Abstract:
A nonvolatile memory device including one-time programmable (OTP) unit cell is provided. The nonvolatile memory device includes: a unit cell; a detecting unit configured to detect data from the unit cell; and a read voltage varying unit configured to vary an input voltage and supply a varied read voltage to the unit cell.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2008-0035208, filed on Apr. 16, 2008, the entire disclosure of which is incorporated herein by reference for all purposes. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The following description relates to a semiconductor design technology; and, more particularly, to a nonvolatile memory device including one-time programmable (OTP), unit cell. 
     2. Description of Related Art 
     One-time programmable (OTP) unit cells are formed inside a volatile or nonvolatile memory device, such as DRAM, EEPROM or flash memory, and are used for memory repair purpose. In addition, OTP unit cells are used for internal operating voltage and frequency trimming in a mixed-signal chip where an analog chip and a digital chip are mixed. 
     Generally, each OTP unit cell includes an antifuse implemented with a metal-oxide-semiconductor field effect transistor (MOSFET), which will be referred to as a MOS transistor, and one or more MOS transistors. Such an OTP unit cell is formed inside each memory chip in a single or array configuration and is used for repair or trimming. 
       FIG. 1  is an equivalent circuit diagram for explaining a conventional nonvolatile memory device including an OTP unit cell. 
     Referring to  FIG. 1 , the conventional nonvolatile memory device includes an OTP unit cell  10  and a detecting unit  20 . The OTP unit cell  10  includes an antifuse ANT_FS, an n-channel transistor NM 1  connected between the antifuse ANT_FS and an output terminal C (an output terminal through which data is outputted in a read operation), and an n-channel transistor NM 2  connected between the output terminal C and a fourth input terminal E. The detecting unit  20  is configured with an inverter. 
     The following description will be made on read and write operations of the conventional nonvolatile memory device. 
     
       
         
               
               
             
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 Terminal (Node) 
               
             
          
           
               
                 Mode 
                 A 
                 B 
                 D 
                 E 
                 C 
                 DA_OUT 
               
               
                   
               
               
                 Write 
                 Ground 
                 H 
                 H 
                 High 
                 — 
                 — 
               
               
                 Operation 
                 Voltage 
                   
                   
                 Voltage 
               
               
                 Read 
                 Ground 
                 H 
                 H 
                 Power 
                 L 
                 H 
               
               
                 Operation 
                 Voltage 
                   
                   
                 Supply 
               
               
                   
                   
                   
                   
                 Voltage 
               
               
                   
               
             
          
         
       
     
     Write Operation 
     First, a ground voltage is applied to a first input terminal A, and a high voltage is applied to a fourth input terminal E. Also, a signal having a logic level corresponding to a power supply voltage, which will be referred to as a logic high signal hereinafter, is applied to a second input terminal B and a third input terminal D. Accordingly, a gate dielectric breakdown occurs due to a high electric field formed between a substrate and a gate of the antifuse ANT_FS implemented with the MOS transistor. Thus, the gate of the antifuse ANT_FS and the substrate are electrically shorted. 
     Read Operation 
     After the write operation, the ground voltage is applied to the first input terminal A, and the power supply voltage is applied to the fourth input terminal E. A logic high signal is inputted to the second input terminal B and the third input terminal D. Accordingly, a current path is formed from the first input terminal A to the fourth input terminal E through the antifuse ANT_FS, the first transistor NM 1  and the second transistor NM 2 . Thus, a logic level corresponding to the ground voltage (hereinafter, referred to as a logic low level) is outputted through the output terminal C. 
     However, the conventional nonvolatile memory device has the following limitations. 
     In the conventional nonvolatile memory device, if the antifuse does not stably break down in the read operation and thus the unit cell has high resistance, the detecting unit  20  implemented with the inverter cannot accurately detect the data in the read operation due to a narrow sensing margin of data detected through the output terminal C. Therefore, the inaccurate data detection degrades the reliability in the read operation of the nonvolatile memory device. 
     SUMMARY OF THE INVENTION 
     An example is directed to a nonvolatile memory device which may be capable of preventing malfunctions caused by high resistance of a unit cell in a read operation and, as a result, improving the reliability of the read operation. 
     In one general aspect, there is provided a nonvolatile memory device, including: a unit cell; a detecting unit configured to detect data from the unit cell; and a read voltage varying unit configured to vary an input voltage and supply a varied read voltage to the unit cell. 
     In another general aspect, there is provided a nonvolatile memory device, including: a cell array including a plurality of unit cells arranged in a matrix type; a plurality of data lines commonly connected to output terminals of the unit cells; a plurality of detecting units configured to detect data from the data lines; and a read voltage varying unit configured to vary an input voltage and supply a varied read voltage to the data lines. 
     In another general aspect, there is provided a nonvolatile memory device, including: a cell array including a plurality of unit cells arranged in a matrix type; a plurality of data lines commonly connected to output terminals of the unit cells; a plurality of detecting units configured to detect data from the data lines; and a read voltage varying unit configured to vary an input voltage and supply a varied read voltage to the data lines. 
     Other features and aspects may be understood by the following description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram of a conventional nonvolatile memory device. 
         FIG. 2  is a configuration diagram illustrating an example of a nonvolatile memory device. 
         FIG. 3  is a circuit diagram of a read voltage varying unit ( 130 ) of  FIG. 2 . 
         FIGS. 4 to 9  are circuit diagrams of a variable current supplying unit  122  of  FIG. 3 . 
         FIG. 10  is a circuit diagram of a unit cell  110  of  FIG. 2 . 
         FIG. 11  is a circuit diagram illustrating an example of an explanation of an operation characteristic of the nonvolatile memory device. 
         FIGS. 12 to 14  are configuration diagrams illustrating an examples of memory cell arrays of the nonvolatile memory device. 
     
    
    
     DETAILED DESCRIPTION 
     Features and aspects may become apparent from the following description of example embodiments with reference to the accompanying drawings, which is set forth hereinafter. Furthermore, the term “transistor” described throughout this specification refers to a switching element operating in response to a control signal inputted to its gate. For example, examples of the transistor include a junction field effect transistor (JFET) and a metal-oxide-semiconductor field effect transistor (MOSFET). Moreover, like reference numerals or symbols refer to like elements throughout. 
     Embodiment 
       FIG. 2  is a configuration diagram illustrating an example of a nonvolatile memory device. 
     Referring to  FIG. 2 , an example of the nonvolatile memory device includes a unit cell  110 , a detecting unit  120 , and a read voltage varying unit  130 . The detecting unit  120  detects data from the unit cell  110 . The read voltage varying unit  130  varies an input voltage and supplies a read voltage having a varied level to the unit cell  110 . 
     Referring to  FIG. 3 , the read voltage varying unit  130  includes a first current mirror  121  and a variable current supplying unit  122 . The first current mirror  121  receives a power supply voltage as the input voltage and supplies the read voltage to the unit cell  110 . The variable current supplying unit  122  supplies a variable current or a variable voltage to an input terminal G of the first current mirror  121 . 
     The first current mirror  121  includes a first transistor PM 1  and a second transistor PM 2 . The first transistor PM 1  is connected between a power supply voltage terminal VDD and an output terminal F of the unit cell  110 . The second transistor PM 2  is connected between the output terminal G of the variable current supplying unit  122  (the input terminal of the first current mirror  121 ) and the power supply voltage terminal VDD. Also, a gate of the second transistor PM 2  and a gate of the first transistor PM 1  are commonly connected to the input terminal G of the first current mirror  121 . In this case, the first transistor PM 1  and the second transistor PM 2  may be implemented with p-channel transistors having more excellent driving characteristics than n-channel transistors. 
     The variable current supplying unit  122  supplies the variable current varying the potential of the input terminal G of the first current mirror  121  in order to control the operation of the first current mirror  121 . To this end, the variable current supplying unit  122  includes a variable resistor whose resistance is varied by a plurality of control signals. 
     To take an example, as illustrated in  FIG. 4 , the variable current supplying unit  122  includes a plurality of resistors R 1  to R 3  connected in series between the input terminal G of the first current mirror  121  and the ground voltage terminal VSS, and a plurality of first switching units NM 1  to NM 3  connected in parallel to the plurality of resistors R 1  to R 3 , respectively. The first switching units NM 1  to NM 3  are implemented with transistors operating in response to control signals H, I and J inputted to their gates. More specifically, the first switching units NM 1  to NM 3  are implemented with n-channel transistors. There is no limitation in the number of the resistors R 1  to R 3  and the first switching units NM 1  to NM 3 . 
     As another example, as illustrated in  FIG. 5 , the variable current supplying unit  122  includes a plurality of transistors NM 1  to NM 3  connected in parallel between the input terminal G of the first current mirror  121  and the ground voltage terminal VSS. There is no limitation in the number of the transistors NM 1  to NM 3 . Furthermore, the plurality of transistors NM 1  to NM 3  have the same or different length width and length so that they have the same or different resistances according to the control signals H, I and J inputted to their gates. 
     As another example, as illustrated in  FIGS. 6 and 7 , the variable current supplying unit  122  includes a second current mirror receiving an external bias EX_BI and supplying a variable current to the input terminal G of the first current mirror  121  in response to a plurality of control signals H, I, J and K. In this case, the external bias EX_BI is a fixed voltage or current which is applied with a constant magnitude without being varied. 
     Referring to  FIG. 6 , the variable current supplying unit  122  includes a third transistor NM 1 , a plurality of fourth transistors NM 2  to NM 4 , a plurality of first switching units NM 5  to NM 7 , and a second switching unit NM 8 . The third transistor NM 1  is connected between the input terminal G of the first current mirror  121  and the ground voltage terminal VSS, and has a gate connected to a first node L. 
     The plurality of fourth transistors NM 2  to NM 4  are connected in parallel between the first node L and the ground voltage terminal VSS, and have gates commonly connected to the gate of the third transistor NM 1 , which is connected to the first node L. The plurality of first switching units NM 5  to NM 7  are connected in series between the respective fourth transistors NM 2  to NM 4  and the first node L, and transfer the external bias EX_BI from the first node L to the fourth transistors NM 2  to NM 4 . The second switching unit NM 8  transfers the external bias EX_BI to the first node L. 
     Referring to  FIG. 7 , as another example, the variable current supplying unit  122  includes a third transistor NM 1 , a plurality of fourth transistors NM 2  to NM 4 , a plurality of first switching units NM 5  to NM 7 , and a second switching unit NM 8 . The third transistor NM 1  is connected between the input terminal G of the first current mirror  121  and a first node M, and has a gate connected to a second node L. 
     The plurality of fourth transistors NM 2  to NM 4  are connected in parallel between the first node M and the second node L, and have gates commonly connected to the gate of the third transistor NM 1 , which is connected to the second node L. The plurality of first switching units NM 5  to NM 7  are connected in series between the respective fourth transistors NM 2  to NM 4  and the second node L, and transfer the external bias EX_BI from the second node L to the fourth transistors NM 2  to NM 4 . The second switching unit NM 8  is connected between the first node M and the ground voltage terminal VSS. 
     In  FIGS. 6 and 7 , the third and fourth transistors NM 1  to NM 4  are implemented with n-channel transistors and have the same or different channel width and length so that they have the same or different resistances. Furthermore, the first and second switching units NM 5  to NM 8  are implemented with n-channel transistors operating in response to the control signals H, I, J and K inputted to their gates. In this case, there is no limitation in the number of the fourth transistors NM 2  to NM 4  and the first switching units NM 5  to NM 7 . 
     As another example, as illustrated in  FIGS. 8 and 9 , the variable current supplying unit  122  includes a second current mirror receiving a variable external bias EX_BI and supplying a variable current to the input terminal G of the first current mirror  121 . The external bias EX_BI used herein is a variable voltage, not a fixed voltage having a constant level like the external bias described with reference to  FIGS. 6 and 7 . For example, the variation width is determined in 0.1 V to 1 V within a range of 1 V to 5 V. 
     Referring to  FIG. 8 , the variable current supplying unit  122  includes a third transistor NM 1 , a fourth transistor NM 2 , and a first switching unit NM 3 . The third transistor NM 1  is connected between the input terminal G of the first current mirror  121  and the ground voltage terminal VSS, and has a gate connected to a first node L. The fourth transistor NM 2  is connected between the first node L and the ground voltage terminal VSS, and has a gate connected to the gate of the third transistor NM 1 , which is connected to the first node L. The first switching unit NM 3  transfers an external bias EX_BI from the first node L to the fourth transistor NM 2 . 
     Referring to  FIG. 9 , the variable current supplying unit  122  includes a third transistor NM 1 , a fourth transistor NM 2 , and a first switching unit NM 3 . The third transistor NM 1  is connected between the input terminal G of the first current mirror  121  and a first node M, and has a gate connected to a second node L. The fourth transistor NM 2  is connected between the first node M and the second node L to which an external bias EX_BI is inputted, and has a gate connected to the gate of the third transistor NM 1 , which is connected to the second node L. The first switching unit NM 3  is connected between the first node N and the ground voltage terminal VSS. 
     In  FIGS. 8 and 9 , the third transistor NM 1  and the fourth transistor NM 2  are implemented with n-channel transistors. In addition, the first switching unit NM 3  enables the second current mirror and is implemented with an n-channel transistor operating in response to a control signal K inputted to its gate. 
     In an example of the nonvolatile memory device, there is no limitation in the structure of the unit cell  110 . For example, the unit cell  110  may include one antifuse and one switching unit. Alternatively, the unit cell  110  may include one antifuse and two switching units. As illustrated in  FIG. 10 , the unit cell  110  may have a parallel configuration of one antifuse  113  and two switching units  111  and  112 . 
     Specifically, referring to  FIG. 10 , the unit cell  110  includes an antifuse  113 , a third switching unit  111 , and a fourth switching unit  112 . The antifuse  113  is connected between a third node C and a ground voltage terminal VSS. The third switching unit  111  is connected between a first node A and the third node C and is configured to operate in response to a control signal inputted through a second input terminal D. The fourth switching unit  112  is connected between the third node C and an output terminal F (a terminal through which data is outputted in a read operation) and is configured to operate in response to a control signal inputted through a third input terminal B. 
     The third switching unit  111  may be implemented with a transistor being an active element for transferring a write voltage inputted through the first input terminal A to the third node C. The fourth switching unit  112  may be implemented with a transistor being an active element for transferring a read voltage to the third node C. In this case, the transistors may be n-channel transistors or p-channel transistors. Furthermore, the transistors may be high-voltage transistors or low-voltage transistors. 
     The antifuse  113  may be implemented with a transistor being an active element or a capacitor being a passive element. In this case, the transistor may be a p-channel transistor or an n-channel transistor. Specifically, the transistor has a gate connected to the third node C, and a drain and a source commonly connected to the ground voltage terminal VSS. Moreover, when the antifuse  113  is implemented with the capacitor, the capacitor has a first terminal, which is a top electrode, connected to the third node C, and a second terminal, which is a bottom electrode, connected to the ground voltage terminal VSS. 
     Referring to  FIG. 10 , the nonvolatile memory device has the parallel configuration of the antifuse  113  and the third and fourth switching units  111  and  112 . Accordingly, by transferring the write voltage and the read voltage to the antifuse  113  through the different paths, the loss of the read voltage in the read operation may be minimized compared with the unit cell having the series configuration of the antifuse and the switching units. Thus, the data sensing margin at the output terminal of the unit cell may be secured to thereby improve the operational reliability of the nonvolatile memory device. 
     The following description will be made on the write and read operations of an example of the unit cell of the nonvolatile memory device with reference to  FIG. 11 . Referring to  FIG. 11 , the third switching unit  111 , the fourth switching unit  112 , and the antifuse  113  are implemented with a p-channel transistor, an n-channel transistor, and an n-channel transistor, respectively. The variable current supplying unit  122  having the structure of  FIG. 6  will be used as an example. 
     
       
         
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                 Terminal (Node) 
               
             
          
           
               
                 Mode 
                 A 
                 B 
                 D 
                 F 
                 H 
                 I 
                 J 
                 K 
               
               
                   
               
               
                 Write 
                 VPP 
                 L 
                 L 
                 — 
                 — 
                 — 
                 — 
                 L 
               
               
                 Operation 
               
               
                 Read 
                 — 
                 H 
                 H 
                 L 
                 H 
                 L 
                 L 
                 H 
               
               
                 Operation 
               
               
                   
               
             
          
         
       
     
     In Table 2, “-” represents a logic high (H) or logic low (L) state, or a floating state. 
     The following description will be made with reference to Table 2 and  FIG. 11 . 
     Write Operation 
     First, the high voltage VPP is applied to the first input terminal A, and a logic low signal is inputted to the second input terminal D and the third input terminal B. Due to those conditions, the third switching unit  111  is turned on, and the fourth switching unit  112  is turned off. Accordingly, the first input terminal and the node C are electrically connected, and the node C and the output terminal F are electrically opened so that the high voltage VPP is transferred to the antifuse  113  through the third switching unit  111 . Thus, dielectric breakdown occurs in a gate dielectric layer formed between the gate of the antifuse  113  and the substrate. 
     Read Operation 
     After the completion of the write operation, a logic high signal is inputted to the second input terminal D and the third input terminal B. In addition, the control signals H and K having a logic high state are inputted to the first switching unit NM 5  and the second switching unit NM 8 . Due to those conditions, the third node C and the output terminal F are electrically connected so that a current path is formed between the output terminal F and the antifuse  113 . 
     Furthermore, the second switching unit MN 8  is turned on to enable the second current mirror of the variable current supplying unit  122 . Accordingly, the external bias EX_BI is transferred to the first node L through the second switching unit NM 8 , and the third transistor NM 1  is turned on by the external bias EX_BI. Moreover, since only the switching unit NM 5  among the first switching units NM 5  to NM 7  is turned on, only the transistor NM 2  among the fourth transistors NM 2  to NM 4  is turned on by the external bias EX_BI. 
     Since the third transistor NM 1  is turned on by the external bias EX_BI, the potential corresponding to the ground voltage is applied to the input terminal G of the first current mirror  121 . In this case, the potential of the input terminal G of the first current mirror  121  increases or decreases in correspondence to a drain current of the transistor NM 2 . 
     That is, since the third transistor NM 1  and the fourth transistor NM 2  form a current mirror, a drain current of the third transistor NM 1  (a current flowing through the input terminal of the first current mirror) is determined by the drain current of the fourth transistor NM 2 . The drain current of the third transistor NM 1  decreases when the drain current of the fourth transistor NM 2  decreases, and increases when the drain current of the fourth transistor NM 2  increases. 
     The first transistor PM 1  and the second transistor PM 2  are turned on by the variable current (the drain current of the third transistor NM 1 ) inputted to the input terminal G of the first current mirror  121 . Accordingly, the input voltage applied from the power supply voltage terminal VDD drops down by a threshold voltage of the first transistor PM 1 . 
     That is, the read voltage transferred to the output terminal F is equal to “the power supply voltage—the threshold voltage of the first transistor PM 1 ”. At this point, the threshold voltage of the first transistor PM 1  is determined by the potential of the input terminal G of the first current mirror  121 . The threshold voltage of the first transistor PM 1  decreases as the potential of the input terminal G decreases, and increases as the potential of the input-terminal G increases. 
     After the write operation, the antifuse  113  of the unit cell  110  becomes a dielectric breakdown state. For this reason, a current path is formed between the output terminal F and the ground voltage terminal VSS. Therefore, the read voltage flows to the ground voltage terminal VSS through the second switching unit  112  and the antifuse  113 , so that the output terminal F has a potential corresponding to the ground voltage. Consequently, the inverter-type detecting unit  120  outputs an output signal DA_OUT having a logic high state. 
     Meanwhile, after the write operation, the antifuse  113  of the unit cell  110  must have a resistance of about 100Ω to 300Ω when its dielectric normally or stably breaks down. However, if the dielectric breakdown of the antifuse  113  does not normally occur after the write operation, the antifuse  113  has a high resistance of about 1 MΩ. If the antifuse  113  has the high resistance of about 1 MΩ after the write operation, the read voltage inputted to the output terminal F does not normally flow to the ground voltage terminal VSS through the antifuse  113 . 
     Accordingly, since the potential corresponding to the read voltage is applied to the output terminal F, the detecting unit  120  of the unit cell  110  outputs the output signal DA_OUT having a logic low state. That is, when the read operation on the unit cell  110  is normally completed, the detecting unit  120  must output the output signal DA_OUT having a logic high state. However, due to the high resistance of the antifuse  113 , the detecting unit  120  outputs the output signal DA_OUT having a logic low state. 
     Therefore, there is proposed a method which stably detects data of the unit cell  110  even when the antifuse  113  has the high resistance. In the read operation, the potential of the input terminal G of the first current mirror  121  is varied using the variable current supplying unit  122 , and the threshold voltage of the first transistor PM 1  is controlled by the varied potential. In this way, the read voltage transferred to the output terminal F is appropriately varied. 
     Referring to  FIG. 11 , the potential of the input terminal G of the first current mirror  121  corresponds to the drain current of the third transistor NM 1 , and the drain current of the third transistor NM 1  is determined by the number of the turned-on transistors among the fourth transistors NM 2  to NM 4 . That is, when the number of the turned-on transistors among the fourth transistors NM 2  to NM 4  is increased, the drain current of the third transistor NM 1  is increased. When the number of the turned-on transistors among the fourth transistors NM 2  to NM 4  is decreased, the drain current of the third transistor NM 1  is decreased. 
     As described above, the read voltage can be varied by adjusting the threshold voltage of the first transistor PM 1  through the variable current supplying unit  122 . That is, when the resistance of the antifuse  113  is high, the read voltage transferred to the output terminal F is reduced by increasing the threshold voltage of the first transistor PM 1 . When the resistance of the antifuse  113  is low, the read voltage is increased by reducing the threshold voltage of the first transistor PM 1 . 
     For example, in the case where the dielectric breakdown of the antifuse  113  occurs normally, the data signal DA_OUT having a logic high state is outputted when only the transistor NM 2  among the fourth transistors NM 2  to NM 4  is turned on. However, in the case where the dielectric breakdown of the antifuse  113  does not occur normally, the data signal DA_OUT having a logic low state instead of a logic high state is outputted when only the transistor NM 2  among the fourth transistors NM 2  to NM 4  is turned on. 
     When the antifuse  113  has a high resistance (for example, more than 300Ω) due to an abnormal dielectric breakdown, the transistors NM 3  and NM 4  among the fourth transistors NM 2  to NM 4  are sequentially turned on in correspondence to the magnitude of the high resistance, so that the drain current of the third transistor NM 1  is increased. 
     When the drain current of the third transistor NM 1  is increased, the potential of the input terminal of the first current mirror  121  is increased and thus the potential of the read voltage transferred to the output terminal F is reduced. At this point, the potential of the read voltage is reduced to the level corresponding to the potential when the dielectric breakdown of the antifuse  113  occurs normally through the detecting unit  120 . 
     Hereinafter, an example of the memory cell array of the nonvolatile memory device will be described. 
       FIG. 12  is a configuration diagram of illustrating an example the memory cell array of the nonvolatile memory device. 
     Referring to  FIG. 12 , an example of the memory cell array of the nonvolatile memory device includes a plurality of unit cells UC arranged in a matrix type. Each of the unit cells UC includes two switching units SW 1  and SW 2  and one antifuse ANT_FS. As one example, in the unit cell UC, the third switching unit SW 1  and the fourth switching unit SW 2  are implemented with a p-channel transistor and an n-channel transistor, respectively. 
     In addition, an example of the memory cell array of the nonvolatile memory device includes a plurality of write driving lines, WR_CT 0  to WR_CTn (where n is a natural number), for selecting the third switching units SW 1  of the unit cells UC, and a plurality of read driving lines RD_CT 0  to RD_CTm (where m is a natural number) for selecting the fourth switching units SW 2  of the unit cells UC. 
     The write driving lines WR_CT 0  to WR_CTn extend in a row direction and are connected to the respective third switching units SW 1  of the unit cells UC arranged in a row direction, that is, gates of the p-channel transistors. The read driving lines RD_CT 0  to RD_CTm extend in a column direction to cross the write driving lines WR_CT 0  to WR_CTn, and are connected to the respective fourth switching units SW 2  of the unit cells UC arranged in a column direction, that is, gates of the n-channel transistors. 
     Furthermore, the memory cell array of the nonvolatile memory device includes data lines DL 0  to DLn (where n is a natural number) for transferring the read voltage the unit cells UC in the read operation and transferring data outputted from the unit cells UC to the detecting units  120 _ 0  to  120   —   n  (where n is a natural number) in the read operation, and write voltage supplying lines WRL 0  to WRLm (where m is a natural number) for transferring the write voltage to the unit cells UC in the write operation. 
     The data lines DL 0  to DLn extend in a row direction and are connected to the output terminals F of the unit cells UC arranged in a row direction and the input terminals of the detecting units  120 _ 0  to  120   —   n . The data lines DL 0  to DLn transfer the read voltage from the read voltage varying units  130 _ 0  to  130   —   n  to the fourth switching units SW 2  in the read operation, and transfer data outputted from the output terminals F to the corresponding detecting units  120 _ 0  to  120   —   n.    
     The write data lines WRL 0  to WRLn extend in a column direction and are commonly connected to the respective third switching units SW 1  of the unit cells UC arranged in a column direction. The write voltage supplying lines WRL 0  to WRLn transfer the write voltage, that is, the high voltage VPP, to the third switching units SW 1  of the unit cells UC arranged in a column direction in the write operation. 
     Furthermore, an example of the memory cell array of the nonvolatile memory device includes the plurality of detecting units  120 _ 0  to  120   —   n  arranged in the respective data lines DL 0  to DLn to detect data outputted through the corresponding data lines DL 0  to DLn. The detecting units  120 _ 0  to  120   —   n  may be implemented with inverters or differential amplifiers. Since the inverters have a simple circuit configuration, they may be advantageous in view of the reduction of the circuit area and power consumption. 
     An example of the memory cell array of the nonvolatile memory device includes the read voltage varying units  130 _ 0  to  130   —   n  varying the power supply voltage in the read operation and transferring the varied read voltage to the corresponding data lines DL 0  to DLn. In this case, the read voltage varying units  130 _ 0  to  130   —   n  may have any one of the structures illustrated in  FIGS. 3 to 9 . 
       FIG. 13  is a configuration diagram illustrating another example of a memory cell array of a nonvolatile memory device. 
     Unlike the memory cell array of  FIG. 12 , the memory cell array of  FIG. 13  has a structure in which read voltage varying units  130 _ 00  to  130   —   nm  are arranged corresponding to unit cells UC. Meanwhile, like in  FIG. 12 , detecting units  120 _ 0  to  120   —   n  are arranged corresponding to data lines DL 0 _DLn. 
       FIG. 14  is a configuration diagram illustrating another example of a memory cell array of a nonvolatile memory device. 
     Unlike the memory cell array of  FIG. 13 , the memory cell array of  FIG. 14  has a structure in which detecting units  120 _ 00  to  120   —   nm  as well as read voltage varying units  130 _ 00  to  130   —   nm  are arranged corresponding to unit cells. 
     Accordingly, there is no need for a plurality of data lines DL 0  to DLn (see  FIG. 13 ) for commonly connecting the detecting units  120 _ 00  to  120   —   nm  to the output terminals of the unit cells UC arranged in a row direction. Consequently, the data sensing margin can be improved by minimizing the data loss occurring in the memory cell arrays of  FIGS. 12 and 13 , that is, the data loss caused by the resistances of the data lines. 
     The above-referenced examples may obtain the following effects. 
     First, by varying the input voltage in the read operation and supplying the read voltage having the varied level to the unit cells, the sensing margin may be increased and thus the cell data may be stably detected even when the unit cell has the high resistance due to the abnormal dielectric breakdown of the antifuse. Therefore, the nonvolatile memory device may be capable of preventing malfunctions caused by the high resistance of the unit cell, thereby improving the reliability of the read operation. 
     Second, by connecting the antifuse and the first and second switching units in parallel, the write voltage and the read voltage are transferred to the antifuse through the different paths. Therefore, the loss of the read voltage in the read operation may be minimized compared with the unit cell having the series configuration. Consequently, the sensing margin of the data detected through the output terminal of the unit cell can be increased, thereby improving the operational reliability of the nonvolatile memory device. 
     While examples have been described, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the following claims.