Abstract:
A magnetic racetrack memory device includes; a magnetic track having a plurality of magnetic domains partitioned by at least one magnetic domain wall, a current source applying current to the magnetic track sufficient to move the at least one magnetic domain wall and the plurality of magnetic domains along the magnetic track, a writing device disposed at a first location along the magnetic track and storing write data to the magnetic domains, a reading device disposed at a second location along the magnetic track and retrieving read data from the magnetic domains, and a write-back loop connecting the reading device and the writing device and communicating read data obtained by the reading device to the writing device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of Korean Patent Application No. 10-2008-0053804 filed on Jun. 9, 2008, the subject matter of which is hereby incorporated by reference. 
       BACKGROUND 
       [0002]    The inventive concept relates to a data storage device, and more particularly to a magnetic racetrack memory device that uses transfer of magnetic domains and magnetic domain walls. 
         [0003]    Hard disk drives (HDDs) are data storage devices that allow the storage of “write data” on a rotating magnetic disk (or similar magnetic recording medium) via operation of a read/write head positioned over the magnetic recording medium. Upon subsequent demand, stored data may be retrieved as “read data” from the magnetic recording medium using the read/write head. Contemporary HDDs are high-density, nonvolatile data storage devices, and are generally implemented using a number of moving mechanical components and related electro-mechanical circuits. The increasing demand for denser data storage together with the relatively delicate nature of the moving mechanical components forming an HDD lead inexorably to problems associated with deterioration of mobility, accuracy of positioning and general reliability. Further, manufacturing complexity and corresponding costs, as well as concerns over power consumption and noise generation have negative competitive implications for conventional HDDs. 
         [0004]    Accordingly, a number of recent development efforts have been directed to replacement data storage devices capable of providing commensurate data storage capabilities, but without all the complex, moving mechanical systems. One possible replacement device commonly referred to as the “magnetic racetrack memory device” uses a physics principle that recognizes that magnetic domains and magnetic domain walls move within a magnetic material (i.e., a magnetic body). One example of a known magnetic racetrack memory device is disclosed in published U.S. Patent Application 2004/0252538. 
         [0005]    In general, conventional magnetic racetrack memory devices include a magnetic body constructed in a linear magnetic track shape of predetermined length. The magnetic track includes a plurality of magnetic domains which are partitioned by magnetic domain walls. 
         [0006]    Unfortunately, in a conventional magnetic racetrack memory device, data cannot be written to an area corresponding to at least half of the magnetic track. That is, at least half of the magnetic track must be set aside as a buffer area. In the absence of this buffer area (although magnetic domains need to pass below a reading device in order to read information from the magnetic domains), some of the magnetic domains are moved outside an end of the magnetic track and corresponding data is lost. 
       SUMMARY 
       [0007]    The inventive concept provides a magnetic racetrack memory device capable of reducing or preventing the significant loss of magnetic track area as an empty buffer area. 
         [0008]    According to one embodiment, the inventive concept provides a magnetic racetrack memory device comprising; a magnetic track having a plurality of magnetic domains partitioned by at least one magnetic domain wall, a current source applying current to the magnetic track sufficient to move the at least one magnetic domain wall and the plurality of magnetic domains along the magnetic track, a writing device disposed at a first location along the magnetic track and storing write data to the magnetic domains, a reading device disposed at a second location along the magnetic track and retrieving read data from the magnetic domains, and a write-back loop connecting the reading device and the writing device and communicating read data obtained by the reading device to the writing device. 
         [0009]    In one related aspect, the magnetic track comprises only a data region including magnetic domains capable of storing write data and does not comprise an empty buffer area designated to buffering the magnetic domains in the data area. 
         [0010]    In another related aspect, the writing device re-writes the read data received from the write-back loop to the magnetic domains of the magnetic track. The writing device may be disposed at one end of the magnetic track, and the reading device may be disposed at another end of the magnetic track. 
         [0011]    In another related aspect, the write-back loop may include a buffer to temporarily store the read data provided by the reading device. 
         [0012]    In another related aspect, the magnetic racetrack memory device may further include a conversion circuit connected between the reading device and the write-back loop and configured to amplify an analog read data signal provided by the reading device, convert the analog read data signal to digital read data, and provide the digital read data to the write-back loop. The conversion circuit may include an amplifier amplifying the analog read data signal provided by the reading device and proving an output signal, an analog-to-digital converter (ADC) converting the output signal of the amplifier into the digital read data, a decoder decoding the digital read data and outputting the decoded digital read data to the write-back loop, and a cash memory temporarily storing the decoded digital read data and providing the stored decoded digital read data to an input/output device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    Exemplary embodiments will be more clearly understood from the following detailed description made in conjunction with the accompanying drawings in which: 
           [0014]      FIG. 1  schematically illustrates a magnetic racetrack memory device according to the inventive concept; 
           [0015]      FIG. 2A  is a view illustrating an operational principle of the magnetic racetrack memory device according to the inventive concept illustrated in  FIG. 1 ; 
           [0016]      FIG. 2B  is a view illustrating an operational principle of the magnetic racetrack memory device according to the inventive concept illustrated in  FIG. 1 ; 
           [0017]      FIG. 3  illustrates another embodiment of the magnetic racetrack memory device according to the inventive concept; and 
           [0018]      FIG. 4  illustrates yet another embodiment of the magnetic racetrack memory device according to the inventive concept. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    The inventive concept will now be described in some additional detail with reference to the accompanying drawings. Throughout the drawings and written description like reference numerals are used to indicate like or similar elements. 
         [0020]      FIG. 1  schematically illustrates a magnetic racetrack memory device according to an embodiment of the inventive concept. Referring to  FIG. 1 , the magnetic racetrack memory device includes a magnetic track  10 , a current source  11 , a writing device  12 , a reading device  13 , and a write-back loop  15 . 
         [0021]    The magnetic track  10  includes a plurality of magnetic domains  101  partitioned by magnetic domain walls. The magnetic domains  101  denote magnetic fine regions that constitute a magnetic body, that is, the magnetic track  10 . In each of the magnetic domains  101 , the directions of magnetic moments are identical. The magnetic domain walls are boundaries between the magnetic domains having different magnetization directions, and the magnetic domain walls may be moved by an electrical current or magnetic field applied to the magnetic track  10 . 
         [0022]    The current source  11  applies a current to the magnetic track  10  in order to move the magnetic domain walls and the magnetic domains  101  along the magnetic track  10 . For example, if the current source  11  applies a current to the magnetic track  10 , which has a linear shape of predetermined length, in a first direction, the magnetic domain walls and the magnetic domains  101  in the magnetic track  10  may move in a direction opposite to the first direction, because the magnetic domain walls move in the direction of electron flow. 
         [0023]    When the movement principle of the magnetic domain walls is applied to an information storage device, the movement of the magnetic domain walls allows the magnetic domains  101  to pass a fixed writing device  12  (e.g., a device similar to that of a write head for a conventional HDD) and a fixed reading device  13  (e.g., a device similar to that of a read head for a conventional HDD), whereby information may be written to and/or read from the magnetic domains  101 . 
         [0024]    The writing device  12  is installed at a predetermined location along the magnetic track  10 , and writes information (i.e., write data) to the magnetic domains  101  when the magnetic domain walls and the magnetic domains  101  in the magnetic track  10  move. The reading device  13  is installed at a predetermined location along the magnetic track  10 , and retrieves information as read data from of the magnetic domains  101  as a consequence of moved magnetic domain walls and the magnetic domains  101  in the magnetic track  10 . In  FIG. 1 , the writing device  12  is installed proximate one end of the magnetic track  10 , and the reading device  13  is installed proximate the other opposite end of the magnetic track  10 . However, the writing device  12  and the reading device  13  may be disposed at any arbitrary locations along the magnetic track  10  as application demands. 
         [0025]    The write-back loop  15  is connected between the reading device  13  and the writing device  12 , and communicates read data obtained by the reading device  13  to the writing device  12 . 
         [0026]      FIGS. 2A and 2B  are views illustrating some operating principles for the magnetic racetrack memory device according to embodiment illustrated in  FIG. 1 . 
         [0027]    With reference to  FIGS. 1 ,  2 A and  2 B, the magnetic track  10  is completely filled with write data (i.e., written to without significant empty areas) during previous write operations or during a load operation which is different from normal read/write operations. In other words, as illustrated in  FIG. 1 , following the write or load operations, the magnetic track  10  will continuously store data (i.e., store data without significant empty spaces) in a defined (first) data region  14 A including magnetic domains  101 . The empty buffer area conventionally necessary to buffer the magnetic domains  101  in relation to the data region  14  is not provided. 
         [0028]    During a subsequent read operation, as illustrated in  FIG. 2A , the magnetic domains  101  in the magnetic track  10  sequentially pass under the reading device  13 , and reading device  13  reads information from the passing magnetic domains  101 . At this time, information written to magnetic domains that are moved beyond the end of the magnetic track  10  and thus deviate from the defined magnetic track  10  is erased. Read data from the reading device  13 , as illustrated in  FIG. 2B , is communicated via the write-back loop  15  to the writing device  12 , and re-written to the magnetic track  10  in a defined (second) data region  14 B by the writing device  12 . 
         [0029]    In accordance with this operation, the magnetic racetrack memory device of  FIG. 1  may be fully loaded with data and yet prevent the loss of read data. Due to the inclusion of the write-back loop  15  for preventing information loss, the magnetic track  10  does not need to include an empty buffer area. 
         [0030]    It should be noted that in certain embodiments, the speed at which a read operation is performed by the reading device  13  may be less than the speed at which a write (or re-write) operation is performed by the writing device  12 . In such cases, the write-back loop  15  may include a conventional data buffer for temporarily storing read data provided by the reading device  13 . 
         [0031]      FIG. 3  illustrates another embodiment of the inventive concept. Referring to  FIG. 3 , the magnetic racetrack memory device includes a plurality of magnetic tracks  30 , a current source  31 , a writing device  32 , a reading device  33 , a conversion circuit  34 , and a write-back loop  35 . 
         [0032]    The plurality of magnetic tracks  30  may be arranged parallel to implement a memory array  300 . The magnetic track  30 , current source  31 , writing device  32 , reading device  33 , and write-back loop  35  of  FIG. 3  correspond respectively to the magnetic track  10 , current source  11 , writing device  12 , reading device  13 , and write-back loop  15  of  FIG. 1 . 
         [0033]    A read path for the magnetic racetrack memory device of  FIG. 3  is similar to that of a conventional HDD. Accordingly, the magnetic racetrack memory device of  FIG. 3  has an arrangement of components in which the write-back loop  35  is added to a typical read path of a HDD. The conversion circuit  34 , which generally corresponds to the read path of the magnetic racetrack memory device of  FIG. 3 , amplifies read data obtained by the reading device  33 , converts the amplified read data into digital data, and then provides the digital read data to the write-back loop  35 . 
         [0034]    In the illustrated embodiment, the conversion circuit  34  comprises an amplifier  341 , an analog-to-digital converter (ADC)  342 , a decoder  343 , and a cash memory  344 . The amplifier  341  receives read data consistent with the magnetic domains in the magnetic track  30  by operation of the reading device  33 , and amplifies the received read data. The ADC  342  converts an output signal from the amplifier  341  into digital read data. The decoder  343  decodes the digital read data and outputs the decoded digital read data (for example, 10011010 . . . ) to the write-back loop  35 . The cash memory  344  temporarily stores the decoded digital read data (for example, 10011010 . . . ) and outputs the stored digital read data to an external input/output (I/O) device. 
         [0035]    In the illustrated embodiment, the structure of the magnetic racetrack memory device is divided into the read path and the write-back loop  35  after the decoder  343 , because analog read signal “A” corresponding to the read data obtained from the magnetic domains of the magnetic track  30  by the reading device  33  is not a voltage signal having high and low levels but a signal that represents a peak only when the magnetization directions of adjacent magnetic domains are different and has no change when the magnetization directions of adjacent magnetic domains are identical. In other words, the analog read signal “A” needs to be converted into a corresponding voltage signal (for example, 10011010 . . . ) having high and low levels corresponding to 0 and 1 so as to be easily used in the write-back loop  35 . 
         [0036]    The write-back loop  35  includes a read data buffer  351  and a write driver  352 . The read data buffer  351  buffers the decoded digital read data (for example, 10011010 . . . ) provided by the decoder  343 . The write driver  352  receives stored read data from the read data buffer  351  and outputs the read data to the writing device  32 . 
         [0037]    As described above, if the speed of a read operation performed by reading device  33  is different from the speed of the write operation performed by the writing device  33 , the buffer  351  will temporarily store read data. Otherwise, the buffer  351  will not be needed and may be omitted from certain embodiments of the inventive concept. If the buffer  351  is not included, the write driver  352  directly receives the decoded digital read data (for example, 10011010 . . . ) from the decoder  343  and outputs the decoded digital data to the writing device  32 . 
         [0038]    Although the magnetic racetrack memory device of  FIG. 3  includes the conversion circuit  34 , it need not include this circuit. If the conversion circuit  34  is not included, the read data obtained by the reading device  33  may be directly provided to the writing device  32  via the write-back loop  35 . The writing device  32  then re-writes the information received via the write-back loop  35  to the magnetic track  10 . 
         [0039]      FIG. 4  illustrates another embodiment of the magnetic racetrack memory device according to an embodiment of the inventive concept. 
         [0040]    In the magnetic racetrack memory device of  FIG. 4 , the write-back loop  35  does not include a buffer, but a cash memory  344  in the conversion circuit  34  is used as a buffer. That is, the magnetic racetrack memory device of  FIG. 4  is the same as that of  FIG. 3  except that the cash memory  344  in the conversion circuit  34  is used as a buffer. Accordingly, a detailed description of the duplicate components of the magnetic racetrack memory device of  FIG. 4  will be omitted. 
         [0041]    As noted above, a magnetic racetrack memory device according to an embodiment of the inventive concept does not require a significant empty buffer area within a constituent magnetic track. However, the conventional data loss necessitating the use conventional use of the empty buffer area is prevented by use of a write-back loop. 
         [0042]    While the inventive concept has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the scope of the following claims.