JP2013131271A - Nonvolatile memory cell, nonvolatile memory cell array, and nonvolatile memory - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonvolatile memory capable of providing high speed read operation.SOLUTION: A nonvolatile memory cell includes a first variable resistance element R1 and a first selection transistor T1 connected in series between a bit line BL and a source line SL, and a second variable resistance element R2 and a second selection transistor T2 connected in series between a complementary bit line BLB and the source line SL. The selection transistors T1, T2 are turn on and off by selection voltage supplied through a word line WL. With the selection transistors T1, T2 turned on, voltage of polarity corresponding to write data is applied between the bit line BL and the source line SL and between the complementary bit line BLB and the source line SL, which alters resistance values of the variable resistance elements R1, R2 in the opposite direction. Thus, a large difference arises between the signal on the bit line BL and the signal on the complementary bit line BLB during read operation, which allows for high speed reading of data.

Description

  The present invention relates to a nonvolatile memory cell using a resistance change element, a nonvolatile memory cell array including the nonvolatile memory cell, and a nonvolatile memory.

  In recent years, a resistance change type memory for storing data using a resistance change type element has attracted attention as a next-generation non-volatile memory in place of a flash memory or a DRAM that has become limited in miniaturization. Examples of the resistance change element include MRAM (Magnetoretic Random Access Memory), PRAM (Phase change Random Access Memory), ReRAM (Resistance Random Access Memory). The thing that is. A memory using such a resistance variable element does not require a complicated process like a flash memory, is compatible with a standard logic process, is suitable for miniaturization, and operates at a low voltage. The future is promising. An element configuration, characteristics, and array configuration of a memory using this type of variable resistance element are disclosed in Patent Document 1 or Non-Patent Document 1, for example.

  FIGS. 12A and 12B are diagrams showing the configuration and operation of a nonvolatile memory cell using a typical MTJ (Magnetic Tunnel Junction) element as a variable resistance element. As shown in FIGS. 12A and 12B, the MTJ element includes a pinned layer having a constant magnetic direction, a tunnel barrier film, and a free layer whose magnetic direction changes. As shown in FIG. 12A, when a current in the direction from the free layer to the pinned layer is passed, the magnetization direction of the free layer becomes the same as that of the pinned layer, the MTJ element has a low resistance, and data “0” is stored. It becomes a state. Conversely, as shown in FIG. 12B, when a current in the direction from the pinned layer toward the free layer is passed, the magnetization direction of the free layer is opposite to that of the pinned layer, the MTJ element becomes high resistance, and data “1” "Is stored. When a nonvolatile memory cell is configured with such an MTJ element, as illustrated in FIGS. 12A and 12B, an N-channel transistor Ts is used as the MTJ element as a switch for selecting the MTJ element. Connected in series. The configuration of such a nonvolatile memory cell is disclosed in Patent Document 1, for example.

  FIG. 13 is a diagram illustrating a cross-sectional structure of a conventional nonvolatile memory cell array composed of nonvolatile memory cells as shown in FIGS. 12 (a) and 12 (b). In the example shown in FIG. 13, the N-channel transistor Ts for selection shown in FIGS. 12A and 12B is formed on the semiconductor substrate. A selection voltage WL is applied to the gates of the two N-channel transistors Ts constituting one nonvolatile memory cell. The sources of these N-channel transistors Ts are connected to the source line SL of the second metal layer 2M through the through holes and the first metal layer 1M. The drain shared by the two N-channel transistors Ts is connected to the pin layer of the MTJ element through a through hole, and the free layer of the MTJ element is connected to the bit line BL formed by the second metal layer 2M through the through hole. It is connected.

  FIG. 14 is a diagram showing a circuit configuration of a conventional nonvolatile memory cell array, and FIG. 15 is a diagram showing a layout example of the nonvolatile memory cell array. 14 and 15, a region surrounded by a broken line indicates one nonvolatile memory cell. The nonvolatile memory cell array is an array of these nonvolatile memory cells. As shown in FIGS. 14 and 15, in the nonvolatile memory cell array, row selection lines WL00, WL01, WL10, WL11, WL20, and WL21 made of a polysilicon layer are wired in the horizontal direction. In the nonvolatile memory cell array, a plurality of rectangular N-type impurity regions extending in the vertical direction are formed in parallel in the horizontal direction. The intersection between the row selection line, which is a polysilicon layer, and these N-type impurity layers becomes the gate of the N-channel transistor Ts shown in FIGS. 12 and 13, and the N-type impurity layers on both sides of the gate are N-channel transistor. It becomes the source or drain of Ts.

  In the nonvolatile memory cell array, source lines SL0, SL1, SL2, and SL3 formed of a second metal layer extending in the vertical direction and bit lines BL0, BL1, BL2, and BL3 formed of the second metal layer are alternately arranged in the horizontal direction. ing. In the illustrated example, in a nonvolatile memory cell surrounded by a broken line, a source line SL1 is connected to a source of an N-channel transistor whose gate is the row selection line WL10 and a source of an N-channel transistor whose gate is the row selection line WL11. Has been. An MTJ element is interposed between the common drain of the N-channel transistor whose gate is the row selection line WL10 and the N-channel transistor whose gate is the row selection line WL11, and the bit line BL1 formed by the second metal layer M2. ing.

  When “0” is written in the MTJ element of a desired nonvolatile memory cell, a selection voltage WL of 1.2 V is applied to the gate of the N-channel transistor of the nonvolatile memory cell, 1.2 V is applied to the bit line BL, and the source line Apply 0V to SL. As a result, a current of about 49 μA in the direction from the free layer to the pinned layer flows through the MTJ element of the nonvolatile memory cell, the MTJ element becomes low resistance, and “0” is stored. On the other hand, when “1” is written to the MTJ element of a desired nonvolatile memory cell, a selection voltage WL of 1.2 V is applied to the gate of the N-channel transistor of the nonvolatile memory cell, 0 V is applied to the bit line BL, and the source line Apply 1.2V to SL. As a result, a current of about 49 μA in the direction from the pinned layer to the free layer flows through the MTJ element of the nonvolatile memory cell, the MTJ element becomes high resistance, and “1” is stored.

  When data is read from a desired nonvolatile memory cell, a selection voltage WL of 1.2 V is applied to the gate of the N-channel transistor of the nonvolatile memory cell, 0.15 V is applied to the bit line BL, and 0 V is applied to the source line SL. give. Then, a current flowing from the bit line BL to the MTJ element of the nonvolatile memory cell is detected. When the MTJ element stores “0” and has a low resistance, a current of about 15 μA flows through the MTJ element. On the other hand, when the MTJ element stores “1” and has a high resistance, a current of about 10 μA flows through the MTJ element. Therefore, it is possible to determine whether the MTJ element stores “0” or “1” by detecting the current flowing into the MTJ element and comparing it with a threshold value. Note that the configuration of such a nonvolatile memory cell array and the operating conditions of the nonvolatile memory cells constituting the nonvolatile memory cell array are disclosed in Non-Patent Document 2, for example.

JP 2009-187631 A

ISSCC Digest of Technical Papers, pp. 258, Feb. 2010. Non-Patent Literature IEICE IEICE Technical Report ICD Technical Report ICD2010-7 p35-p40

  The MRAM described above is very fast, and can perform writing and reading in 10 ns, for example. However, the difference between the “1” state (high resistance) and the “0” state (low resistance) is not so large as about 2 to several times, so this MRAM is slightly non-volatile due to wiring resistance or parasitic capacitance. Location dependence occurs in the value of current flowing through the memory cell and the discharge time. For this reason, it is difficult to accurately and accurately set the reference voltage for comparison of the sense amplifier for determining the current flowing through the resistance variable element, and determination of the current flowing through the resistance variable element, that is, the resistance variable type There has been a problem that it is difficult to determine “1” / “0” of the stored contents of the element at high speed. Here, in the MRAM or ReRAM, a bipolar element whose resistance change direction is reversed depending on the direction of the current is used as the resistance variable element, and the current passed through the resistance variable element in “0” writing and “1” writing. It is also possible to adopt a configuration that reverses the direction of. However, in this case, there is a problem that the circuit configuration of the circuit that controls access to the memory cell becomes complicated.

  The present invention has been made in view of the circumstances described above, and an object thereof is to provide a nonvolatile memory cell, a nonvolatile memory cell array, and a nonvolatile memory capable of high-speed reading. Furthermore, an object of the present invention is to provide a nonvolatile memory cell, a nonvolatile memory cell array, and a nonvolatile memory that can reduce the area and are easy to write.

  The present invention is a non-volatile memory having a non-volatile memory cell array in which a plurality of non-volatile memory cells are arranged in a matrix, and the non-volatile memory cell array is provided for each row of the matrix of the plurality of non-volatile memory cells. A plurality of word lines wired to each of the plurality of bit lines, a plurality of bit lines wired for each column of the matrix of the plurality of nonvolatile memory cells, and a column for each column of the plurality of the nonvolatile memory cells. A plurality of inverted bit lines that are wired and a plurality of source lines that are wired for each column of the matrix of the plurality of nonvolatile memory cells, and each of the plurality of nonvolatile memory cells includes: ON / OFF is switched by the second resistance change element and the row selection voltage supplied via the word line of the row to which each belongs, and in the ON state, the bit line of each column to which it belongs and Switch means for connecting the first variable resistance element between the source lines and connecting the second variable resistance element between the inverted bit line and the source line of each column to which the first variable resistance element belongs; And the second variable resistance element has a resistance value of the second direction in the first direction and in the opposite direction when currents flowing from the bit line and the inverted bit line to the source line are respectively flowed. Each resistance value changes in the second direction and the first direction when currents flowing from the source line to the bit line and the inversion bit line respectively flow through the source line. The nonvolatile memory generates a row selection voltage for turning on the switch means of the nonvolatile memory cell to be accessed, and at the time of write access, the bit line of the column to which the nonvolatile memory cell belongs is assigned. A write voltage having a polarity corresponding to the write data is applied between the pair of inverted bit lines and the source line, and at the time of reading, based on a signal generated on the bit line and the inverted bit line of the column to which the nonvolatile memory cell belongs. Provided is a nonvolatile memory characterized by determining read data from the nonvolatile memory cell.

  According to this nonvolatile memory, the first operation is performed by applying a write voltage having a polarity according to the write data between the pair of the bit line and the inverted bit line of the nonvolatile memory cell to be accessed and the source line. Data writing can be performed by changing the resistance values of the first variable resistance element and the second variable resistance element in opposite directions. Therefore, at the time of reading, a large difference is generated between signals generated on the bit line and the inverted bit line of the column to which the nonvolatile memory cell belongs, and data can be read from the nonvolatile memory cell at high speed. Further, according to this nonvolatile memory, the nonvolatile memory cell can be constituted by two resistance change elements and one or two transistors, and the area per memory cell can be reduced. The area of the nonvolatile memory can be reduced.

1 is a circuit diagram showing a configuration of a nonvolatile memory cell according to a first embodiment of the present invention. FIG. It is a figure which shows the operating condition of the non-volatile memory cell. It is a circuit diagram which shows the structure of the non-volatile memory cell which is 2nd Embodiment of this invention. It is a figure which shows the operating condition of the non-volatile memory cell. It is a circuit diagram which shows the structure of the non-volatile memory cell which is 3rd Embodiment of this invention. It is a circuit diagram which shows the structure of the non-volatile memory which is 4th Embodiment of this invention. It is a top view which shows the example of a layout of the non-volatile memory cell array which is 5th Embodiment of this invention. FIG. 8 is a cross-sectional view taken along line A-A ′ of FIG. 7. FIG. 8 is a sectional view taken along line B-B ′ of FIG. 7. FIG. 8 is a cross-sectional view taken along line C-C ′ of FIG. 7. FIG. 8 is a sectional view taken along line D-D ′ in FIG. 7. It is a figure which shows the structure and operation | movement of an MTJ element. It is a figure which illustrates the cross-sectional structure of the non-volatile memory cell using an MTJ element. It is a figure which illustrates the circuit structure of the non-volatile memory cell array using the non-volatile memory cell. It is a figure which shows the example of a layout of the non-volatile memory cell array.

  Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the transistor refers to a MOSFET (Metal Oxide Semiconductor Field Effect Transistor; field-effect transistor having a metal-oxide film-semiconductor structure).

<First Embodiment>
FIG. 1 is a circuit diagram showing a configuration of a nonvolatile memory cell having a 2T2R configuration according to the first embodiment of the present invention. This nonvolatile memory cell has first and second variable resistance elements R1 and R2, and first and second select transistors T1 and T2 which are N-channel transistors, respectively. Here, the first variable resistance element R1 and the first selection transistor T1 are interposed in series between the bit line BL and the source line SL, and the second variable resistance element R2 and the second selection transistor are inserted. The transistor T2 is interposed in series between the inverted bit line BLB and the source line SL. The first and second variable resistance elements R1 and R2 are provided on the bit line BL and inverted bit line BLB sides, respectively, and the first and second selection transistors T1 and T2 are provided on the source line SL side, respectively. ing. As the resistance variable elements R1 and R2, resistance variable elements similar to those used for MRAM, PRAM, ReRAM, and the like can be used. In the illustrated example, the resistance variable elements R1 and R2 are MTJ elements used for MRAM. The variable resistance element R1 has a free layer connected to the bit line BL and a pin layer connected to the drain of the selection transistor T1, and the variable resistance element R2 has a pin layer connected to the inverted bit line BLB and a free layer. The drain of the selection transistor T2 is connected.

  FIG. 2 is a diagram showing operating conditions of the nonvolatile memory cell according to the present embodiment. In the case of writing “0”, 1.2 V is applied to the word line WL, 1.2 V is applied to the bit line BL and the inverted bit line BLB, and 0 V is applied to the source line SL. As a result, a current flows from the bit line BL to the source line SL via the resistance change element R1 and the selection transistor T1, and from the inverted bit line BLB to the source line SL via the resistance change element R2 and the selection transistor T2. An electric current flows toward. Here, since a current from the free layer to the pinned layer flows in the resistance variable element R1, the resistance variable element R1 is in a low resistance state. On the other hand, since a current flowing from the pinned layer to the free layer flows through the resistance variable element R2, the resistance variable element R2 enters a high resistance state. In this manner, the nonvolatile memory cell is in a state in which the variable resistance element R1 is in the low resistance state, the variable resistance element R2 is in the high resistance state, and data “0” is stored.

  In the case of writing “1”, 1.2 V is applied to the word line WL, 0 V is applied to the bit line BL and the inverted bit line BLB, and 1.2 V is applied to the source line SL. As a result, a current flows from the source line SL to the bit line BL via the selection transistor T1 and the resistance variable element R1, and from the source line SL to the inverted bit line BLB via the selection transistor T2 and the resistance variable element R2. An electric current flows toward. Here, since a current from the pinned layer to the free layer flows through the resistance variable element R1, the resistance variable element R1 is in a high resistance state. On the other hand, since a current from the free layer to the pinned layer flows through the resistance variable element R2, the resistance variable element R2 is in a low resistance state. In this manner, the nonvolatile memory cell is in a state in which the variable resistance element R1 is in the high resistance state, the variable resistance element R2 is in the low resistance state, and data “1” is stored.

  In the case of reading, 0 V is applied to the source line SL and 0.5 V is applied to the word line WL. In this state, a sense amplifier (not shown) applies a bias of about 0.2 V to the bit line BL and the inverted bit line BLB to cause a current to flow through the resistance variable elements R1 and R2, and is generated in the bit line BL and the inverted bit line BLB. Differential amplification of each signal is performed.

  Here, when the nonvolatile memory cell stores data “0”, the resistance variable element R1 has a low resistance, and the resistance variable element R2 has a high resistance, the data flows from the bit line BL toward the source line SL. The current is larger than the current flowing from the inverted bit line BLB toward the source line SL. For this reason, the voltage of the bit line BL becomes lower than the voltage of the bit line BLB. As a result, the sense amplifier outputs a signal indicating that the read data is “0”.

  On the other hand, when the volatile memory cell stores data “1”, the resistance variable element R1 has a high resistance, and the resistance variable element R2 has a low resistance, the current flowing from the bit line BL toward the source line SL. Is smaller than the current flowing from the inverted bit line BLB toward the source line SL. For this reason, the voltage of the bit line BL becomes higher than the voltage of the bit line BLB. As a result, the sense amplifier outputs a signal indicating that the read data is “1”.

  In the above read operation, the selection voltage for the word line WL is set to 0.5 V, and the voltage for the bit line BL and the inverted bit line BLB is set to 0.2 V. The current flowing through the resistance variable elements R1 and R2 is reduced. This is to prevent erroneous writing. In this example, since the voltage with respect to the bit line BL and the inverted bit line BLB is lowered to about 0.2 V, if the current flowing through the resistance variable elements R1 and R2 can be sufficiently suppressed by this voltage, the word line Normal operation is possible even when the selection voltage for WL is 1.2V.

  As described above, according to the present embodiment, the resistance values of the resistance variable elements R1 and R2 are changed in the opposite directions by a simple operation of applying the same voltage to the bit line BL and the inverted bit line BLB. Thus, data writing can be performed. Therefore, a nonvolatile memory having a wide operation margin can be realized.

Second Embodiment
FIG. 3 is a circuit diagram showing a configuration of a nonvolatile memory cell according to the second embodiment of the present invention. In the nonvolatile memory cell according to the present embodiment, the positional relationship between the resistance variable elements R1 and R2 and the selection transistors T1 and T2 is changed from that in the first embodiment (FIG. 1), and the resistance variable elements R1 and R2 are Provided on the source line SL side. In the present embodiment, the polarities of the resistance change elements R1 and R2 are opposite to those of the first embodiment, and the resistance change element R1 has a pin layer as a source of the selection transistor T1 and a free layer. Is connected to the source line SL, and the variable resistance element R2 has a free layer connected to the source of the selection transistor T2 and a pinned layer connected to the source line SL.

  FIG. 4 is a view showing operating conditions of the nonvolatile memory cell according to the present embodiment. The voltage applied to the word line WL, the bit line BL, the inverted bit line BLB, and the source line SL for data writing and data reading is the same as in the first embodiment. In this embodiment, since the polarities of the resistance variable elements R1 and R2 are opposite to those of the first embodiment, the storage state of data “0” and the storage state of data “1” are different from those of the first embodiment. Vice versa.

  When “0” is written, when 1.2 V is applied to the word line WL, 1.2 V is applied to the bit line BL and the inverted bit line BLB, and 0 V is applied to the source line SL, the resistance variable element R1 has a pinned layer to a free layer. The current flowing from the free layer to the pinned layer flows through the resistance variable element R2. As a result, the resistance variable element R1 has a high resistance and the resistance variable element R2 has a low resistance. This is a state where data “0” is stored. When “1” is written, when 1.2 V is applied to the word line WL, 0 V is applied to the bit line BL and the inverted bit line BLB, and 1.2 V is applied to the source line SL, the resistance variable element R1 has a free layer to a pinned layer. Current flows toward the free layer through the resistance variable element R2. As a result, the resistance variable element R1 has a low resistance and the resistance variable element R2 has a high resistance. This is a state in which data “1” is stored. The configuration and operation of this embodiment are the same as those of the first embodiment, except that the state in which data “0” is stored and the state in which data “1” is stored are reversed. Also in this embodiment, the same effect as the first embodiment can be obtained.

<Third Embodiment>
FIG. 5 is a circuit diagram showing a configuration of a nonvolatile memory cell according to the third embodiment of the present invention. In the first embodiment, the switch means for switching whether or not the resistance variable elements R1 and R2 are connected between the bit line BL and the inverted bit line BLB and the source line SL are the first and second selections. It was constituted by transistors T1 and T2. On the other hand, in the nonvolatile memory cell according to the present embodiment, such switch means is constituted by one selection transistor T. More specifically, in the present embodiment, the first resistance change element R1 is interposed between the bit line BL and the common node CN, and the second resistance change is between the inverted bit line BLB and the common node CN. A type element R2 is inserted, and a selection transistor T as a switch means is inserted between the common node CN and the source line SL. In this embodiment, the selection transistor T is switched on / off by the selection voltage supplied via the word line WL. Also in this embodiment, the same effect as the first embodiment can be obtained.

<Fourth embodiment>
FIG. 6 is a circuit diagram showing a configuration of a nonvolatile memory according to the fourth embodiment of the present invention. In the nonvolatile memory according to the present embodiment, the nonvolatile memory cell array 100 is configured by nonvolatile memory cells Mkj (k = 0 to m, j = 0 to n) arranged in a matrix. These nonvolatile memory cells Mkj (k = 0 to m, j = 0 to n) are the nonvolatile memory cells in FIG. In the present embodiment, the nonvolatile memory cell Mkj (k = 0 to m, j = 0 to n) is operated according to the operating conditions of the first embodiment (FIG. 2).

  In the nonvolatile memory cell array 100, word lines WLk (k = 0 to m) are wired along the respective rows k of the nonvolatile memory cells Mkj (k = 0 to m, j = 0 to n). Here, the word line WLk corresponding to the row k is connected to the gates of the select transistors T1 and T2 of the nonvolatile memory cells Mkj (j = 0 to n) belonging to the row k.

  In the nonvolatile memory cell array 100, the bit line BLj (j = 0 to n) and the inverted bit line BLBj are arranged along each column j of the nonvolatile memory cells Mkj (k = 0 to m, j = 0 to n). (J = 0 to n) and source line SLj (j = 0 to n) are respectively wired. Here, the bit line BLj and the inverted bit line BLBj corresponding to the column j have one ends of the resistance change elements R1 and R2 of the nonvolatile memory cell Mkj (k = 0 to m) (in the example shown in FIG. A free layer of the resistance variable element R1 and a pinned layer of the resistance variable element R2) are connected to each other. Further, the sources of the select transistors T1 and T2 of the nonvolatile memory cell Mkj (k = 0 to m) are connected to the source SLj corresponding to the column j.

  The row decoder 200 decodes the row address of the nonvolatile memory cell to be accessed at the time of write access or read access to the nonvolatile memory cell array 100, and the row address of the word line WLk (k = 0 to m) is indicated. A row selection voltage for turning on the selection transistors T1 and T2 is output to the word line WLk of the row k.

  The column gate unit 400 includes a bit line column selection transistor CGj (j = 0 to n), an inverted bit line column selection transistor CGBj (j = 0 to n), and a source line column selection transistor CGSj (j = 0 to n). ). Here, the bit line column select transistors CGj (j = 0 to n) are respectively interposed between the data lines DL and the bit lines BLj (j = 0 to n). Further, the inverted bit line column select transistor CGBj (j = 0 to n) is interposed between the inverted data line DLB and the inverted bit line BLBj (j = 0 to n). The source line column select transistors CGSj (j = 0 to n) are respectively interposed between the global source line GSL and the source lines SLj (j = 0 to n). The gates of the bit line column select transistor CGj (j = 0 to n), the inverted bit line column select transistor CGBj (j = 0 to n), and the source line column select transistor CGSj (j = 0 to n). Are connected to column selection lines COLj (j = 0 to n), respectively.

  The column decoder 300 decodes a column address of a nonvolatile memory cell to be accessed at the time of write access or read access to the nonvolatile memory cell array 100, and selects a bit line column select transistor CGj (j = 0 to n), Among the inverted bit line column selection transistors CGBj (j = 0 to n) and the source line column selection transistors CGSj (j = 0 to n), the column selection transistors CGj, CGBj and CGSj of the column j indicated by the column address are turned on. The selection voltage is output to the column selection line COLj.

  The write driver 500 includes a three-state buffer that can take three states of a high level output, a low level output, and an output high impedance state. The write driver 500 applies a voltage having a polarity according to write data between the set of the data line DL and the inverted data line DLB and the global source line GSL at the time of write access. In read access, the write driver 500 applies a reference voltage of 0 V to the source line SL, separates the data line DL and the inverted data line DLB, and puts them in a floating state.

  At the time of read access, the sense amplifier 600 applies a voltage of 0.2 V to the bit line BLj and the inverted bit line BLBj connected via the data line DL and the inverted data line DLB according to the conditions of FIG. This circuit determines read data from a nonvolatile memory cell that is an access destination based on signals generated on the line DL and the inverted data line DLB. The output circuit 700 is a circuit that amplifies the output signal of the sense amplifier 600 and outputs it from a port (not shown).

  The write control circuit 800 is supplied with a write signal WE and input data Din. When the write signal WE is at the active level, the write control circuit 800 supplies the input data Din to the write driver 500 as write data.

  In the above configuration, at the time of write access, the write signal WE is set to the active level. Thereby, the write control circuit 800 supplies the input data Din to the write driver 500 as write data. If the write data is “0”, the write driver 500 outputs 1.2 V to the data line DL and the inverted data line DLB, and outputs 0 V to the global source line GSL. If the write data is “1”, the write driver 500 outputs 0 V to the data line DL and the inverted data line DLB, and outputs 1.2 V to the global source line GSL. The row decoder 200 outputs a row selection voltage = 1.2 V to the word line WLk corresponding to the row k indicated by the row address, and the selection transistors T1 and T2 of the nonvolatile memory cell Mkj (j = 0 to n) in the row k. Turn on. Further, the column decoder 300 decodes the column address, and among the column selection transistors CGj (j = 0 to n), CGB (j) (j = 0 to n), and CGS (j) (j = 0 to n). The column select transistors CGj, CGB (j) and CGS (j) of the column j indicated by the column address are turned on, the bit line BLj of the column j is set to the data line DL, the inverted bit line BLBj is set to the inverted data line DLB, and the source line SLj is connected to the global source line GSL.

  As a result, the resistance change elements R1 and R2 of the nonvolatile memory cell Mkj corresponding to the row k indicated by the row address and the column k indicated by the column address are connected between the data line DL and the inverted data line DLB and the global source line GSL. Is applied to write data to the resistance variable elements R1 and R2.

  On the other hand, at the time of read access, the write signal WE becomes an inactive level, and the write driver 500 sets the global source line GSL to 0 V and sets the data line DL and the inverted data line DLB to a floating state. In this state, the non-volatile memory cell Mkj corresponding to the row k indicated by the row address and the column j indicated by the column address is selected, and the resistance change element R1 of the non-volatile memory cell Mkj becomes the data line DL and the global source line GSL. The resistance variable element R2 is inserted between the inverted data line DLB and the global source line GSL. At this time, the sense amplifier 600 applies a bias of about 0.2 V to the data line DL and the inverted data line DLB, and differentially amplifies each voltage of the data line DL and the inverted data line DLB. A signal indicating the read data is output. The output circuit 700 amplifies the output signal of the sense amplifier 600 and outputs it as read data from the accessed non-volatile memory cell.

  As described above, according to the present embodiment, the access is performed by a simple operation of applying a voltage having a polarity corresponding to the write data between the set of the data line DL and the inverted data line DLB and the global bus source line GSL. Data can be written by changing the resistance values of the resistance variable elements R1 and R2 of the target nonvolatile memory cell in opposite directions. Therefore, a nonvolatile memory having a wide operation margin can be realized. Further, according to the present embodiment, a 1-bit nonvolatile memory cell can be configured by two transistors and two resistance variable elements. Then, as shown in FIG. 6, the nonvolatile memory cells are arranged in a matrix, the word lines WLk are wired along the row direction, and the bit lines BLj, the inverted bit lines BLBj, and the source lines SLj are aligned along the column direction. Thus, a nonvolatile memory cell array with a small area can be configured. Therefore, a nonvolatile memory cell with a small area can be realized.

  When the nonvolatile memory cell of the third embodiment (FIG. 5) is applied to the nonvolatile memory of the fourth embodiment (FIG. 6), the bit line BL and the inverted bit line of the nonvolatile memory cell arranged in the column direction. Since BLB is short-circuited via the resistance variable elements R1 and R2, the operation margin at the time of reading is affected. However, if the resistance difference between the variable resistance elements R1 and R2 is, for example, twice or more, if k = 1023 (that is, 1024 memory cells), then between the selected bit line BL and the inverted bit line BLB. Are selected even though they are connected by a resistance (R1 + R2) / 1023 in which resistance change elements R1 and R2 of 1023 nonvolatile memory cells excluding the selected nonvolatile memory cell are parallelized. Since a current difference determined by the ratio of the resistance values of the resistance change elements R1 and R2 of the nonvolatile memory cell can be obtained, read data can be sufficiently determined using a current sense amplifier (not shown). If the nonvolatile memory cell of FIG. 5 is used, a nonvolatile memory having a smaller area can be realized.

<Fifth Embodiment>
The present embodiment is an embodiment relating to the layout of the nonvolatile memory cell array in each of the above embodiments. FIG. 7 is a layout diagram of the nonvolatile memory cell array according to the present embodiment. 8 is a cross-sectional view taken along line AA ′ of FIG. 7, FIG. 9 is a cross-sectional view taken along line BB ′ of FIG. 7, FIG. 10 is a cross-sectional view taken along line CC ′ of FIG. It is D 'sectional view.

  As shown in FIGS. 8 to 11, in this embodiment, a trench isolation layer 2 is formed in a p-type semiconductor substrate 1 for isolating columns of nonvolatile memory cells. In the semiconductor substrate 1, n-type diffusion regions 3 and 4 that are sources or drains of the selection transistor T 1 and the selection transistor T 2 of the nonvolatile memory cell are formed in a region sandwiched between the trench isolation layers 2. ing.

  In this embodiment, a polysilicon wiring layer, a first metal layer M1, a second metal layer M2 as an upper layer, and a third metal layer M3 as an upper layer are used as the wiring layers. . In the layout example shown in FIG. 7, a plurality of word lines WLk made of polysilicon layers are wired along the row direction, and the bit lines BLj and inverted bit lines BLBj made of the first metal layer M1 along the column direction. A plurality of sets of source lines SLj formed of the third metal layer M3 are wired. In the example shown in FIG. 7, in the set of the bit line BLj, the inverted bit line BLBj, and the source line SLj, the source line SLj is located between the bit line BLj and the inverted bit line BLBj.

  In FIG. 7, a 1-bit nonvolatile memory cell is formed in a region surrounded by a broken line. The nonvolatile memory cell for one bit has first and second selection transistors T1 and T2 that are arranged in the row direction. In the case of a nonvolatile memory cell surrounded by a broken line, the select transistors T1 and T2 use the word line WL0 as a gate electrode, and use the diffusion regions arranged along the column direction with the word line WL0 interposed therebetween as sources and drains. . The source of the selection transistor T1 and the source of the selection transistor T2 are connected to the source line SL0 by the third metal layer M3 through the first metal layer, the second metal layer, and the interlayer contact.

  As shown in FIG. 8, the resistance variable elements R1 and R2 are placed on the first electrode connected to the second metal layer M2 via the second contact 9 and the second first metal layer M1. And a second electrode. When the resistance variable elements R1 and R2 are MTJ elements, the first electrode is, for example, a free layer, and the second electrode is, for example, a pinned layer. In this case, an equivalent circuit of the nonvolatile memory cell is as shown in FIG. As described above, the resistance change elements R1 and R2, which are MTJ elements, change their resistance values in different directions depending on the direction of current flowing between the first and second electrodes (free layer and pin layer). It is an element.

  In the nonvolatile memory cell surrounded by a broken line in FIG. 7, as shown in FIG. 8, the first electrode of the first resistance change element R1 is connected to the second contact 9, the second metal layer M2, and the second contact. 9 is connected to the bit line BL0 by the first metal layer M1. Further, as shown in FIG. 8, the second electrode of the first variable resistance element R <b> 1 is connected to the diffusion layer 3 via the first metal layer M <b> 1 and the first contact 6. The diffusion layer 3 to which the second electrode of the first variable resistance element R1 is connected is one of the diffusion layers 3 and 4 arranged along the column direction across the word line WL0 as shown in FIG. The diffusion layer 3 is the drain of the first selection transistor T1. 11 out of the diffusion layers 3 and 4 arranged along the column direction with the word line WL0 interposed therebetween in FIG. 11, is the source of the first selection transistor T1, and as shown in FIG. The contact 6, the first metal layer M 1, the second contact 9, the second metal layer M 2, and the third contact 11 are connected to the source line SL 0 by the third metal layer M 3.

  On the other hand, as shown in FIG. 8, the second resistance change element R2 of the nonvolatile memory cell surrounded by the broken line in FIG. 7 has the second electrode on the inverted bit line BLB0 formed by the first metal layer M1. It is directly connected to the inverted bit line BLB0. As shown in FIGS. 8 to 10, the first electrode of the variable resistance element R2 includes the second contact 9, the second metal layer M2, the second contact 9, the first metal layer M1, and the first contact. 6 is connected to the diffusion layer 3 (FIG. 10) of the diffusion layers 3 and 4 arranged in the column direction with the word line WL0 interposed therebetween. The diffusion layer 3 is the drain of the second selection transistor T2. In FIG. 10, among the diffusion layers 3 and 4 arranged in the column direction with the word line WL0 interposed therebetween, the diffusion layer 4 is the source of the second selection transistor T2, and includes the first contact 6 and the first metal layer. It is connected to the source line SL0 by the third metal layer M3 through M1, the second contact 9, the second metal layer M2, and the third contact 11.

  The above is the configuration of the nonvolatile memory cell for 1 bit. In the present embodiment, the nonvolatile memory cells are arranged in a matrix as shown in FIG. In this embodiment, the sources of the first select transistors T1 of the adjacent two rows of nonvolatile memories share the same diffusion region 4 (see FIG. 11), and the second adjacent rows of the nonvolatile memories 2 Each source of the select transistor T2 shares the same diffusion region 4 (see FIG. 10). Therefore, according to this embodiment, the size of the nonvolatile memory cell array in the column direction can be reduced.

  As described above, according to the present embodiment, a small-sized nonvolatile memory cell array can be realized by arranging the elements as shown in FIGS.

<Other embodiments>
Although the first to fifth embodiments of the present invention have been described above, other embodiments are conceivable for the present invention. For example, in the fourth embodiment, the nonvolatile memory cell Mkj having the configuration of the first embodiment (FIG. 1) is used. However, the configuration of the second embodiment (FIG. 3) or the third embodiment (FIG. You may use the thing of the structure of 5).

T1, T2, T... Selection transistor, R1, R2... Variable resistance element, BL, BLj (j = 0 to n)... Bit line, BLB, BLBj (j = 0 to n). , WL, WLk (k = 0 to m)... Word line, SL, SLj (j = 0 to n)... Source line, 100... Nonvolatile memory cell array, Mkj (k = 0 to m, j = 0) ˜n)... Nonvolatile memory cell 200... Row decoder 300... Column decoder 400. Column gate portion CGj (j = 0 to n). 0 to n) ... inverted bit line column select transistor, CGSj (j = 0 to n) ... source line column select transistor, DL ... data line, DLB ... inverted data line, GSL ... global source line , 800 …… Writing system Circuit, 500 ...... write driver, 600 ...... sense amplifier, 700 ...... output circuit.

Claims (12)

A first variable resistance element and a first select transistor interposed in series between the bit line and the source line;
A second variable resistance element and a second selection transistor interposed in series between the inverted bit line and the source line;
The first and second selection transistors are switched on / off by a selection voltage supplied via a word line,
The first and second variable resistance elements have respective resistance values in the first direction and in the opposite direction when currents respectively flowing from the bit line and the inverted bit line to the source line are passed. Each of the resistance values changes in the second direction and the first direction when currents respectively changing in the second direction and flowing from the source line to the bit line and the inverted bit line are supplied to the second direction and the first direction, respectively. A nonvolatile memory cell, which is a variable resistance element that changes.   2. The nonvolatile memory cell according to claim 1, wherein the first and second variable resistance elements are provided on the bit line side and the inverted bit line side, respectively.   2. The nonvolatile memory cell according to claim 1, wherein the first and second variable resistance elements are respectively provided on the source line side. A non-volatile memory having a non-volatile memory cell array comprising a plurality of the non-volatile memory cells according to any one of claims 1 to 3,
At the time of data writing, a selection voltage for turning on the first and second selection transistors is supplied to the nonvolatile memory cell to be accessed, and the set between the bit line and the inverted bit line and the source line are supplied. Apply a voltage with polarity according to the write data,
At the time of data reading, a reference voltage is applied to the source line, a selection voltage for turning on the first and second selection transistors is supplied to the nonvolatile memory cell to be accessed, and the nonvolatile memory to be accessed is A non-volatile memory, characterized in that read data from the non-volatile memory is determined based on signals generated on a connected bit line and an inverted bit line. A first resistance variable element interposed between the bit line and the common node;
A second variable resistance element interposed between the inverted bit line and the common node;
A selection transistor that is inserted in series between the common node and the source line, and that is switched on / off by a selection voltage supplied via a word line;
The first and second variable resistance elements have respective resistance values in the first direction and in the opposite direction when currents respectively flowing from the bit line and the inverted bit line to the source line are passed. Each of the resistance values changes in the second direction and the first direction when currents respectively changing in the second direction and flowing from the source line to the bit line and the inverted bit line are supplied to the second direction and the first direction, respectively. A nonvolatile memory cell, which is a variable resistance element that changes. A non-volatile memory having a non-volatile memory cell array comprising a plurality of the non-volatile memory cells according to claim 5,
At the time of data writing, a selection voltage for turning on the selection transistor is supplied to the nonvolatile memory cell to be accessed, and the polarity according to the write data between the set of the bit line and the inverted bit line and the source line Apply a voltage of
At the time of data reading, a reference voltage is applied to the source line, a selection voltage for turning on the selection transistor is supplied to a nonvolatile memory cell to be accessed, and a bit line connected to the nonvolatile memory to be accessed is inverted. A non-volatile memory, wherein read data from the non-volatile memory is determined based on a signal generated in a bit line. A nonvolatile memory having a nonvolatile memory cell array in which a plurality of nonvolatile memory cells are arranged in a matrix,
The nonvolatile memory cell array includes:
A plurality of word lines respectively wired for each row of the matrix of the plurality of nonvolatile memory cells;
A plurality of bit lines respectively wired for each column of the matrix of the plurality of nonvolatile memory cells;
A plurality of inverted bit lines respectively wired for each column of the matrix of the plurality of nonvolatile memory cells;
A plurality of source lines wired for each column of the matrix of the plurality of nonvolatile memory cells,
Each of the plurality of nonvolatile memory cells includes:
First and second variable resistance elements;
ON / OFF is switched by a row selection voltage supplied via the word line of each row to which the first variable resistance element is connected between the bit line and source line of each column to which the column belongs. And switch means for connecting the second variable resistance element between the inverted bit line and the source line of the column to which each belongs,
The first and second variable resistance elements have respective resistance values in the first direction and in the opposite direction when currents respectively flowing from the bit line and the inverted bit line to the source line are passed. Each of the resistance values changes in the second direction and the first direction when currents respectively changing in the second direction and flowing from the source line to the bit line and the inverted bit line are supplied to the second direction and the first direction, respectively. Change,
The nonvolatile memory is
A row selection voltage is generated to turn on the switch means of the nonvolatile memory cell to be accessed, and at the time of write access, between the bit line and inverted bit line pair of the column to which the nonvolatile memory cell belongs and the source line Applying a write voltage having a polarity according to the write data, and at the time of reading, determining the read data from the nonvolatile memory cell based on the signals generated on the bit line and the inverted bit line of the column to which the nonvolatile memory cell belongs Nonvolatile memory characterized by. A row decoder for outputting a row selection voltage for turning on the switch means to a word line corresponding to a row indicated by a row address among the plurality of word lines;
A plurality of bit line column selection switches respectively inserted between a data line and a plurality of bit lines corresponding to each column of the matrix of the plurality of nonvolatile memory cells; an inverted data line; and the plurality of nonvolatile memories A plurality of inverted bit line column selection switches each inserted between a plurality of inverted bit lines corresponding to each column of the matrix of cells, and each column of a matrix of global source lines and the plurality of nonvolatile memory cells A column gate portion having a plurality of source line column selection switches respectively inserted between a plurality of source lines corresponding to
Of the plurality of bit line column selection switches, the plurality of inverted bit line column selection switches, and the plurality of source line column selection switches, bit line column selection switches corresponding to columns indicated by column addresses, and inverted bit line columns A column decoder for outputting a column selection voltage for turning on the selection switch and the source line column selection switch;
A write driver that applies a write voltage having a polarity corresponding to write data between the set of the data line and the inverted data line and the global source line during write access;
The sense amplifier according to claim 7, further comprising: a sense amplifier that determines read data from a nonvolatile memory cell that is an access destination based on a signal generated in the data line and the inverted data line during read access. Non-volatile memory. A non-volatile memory cell array in which a plurality of non-volatile memory cells are arranged in a matrix,
A plurality of word lines respectively wired for each row of the matrix of the plurality of nonvolatile memory cells;
A plurality of bit lines respectively wired for each column of the matrix of the plurality of nonvolatile memory cells;
A plurality of inverted bit lines respectively wired for each column of the matrix of the plurality of nonvolatile memory cells;
A plurality of source lines wired for each column of the matrix of the plurality of nonvolatile memory cells,
Each nonvolatile memory cell
First and second select transistors arranged along the row direction, each of which has the word line as a gate electrode and each diffusion region arranged along the column direction across the word line as a source and a drain First and second select transistors, each source connected to a source line of a column to which the nonvolatile memory belongs,
First and second variable resistance elements having first and second electrodes, respectively, whose resistance values change in different directions depending on the direction of current passed between the first and second electrodes. And
The first electrode of the first resistance change element is connected to a bit line of a column to which the nonvolatile memory belongs, and the second electrode of the first resistance change element is the first select transistor. A second electrode of the second variable resistance element is connected to an inverted bit line of a column to which the nonvolatile memory belongs, and a first electrode of the second variable resistance element is A nonvolatile memory cell array connected to the drain of the second selection transistor.   In each column of the nonvolatile memory cells, the bit line and the inverted bit line occupy left and right positions of the nonvolatile memory cell along the row direction, and the source line includes the bit line and the inverted bit. 10. The nonvolatile memory cell array according to claim 9, occupying a position between the lines. The nonvolatile memory cell array includes, as wiring layers, a polysilicon wiring layer, a first metal layer, an upper second metal layer, and an upper third metal layer.
The plurality of word lines are constituted by a polysilicon wiring layer,
The plurality of bit lines and the plurality of inverted bit lines are constituted by a first metal layer,
The plurality of source lines are constituted by a third metal layer,
The first electrode of the first variable resistance element is connected to the bit line that is the first metal layer via a second metal layer, and the second electrode of the first variable resistance element is Connected to the drain of the first select transistor through a first metal layer;
The second electrode of the second variable resistance element is directly connected to the inverted bit line, which is a first metal layer, and the first electrode of the second variable resistance element includes a second metal layer and Connected to the drain of the second select transistor through a first metal layer;
11. The nonvolatile memory according to claim 9, wherein each source of the first and second selection transistors is connected to the source line through a first metal layer and a second metal layer, respectively. Memory cell array.   Each source of the first selection transistors of two adjacent rows of nonvolatile memory shares the same diffusion region, and each source of the second selection transistor of two adjacent rows of nonvolatile memory shares the same diffusion region The volatile memory cell array according to any one of claims 9 to 11, wherein the volatile memory cell array is provided.

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