Abstract:
Apparatus and method for transducing data from a ferroelectric data storage medium using high frequency read modulation. In accordance with some embodiments, a ferroelectric data transducer has a write electrode, a doped semiconductor layer with a source, a drain and a channel therebetween, and an insulating layer disposed between the channel and the write electrode. A write circuit applies a time varying write signal at a first frequency to the write electrode to write a corresponding sequence of data bits to an adjacent ferroelectric data storage medium. A read circuit reads the sequence of data bits from the data storage medium by applying a time varying read signal at a higher, second frequency to the write electrode and detecting changes in electrical resistance of the channel.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of copending U.S. patent application Ser. No. 12/489,560 filed Jun. 23, 2009 which claims priority to Korean Patent Application No. 10-2008-0059768 filed on Jun. 24, 2008 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     
    
     BACKGROUND 
       [0002]    Currently, in most hard disk drives (HDDs) installed in personal computers (PCs), information is recorded by a magnetic field. In such a recording medium, a plurality of magnetic domains, which are magnetized in a first or second direction (i.e., the second direction is opposite to the first direction), are formed on a surface of the recording medium, and information “0” or “1” is recorded in each respective magnetic domain. 
         [0003]    Recently, research has been conducted with respect to a recording medium and an electric field read/write head which records and reproduces information by an electric field. Such a recording medium has a plurality of electric domains formed on a surface thereof. These electric domains are magnetized in a first or second direction (i.e., the second direction is opposite to the first direction), and information of “0” or “1” is recorded in a respective electric domain. 
         [0004]    The electric field read/write head reproduces the recorded information recorded from these electric domains using an electric field generated from the recording medium. 
         [0005]    However, there is a need for a method of correctly reading out the information recorded in the recording medium, even if an intensity of the electric field generated from the recording medium is weak and there is noise interference in the electric field. The higher is a density of information written in the recording medium, the smaller is an electric domain generated in the recording medium. Thus, an intensity of an electric field generated in the electric domain also becomes weaker. Accordingly, the need for the above-described method increases due to higher integration of the recording medium. 
       SUMMARY 
       [0006]    Various embodiments of the present disclosure are generally directed to an apparatus and method for Apparatus and method for transducing data from a ferroelectric data storage medium using high frequency read modulation. 
         [0007]    In accordance with some embodiments, an apparatus generally comprises a ferroelectric data transducer comprising a write electrode, a doped semiconductor layer having a source, a drain and a channel therebetween, and an insulating layer disposed between the channel and the write electrode. A write circuit is adapted to apply a time varying write signal at a first frequency to the write electrode to write a corresponding sequence of data bits to an adjacent ferroelectric data storage medium. A read circuit adapted to read the sequence of data bits from the data storage medium by applying a time varying read signal at a higher, second frequency to the write electrode and detecting changes in electrical resistance of the channel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The above and other aspects of the present disclosure will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings, in which: 
           [0009]      FIG. 1  is a structural view of a recording medium and a header according to an exemplary embodiment; 
           [0010]      FIG. 2A  is a perspective view of an electric field read/write head illustrated in  FIG. 1 , according to an exemplary embodiment; 
           [0011]      FIG. 2B  is a front view of the electric field read/write head illustrated in  FIG. 1 , according to an exemplary embodiment; 
           [0012]      FIG. 3  is a block diagram of an electric field read/write apparatus according to an exemplary embodiment; 
           [0013]      FIG. 4  is a reference view illustrating an operation of a modulation unit illustrated in  FIG. 3 , according to an exemplary embodiment; 
           [0014]      FIG. 5  is a circuit diagram of a modified version of a read unit and a demodulation unit illustrated in  FIG. 3 , according to an exemplary embodiment; 
           [0015]      FIG. 6  is a circuit diagram of a modified version of the read unit and the demodulation unit illustrated in  FIG. 3 , according to another exemplary embodiment; and 
           [0016]      FIG. 7  is a flow chart of an electric field read/write method, according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Exemplary embodiments will now be described more fully with reference to the accompanying drawings. Hereinafter, an electric field according to exemplary embodiments will be described with reference to the attached drawings. Like reference numerals in the drawings denote like elements. 
         [0018]    The term “unit”, as used herein, indicates, but is not limited to, a software or hardware component, such as a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks. A unit may advantageously be configured to reside on the addressable storage medium and configured to be executed on one or more processors. Thus, a unit may include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. The functionality provided for in the components and units may be combined into fewer components and units or further separated into additional components and units. In addition, the components and units may be implemented such that they execute one or more computers in a communication system. 
         [0019]      FIG. 1  is a structural view of a recording medium  100  and an electric field read/write head  110  according to an exemplary embodiment. 
         [0020]    The recording medium  100  may be a ferroelectric recording medium, and may be a structure including a substrate, an electrode and a ferroelectric layer which are sequentially stacked. In this case, the substrate may be formed of Si, glass, etc. The electrode may be formed of a metal such as Pt, Al, Au, Ag, Cu, etc. or metal oxide such as LaCoO, and may be grounded. The ferroelectric layer is formed of a ferroelectric material such as PbTiO 3 , PbZrO 3 , etc. 
         [0021]    Information is recorded in the recording medium  100  using an electric field. In the recording medium  100 , a plurality of electric domains polarized in a first direction or a second direction (here, the first direction is an opposite direction to the second direction) are formed on a surface of the recording medium  100 . Information of “0” or “1” is recorded in these electric domains. 
         [0022]    The electric field read/write head  110  may read information written to the recording medium  100  or may write information to the recording medium  100  while floating above a surface of the rotating recording medium  100  with a given space therebetween. 
         [0023]    The electric field read/write head  110  is attached to a head suspension  120 . The head suspension  120  is disposed at a tip of a swing arm  130 . The swing arm  130  is moved by a voice coil motor  140 . By virtue of the rotation of the swing arm  130 , the electric field read/write head  110  can be positioned over a desired location of the recording medium  100 . 
         [0024]      FIG. 2A  is a perspective view of the electric field read/write head  110  illustrated in  FIG. 1 , according to an exemplary embodiment.  FIG. 2B  is a front view of the electric field read/write head  110  illustrated in  FIG. 1 , according to the exemplary embodiment. 
         [0025]    Referring to  FIGS. 2A and 2B , the electric field read/write head  110  is embodied on a semiconductor substrate  210  formed of a p-type or n-type semiconductor material. The semiconductor substrate  210  includes a first surface  211  facing the recording medium  100  and a second surface  212  abutting the first surface  211 . The first surface  211  and the second surface  212  may be perpendicular to each other. 
         [0026]    An air bearing surface (ABS) pattern  230  may be formed on the first surface  211  of the semiconductor substrate  210 . The ABS pattern  230  functions such that the electric field read/write head  110  may float above a surface of the recording medium  100 . 
         [0027]    A channel C that is a low concentration impurity region and a source region S and a drain region D that are high concentration impurity regions are formed on the semiconductor substrate  210 . The source region S and the drain region D are disposed on opposite sides of the channel C. A source electrode E 1  is electrically connected to the source region S. A drain electrode E 2  is electrically connected to the drain region D. When the semiconductor substrate  210  is formed of a p-type semiconductor, the channel C is an n−impurity region, and the source region S and the drain region D are n+ impurity regions. On the other hand, when the semiconductor substrate  210  is formed of an n-type semiconductor, the channel C is a p− impurity region, and the source region S and the drain region D are p+ impurity regions. A first insulating layer  221  is disposed on the channel C. A writing electrode WR is disposed on the first insulating layer  221 . A second insulating layer  222  is disposed on an exposed portion of the source region S and an exposed portion of the drain region D. 
         [0028]    The channel C provides a path through which a current flows between the source region S and the drain region D. A resistance of the channel C varies according to at least one of a polarization direction and an electric charge of an electric domain facing the channel C. The electric field read/write head  110  detects the resistance of the channel C to read information written in the electric domain facing the channel C. 
         [0029]    Thus, a writing operation of the electric field read/write head  110  will be described for reference. When a positive voltage (+) or negative voltage (−) whose absolute value is equal to or greater than a threshold voltage is applied to the writing electrode WR of the electric field read/write head  110 , particular information of “0” or “1” is recorded in the electric domain facing the channel C. For example, when a positive (+) voltage equal to or greater than the threshold voltage is applied to the writing electrode WR, the electric domain facing the channel C is polarized in a first direction, and the information of “0” is recorded in the electric domain. In addition, when a negative (−) voltage whose absolute value is equal to or greater than the threshold voltage is applied to the writing electrode WR, the electric domain facing the channel C is polarized in a second direction, and thus information of “1” is recorded in the electric domain. 
         [0030]      FIG. 3  is a block diagram of an electric field read/write apparatus according to an exemplary embodiment. The electric field read/write apparatus according to the present exemplary embodiment may include a modulation unit  310 , a detection unit  320 , a read unit  330  and a demodulation unit  340 . In this case, the modulation unit  310 , the read unit  330  and demodulation unit  340  may be provided outside of the electric field read/write head  110  illustrated in  FIG. 1 , and the detection unit  320  may be disposed inside of the electric field read/write head  110  illustrated in  FIG. 1 . 
         [0031]    The modulation unit  310  modulates an electric field generated from the recording medium  100  by using a modulation signal. Since the recording medium  100  operates while data is being read, the electric domain facing the channel C of the electric field read/write head  110  continuously varies. Thus, the modulation unit  310  modulates an electric field variation transition (i.e., an electric field value based on a time sequence) of the electric field which is generated from the electric domain facing the channel C of the electric field read/write head  110  by using the modulation signal. The modulation signal has a given frequency, and is applied to the writing electrode WR of the electric field read/write head  110 . The size of the modulation signal may be less than a threshold voltage. 
         [0032]    The detection unit  320  detects the electric field variation (more specifically, the electric field variation transition), which is modulated by the modulation unit  310 . In particular, the detection unit  320  detects a resistance variation (more specifically, a resistance variation transition) of the channel C occurring due to the electric field modulated by the modulation unit  310 . 
         [0033]    The read unit  330  outputs a voltage signal determined according to the electric field variation (more specifically, the electric field variation transition), which is detected by the detection unit  320 . The read unit  330  is embodied by a plurality of circuitry devices (e.g., a resistor and an amplifier) including the electric field read/write head  110 . In addition, the read unit  330  receives a given voltage to output a voltage signal determined according to the electric field variation detected by the detection unit  320 . In this case, the circuit devices constituting the read unit  330  may be arranged according to a given design. Thus, the read unit  330  outputs the voltage signal determined according to the electric field variation (more specifically, the electric field variation transition) detected by the detection unit  320  by using a given method. 
         [0034]    The demodulation unit  340  demodulates the voltage signal input from the read unit  330  by using the modulation signal used by the modulation unit  310  to generate the electric field from the recording medium  100 . According to a demodulation result, the demodulation unit  340  determines information written in the recording medium  100 . 
         [0035]    The demodulation unit  340  demodulates the voltage signal input from the read unit  330  by using the modulation signal, performs low pass filtering (LPF) with a filter coefficient with respect to the demodulation result, and then determines the information written in the recording medium  100  according to an LPF result. At this time, by performing the LFP with respect to the demodulation result, the demodulation unit  340  may extract only a direct current (DC) component from the LPF result to determine the information written in the recording medium  100  according to the extracted DC component. 
         [0036]    The demodulation unit  340  may remove an offset contained in the demodulation result, and may determine the information written in the recording medium  100  according to the demodulation result from which the offset is removed. 
         [0037]    In short, the information written in the recording medium  100  is reproduced by detecting a resistance variation of the channel C of the electric field read/write head  110  floating above a surface of the recording medium  100 . 
         [0038]    A resistance of a resistor can be determined by a voltage or a current of a circuit including the resistor. In this regard, when a voltage signal (or, a current signal) having information regarding a resistance of a resistor is obtained, noise in the circuit may interfere with the voltage signal. Thus, when a voltage signal at a given point of a circuit including a resistor is obtained in order to correctly determine a resistance of the resistor, as much noise as possible in the circuit must be prevented from interfering with the voltage signal. 
         [0039]    Accordingly, in order to correctly reproduce the information written in the recording medium  100 , a resistance variation of the channel C, dependent on an electric field generated in the recording medium  100 , needs to be correctly detected. To achieve this, a voltage signal (or, a current signal) of a circuit including the channel C, which has information regarding the resistance variation of the channel C, needs to be correctly obtained so that as much noise as possible in the circuit can be prevented from interfering with the voltage signal. 
         [0040]    According to the present exemplary embodiment, the electric field read/write apparatus according to the present exemplary embodiment does not simply use a voltage signal containing information regarding a resistance variation of the channel C occurring due to an electric field generated in the recording medium  100 , in order to reproduce information recorded in the recording medium. Instead, in the present exemplary embodiment, the electric field is first modulated by a modulation signal. Next, a voltage signal containing information regarding a resistance variation of the channel C occurring due to a modulation result is demodulated using the modulation signal, and then information written in the recording medium  100  is reproduced according to a demodulation result. A frequency of the modulation signal is much higher than that of the electric field generated in the recording medium  100 , and accordingly, the modulated electric field is nearly completely unaffected by noise. Thus, according to the present exemplary embodiment, since the voltage signal containing information regarding the resistance variation of the channel C occurring due to the electric field modulated by the modulation signal is obtained as a voltage signal that is nearly completely unaffected by the noise in a circuit constituting the read unit  330 , the information written in the recording medium  100  may be correctly reproduced. 
         [0041]      FIG. 4  is a reference view illustrating an operation of the modulation unit  310  illustrated in  FIG. 3 , according to an exemplary embodiment.  FIG. 4  illustrates a source region S, a drain region D and a channel C of the electric field read/write head  110  illustrated in  FIG. 1 . Referring to  FIG. 4 , a current may flow from the drain region D to the source region S through the channel C having width W, thickness T and length L. 
         [0042]    The width W of the channel C is determined according to an electric field  410  generated from the recording medium  100 . Accordingly, a resistance of the channel C is determined according to the electric field  410  generated in the recording medium  100 . 
         [0043]    Similarly, since a writing electrode WR is disposed above the first insulating layer  221  disposed above the channel C, the thickness T of the channel C is determined by the modulation signal  420  applied to the writing electrode WR. That is, the resistance of the channel C is affected by the modulation signal  420 . 
         [0044]    Thus, the resistance of the channel C is given by Equation 1 as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         
                           r 
                           F 
                         
                         = 
                           
                          
                         
                           ρ 
                            
                           
                             L 
                             A 
                           
                         
                       
                     
                   
                   
                     
                       
                         = 
                           
                          
                         
                           ρ 
                            
                           
                             L 
                             
                               
                                 ( 
                                 
                                   W 
                                   - 
                                   w 
                                 
                                 ) 
                               
                                
                               
                                 ( 
                                 
                                   T 
                                   - 
                                   t 
                                 
                                 ) 
                               
                             
                           
                         
                       
                     
                   
                   
                     
                       
                         
                           ≈ 
                             
                            
                           
                             ρ 
                              
                             
                               L 
                               WT 
                             
                              
                             
                               ( 
                               
                                 1 
                                 + 
                                 
                                   w 
                                   W 
                                 
                                 + 
                                 
                                   t 
                                   T 
                                 
                                 - 
                                 
                                   
                                     w 
                                     2 
                                   
                                   
                                     W 
                                     2 
                                   
                                 
                                 - 
                                 
                                   wt 
                                   WT 
                                 
                                 - 
                                 
                                   
                                     t 
                                     2 
                                   
                                   
                                     T 
                                     2 
                                   
                                 
                               
                               ) 
                             
                           
                         
                         , 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where r F  is the resistance of the channel C, ρ is the resistivity of the channel C, A is a cross section of the channel C, L is the length of the channel C, W is the width of the channel C, T is the thickness of the channel C, w is the variation in width of the channel C occurring with respect to change in carrier distribution in the channel C due to an electric field generated in the recording medium  100 , and t is the variation in thickness of the channel C occurring with respect to carrier distribution in the channel C due to a modulation signal. 
         [0045]    When only a component r ω  having a frequency w of the modulation signal is extracted from among components of r F  of Equation 1, the component r ω  can be given by Equation 2: 
         [0000]    
       
         
           
             
               
                 
                   
                     r 
                     ω 
                   
                   = 
                   
                     ρ 
                      
                     
                       L 
                       WT 
                     
                      
                     
                       ( 
                       
                         1 
                         - 
                         
                           w 
                           W 
                         
                       
                       ) 
                     
                      
                     
                       t 
                       T 
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0046]      FIG. 5  is a circuit diagram of a modified version of the read unit  330  and the demodulation unit  340  illustrated in  FIG. 3 , according to an exemplary embodiment. 
         [0047]    Referring to  FIG. 5 , a read unit  330 A includes a wheatstone bridge circuit and an instrumentation amplifier. The instrumentation amplifier may be implemented using a plurality of ideal operational amplifiers (OP AMPs) to perform a given operation. In  FIG. 5  r F  is a resistance of the channel C, V SS  is a given voltage input to the read unit  330 A, R is a resistance, v 1  is a voltage of a non-inverting terminal of the instrumentation amplifier, and v 2  is a voltage of an inverting terminal of the instrumentation amplifier. The instrumentation amplifier amplifies and outputs v o , which is A (A is a positive integer) times a difference between v1 and v2. At this time, v o  represents the voltage signal determined according to the electric field variation (more specifically, the electric field variation transition) detected by the detection unit  320  as described above. 
         [0048]    As illustrated in  FIG. 5 , a demodulation unit  340 A demodulates v o  by using a modulation signal v t , performs LPF with respect to a demodulation result v om ), and determines information written in the recording medium  100  according to a result v out  of the LPF. 
         [0049]    In particular, v 1 , v 2 , v o , v om  and v out , as illustrated in  FIG. 5 , are each given by Equation 3 as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       v 
                       1 
                     
                     = 
                     
                       
                         
                           r 
                           F 
                         
                         
                           
                             P 
                             t 
                           
                           + 
                           
                             r 
                             F 
                           
                         
                       
                        
                       
                         V 
                         SS 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       v 
                       2 
                     
                     = 
                     
                       
                         1 
                         2 
                       
                        
                       
                         V 
                         SS 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       v 
                       0 
                     
                     = 
                     
                       
                         A 
                          
                         
                           ( 
                           
                             
                               v 
                               1 
                             
                             - 
                             
                               v 
                               2 
                             
                           
                           ) 
                         
                       
                       = 
                       
                         
                           1 
                           2 
                         
                          
                         
                           
                             
                               r 
                               F 
                             
                             - 
                             
                               P 
                               t 
                             
                           
                           
                             
                               P 
                               t 
                             
                             + 
                             
                               r 
                               F 
                             
                           
                         
                          
                         
                           V 
                           SS 
                         
                          
                         A 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         
                           
                             v 
                             om 
                           
                           = 
                             
                            
                           
                             
                               1 
                               2 
                             
                              
                             
                               
                                 
                                   r 
                                   F 
                                 
                                 - 
                                 
                                   P 
                                   t 
                                 
                               
                               
                                 
                                   P 
                                   t 
                                 
                                 + 
                                 
                                   r 
                                   F 
                                 
                               
                             
                              
                             
                               V 
                               SS 
                             
                              
                             
                               Av 
                               t 
                             
                           
                         
                       
                     
                     
                       
                         
                           
                             ≈ 
                               
                              
                             
                               
                                 
                                   
                                     V 
                                     SS 
                                   
                                   
                                     2 
                                      
                                     
                                       ( 
                                       
                                         
                                           P 
                                           t 
                                         
                                         + 
                                         
                                           r 
                                           0 
                                         
                                       
                                       ) 
                                     
                                   
                                 
                                  
                                 
                                   [ 
                                   
                                     
                                       r 
                                       0 
                                     
                                     - 
                                     
                                       P 
                                       t 
                                     
                                     + 
                                     
                                       r 
                                       ω 
                                     
                                     + 
                                     
                                       r 
                                       
                                         2 
                                          
                                         ω 
                                       
                                     
                                   
                                   ] 
                                 
                               
                                
                               
                                 Av 
                                 t 
                               
                             
                           
                           , 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where r o  is a DC component of r F , r 2ω  is a component having a frequency 2ω that is twice the frequency ω of the modulation signal, extracted from among the components of r F . In components of v om , (r o *v t ) has only a component of ω, (R*v t ) has only a component of ω, (rω*v t ) has only a DC component and a component of 2ω, and a DC component of (r 2ω * v t ) has only components of ω and 3ω. 
         [0050]    Thus, the demodulation unit  340 A may perform LPF with respect to the demodulation result v om  to extract only a DC component from the demodulation result v om . That is, the demodulation unit  340 A may perform LPF with respect to the demodulation result v om  to obtain only information regarding (r ω *v t ) from among information regarding (r o *v t ), (R*v t ), (r ω *v t ) and (r 2ω *v t ), and may reproduce information written in the recording medium  100  according to the obtained information. 
         [0051]      FIG. 6  is a circuit diagram of a modified version of the read unit  330  and the demodulation unit  340  illustrated in  FIG. 3 , according to another exemplary embodiment. 
         [0052]    As illustrated in  FIG. 6 , a read unit  330 B is embodied using an ideal OP AMP including a closed-loop. Referring to  FIG. 6 , is a resistance of the channel C, V SS  is a given voltage input to read unit  330 B, R is a resistance, i 1  is a current flowing through the resistance R connected to a non-inverting terminal of the OP AMP, v 1  is a voltage of a non-inverting terminal of the OP AMP and v o  is the voltage signal determined according to the electric field variation (more specifically, the electric field variation transition) detected by the detection unit  320  as described above. 
         [0053]    As illustrated in  FIG. 6 , a demodulation unit  340 B demodulates v o  by using the modulation signal v t , performs LPF with respect to the demodulation result v om , and determines information written in the recording medium  100  according to a result v out  of the LPF. 
         [0054]    In particular, v 1 , v 2 , v o , v om  and v out , as illustrated in  FIG. 6  are each given by Equation 4 as follows: 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       v 
                       2 
                     
                     = 
                     
                       
                         1 
                         2 
                       
                        
                       
                         V 
                         SS 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       v 
                       1 
                     
                     = 
                     
                       v 
                       2 
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       i 
                       1 
                     
                     = 
                     
                       
                         
                           
                             V 
                             SS 
                           
                           - 
                           
                             v 
                             2 
                           
                         
                         R 
                       
                       = 
                       
                         
                           V 
                           SS 
                         
                         
                           2 
                            
                           R 
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       v 
                       1 
                     
                     = 
                     
                       
                         
                           r 
                           F 
                         
                          
                         
                           i 
                           1 
                         
                       
                       + 
                       
                         v 
                         0 
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         
                           
                             v 
                             0 
                           
                           = 
                             
                            
                           
                             
                               v 
                               1 
                             
                             - 
                             
                               
                                 r 
                                 F 
                               
                                
                               
                                 i 
                                 1 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           = 
                             
                            
                           
                             
                               - 
                               
                                 
                                   
                                     r 
                                     F 
                                   
                                   - 
                                   R 
                                 
                                 
                                   2 
                                    
                                   R 
                                 
                               
                             
                              
                             
                               V 
                               SS 
                             
                           
                         
                       
                     
                   
                    
                   
                     
 
                   
                    
                   
                     
                       
                         v 
                         om 
                       
                       = 
                       
                         
                           - 
                           
                             
                               
                                 V 
                                 SS 
                               
                               
                                 2 
                                  
                                 R 
                               
                             
                              
                             
                               [ 
                               
                                 
                                   r 
                                   0 
                                 
                                 - 
                                 R 
                                 + 
                                 
                                   r 
                                   ω 
                                 
                                 + 
                                 
                                   r 
                                   
                                     2 
                                      
                                     
                                         
                                     
                                      
                                     ω 
                                   
                                 
                               
                               ] 
                             
                           
                         
                          
                         
                           v 
                           t 
                         
                       
                     
                     , 
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where r o  is a DC component of r F  and r 2ω , is a component having a frequency 2ω that is twice the frequency ω of the modulation signal, extracted from among the components of r t . In components v om , (r o *v t ) has only a component of ω, (R*v t ) has only a component of ω, (r ω *v t ) has only a DC component and a component of 2ω, and a DC component of (r 2ω *v t ) has only components of ω and 3ω. 
         [0055]    Thus, a demodulation unit  340 B may perform LPF with respect to the demodulation result v om  to extract only a DC component from the demodulation result v om . That is the demodulation unit  340 A may perform LPF with respect to the demodulation result v om  to obtain only information regarding (r ω *v t ) from among information regarding (r o *v t ), (R* v t ), (r ω *v t ) and (r 2ω *v t ), and may reproduce information written in the recording medium  100  according to the obtained information. 
         [0056]      FIG. 7  is a flow chart of an electric field read/write method, according to an exemplary embodiment. The method according to the present exemplary embodiment may include correctly detecting a resistance of a channel, which varies according to an electric field generated from a recording medium in which information is written by an electric field, to correctly reproduce information written in the recording medium (operations  710  through  730 ). The method of  FIG. 7  will be described with reference to  FIGS. 1 ,  2 A,  2 B, and  3 . 
         [0057]    The modulation unit  310  modulates an electric field generated from the recording medium  100  by using a given modulation signal (operation  710 ). 
         [0058]    Next, the detection unit  320  detects a variation in the modulated electric field (operation  720 ). In particular, the detection unit  320  detects a variation in the resistance of the channel C occurring due to the modulated electric field. 
         [0059]    The demodulation unit  340  then demodulates a voltage signal determined according to the detected variation by using the modulation signal, and determines information written in the recording medium  100  according to a demodulation result (operation  730 ). 
         [0060]    Computer programs for executing the electric field read/write method according to the exemplary embodiments in a computer can be stored in a computer readable recording medium. Examples of the computer readable recording medium include magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.), and optical recording media (e.g., CD-ROMs, or DVDs). The exemplary embodiments can also be transmitted through a transmission medium, which include carrier waves transmitted through the Internet or various types of communication channel. The computer readable recording medium can also be distributed over network-coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. 
         [0061]    While the present disclosure has set forth various exemplary embodiments, it will be understood by one of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.