The crystallization spot of spot  42  may promote crystallization of the phase-change material, as may the crystallization spot of spot  44 . When initialization track  30  passes through the amorphous melt spot of spot  44 , however, the phase-change material melts and quenches rapidly from the melting temperature into an amorphous state. The phase-change material does not remain in the amorphous state, because the crystallization spots of spots  44  and  46  heat the phase-change material sufficiently to cause the material to return to a crystalline state.  
         [0033]    When initialization track  30  passes through the amorphous melt spot of spot  46 , the material quenches into an amorphous state. The material then returns to a crystalline state when passing through the crystallization spots of spots  46  and  48 . When initialization track  30  passes through the amorphous melt spot of spot  48 , the material again quenches into an amorphous state. The material in initialization track  30  returns to crystalline state after passing through the crystallization spots of spots  48 ,  50 ,  52  and  54 , as shown in FIGS. 2B and 2C. Spot  56  does not substantially affect initialization track  30 .  
         [0034]    After initialization track  30  has passed spots  34 - 56 , the phase-change material in initialization track  30  is in the crystalline state. Passing spots  34 - 56  has caused the phase-change material in initialization track  30  to undergo three media cycles, changing from amorphous to crystalline three times.  
         [0035]    Notably, initialization track  30  undergoes three media cycles in a single pass. Initialization track  30  need not pass by the light sources that generate spots  34 - 56  three times. Moreover, tracks neighboring initialization track  30  undergo media cycling at nearly the same time. In this way, a single pass can produce thrice-cycled region  24  shown in FIG. 1, consisting of several initialization tracks.  
         [0036]    By different arrangements of light sources and spots, any number of media cycles may be accomplished on a single pass of the optical medium past the light sources. The invention is not limited to a one-dimensional array of spots.  
         [0037]    [0037]FIG. 3 illustrates an alternate embodiment of the invention, in which spots are oriented in two dimensions. The optical head may generate spots in columns  60 ,  62  and  64  on optical medium  10 . Like FIGS. 1, 2A,  2 B and  2 C, each spot includes an amorphous melt spot and a crystallization spot.  
         [0038]    As optical medium  10  moves in direction  22 , phase-change material in typical initialization track  58  encounters subset of spots  66 , which may include several crystallization spots and at least one amorphous melt spot  68 . Phase-change material in initialization track  58  quenches into an amorphous state when the material encounters amorphous melt spot  68 , then returns to a crystalline state after encountering crystallization spots of subset  66 . The encounter with spot subset  66  causes the phase-change material to undergo a media cycle.  
         [0039]    The phase-change material in initialization track  58  undergoes two more media cycles when it encounters spot subsets  70  and  74 , which include amorphous melt spots  72  and  76 . When material has passed array of spots  64 , the material has undergone three media cycles. The three media cycles occurred in a single pass of optical medium  10  past the optical head.  
         [0040]    [0040]FIG. 4 illustrates a further embodiment of the invention. FIG. 4 shows three elongated spots  80 ,  82  and  84  on optical medium  10 . Elongated spot  80 , for example, includes bar-shaped amorphous melt region  86  and bar-shaped crystallization region  88  surrounding amorphous melt region  86 . Elongated spots  82  and  84  likewise include amorphous melt regions and crystallization regions.  
         [0041]    Elongated spots  80 ,  82  and  84  may be created by an array of lasers, with the energy of the individual lasers focused to form bar-shaped amorphous melt regions and bar-shaped crystallization regions. The shape of elongated spots  80 ,  82  and  84  may be slightly irregular.  
         [0042]    Elongated spots sweep over wide initialization track  78 . As optical medium  10  moves in direction  22 , phase-change material encounters crystallization region  88  of elongated spot  80 , followed by amorphous melt region  86 , followed by crystallization region  88 . The encounter with elongated spot  80  causes the phase-change material to undergo a media cycle.  
         [0043]    The phase-change material in data track  30  undergoes two more media cycles when it encounters elongated spots  82  and  84 . When material has passed elongated spot  84 , the material has undergone three media cycles, and the three media cycles took place in a single pass.  
         [0044]    [0044]FIG. 5 shows a system  102  for initializing optical medium  10 . System  102  may initialize a phase-change disk, but a similar arrangement may be employed to initialize other forms of phase-change media. System  102  includes optical head  90 , which may be held on support  92 , while optical medium  10  is rotated proximal to optical head  90 . Drive  98  rotates optical medium  10 . Optical head  90  initializes initialization swath  100 , which may comprise one or more initialization tracks.  
         [0045]    Optical head  90  can move radially along support  92 , under the control of positioning controller  96 . Positioning controller  92  may cooperate with drive  98  to control the position of optical head  90  with respect to optical medium  10 . In particular, positioning controller  92  may radially move optical head  90  and drive  98  may rotate optical medium  10  to bring optical head  90  in proximity to any region of the recording zone of optical medium  10 . In this way, positioning controller  92  and drive  98  regulate the position of initialization swath  100 .  
         [0046]    Positioning controller  92  and drive  98  cooperate to sweep initialization swath  100  in a spiral path along the surface of optical medium  10 . Initialization swath  100  covers the recording zone of optical medium  10  with some overlap. Because a single pass of optical head  90  relative to optical medium  10  cycles the phase-change material multiple times, initialization swath  100  overlap is not needed to achieve media cycling. Once optical head  90  has initialized a region, that region need not be initialized again. Ideally, therefore, the amount of overlap should be minimal. As a practical matter, however, a modest amount of overlap may be beneficial, to correct for errors such as variations in the path of initialization swath  100 .  
         [0047]    The entire recording zone of optical medium  10  is thus initialized in one pass. Initialization by multiple media cycles conditions the microscopic material mixture in the phase-change layer. The conditioning enhances the reliability of the medium and reduces errors in recovering data, including errors caused by jitter. Initialization of optical medium  10  in a single pass of optical head  90  results in a saving of time in the manufacturing process. Mass production of media multiplies the time saving.  
         [0048]    Optical head  90  may produce spots on optical medium  10  according to one of the patterns described above, or according to another pattern. Optical head  90  may include any number of lasers or other light sources, arranged in one of any number of single or multiple-dimension configurations.  
         [0049]    System  102  may further include head controller  94 , configured to activate or deactivate individual light sources in optical head  90 . Head controller  94  also may control, for example, the pulse width and modulation frequency of individual lasers in optical head  90 . Head controller  94  also may also deactivate light sources in some circumstances. When initializing data tracks near the extreme interior or exterior edges of the recording zone of a disk, for example, some of the light sources may produce spots beyond the recording zone, and consequently those spots are not needed to initialize any phase-change material. The light sources generating such spots may be deactivated by laser controller  94 .  
         [0050]    A number of embodiments of the present invention have been described. Nevertheless, various modifications may be made without departing from the scope of the invention. For example, the invention is not limited to the particular arrangement of spots as shown in the figures. Many other configurations of spots may be used to achieve multiple media cycles in a single pass.  
         [0051]    Although the described embodiments result in three media cycles, the invention is not limited to three media cycles. Some kinds of optical media may work well after more than three media cycles, and other kinds may work well after fewer than three media cycles.  
         [0052]    Nor is the invention limited to any particular number of light sources. The light sources need not be arranged in straight lines. Moreover, the light sources need not be arranged to focus their energy into a circular or bar-shaped spot.  
         [0053]    Although initialization techniques in accordance with the invention may be particularly useful in the manufacturing process of optical media, they alternatively could be implemented post-manufacture, e.g., by an intermediate value added service provider or even an end user, albeit at reduced speed.  
         [0054]    These and other embodiments are within the scope of the following claims.