Abstract:
The present invention relates to a resistance variable memory device, and more particularly, to a resistance variable memory device capable of preventing an effect of coupling noise. The resistance variable memory device includes: a memory cell connected to a bit line; a precharge circuit precharging the bit line in response to a precharge signal; a bias circuit providing a bias voltage to the bit line in response to a bias signal; and a control logic controlling the precharge signal and the bias signal. The control logic provides the bias signal to the bias circuit at a precharge interval. Accordingly, the resistance variable memory device according to the present invention can prevent an effect coupling noise.

Description:
REFERENCE TO PRIORITY APPLICATION 
     This U.S. nonprovisional patent application claims priority to Korean Patent Application 10-2008-105399, filed Oct. 27, 2008, the contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a resistance variable memory device, and more particularly, to a resistance variable memory device for preventing an effect of coupling noise. 
     BACKGROUND OF THE INVENTION 
     Semiconductor memory devices are storage devices that can store data and can output the stored data, if necessary. Generally, the semiconductor memory devices may be classified into Random Access Memories (RAMs) and Read-Only Memories (ROMs). The ROMs are a non-volatile memory that retains their stored data even when the power supply is interrupted. Examples of the ROMs include PROMs (Programmable ROMs), EPROMs (Erasable PROMs), EEPROMs (Electrically EPROMs), flash memories, and the like. The flash memories are classified into NOR-type flash memories and NAND-type flash memories. Meanwhile, the RAMs are a volatile memory that loses their stored data when the power supply is interrupted. Examples of the RAMs include Dynamic RAMs (DRAMs) and Static RAMs (SRAMs). 
     Recently, semiconductor memory devices in which non-volatile materials are substituted for the capacitor of the DRAM have been introduced. Examples of the semiconductor memory devices include ferroelectric RAMs (FRAMs) employing ferroelectric capacitors, magnetic RAMs (MRAMs) employing tunneling magneto-resistive (TMR) films, and phase change memory devices using chalcogenide alloys. Especially, the phase change memory devices are non-volatile memory devices using phase change, that is, resistance change according to temperature change. The phase change memory devices have a relatively simple manufacturing process and can realize capacious memory at a low cost. 
     The phase change memory device includes a write driver circuit supplying a program current to a phase change material (GST) during a programming operation. The write driver circuit supplies the program current such as a set current or reset current to memory cells by using power supply voltage (for example, 2.5V or more) provided from an external apparatus. The set current changes the phase change material (GST) of the memory cell into a set state, while the reset current changes the phase change material (GST) of the memory cell into a reset state. 
     SUMMARY 
     The present invention is directed to a resistance variable memory device capable of preventing an effect of coupling noise. 
     One aspect of the present invention is to provide a resistance variable memory device including: a memory cell connected to a bit line; a precharge circuit precharging the bit line in response to a precharge signal; a bias circuit providing a bias voltage to the bit line in response to a bias signal; and a control logic controlling the precharge signal and the bias signal. In this case, the control logic provides the bias signal to the bias circuit at a precharge interval. 
     According to one aspect of the present invention, the bias voltage may be applied to the bit line to read out the memory cell. 
     According to one aspect of the present invention, the precharge circuit may be configured by an NMOS transistor, and the NMOS transistor may be activated in response to the precharge signal at the precharge interval. 
     According to one aspect of the present invention, a voltage level of the precharge signal may be larger than a power supply voltage and smaller than the bias voltage so as to prevent a leakage current flowing from the bias circuit to the precharge circuit. 
     According to one aspect of the present invention, the precharge circuit may be configured by an NMOS transistor and a PMOS transistor connected to each other in parallel, and the NMOS transistor and the PMOS transistor may be activated in response to the precharge signal at the precharge interval. 
     According to one aspect of the present invention, a voltage level of the precharge signal may be larger than a power supply voltage and smaller than the bias voltage so as to prevent a leakage current flowing from the bias circuit to the precharge circuit. 
     According to one aspect of the present invention, the resistance variable memory device may further include a discharge circuit discharging initializing the bit line. 
     According to one aspect of the present invention, the resistance variable memory device may further include a sense amplifier comparing a voltage of the bit line with a reference voltage to output the compared result when the bias voltage is applied by the bias circuit. 
     According to one aspect of the present invention, the memory cell may include a storage element having a phase change material. 
     Another aspect of the present invention is to provide a portable electronic system including: a resistance variable memory device; and a central processing unit controlling the resistance variable memory device. The resistance variable memory device includes: a memory cell connected to a bit line; a precharge circuit precharging the bit line in response to a precharge signal; a bias circuit providing a bias voltage to the bit line in response to a bias signal; and a control logic controlling the precharge signal and the bias signal. Furthermore, the control logic provides the bias signal to the bias circuit at a precharge interval. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a general resistance variable memory device; 
         FIG. 2  is a circuit diagram illustrating more fully a sense amplifier illustrated in  FIG. 1 ; 
         FIG. 3  is a timing diagram explaining a reading operation of the sense amplifier illustrated in  FIG. 1 ; 
         FIG. 4  is a circuit diagram of a resistance variable memory device according to a first embodiment of the present invention; 
         FIG. 5  is a circuit diagram of a resistance variable memory device according to a second embodiment of the present invention; 
         FIG. 6  is a timing diagram explaining a reading operation of the resistance variable memory device illustrated in  FIGS. 4 and 5 ; 
         FIG. 7  is a diagram illustrating simulation result of the sense amplifier illustrated in  FIG. 2 ; 
         FIG. 8  is a diagram illustrating simulation result of the sense amplifier illustrated in  FIGS. 4 and 5 ; and 
         FIG. 9  is a block diagram of a portable electronic system embodying the resistance variable memory devices according to the embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below in more detail with reference to the accompanying drawings. The present invention may, however, be embodied in different forms and should not be constructed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
       FIG. 1  is a block diagram of a general resistance variable memory device. Referring to  FIG. 1 , the resistance variable memory device  100  includes a memory cell array  110 , a bit line selection circuit  120 , a write driver  130 , a sense amplifier  140 , a data input and output buffer (data I/O buffer)  150 , a control logic  160 , an address decoder  170 , and an Y-pass driver  180 . 
     The memory cell array  110  may include a plurality of memory cells, and each memory cell may include a resistance variable memory element. Generally, the resistance variable memory element may include a phase change memory cell. 
     Each memory cell included in the memory cell array  110  may be configured by a memory element and a selection element. The memory element includes a phase change material such as GST (Ge—Sb—Te), and the selection element may be embodied by an NMOS transistor or a diode. The memory element includes the phase change material such as GST. The phase change material (GST) is a variable resistance element such as Ge—Sb—Te that varies in resistance according to a temperature. The phase change material (GST) takes either of two stable states, for example, a crystal state and an amorphous state according to the temperature. The phase change material (GST) is changed into the crystal state or the amorphous state based on currents supplied through a bit line BL. A phase change memory device programs data by using these characteristics of the phase change material (GST). 
     The address decoder  170  is connected to the memory cell array  110  through a word line WL. The address decoder  170  executes a decoding of an address ADDR input from an external apparatus and provides a bias current to a selected word line. In addition, the Y-pass driver  180  generates a selection signal Yi to select the bit line BL. The selection signal Yi is provided to the bit line selection circuit  120 . The address decoder  170  receives an address ADDR to select the memory cell array  110  during a reading operation. 
     The bit line selection circuit  120  is connected to the memory cell array  110  through the bit line BL. The bit line selection circuit  120  selects a bit line BL of the memory cell array  110  in response to the selection signals Yi supplied from the Y-pass driver  180  during the reading operation and the programming operation. The bit line selection circuit  120  includes a plurality of NMOS transistors. The plurality of NMOS transistors connects electrically the bit line BL to a data line DL in response to the selection signal Yi. 
     The write driver  130  receives data DQ[15:0] from the data I/O buffer. Furthermore, the write driver  130  receives a program pulse from the control logic  160  and provides a program current to the data line DL. Here, the program pulse is provided by a program loop circuit (not shown) configured in the control logic  160  and includes a set pulse and a reset pulse. The program current includes a set current and a reset current. The write driver  130  provides the set current in response to the set pulse when data ‘ 0 ’ is input and provides the reset current in response to the reset pulse when data ‘ 1 ’ is input. 
     During a reading operation and a program verifying operation, the sense amplifier  140  reads out data stored in the memory cell and outputs the read data to the data I/O buffer  150 . The sense amplifier  140  reads out the data stored in the memory cell during the program verifying operation to perform the program verifying operation. The control logic  160  controls the write driver  130  and the sense amplifier  140  so as to execute the reading operation and the program verifying operation in response to a control signal CNTL. The configuration and operation of the sense amplifier  140  will be described in detail with reference to  FIGS. 2 and 3 . 
       FIG. 2  is a circuit diagram illustrating in detail the sense amplifier illustrated in  FIG. 1 . 
     Referring to  FIG. 2 , the sense amplifier  140  includes a clamping circuit  141 , a discharge circuit  142 , a precharge circuit  143 , a bias circuit  144 , and a comparator  145 . 
     The discharge circuit  142  initializes it by discharging a sensing node NSA to execute a correct sensing operation. The discharge circuit  142  is configured by two NMOS transistors N 3  and N 4 . 
     The clamping circuit  141  clamps the data line DL to a predetermined voltage level during the reading operation and ultimately clamps a voltage level of a selected bit line BLi to a designated value. As illustrated in  FIG. 2 , the clamping circuit  141  is connected between the sensing node NSA and the data line DL. The clamping circuit  141  is configured by an NMOS transistor N 5 . The NMOS transistor N 5  forms a current path between the sensing node NSA and the data line DL in response to a clamp voltage signal VCMP. 
     The clamp voltage signal VCMP is supplied from the control logic and has a constant DC voltage level during the reading operation. For example, the clamp voltage signal VCMP has a value obtained by adding a voltage of the bit line and a threshold voltage Vth of the NMOS transistor N 5  to perform the reading operation. In order to perform the reading operation, assuming that the voltage of the bit line is 1V and the threshold voltage Vth of the NMOS transistor N 5  is 0.5V, the clamp voltage signal VCMP has 1.5V DC voltage. The clamp voltage signal VCMP may generated by an internal voltage generator (not shown) insensitive to PVT (Process-Voltage-Temperature) variation. In  FIG. 1 , the control logic  160  includes the internal voltage generator. 
     The precharge circuit  143  precharges the sensing node NSA with a power supply voltage VCC before a sensing operation of the sense amplifier  140  and precharges the selected bit line BLi with a clamping voltage at the same time. Referring to  FIG. 2 , the precharge circuit  143  is connected between the sensing node NSA and a power supply terminal. The precharge circuit  143  receives the power supply voltage VCC through the power supply terminal during the reading operation. The precharge circuit  143  is configured by a PMOS transistor P 3 . The PMOS transistor P 3  precharges the sensing node NSA with the power supply voltage VCC and precharges the selected bit line BLi with the clamping voltage, in response to a precharge signal nPRE. The precharge signal nPRE is supplied from the control logic  160 . 
     The bias circuit  144  supplies a read current to the selected bit line BLi during the reading operation. Referring to  FIG. 2 , the bias circuit  144  is connected between the sensing node NSA and the power supply terminal. The bias circuit  144  receives a boosted voltage VPP through the power supply terminal during the reading operation. The bias circuit  144  is configured such that two PMOS transistors P 1  and P 2  are connected to each other in series. 
     The first PMOS transistor P 1  supplies the boosted voltage VPP to the second PMOS transistor P 2  in response to an nPBIAS signal. The second PMOS transistor P 2  supplies the read current to the selected bit line BLi in response to a bias voltage signal VBIAS. The bias voltage current VBIAS is supplied from the control logic  160  and has a predetermined DC voltage during the reading operation. 
     The comparator  145  senses difference between the sensing node NSA voltage and a reference voltage Vref during the reading operation to provide a sensing result to the data I/O buffer  150 . Here, the reference voltage Vref is supplied from a reference voltage generator (not shown). The sense amplifier  140  receives control signals from the control logic  160  during the reading operation and receives the boosted voltage VPP from a booster (not shown). 
     The control logic  160  outputs control signals in response to a command CMD supplied from an external source to control the clamping circuit  141 , the discharge circuit  142 , the precharge circuit  143 , and the bias circuit  144 . 
       FIG. 3  is a timing diagram explaining a reading operation of the sense amplifier  140  illustrated in  FIG. 2 . For convenience of description, the operation of the resistance variable memory device  100  will be described with respect to a discharge interval, a bit line BL precharge interval, a develop interval, and a sensing interval. 
     First, the operation of the resistance variable memory device  100  will be described with respect to the discharge interval. Referring to  FIGS. 1 to 3 , the word line WLi maintains a high level, but the bit line BLi maintains a low level depending on the discharge circuit  142 . Since the precharge signal nPRE maintains a high level, the precharge transistor P 3  maintains a turn-off state. Since the bias voltage signal VBIAS is maintained at a constant DC voltage, for example, a voltage that is lower than the power supply voltage VCC and higher than a ground voltage GND to supply the read current required for the reading operation, the sensing node NSA maintains a boosted voltage level VPP higher than the power supply voltage VCC. 
     Next, the operation of the resistance variable memory device  100  will be described with respect to the bit line BL precharge interval. Referring  FIGS. 1 to 3 , since the precharge signal nPRE maintains a low level, the precharge transistor P 3  is turned on and the sensing node NSA maintains the power supply voltage VCC. When the voltage of 1V is supplied to the bit line so as to perform the reading operation, since the clamp voltage signal VCMP is maintained at the constant DC voltage, for example, the voltage obtained by adding the threshold voltage of the clamping transistor N 5  to the voltage of 1V, the data line DL and the bit line BLi rise to approximately 1V. 
     Next, the operation of the resistance variable memory device  100  will be described with respect to the develop interval. Referring  FIGS. 1 to 3 , since the precharge signal nPRE maintains a high level, the precharge transistor P 3  is turned off. Since the bias voltage signal VBIAS maintains a constant DC voltage, the bias circuit  144  supplies successively the read current to the selected memory cell. As nPBIAS signal is activated, the bias voltage signal VBIAS is affected by a coupling noise. 
     Since the clamp voltage signal VCMP successively maintains a constant DC voltage and the selected word line WLi maintains a ground voltage, the sensing node NSA changes according to a cell state of the selected memory cell, that is, a set or reset state, as illustrated in  FIG. 3 . 
     As illustrated in  FIG. 3 , when the selected memory cell is in the set state, the voltage of the sensing node NSA never drops to the ground voltage GND due to the threshold voltage of the diode in the selected memory cell. However, as illustrated in  FIG. 3 , when the selected memory cell is in the reset state, the voltage of the sensing node NSA maintains the boosted voltage VPP to obtain a sufficient sensing margin. In this case, the reading operation is performed more efficiently. Preferably, the boosted voltage VPP may have the value obtained by adding the threshold voltage of the diode in the selected memory cell configuring the memory cell array  110  to the power supply voltage VCC. 
     In the course of transition from the precharge interval to the develop interval, the coupling noise is generated in the VBIAS signal due to the activation of the nPBIAS signal. For example, when the sense amplifier connected to 128 bit lines is simultaneously operated, as illustrated in  FIG. 3 , the bias voltage signal VBIAS rises temporarily at the develop interval due to the activation of the nPBIAS signal. This affects a sensing speed (that is, reading operation time) of the resistance variable memory device  100 . In addition, the coupling noise changes the bias voltage signal VBIAS during a resistance scattering measurement of the resistance variable memory cell, thereby affecting a reading margin. Accordingly, since the operation of the sense amplifier  140  waits until the VBIAS signal is stabilized at the develop interval, the develop interval should be maintained for a long time. 
     The resistance variable memory device according to the embodiment of the present invention removes the coupling noise by activating the nPBIAS signal in the precharge operation. Specifically, the resistance variable memory device according to the embodiment of the present invention will be described more fully with reference to  FIGS. 4 to 8 . 
       FIG. 4  is a circuit diagram of a resistance variable memory device according to a first embodiment of the present invention, and  FIG. 5  is a circuit diagram of a resistance variable memory device according to a second embodiment of the present invention. The resistance variable memory device of  FIGS. 4 and 5  are the same as that of  FIG. 2  except for the precharge circuit. Therefore, the duplicated description will be omitted. 
     Referring to  FIG. 4 , the resistance variable memory device  200  includes a memory cell array  210 , a bit line selection circuit  220 , a sense amplifier  240 , and a data input and output buffer (data I/O buffer)  250 . Furthermore, the resistance variable memory device  200  may further include a write driver, a control logic, an address decoder, and an Y-pass driver, even though not illustrated in  FIG. 4 . 
     The sense amplifier  240  includes a clamping circuit  241 , a discharge circuit  242 , a precharge circuit  243 , a bias circuit  244 , and a comparator  245 . 
     The precharge circuit  243  precharges the sensing node NSA with a power supply voltage VCC before a sensing operation of the sense amplifier  240  and precharges the selected bit line BLi with a clamping voltage at the same time. 
     Subsequently, referring to  FIG. 4 , the precharge circuit  243  is connected between the sensing node NSA and a power supply terminal. The precharge circuit  243  receives the power supply voltage VCC through the power supply terminal during the reading operation. The precharge circuit  243  is configured by an NMOS transistor N 6 . The NMOS transistor N 6  precharges the sensing node NSA with the power supply voltage VCC and precharges the selected bit line BLi with the clamping voltage, in response to a precharge signal PRE. The precharge signal PRE is supplied from the control logic. 
     Referring to  FIG. 5 , the resistance variable memory device  300  includes a memory cell array  310 , a bit line selection circuit  320 , a sense amplifier  340 , and a data input and output buffer (data I/O buffer)  350 . Furthermore, the resistance variable memory device  300  may further include a write driver, a control logic, an address decoder, and an Y-pass driver, even though not illustrated in  FIG. 5 . 
     The sense amplifier  340  includes a clamping circuit  341 , a discharge circuit  342 , a precharge circuit  343 , a bias circuit  344 , and a comparator  345 . 
     The precharge circuit  343  precharges the sensing node NSA with a power supply voltage VCC before a sensing operation of the sense amplifier  340  and precharges the selected bit line BLi with a clamping voltage at the same time. 
     Subsequently, referring to  FIG. 5 , the precharge circuit  343  is connected between the sensing node NSA and a power supply terminal. The precharge circuit  343  receives the power supply voltage VCC through the power supply terminal during the reading operation. The precharge circuit  343  is configured by an NMOS transistor N 6  and a PMOS transistor P 3  connected to each other in parallel. A precharge signal PRE is input to a gate terminal of the NMOS transistor N 6 , and an output signal of an inverter is input to a gate terminal of the PMOS transistor P 3 . Here, the inverter receives the precharge signal PRE. 
     The precharge circuit  343  precharges the sensing node NSA with the power supply voltage VCC and precharges the selected bit line BLi with the clamping voltage, in response to the precharge signal PRE. The precharge signal PRE is supplied from the control logic. 
     The reading operation of the resistance variable memory device illustrated in  FIGS. 4 and 5  will be described more fully with reference to  FIG. 6 . 
       FIG. 6  is a timing diagram explaining the reading operation of the resistance variable memory device illustrated in  FIGS. 4 and 5 . The reading operation of  FIG. 4  is equal to that of  FIG. 5 . Therefore, the reading operation of  FIG. 5  may be substituted by the reading operation of  FIG. 4 . 
     For convenience of description, the operation of the resistance variable memory device  200  will be described with respect to a discharge interval, a bit line BL precharge interval, a develop interval, and a sensing interval. 
     First, the operation of the resistance variable memory device  200  will be described with respect to the discharge interval. Referring to  FIGS. 4 to 6 , the word line WLi maintains a high level, but the bit line BLi maintains a low level depending on the discharge circuit  142 . Since the precharge signal PRE maintains a low level, the precharge transistor N 6  maintains a turn-off state. Since the bias voltage signal VBIAS is maintained at a constant DC voltage, for example, a voltage that is lower than the power supply voltage VCC and higher than a ground voltage GND to supply the read current required for the reading operation, the sensing node NSA maintains a boosted voltage level higher than the power supply voltage VCC. 
     Next, the operation of the resistance variable memory device  200  will be described with respect to the bit line BL precharge interval. Referring  FIGS. 4 to 6 , since the precharge signal PRE maintains a high level, the precharge transistor N 6  is turned on and the sensing node NSA maintains the power supply voltage VCC. When the voltage of 1V is supplied to the bit line so as to perform the reading operation, since the clamp voltage signal VCMP is maintained at the constant DC voltage, for example, the voltage obtained by adding the threshold voltage of the clamping transistor N 5  to the voltage of 1V, the data line DL and the bit line BLi rise to approximately 1V. 
     As the nPBIAS signal is activated, the bias voltage signal VBIAS is affected by the coupling noise. However, the bias voltage signal VBIAS is stabilized in the develop operation. 
     Next, the operation of the resistance variable memory device  200  will be described with respect to the develop interval. Referring  FIGS. 4 to 6 , since the precharge signal PRE maintains a low level, the precharge transistor N 6  is turned off. Since the bias voltage signal VBIAS maintains a constant DC voltage, the bias circuit  144  supplies successively the read current to the selected memory cell. Since the clamp voltage signal VCMP successively maintains a constant DC voltage and the selected word line WLi maintains a ground voltage, the sensing node NSA changes according to a cell state of the selected memory cell, that is, a set or reset state, as illustrated in  FIG. 3 . 
     As illustrated in  FIG. 6 , when the selected memory cell is in the set state, the voltage of the sensing node NSA never drops to the ground voltage GND due to the threshold voltage of the diode in the selected memory cell. However, as illustrated in  FIG. 6 , when the selected memory cell is in the reset state, the voltage of the sensing node NSA maintains the boosted voltage VPP to obtain a sufficient sensing margin. In this case, the reading operation is performed more efficiently. Preferably, the boosted voltage VPP may have the value obtained by adding the threshold voltage of the diode in the selected memory cell configuring the memory cell array  210  to the power supply voltage VCC.  FIGS. 7 and 8  illustrate results of really simulating the timing diagrams illustrated in  FIGS. 3 and 6 . 
     The resistance variable memory device according to the first embodiment of the present invention applies the bias voltage during the precharge operation. In this case, since the coupling noise occurs in the precharge operation, the resistance variable memory device is not affected in the develop operation. 
     Furthermore, the precharge circuit according to the first embodiment of the present invention is configured by the NMOS transistor, and the precharge circuit according to the second embodiment of the present invention is configured by the NMOS transistor and the PMOS transistor connected to each other in parallel. This prevents the current from flowing to the power supply voltage VCC of the precharge circuit  243  from the boosted voltage VPP of the bias circuit  244 . That is, in order to prevent the current from flowing to the precharge circuit  243  from the bias circuit  244 , the voltage level of the precharge signal is set to be smaller than the sum of the power supply voltage and the threshold voltage. For example, if the voltage level of the precharge signal PRE is set to be smaller than the sum of the power supply voltage and the threshold voltage, the NMOS transistor N 6  of the precharge circuit  243  may be interrupted. Accordingly, the current is prevented from flowing to the precharge circuit  243  from the bias circuit  244 . 
       FIG. 7  is a diagram illustrating simulation result of the sense amplifier illustrated in  FIG. 2 , and  FIG. 8  is a diagram illustrating simulation result of the sense amplifier illustrated in  FIGS. 4 and 5 . 
     As illustrated in  FIG. 7 , the bias voltage VBIAS leaps due to the coupling noise during the develop operation. 
     As illustrated in  FIG. 8 , the bias voltage VBIAS leaps due to the coupling noise during the precharge operation. Therefore, the bias voltage VBIAS is not affected by the coupling noise during the develop operation. 
       FIG. 9  is a block diagram of a portable electronic system embodying the resistance variable memory devices according to the embodiments of the present invention. An example of the resistance variable memory device according to the embodiments of the present invention may include a phase change memory device. 
     The resistance variable memory device  100  is connected to a microprocessor  500  through a bus line L 3  and functions as a main memory of a portable electronic system. A battery  400  supplies power supply to the microprocessor  500 , I/O device  600 , resistance variable memory device  100  through a power supply line L 4 . 
     When the received data is provided to the I/O device  600  through a line L 1 , the microprocessor  500  receives and processes the received data through a line L 2  and then applies the received or processed data to the resistance variable memory device  100  through the bus line L 3 . The resistance variable memory device  100  stores the data applied through the bus line L 3  in the memory cell. In addition, the data stored in the memory cell is read out by means of the microprocessor  500 , and the read data is output to an external apparatus through the I/O device  600 . 
     Even when the power supply of the battery  400  is not supplied to the power supply line L 4 , the data stored in the memory cell of the resistance variable memory device  100  is not lost due to the characteristics of the phase change materials. This is because the resistance variable memory device  100  is a non-volatile memory device unlike DRAM. Besides, the resistance variable memory device  100  has a fast operation speed and small power consumption compared to other memory devices. 
     The resistance variable memory device according to the embodiments of the present invention can prevent the effect of coupling noise. 
     Although the present invention has been described in connection with the embodiment of the present invention illustrated in the accompanying drawings, it is not limited thereto. It will be apparent to those skilled in the art that various substitution, modifications and changes may be thereto without departing from the scope and spirit of the invention.