Abstract:
Provided is a ferroelectric recording medium including a ferroelectric recording layer formed of a polarization reversal ferroelectric material and an anisotropic conduction layer that covers the ferroelectric recording layer and changes into a conductor or a non-conductor based on external energy.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This application claims priority from Korean Patent Application No. 10-2004-0087040, filed on Oct. 29, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a ferroelectric recording medium, a recording apparatus comprising the same, and a recording method of the same, and more particularly, to a ferroelectric recording medium comprising an anisotropic conduction layer and a recording method of the same. 
     2. Description of the Related Art 
     In general a ferroelectric material has spontaneous polarization, which is reversed by an electric field. A ferroelectric recording medium is a nonvolatile recording medium having a high capacity on which data is recorded, corrected, and stored by using such a property of ferroelectric materials. 
     Japanese Laid-open Patent No. 2002-175602 discloses an example of a conventional ferroelectric recording medium, which is illustrated in  FIG. 1 . 
     Referring to  FIG. 1 , a ferroelectric recording layer  2  and a reading/writing head tip  1  are in direct contact in a conventional ferroelectric recording medium, and thus both the ferroelectric recording layer  2  and the reading/writing head tip  1  may be damaged. More specifically, the ferroelectric recording layer  2  and the reading/writing head tip  1  are formed of hard materials, and thus the damage may be serious. In other words, scratches may be formed on the ferroelectric recording layer  2 , resulting in the deterioration of the stability of data recorded on the ferroelectric recording layer  2 . In addition, the reading/writing head tip  1  may be damaged, resulting in the deterioration of reading/writing performance. 
     In order to prevent such problems, a soft protective film  3  covers the ferroelectric recording layer  2 , as shown in  FIG. 2 . The soft protective film  3  prevents direct contact between the ferroelectric recording layer  2  and the reading/writing head tip  1  during a reading/writing operation, and thus the damage of the ferroelectric recording layer  2  and the reading/writing head tip  1  are prevented. 
     However, the protective film  3  on the ferroelectric recording layer  2  has low permittivity, and thus a voltage applied by the head tip  1  to the protective film  3  is distributed through the protective film  3 . As a result, a high voltage is required for a writing operation. More specifically, permittivity determines a ratio between an electric flux density and an electric field, and since the permittivity of the protective film  3  is very low, the protective film  3  has a high resistance. Accordingly, when a writing operation is performed on the ferroelectric recording layer  2 , a large applied voltage is distributed to the protective film  3  according to the ratio of the resistance of the protective film  3  and the ferroelectric recording layer  2 . Thus, a high voltage is required to perform a writing operation on the ferroelectric recording layer  2 , considering a voltage distribution ratio of the protective film  3  and the ferroelectric recording layer  2 . 
     SUMMARY OF THE INVENTION 
     The present invention provides a ferroelectric recording medium, a recording apparatus comprising the same, and a recording method of the same which allows a reading/writing operation to be performed by applying a low voltage from a reading/writing head tip to a ferroelectric recording layer by reducing a voltage distributed to a protective film which covers the ferroelectric recording layer. 
     According to an aspect of the present invention, there is provided a ferroelectric recording medium comprising: a ferroelectric recording layer formed of a polarization reversal ferroelectric material; and an anisotropic conduction layer that covers the ferroelectric recording layer and changes into a conductor or a non-conductor based on external energy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a perspective view of a conventional ferroelectric recording medium without a protective film; 
         FIG. 2  is a perspective view of a conventional ferroelectric recording medium on which a protective film is formed; 
         FIG. 3  is a perspective view of a ferroelectric recording medium according to an embodiment of the present invention; 
         FIG. 4  is a graph illustrating the conductive transition of a volatile anisotropic conduction layer installed in a ferroelectric recording medium according to an embodiment of the present invention; and 
         FIG. 5  is a graph illustrating the conductive transition of a nonvolatile anisotropic conduction layer installed in a ferroelectric recording medium according an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
       FIG. 3  is a perspective view of a ferroelectric recording medium according to an embodiment of the present invention. 
     Referring to  FIG. 3 , the ferroelectric recording medium according to an embodiment of the present invention includes a transferable reading/writing head tip  10 , a ferroelectric recording layer  30  on which a reading/writing operation is performed by the reading/writing head tip  10 , and an anisotropic conduction layer  20  which covers the ferroelectric recording layer  30 . The ferroelectric recording layer  30  includes sectors  31 ,  32 ,  33 , and  34 , and the anisotropic conduction layer  20  includes sectors  21 ,  22 ,  23 , and  24  disposed on the sectors  31 ,  32 ,  33 , and  34  of the ferroelectric recording layer  30 , respectively. 
     The reading/writing head tip  10  moves above the ferroelectric recording layer  30  to perform a reading/writing operation at a predetermined location of the ferroelectric recording layer  30 . The reading/writing heat tip  10  is formed of a hard material. 
     Data may be recorded in the ferroelectric recording layer  3  as 0 or 1, or ON or OFF, based on a direction of dielectric polarization. Each of the sectors  31 ,  32 ,  33 , and  34  can individually store data recorded by the reading/writing heat tip  10 . 
     The anisotropic conduction layer  20  covers the ferroelectric recording layer  30  such that the reading/writing head tip  10  does not directly contact the ferroelectric recording layer  30 . Accordingly, the anisotropic conduction layer  20  prevents the generation of scratches on the ferroelectric recording layer  30  and damage to data and prevents damage to the reading/writing head tip  10  and the deterioration of reading/writing performance. The anisotropic conduction layer  20  may be formed of a soft material in order to improve the protection of the reading/writing head tip  10 . Examples of a soft material are as follows: PFP (Para-Fluorophenylalanine), PMMA (Poly Methyl Meta Acrylate), PI (Polymide), Epoxy compound, etc. In addition, the anisotropic conduction layer  20  may be attached to the ferroelectric recording layer  30 . 
     Since the anisotropic conduction layer  20  becomes conductive at a voltage greater than a critical voltage, thus operating as an electrode, the spontaneous polarization of the ferroelectric recording layer  30  may be reversed even when a voltage greater than a critical voltage is applied by the reading/writing head tip  10  to the ferroelectric recording layer  30 . Accordingly, data may be recorded to the ferroelectric layer  30  by applying a low voltage. More specifically, when a voltage is applied by the reading/writing head tip  10 , one of the sectors  21 ,  22 ,  23 , and  24  of the anisotropic conduction layer  20  located under the reading/writing head tip  10  becomes a conductor. Then, the resistance of the anisotropic conduction layer  20  is reduced, and electric power supplied from the reading/writing head tip  10  to the ferroelectric recording layer  30  can smoothly flow. As a result, data can be efficiently recorded to the ferroelectric recording layer  30  through the anisotropic conduction layer  20 , even when a low voltage (for example, a range of higher than 0 and no more than 10) is applied by the reading/writing head tip  10  to the ferroelectric recording layer  30 . A method of changing the anisotropic conduction layer  20  into a conductor will now be described based on the volatility of the anisotropic conduction layer  20 . 
       FIG. 4  is a graph illustrating the conductive transition of a volatile anisotropic conduction layer installed on a ferroelectric recording medium according to an embodiment of the present invention. 
     Referring to  FIG. 4 , the anisotropic conduction layer  20  disposed on the ferroelectric recording layer  30  is volatile and changes into a conductor or a nonconductor based on a voltage between the reading/writing head tip  10  and the ferroelectric recording layer  30 . 
     The volatile anisotropic conduction layer  20  is nonconductive until the voltage between the reading/writing head tip  10  and the ferroelectric conduction layer  30  reaches a critical voltage Vth. Thereafter, the anisotropic conduction layer  20  becomes a conductor. The conductive state of the anisotropic conduction layer  20  is maintained until the applied voltage is lowered to the critical voltage Vth. When the applied voltage is lowered to the critical voltage Vth, the anisotropic conduction layer  20  is changed into a nonconductor. 
       FIG. 5  is a graph illustrating the conductive transition of a nonvolatile anisotropic conduction layer installed on a ferroelectric recording medium according to the embodiment of the present invention. 
     Referring to  FIG. 5 , the anisotropic conduction layer  20  disposed on the ferroelectric recording layer  30  is nonvolatile and changes into a conductor or a nonconductor based on a voltage between the reading/writing head tip  10  and the ferroelectric recording layer  30 . 
     The anisotropic conduction layer  20  is nonconductive until the voltage between the reading/writing head tip  10  and the ferroelectric conduction layer  30  reaches a critical voltage Vth 1 . Thereafter, the anisotropic conduction layer  20  becomes a conductor, and the conductive state is maintained even when the applied voltage is removed. When the applied voltage reaches another critical voltage Vth 2 , the anisotropic conduction layer  20  is changed into a nonconductor. 
     The operation of a ferroelectric recording medium according to an embodiment of the present invention will now be described. 
     First, the reading/writing head tip  10  of  FIG. 3  is transferred to a location where a reading/writing operation is to be performed on the ferroelectric recording layer  30 . Then, electric power is supplied to the reading/writing head tip  10  to apply a voltage to the anisotropic conduction layer  20 . The anisotropic conduction layer  20  covering the ferroelectric recording layer  30  is initially in a nonconductive state. 
     When the voltage applied to the anisotropic conduction layer  20  is greater than the critical voltage Vth or Vth 1  for changing the anisotropic conduction layer  20  into a conductor, one of the sectors  21 ,  22 ,  23 , or  24  of the anisotropic conduction layer  20  located between the reading/writing head tip  10  and the ferroelectric recording layer  30  is changed into a conductor. Then, the electric resistance of the sector  21 ,  22 ,  23 , or  24  of the anisotropic conduction layer  20  is lowered, allowing the smooth flow of electric power applied between the reading/writing head tip  10  and the ferroelectric recording layer  30 . In this state, the reading/writing head tip  10  performs a reading/writing operation with the ferroelectric recording layer  30 . Since the sector  21 ,  22 ,  23 , or  24  of the anisotropic conduction layer  20  that covers a portion of the ferroelectric recording layer  30  where the reading/writing operation is to be performed is in a conductive state, a low voltage may be applied by the reading/writing head tip  10  to the ferroelectric recording layer  30  to perform the reading/writing operation. 
     After the reading/writing operation is completed, the reading/writing head tip  10  is moved from the location where the reading/writing operation has been performed and transferred to another location of the ferroelectric recording layer  30  in order to perform the reading/writing operation on the other location. 
     On the other hand, the sector  31 ,  32 ,  33 , or  34  of the ferroelectric recording layer  30  that corresponds to the sector  21 ,  22 ,  23  or  24  is conductive, and becomes nonconductive under a predetermined condition. More specifically, if the anisotropic conduction layer  20  is volatile, it becomes nonconductive when the applied voltage is lower than the critical voltage Vth. On the other hand, if the anisotropic conduction layer  20  is nonvolatile, it remains conductive even when the applied voltage is removed and becomes nonconductive when the applied voltage is higher than the critical voltage Vth 2 . Since the transition of the anisotropic conduction layer  20  to a conductor is reversed when an electric field between the reading/writing head tip  10  and the ferroelectric recording layer  30  is removed or when a voltage greater than the critical voltage for changing the anisotropic conduction layer  20  into a conductor is applied, each of the sectors  21 ,  22 ,  23 , and  24  is independent to the transition. 
     A ferroelectric recording medium, a recording apparatus comprising the same, and a recording method of the same according to embodiments of the present invention allow a reading/writing operation to be performed with a low voltage between a reading/writing head tip and a ferroelectric recording layer by changing into a conductor a sector of an anisotropic conduction layer disposed on a sector of the ferroelectric recording layer to which the reading/writing operation is to be performed. 
     In addition, according to the present invention, an anisotropic conduction layer covers a ferroelectric recording layer such that a reading/writing head tip does not directly contact the ferroelectric recording layer, and thus the generation of scratches on the ferroelectric recording layer and the damage to the reading/writing head tip are prevented. Thus, damage to data recorded on the ferroelectric recording layer is prevented to secure the stability of data and to maintain the reading/writing performance of the reading/writing head tip. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.