KR100745601B1 - Phase change memory device and read method thereof - Google Patents

Abstract

The present invention relates to a phase change memory device and a reading method thereof. The phase change memory device according to the present invention includes a memory cell, a boost circuit, a precharge circuit, a bias circuit, and a sense amplifier. The memory cell includes a phase change material and a diode and is connected to the bit line. The boost circuit generates a boost voltage using a power supply voltage. The precharge circuit precharges the bit line using the power supply voltage, and then precharges the bit line using the boosted voltage. The bias circuit uses the boost voltage to provide a read current to the bit line. The sense amplifier uses the boosted voltage to compare the voltage of the bit line with a reference voltage and read data stored in the memory cell. According to the phase change memory device according to the present invention, the burden on the boosting circuit can be reduced during the precharge operation, and the sensing margin can be sufficiently secured during the sensing operation.

Description

Phase change memory device and its reading method {PHASE CHANGE MEMORY DEVICE AND READ METHOD THEREOF}

1 shows a memory cell of a phase change memory device.

2 shows another memory cell of a phase change memory device.

3 is a graph for explaining the characteristics of the phase change material.

4 is a block diagram illustrating a phase change memory device according to the present invention.

FIG. 5 is a timing diagram for describing an operation of the phase change memory device shown in FIG. 4.

FIG. 6 is a circuit diagram illustrating the sense amplifier shown in FIG. 4.

FIG. 7 is a timing diagram for describing an operation of the sense amplifier illustrated in FIG. 6.

8 is a block diagram of a portable electronic system showing an application example of a phase change memory device according to another embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

100; Phase change memory device 110; Memory cell array

120; Address decoder 130; Bit line selection circuit

135, 136; Discharge circuit 140; Clamping circuit

150; Bias circuit 160; Precharge circuit

170; Sense amplifier 180; Control unit

200; Boost circuit

The present invention relates to a semiconductor memory device, and more particularly, to a phase change memory device and a read method thereof.

A semiconductor memory device is a memory device that stores data and can be read out when needed. Semiconductor memory devices can be roughly divided into random access memory (RAM) and read only memory (ROM). ROM is nonvolatile memory that does not lose its stored data even when its power source is interrupted. The ROM includes PROM (Programmable ROM), EPROM (Erasable PROM), EEPROM (Electrically EPROM), and Flash Memory Device. RAM is a so-called volatile memory that loses its stored data when the power is turned off. RAM includes Dynamic RAM (DRAM) and Static RAM (SRAM).

In addition, semiconductor memory devices that replace DRAM capacitors with nonvolatile materials are emerging. Phase change memory devices using ferroelectric RAM (FRAM) using ferroelectric capacitors, magnetic RAM (MRAM) using tunneling magneto-resistive (TMR) membranes, and chalcogenide alloys change memory device). In particular, the phase change memory device is a nonvolatile memory device using a phase change according to a temperature change, that is, a resistance change. The phase change memory device has a relatively simple manufacturing process and can implement a large capacity memory at low cost.

1 shows a memory cell of a phase change memory device. Referring to FIG. 1, the memory cell 10 includes a memory element 11 and a select element 12. The memory element 11 is connected between the bit line BL and the selection element 12, and the selection element 12 is connected between the memory element 11 and the ground.

The memory element 11 includes a phase change material GST. The phase change material GST is a variable resistance element whose resistance varies with temperature, such as Ge-Sb-Te. The phase change material GST has one of two stable states, a crystal state and an amorphous state, depending on the temperature. The phase change material GST changes to a crystal state or an amorphous state according to the current supplied through the bit line BL. Phase change memory devices use this property of phase change material (GST) to program data.

The selection element 12 is composed of an NMOS transistor NT. The word line WL is connected to the gate of the NMOS transistor NT. When a predetermined voltage is applied to the word line WL, the NMOS transistor NT is turned on. When the NMOS transistor NT is turned on, the memory device 11 receives a current through the bit line BL. In FIG. 1, the memory element 11 is connected between the bit line BL and the selection element 12. However, the selection element 12 may be connected between the bit line BL and the memory element 11.

2 shows another memory cell of a phase change memory device. Referring to FIG. 2, the memory cell 20 includes a memory element 21 and a selection element 22. The memory element 21 is connected between the bit line BL and the selection element 22, and the selection element 22 is connected between the memory element 21 and ground. The memory element 21 is the same as the memory element 11 of FIG. 1.

The selection element 22 is composed of a diode D. The memory element 21 is connected to the anode of the diode D, and the word line WL is connected to the cathode. When the voltage difference between the anode and the cathode of the diode D becomes higher than the threshold voltage of the diode D, the diode D is turned on. When the diode D is turned on, the memory device 21 receives a current through the bit line BL.

3 is a graph illustrating the characteristics of the phase change material GST shown in FIGS. 1 and 2. In Fig. 3, reference numeral 1 denotes a condition for the phase change material GST to be in an amorphous state, and reference numeral 2 denotes a condition for becoming a crystal state.

Referring to FIG. 3, the phase change material GST is heated to a temperature higher than the melting temperature Tm during the T1 by a current supply, and then rapidly cooled to a amorphous state. The amorphous state is usually called the reset state and stores data '1'. In contrast, the phase change material is brought into a crystal state by heating for a longer time than T1 at a temperature above the crystallization temperature (Tc) and below the melting temperature (Tm) and then slowly cooling. The decision state is also commonly called the set state and stores data '0'. Memory cells vary in resistance depending on the amorphous volume of the phase change material. The resistance of the memory cell is high in the amorphous state and low in the crystalline state.

The phase change memory device having the memory cells described with reference to FIGS. 1 through 3 receives a power supply voltage VCC from an external source during a read operation and precharges the bit line BL or supplies a read current to the bit line BL. . In general, a phase change memory device includes a precharge circuit, a bias circuit, and a sense amplifier to perform a read operation. The precharge circuit precharges the bit line BL using the power supply voltage VCC. The bias circuit supplies a read current to the bit line BL using the power supply voltage VCC. The sense amplifier uses the supply voltage (VCC) to compare the voltage at the sensing node with the reference voltage and read the data stored in the memory cell.

However, as the power supply voltage VCC provided to the phase change memory device is lowered below a predetermined voltage (for example, 1.5V), the sensing margin of the sense amplifier is reduced during a read operation. Here, the sensing margin refers to the difference in voltages of the sensing nodes when the memory cells are in the reset state and the set state. For example, suppose the power supply voltage VCC is about 1.5V. When the memory cell (see FIG. 1, 10) is in the reset state, the sensing node maintains about 1.5V. When the memory cell 10 is in the set state, the sensing node drops from the power supply voltage VCC to the ground level. This is the case where the selection element 12 of the memory cell 10 is an NMOS transistor NT.

However, in the case where the selection element 22 of the memory cell (see FIG. 2, 20) is a diode D, when the memory cell 20 is in the reset state, the sensing node maintains about 1.5V, but the memory cell 10 In the set state, the sensing node drops to the threshold voltage of the diode D. For this reason, the sensing margin of the phase change memory device using the diode D as the selection element is reduced by the threshold voltage of the diode D. If the threshold voltage of the diode D is increased due to a manufacturing process or the like, the sensing margin is further reduced.

Therefore, the phase change memory device using the diode D as the selection element has a sensing node corresponding to the threshold voltage of the diode D during the read operation, compared to the phase change memory device using the NMOS transistor NT as the selection element. Should be higher.

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above problems, and an object of the present invention is to provide a phase change memory device and a reading method thereof having a boosting circuit to sufficiently secure a sensing margin.

Another object of the present invention is to provide a phase change memory device and a method of reading the same, which reduce the burden on the booster circuit during the precharge operation and ensure sufficient sensing margin during the sensing operation.

The phase change memory device according to the present invention includes a memory cell, a boost circuit, a precharge circuit, a bias circuit, and a sense amplifier. The memory cell includes a phase change material and a diode and is connected to the bit line. The boost circuit generates a boost voltage using a power supply voltage. The precharge circuit precharges the bit line using the power supply voltage, and then precharges the bit line using the boosted voltage. The bias circuit uses the boost voltage to provide a read current to the bit line. The sense amplifier uses the boosted voltage to compare the voltage of the bit line with a reference voltage and read data stored in the memory cell.

In example embodiments, the precharge circuit may include: a first precharge circuit configured to precharge the bit line using the power supply voltage; And a second precharge circuit for precharging the bit line using the boosted voltage.

Another aspect of the phase change memory device according to the present invention includes a memory cell, a clamping circuit, a boost circuit, a precharge circuit, a bias circuit, and a sense amplifier. The memory cell includes a phase change material and a diode and is connected to the bit line. The clamping circuit is connected between the bit line and the sensing node and clamps the voltage of the bit line. The boost circuit generates a boost voltage using a power supply voltage. The precharge circuit is connected to the sensing node, precharges the sensing node using the power supply voltage, and then precharges the sensing node using the boosted voltage. The bias circuit is coupled to the sensing node and provides a read current to the bit line using the boost voltage. The sense amplifier uses the boosted voltage to compare the voltage of the bit line with a reference voltage and read data stored in the memory cell.

 In an embodiment, the precharge circuit is connected between a first power supply terminal and the sensing node, receives the power supply voltage through the first power supply terminal, and supplies the sensing node to the power supply in response to a first precharge signal. A first precharge circuit for precharging with a voltage; And a second precharge connected between a second power terminal and the sensing node, receiving the boost voltage through the second power terminal, and precharging the sensing node to the boost voltage in response to a second precharge signal. It includes a circuit. The first precharge circuit is a PMOS transistor connected between the first power supply terminal and the sensing node and controlled by the first precharge signal. The second precharge circuit is a PMOS transistor connected between the second power supply terminal and the sensing node and controlled by the second precharge signal.

A read method of a phase change memory device according to the present invention includes: discharging a bit line connected to a memory cell; Precharging the bit line using a power supply voltage, and then precharging the bit line using a boosted voltage; Providing a read current to the bit line using the boost voltage; And sensing the voltage of the bit line using the boosted voltage and reading data stored in the memory cell.

In example embodiments, the memory cell may include a memory device having a phase change material; And a selection element for selecting the memory cell. The selection element is a diode connected between the memory element and the word line. In the precharge step, the bit line is clamped to the threshold voltage of the diode.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention.

4 is a block diagram illustrating a phase change memory device according to an exemplary embodiment of the present invention. Referring to FIG. 4, the phase change memory device 100 includes a memory cell array 110, an address decoder 120, a bit line selection circuit 130, discharge circuits 135 and 136, a clamping circuit 140, The precharge circuit 150, the bias circuit 160, the sense amplifier 170, the control unit 180, and the boost circuit 200 are included.

The memory cell array 110 is composed of a plurality of memory cells. The plurality of memory cells are connected to the plurality of word lines WL0 to WLn and the plurality of bit lines BL0 to BLm. Each memory cell is composed of a memory element and a select element. The memory element includes a phase change material GST, and the selection element is composed of a diode D.

Here, instead of the diode D, an NMOS transistor (see FIG. 1, NT) may be used. In general, the phase change memory device 100 supplies a reset current or a set current to a memory cell in order to program the memory cell into a reset state or a set state. The reset current requires a larger current value than the set current. Therefore, when using the NMOS transistor (see Fig. 1, 12) as the selection device, the threshold voltage of the NMOS transistor NT is smaller than the threshold voltage of the MOS transistor used in the sense amplifier 170 for a more efficient reset program. It is desirable to implement.

The address decoder 120 decodes an externally input address ADDR and selects a word line and a bit line. The address ADDR is divided into a row address RA for selecting word lines WL0 to WLn and a column address CA for selecting bit lines BL0 to BLm. In FIG. 4, the word line WL1 is selected from the plurality of word lines WL0 to WLn, and the bit line BLm is selected from the plurality of bit lines BL0 to BLm. One memory cell 111 is selected by the word line WL1 and the bit line BLm.

The bit line selection circuit 130 selects the bit line in response to the selection signal Yi (i = 0 to m) provided from the address decoder 120. The bit line selection circuit 130 includes a plurality of NMOS transistors YT0 to YTm. The plurality of NMOS transistors YT0 to YTm connect the bit lines BL0 to BLm and the data line DL. For example, when the selection signal Ym is enabled, the bit line BLm and the data line DL are electrically connected to each other.

The first discharge circuit 135 is connected between the data line DL and the ground terminal and discharges the data line DL. The second discharge circuit 136 is connected between the sensing node NSA and the ground terminal and discharges the sensing node NSA. Referring to FIG. 4, the first discharge circuit 135 includes an NMOS transistor Ndis which forms a current path between the data line DL and the ground terminal, and is connected to the discharge signal PDIS. In response, the data line DL is discharged. Similarly, the second discharge circuit 136 discharges the sensing node NSA in response to the discharge signal PDIS. The discharge signal PDIS is provided from the control unit 180.

The clamping circuit 140 clamps the data line DL to a predetermined voltage level during a read operation. This is to prevent the voltage level of the selected bit line BLm from exceeding the threshold voltage of the phase change material GST. In other words, the voltage between both ends of the phase change material GST does not exceed the threshold voltage of the phase change material GST. For example, assuming that the threshold voltage of the diode D is 0.5V and the threshold voltage of the phase change material GST is 1V, the voltage of the bit line BLm is less than 1.5V (for example, about 1V). Is clamped).

Referring to FIG. 4, the clamping circuit 140 includes an NMOS transistor Ncmp that forms a current path between the sensing node NSA and the data line DL, and responds to the clamp signal CLMP in response to the clamp signal CLMP. Clamp the voltage level of DL). For example, assuming that the threshold voltage of the NMOS transistor Ncmp is 1V and the clamp signal CLMP is 2V, the data line DL is clamped to about 1V. At this time, the voltage level of the selected bit line BLm is also clamped to about 1V. The clamp signal CLMP is provided from the control unit 180 and has a constant level of direct current (DC) voltage value in a read operation.

The precharge circuit 150 precharges the sensing node NSA to the power supply voltage VCC and then precharges the boosted voltage VSA. At this time, the selected bit line BLm is precharged with a clamping voltage (for example, 1V). Referring to FIG. 4, the precharge circuit 150 includes first and second precharge circuits 151 and 152. The first precharge circuit 151 precharges the sensing node NSA to the power supply voltage VCC in response to the first precharge signal nPCH1, and the second precharge circuit 152 performs the second precharge signal ( In response to nPCH2, the sensing node NSA is precharged to the boosted voltage VSA. The first and second precharge signals nPCH1 and nPCH2 are provided from the control unit 180.

The first precharge circuit 151 is connected between the first power supply terminal and the sensing node NSA, receives the power supply voltage VCC through the first power supply terminal, and responds to the first precharge signal nPCH1. The sensing node NSA is precharged with the power supply voltage VCC. Referring to FIG. 4, the first precharge circuit 151 is composed of a PMOS transistor Ppre. The PMOS transistor Ppre of the first precharge circuit 151 may include a gate for receiving the first precharge signal nPCH1, a source for receiving the power supply voltage VCC, a drain connected to the sensing node NSA, and a boost voltage. It has a bulk (not shown) that receives (VSA) input.

The second precharge circuit 152 is connected between the second power supply terminal and the sensing node NSA, receives the boost voltage VSA through the second power supply terminal, and responds to the second precharge signal nPCH2. The sensing node NSA is precharged with the boosted voltage VSA. Referring to FIG. 4, the second precharge circuit 152 is configured of a PMOS transistor Ppre. The PMOS transistor Ppre of the second precharge circuit 152 may include a gate for receiving the second precharge signal nPCH2, a source for receiving the boost voltage VSA, a drain connected to the sensing node NSA, and a boost voltage. It has a bulk (not shown) that receives (VSA) input.

If it is assumed that the precharge circuit 150 precharges using only the boost voltage VSA, the boost circuit 200 precharges a large number of bit lines BL during a burst read operation. There is a lot of burden because you have to. In addition, since each bit line BLm has a large loading during the precharge operation, the boosting circuit 200 has a greater burden.

The precharge circuit 150 performs two steps of precharge operation in order to reduce such a burden on the boost circuit 200 during the precharge operation. That is, during the first precharge operation, the selected bit line BLm is precharged using the power supply voltage VCC. In this case, the first precharge circuit 151 performs a precharge operation using an externally supplied power supply voltage VCC. Next, during the second precharge operation, the boosted voltage VSA is used to precharge the selected bit line BLm. In this case, the second precharge circuit 152 performs the precharge operation by using the boosted voltage VSA provided by the booster circuit 200.

As described above, the precharge circuit 150 precharges the sensing node NSA from the power supply voltage VCC to the boosted voltage VSA during the second precharge operation. The booster circuit 200 provides the boosted voltage VSA to the precharge circuit 150 only during the second precharge operation. Therefore, the phase change memory device 100 according to the present invention can reduce the burden of the booster circuit 200 during the precharge operation and sufficiently secure the sensing margin of the sense amplifier 170 during the sensing operation. This is explained in more detail in FIG.

The bias circuit 160 is connected between the power supply terminal and the sensing node NSA and supplies a read current to the selected bit line BLm. Referring to FIG. 4, the bias circuit 160 receives a boosted voltage VSA through a power supply terminal. The bias circuit 160 is composed of two PMOS transistors Pdis and Pbias connected in series.

The first PMOS transistor Pdis is connected between the power supply terminal and the second PMOS transistor Pbias and is controlled by the discharge signal PDIS. The second PMOS transistor Pbias is connected between the first PMOS transistor Pdis and the sensing node NSA and controlled by the bias signal BIAS. Here, the bias signal BIAS is provided from the control unit 180 and has a predetermined DC voltage value at the read operation. The bias circuit 160 supplies a read current to the selected bit line BLm when the discharge signal PDIS is in the low level state.

The sense amplifier 170 compares the voltage of the sensing node NSA with the reference voltage Vref during a read operation and outputs a comparison result value SAO. Here, the reference voltage Vref is provided from a reference voltage generation circuit (not shown). The sense amplifier 170 performs a sensing operation using the boosted voltage VSA. The sense amplifier 170 receives control signals nPSA and PMUX from the control unit 180 during the sensing operation. The configuration and operation of the sense amplifier 170 are described in detail with reference to FIGS. 6 and 7.

The control unit 180 outputs control signals PDIS, CLMP, BIAS, nPCH1, nPCH2, nPSA, PMUX, and EN_PUMP in response to an externally provided command CMD. Here, the pump enable signal EN_PUMP is provided to the boost circuit 200. The control signal output from the control unit 180 will be described in detail with reference to FIGS. 5 and 7.

The booster circuit 200 includes a pump circuit 210 and a detection circuit 220. The pump circuit 210 boosts the power supply voltage VCC through a charge pumping operation. The detection circuit 220 detects whether the output node of the pump circuit 210 has reached the boosted voltage VSA. When the output node reaches the boosted voltage VSA, the detection circuit 220 disables the pump circuit 210. However, if the output node has not reached the boosted voltage VSA, the detection circuit 220 enables the pump circuit 210. The boosted voltage VSA is provided to the bias circuit 150, the precharge circuit 160, the sense amplifier 170, and the like.

 FIG. 5 is a timing diagram for describing an operation of the phase change memory device 100 shown in FIG. 4. Referring to FIG. 5, a read operation of the phase change memory device 100 may include a discharge period T0, a first precharge period T1 (a), and a second precharge period T1 (b). ), The sensing section T2, and the discharge section T3. For convenience of explanation, a read operation on the memory cell 111 is described.

In the discharge period TO, the data line DL and the sensing node NSA are discharged to the ground level. Referring to FIG. 5, since the select signal Ym is in a low level state, the bit line BLm and the data line DL are electrically disconnected. Since the discharge signal PDIS is at the high level, the data line DL and the sensing node NSA are discharged to the ground level. In addition, since the discharge signal PDIS is at a high level, the first PMOS transistor Pdis of the bias circuit 160 is in a turned off state. In FIG. 5, the bit line BLm is at the ground level because the bit line BLm is discharged by a bit line discharge circuit (not shown) provided on the bit line BLm.

In the first precharge period T1 (a), the sensing node NSA is precharged with the power supply voltage VCC, and the bit line BLm rises toward the clamping voltage (for example, 1V). Referring to FIG. 5, the selection signal Ym becomes a high level, the discharge signal PDIS becomes a low level, and the first precharge signal nPCH1 becomes a low level. When the select signal Ym becomes high, the bit line BLm and the data line DL are electrically connected. When the discharge signal PDIS becomes low, the NMOS transistors Ndis of the discharge circuits 135 and 136 are turned off, and the first PMOS transistor Pdis of the bias circuit 160 is turned on. When the first precharge signal nPCH1 becomes low, the sensing node NSA is precharged with the power supply voltage VCC. When the sensing node NSA is precharged with the power supply voltage VCC, the bit line BLm rises to the clamping voltage 1V.

In the second precharge period T1 (b), the second precharge signal nPCH2 goes low. When the second precharge signal nPCH2 is at a low level, the sensing node NSA is precharged by the boosted voltage VSA. When the sensing node NSA is precharged with the boosted voltage VSA, the bit line BLm rises to the clamping voltage 1V.

In the sensing period T2, the word line WL1 goes low. When the word line WL1 becomes low, the voltage level of the sensing node NSA varies according to the state of the memory cell 111.

When the memory cell 111 stores the reset state or the data '1', the voltage level of the sensing node NSA maintains the boosted voltage VSA. The reason why the sensing node NSA maintains the boosted voltage VSA is because the read current is supplied through the bias circuit 160. When the memory cell 111 stores the set state or data '0', the voltage level of the sensing node NSA drops to 1V at the boosted voltage VSA. Here, the voltage level of the sensing node NSA does not fall to the ground level GND due to the threshold voltage of the diode D, but drops to 1V. In the T2 section, a sensing operation of the sense amplifier 170 is performed. The sensing operation of the sense amplifier 170 is described in detail with reference to FIGS. 6 and 7.

In the discharge period T3, the word line WL1 goes high, the select signal Ym goes low, and the discharge signal PDIS goes high. When the select signal Ym becomes low, the bit line BLm and the data line DL are electrically disconnected. When the discharge signal PDIS is at a high level, the sensing node NSA is at a ground level.

According to the conventional phase change memory device, the sensing margin of the sensing node NSA is only (VCC-1V). When the supply voltage VCC is lowered below 1.5V, the sensing margin is lowered below 0.5V. This is a major cause of deterioration in the read operation characteristics of the phase change memory device. However, as shown in FIG. 5, according to the phase change memory device 100 according to the present invention, since the sensing margin of the sensing node NSA is (VSA-1V), sufficient sensing margin may be secured and a stable read operation may be performed. can do.

In addition, according to the phase change memory device 100 according to the present invention, since the precharge operation is performed twice using the power supply voltage VCC and the boost voltage VSA, the booster circuit 200 may be operated during the precharge operation. The burden will be greatly reduced.

FIG. 6 is a circuit diagram illustrating the sense amplifier shown in FIG. 4. The sense amplifier 170 compares the voltage of the sensing node NSA with the reference voltage Vref and outputs a sensing result value SAO. The sense amplifier 170 receives the boosted voltage VSA and performs a sensing operation in response to the control signals nPSA and PMUX. Referring to FIG. 6, the sense amplifier 170 includes a sensing unit 310, a latch unit 320, and a dummy latch unit 330.

The sensing unit 310 includes a plurality of PMOS transistors P1 to P3 and a plurality of NMOS transistors N1 to N5. The sensing unit 310 includes a differential amplifier 311 and an equalizer 312. The differential amplifier 311 receives the boosted voltage VSA and senses and amplifies a difference between the voltage of the sensing node NSA and the reference voltage Vref. Equalizer 312 equalizes output nodes Na and Nb of differential amplifier 311 in response to control signal nPSA.

The differential amplifier 311 includes first to second NMOS transistors N1 and N2 and first to third PMOS transistors P1, P2 and P3. The first NMOS transistor N1 forms a current path between the first node Na and ground in response to the voltage of the sensing node NSA. The second NMOS transistor N2 forms a current path between the second node Nb and ground in response to the reference voltage Vref. The first PMOS transistor P1 forms a current path between the third node Nc and the first node Na in response to the voltage of the second node Nb. The second PMOS transistor P2 forms a current path between the third node Nc and the second node Nb in response to the voltage of the first node Na. The third PMOS transistor P3 forms a current path between the power supply terminal and the third node Nc in response to the control signal nPSA. The third PMOS transistor P3 receives the boosted voltage VSA through a power supply terminal.

The equalizer 312 is composed of third to fifth NMOS transistors N3, N4, N5. The third NMOS transistor N3 is connected between the first node Na and ground. The fourth NMOS transistor N4 is connected between the second node Nb and the ground. The fifth NMOS transistor N5 is connected between the first node Na and the second node Nb. The third to fifth NMOS transistors N3 to N5 are simultaneously turned on or off in response to the control signal nPSA.

The latch unit 320 is connected to the first node Na of the sensing unit 310 and outputs a sensing result SAO in response to the control signal PMUX. The latch unit 320 includes an inversion circuit 321 and a latch circuit 322. The inversion circuit 321 is connected between the first node Na and the fourth node Nd and operates in response to the control signal PMUX. The inversion circuit 321 includes sixth and seventh PMOS transistors P6 and P7, sixth and seventh NMOS transistors N6 and N7, and a first inverter IN1. When the control signal PMUX is at the high level, the inversion circuit 321 inverts the voltage level of the first node Na. The latch circuit 322 includes second and third inverters IN2 and IN3.

The dummy latch unit 330 is connected to the second node Nb of the sensing unit 310. The dummy latch unit 330 includes an eighth PMOS transistor P8 and an eighth NMOS transistor N8. The source and the drain of the eighth PMOS transistor P8 are connected to each other, and the gate is connected to the second node Nb. The eighth PMOS transistor P8 receives a power supply voltage VCC through a source terminal. The source and the drain of the eighth NMOS transistor N8 are connected to each other, and the gate is connected to the second node Nb. The source terminal of the eighth NMOS transistor N8 is connected to the ground terminal. Here, it should be noted that the drain of the eighth PMOS transistor P8 and the drain of the eighth NMOS transistor N8 are disconnected from each other. The dummy latch unit 330 is installed to equalize the loading viewed from the first node Na and the second node Nb.

FIG. 7 is a timing diagram for describing an operation of the sense amplifier illustrated in FIG. 6. In FIG. 7, the operation of the sense amplifier 170 in the sensing period T2 of FIG. 5 will be described in more detail. The voltage level of the sensing node NSA of FIG. 7A is the same as the voltage level of the sensing node NSA of FIG. 5G.

In the second precharge period T1 (b), the first control signal nPSA is in the boosted voltage VSA state and the second control signal PMUX is in the low level state. Since the first control signal nPSA is the boosted voltage VSA, the first and second nodes Na and Nb are in a ground level state.

In the first sensing period T2 (a), the voltage level of the sensing node NSA depends on the state of the memory cell 111. The sensing node NSA maintains the boosted voltage VSA when the memory cell 111 is in the reset state and drops to 1V when the memory cell 111 is in the set state.

In the second sensing period T2 (b), the first control signal nPSA becomes the ground voltage GND. Referring to FIG. 6, the third PMOS transistor P3 is turned on, and the third to fifth NMOS transistors N3 to N5 are turned off. In this case, the sensing unit 310 performs a sensing operation by comparing a difference between the voltage of the sensing node NSA and the reference voltage Vref. When the voltage of the sensing node NSA is higher than the reference voltage Vref, the first node Na becomes a ground voltage. When the voltage of the sensing node NSA is lower than the reference voltage Vref, the first node Na becomes the boosted voltage VSA. That is, when the memory cell 111 is in the reset state, the first node Na becomes the ground voltage, and when the memory cell 111 is in the set state, the first node Na becomes the boosted voltage VSA.

In the third sensing period T2 (c), the second control signal PMUX is enabled. When the second control signal PMUX is at the high level, the latch unit 320 inverts the voltage level of the first node Na, and outputs the result SAO. Referring to FIG. 7, the output node of the sense amplifier 170 is in a previous state until the second sensing period T2 (b). In the third sensing period T2 (c), the output node of the sense amplifier 170 becomes the power supply voltage VCC or the ground voltage GND in response to the control signal PMUX. That is, when the first node Na is at the boosted voltage VSA level, the output voltage SAO becomes the ground voltage GND. When the first node Na is at the ground voltage GND level, the output voltage SAO becomes the power supply voltage VCC.

In the discharge period T3, the first control signal nPSA becomes the boosted voltage VSA and the second control signal PMUX becomes the ground voltage. Referring to FIG. 6, the third PMOS transistor P3 of the sensing unit 310 is turned off, and the third to fifth NMOS transistors N3 to N5 are turned on. At this time, the first and second nodes Na and Nb become the ground voltage GND. At this time, the latch circuit 322 latches the voltage level of the output node.

8 is a block diagram of a portable electronic system showing an application example of a phase change memory device according to still another embodiment of the present invention. The phase change memory device 100 connected to the microprocessor 500 through the bus line L3 functions as a main memory of the portable electronic system. The battery 400 supplies power to the microprocessor 500, the input / output device 600, and the phase change memory device 100 through the power line L4. When the received data is provided to the input / output device 600 through the line L1, the microprocessor 500 receives the received data through the line L2, processes the received data, and then changes the phase change memory through the bus line L3. Applies the received or processed data to the device 100. The phase change memory device 100 stores data applied through the bus line L3 in a memory cell. In addition, the data stored in the memory cell is read by the microprocessor 500 and output to the outside through the input / output device 600.

Even when the power of the battery 400 is not supplied to the power line L4, the data stored in the memory cell of the phase change memory device 100 does not disappear due to the characteristics of the phase change material. This is because the phase change memory device 100 is a nonvolatile memory unlike the DRAM. In addition, the phase change memory device 100 has advantages in that the operation speed is faster and power consumption is lower than that of other memory devices.

On the other hand, in the detailed description of the present invention has been described with respect to specific embodiments, various modifications are of course possible without departing from the scope of the invention. Therefore, the scope of the present invention should not be limited to the above-described embodiments, but should be defined by the equivalents of the claims of the present invention as well as the following claims.

As described above, according to the phase change memory device and the reading method thereof according to the present invention, the burden of the boost circuit can be reduced during the precharge operation, and the sensing margin of the sense amplifier can be sufficiently secured during the sensing operation. A stable read operation can be performed.

Claims (14)

A memory cell coupled to the bit line; A boost circuit for generating a boost voltage using a power supply voltage; A precharge circuit which precharges the bit line using the power supply voltage, and then precharges the bit line using the boosted voltage; A bias circuit using the boost voltage to provide a read current to the bit line; And And a sense amplifier configured to sense the voltage level of the bit line using the boosted voltage. The method of claim 1, The memory cell, A memory element having a phase change material; And A selection element for selecting the memory cell, The selection device is a diode connected between the memory device and a word line, The boost voltage is a phase change memory device, characterized in that the sum of the power supply voltage and the threshold voltage of the diode. The method of claim 1, The boost circuit A pump circuit for boosting the power supply voltage; And And a detection circuit for detecting a level of an output voltage of the pump circuit and controlling a boosting operation of the pump circuit. The method of claim 1, The precharge circuit is A first precharge circuit for precharging the bit line using the power supply voltage; And And a second precharge circuit to precharge the bit line using the boosted voltage. The method of claim 1, And the sense amplifier compares the voltage of the bit line with a reference voltage and reads data stored in the memory cell. A memory cell coupled to the bit line; A clamping circuit connected between the bit line and the sensing node and clamping a voltage of the bit line; A boost circuit for generating a boost voltage using a power supply voltage; A precharge circuit connected to the sensing node, precharging the sensing node using the power supply voltage, and then precharging the sensing node using the boosted voltage; A bias circuit coupled to the sensing node and providing a read current to the bit line using the boost voltage; And And a sense amplifier configured to compare the voltage of the sensing node with a reference voltage using the boosted voltage, and to read data stored in the memory cell. The method of claim 6, The memory cell, A memory element having a phase change material; And A selection element for selecting the memory cell, The selection device is a diode connected between the memory device and a word line, The boost voltage is a phase change memory device, characterized in that the sum of the power supply voltage and the threshold voltage of the diode. The method of claim 7, wherein And the clamping circuit clamps the bit line to the threshold voltage of the diode. The method of claim 6, The precharge circuit is A first precharge circuit connected between a first power terminal and the sensing node, receiving the power voltage through the first power terminal, and precharging the sensing node to the power voltage in response to a first precharge signal ; And A second precharge circuit connected between a second power terminal and the sensing node, receiving the boosted voltage through the second power terminal, and precharging the sensing node to the boosted voltage in response to a second precharge signal; Phase change memory device comprising a. The method of claim 9, The first precharge circuit is a PMOS transistor connected between the first power supply terminal and the sensing node and controlled by the first precharge signal; And the second precharge circuit is a PMOS transistor connected between the second power supply terminal and the sensing node and controlled by the second precharge signal. To read a phase change memory device: Discharging a bit line coupled to the memory cell; Precharging the bit line using a power supply voltage, and then precharging the bit line using a boosted voltage; Providing a read current to the bit line using the boost voltage; And And sensing the voltage of the bit line using the boosted voltage and reading data stored in the memory cell. The method of claim 11, The memory cell, A memory element having a phase change material; And A selection element for selecting the memory cell, And said select element is a diode connected between said memory element and a word line. The method of claim 12, And in the precharge step, the bit line is clamped to the threshold voltage of the diode. Phase change memory devices; And A microprocessor for controlling the phase change memory device, The phase change memory device A memory cell coupled to the bit line; A boost circuit for generating a boost voltage using a power supply voltage; A precharge circuit which precharges the bit line using the power supply voltage, and then precharges the bit line using the boosted voltage; A bias circuit using the boost voltage to provide a read current to the bit line; And And a sense amplifier configured to sense the voltage level of the bit line using the boosted voltage.

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