JP5227133B2 - Semiconductor memory device - Google Patents

Description

  The present invention relates to a semiconductor memory device, and more particularly to a technique that is effective when applied to a read or write control method that takes into account the temperature characteristics of a memory cell using magnetoresistance change.

  An MRAM (Magnetoresistive Random Access Memory) using a magnetoresistive change, which is one of nonvolatile memories, is a RAM that can operate at high speed and can be rewritten practically infinitely.

  For example, Japanese Patent Laying-Open No. 2005-116923 (Patent Document 1) discloses a nonvolatile magnetic memory cell including a spin torque magnetization switching layer and a tunnel magnetoresistive film on a C-MISFET.

Also, 2005, IEDM, Tec. Dig. Pp. 473-476 (Non-Patent Document 1) discloses a spin-injection RAM (SPRAM (Spin Transfer Torque) using a spin-injection magnetization reversal technique that changes the spin direction of a free layer by flowing a current perpendicularly to a tunnel magnetoresistive element. RAM)) has been reported.
JP 2005-116923 A 2005 International Electron Device Meeting Technical Digest pp. 473-476 (2005 International Electron Devices Meeting Technical Digest pp.473-476)

  A conventional MRAM memory cell includes a tunnel magnetoresistive element, a select transistor, a word line, a bit line, and a source line. As shown in FIG. 27, the tunnel magnetoresistive element TMR has at least two magnetic layers, one of which is a fixed layer PL whose spin direction is fixed, and the other is whose spin direction is relative to the fixed layer PL. It consists of a free layer FL that takes two states, a parallel state and an antiparallel state. There is a tunnel barrier film TB between these films. Information is stored in the direction of spin of the free layer FL, and the electric resistance of the tunnel magnetoresistive element TMR becomes a high resistance state in the antiparallel state and becomes a low resistance state in the parallel state. In the read operation, the magnitude of the resistance of the tunnel magnetoresistive element TMR is read. On the other hand, in the write operation, current is passed through the word line and the bit line, and the spin direction of the free layer FL is controlled by a synthetic magnetic field excited in the tunnel magnetoresistive element TMR at that time. However, this writing method has a problem that the tunnel magnetoresistive element TMR is scaled (miniaturized) and the magnitude of the magnetic field required for writing increases, so that the currents flowing through the word lines and bit lines also increase.

  On the other hand, for example, in the spin injection RAM described in Non-Patent Document 1, as shown in FIG. 28, a vertical current is allowed to flow through the fixed layer PL, the tunnel barrier film TB, and the free layer FL. A writing method capable of controlling the spin direction of the layer FL has been proposed. This writing method is excellent in scalability because the current required for writing is proportional to the size of the tunnel magnetoresistive element TMR and the writing current can be reduced together with scaling. For example, MgO is used as the tunnel barrier film TB.

  However, in the spin injection RAM, the write characteristics, specifically, the current and time (pulse width) necessary to invert information, and the read characteristics, specifically, the current necessary to read information Time (pulse width) depends on temperature. Therefore, it is necessary to control writing and reading in consideration of this temperature-dependent characteristic.

  Furthermore, as a feature of this spin injection RAM, the write current decreases as scaling progresses. At this time, a problem described below occurs with respect to the read current. That is, in order to avoid read disturb (a phenomenon in which the state of the memory cell is affected by the read current), the read current is generally set sufficiently smaller than the write current. However, when the write current is reduced with scaling, the read current is also reduced. Although it is generally good, for example, if this current is 10 μA or less, high-speed read operation becomes difficult.

  In order to take advantage of the characteristics of the memory cell of the spin injection RAM, which has excellent scalability, it is necessary to solve the above problems. At the same time, it is necessary to consider the temperature characteristics of writing and reading.

  An object of the present invention is to avoid a read disturb and perform a read operation at high speed in a semiconductor memory device having a non-volatile memory composed of memory cells using magnetoresistive changes even if the scaling of the memory cell is advanced. The aim is to provide a technology that can

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in this application, typical embodiments will be briefly described as follows.

  In this embodiment, a plurality of word lines, a plurality of bit lines wired in a direction orthogonal to the plurality of word lines, and a predetermined intersection of the plurality of word lines and the plurality of bit lines are arranged at a fixed layer. A semiconductor memory device having a non-volatile memory constituted by a plurality of memory cells including a tunnel magnetoresistive element in which a tunnel barrier film and a free layer are stacked and a MIS transistor. The memory cell information write operation is performed according to a desired first current value and first time, and the memory cell information read operation is performed by a pulse generation circuit including a temperature sensor that detects the temperature of the memory cell. This is performed according to the second current value and the second time set according to the operating temperature. For example, the first current value and the first time are equal to or larger than the current value and time at the lowest temperature at which the direction of electron spin of the free layer guaranteed in the operating temperature range of the memory cell is reversed. The second current value and the second time are respectively set to values smaller than the current value and the time at the highest temperature at which the direction of electron spin of the free layer guaranteed in the operating temperature range of the memory cell is reversed, for example. Is done.

  In another embodiment, a plurality of word lines, a plurality of bit lines wired in a direction orthogonal to the plurality of word lines, and a plurality of word lines and a plurality of bit lines are arranged at predetermined intersections. , A semiconductor memory device having a nonvolatile memory including a plurality of memory cells including a tunnel magnetoresistive element and a MIS transistor in which a fixed layer, a tunnel barrier film, and a free layer are stacked. The information write operation of the memory cell is performed by the first current value and the first time set to values that can reverse the direction of the electron spin of the free layer. The second current value is the same as the current value and the second time is the same as the first time. After the read operation, the information destroyed by the read operation is rewritten, and the first and second current values and the first and first current values are rewritten. The two hours are set according to the operating temperature of the memory cell by a pulse generation circuit including a temperature sensor that detects the temperature of the memory cell.

  Among the inventions disclosed in the present application, effects obtained by one embodiment of a representative one will be briefly described as follows.

  Even if the scaling of the memory cell progresses, read disturb can be avoided and the read operation can be performed at high speed.

  In the following embodiments, when necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other, and one is the other. There are some or all of the modifications, details, supplementary explanations, and the like.

  Further, in the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), especially when clearly indicated and when clearly limited to a specific number in principle, etc. Except, it is not limited to the specific number, and may be more or less than the specific number. Further, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Needless to say. Similarly, in the following embodiments, when referring to the shapes, positional relationships, etc. of the components, etc., the shapes are substantially the same unless otherwise specified, or otherwise apparent in principle. And the like are included. The same applies to the above numerical values and ranges.

  In all the drawings for explaining the following embodiments, components having the same function are denoted by the same reference numerals in principle, and repeated description thereof is omitted. Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
The memory cell using the magnetoresistive element according to the first embodiment includes a tunnel magnetoresistive element in which a fixed layer, a tunnel barrier film, and a free layer are stacked, and a MIS (Metal Insulator Semiconductor) transistor. The fixed layer is a magnetic material in which the direction of electron spin is fixed in a predetermined direction, and the free layer is a magnetic material in which the direction of electron spin is either parallel or antiparallel to the direction of electron spin of the fixed layer. Is the body. The information writing operation of the memory cell is performed by a desired first current value and a first time that can reliably control the direction of electron spin in the free layer. The first current value and the first time are set constant regardless of the operating temperature of the memory cell. On the other hand, the reading operation of the memory cell information is performed by the second current value and the second time. The second current value and the second time are respectively set to values smaller than the current value and time at the maximum temperature at which the direction of electron spin of the free layer guaranteed in the operating temperature range of the memory cell is reversed. It is set according to the operating temperature of the memory cell by a pulse generation circuit (for example, a pulse generation circuit shown in FIG. 8 described later) including a temperature sensor for detecting the temperature of the cell. Accordingly, since appropriate conditions (current value and time) can be set for the write operation and the read operation, reliable information writing and high-speed information reading that avoids read disturb can be performed. it can.

  Hereinafter, specific examples (first to fourth examples) of the operation method of the memory cell using the magnetoresistance change according to the first embodiment will be described in detail.

  First, a first example of the operation method of the memory cell according to the first embodiment will be described with reference to FIG. FIG. 1 is a graph illustrating the relationship between a write current or read current flowing through a memory cell and a pulse width. The vertical axis in FIG. 1 indicates the current value flowing through the memory cell during writing or the current value flowing through the memory cell during reading, and the horizontal axis indicates the time during which the current flows during writing or reading, that is, the pulse width. Here, the two curves (a) and (b) indicated by the solid lines show the relationship between the current value and the pulse width necessary for writing at low and high temperatures, respectively, of the memory cell used in the first example. . These are characteristics common to the structure of the tunnel magnetoresistive element TMR shown in FIG. 28 and various modifications thereof. Curve (a) shows the characteristics at low temperature, and curve (b) shows the characteristics at high temperature. When compared with the same pulse width, the current value at low temperature is larger than the current value at high temperature. This low temperature is the same as or lower than the minimum temperature guaranteed in the operating temperature range of the memory cell indicated by the product specification, for example. This high temperature is the temperature of the memory cell indicated by the product specification, for example. The same or higher temperature guaranteed in the operating temperature range. In both curves, the required current value increases as the pulse width decreases. This increase becomes significant when the pulse width becomes shorter than 10 ns.

  The memory cell having such characteristics has the following characteristics in the first example. First, as a first feature, the current value flowing through the memory cell during reading and the current value flowing through the memory cell during writing are set to the same current value A. This current value A is a current value larger than the write current value at the low temperature indicated by the curve (a) in the desired write pulse width P1 (for example, a pulse width of 10 ns or more). Therefore, at the time of writing, a sufficient amount of current is applied to the memory cell by the current value A and the pulse width P1. Next, as a second feature, the read pulse width P2 is set to a pulse width (pulse width at which writing does not occur) shorter than the pulse width at a high temperature indicated by the curve (b). Thereby, at the time of reading, the amount of current applied to the memory cell is reduced, and reading disturb can be suppressed to a small value. Also, by selecting the read pulse width P2, the direction of electron spin in the free layer is not reversed, but the amount of current necessary for reading can be obtained, so that a read operation can be performed at high speed.

  As described above, by setting the current value A, the write pulse width P1, and the read pulse width P2 at the time of writing and reading, in the first example, stable writing and reading are performed in the entire temperature range of the product specification. Can do.

  Next, a second example of the operation method of the memory cell according to the first embodiment will be described with reference to FIG. FIG. 2 is a graph illustrating the relationship between the write current or read current flowing through the memory cell and the pulse width, as in FIG. 1 described above.

  The writing in the second example is performed with the current value A and the writing pulse width P1 as in the first example. The current value A and the write pulse width P1 are larger than the curve (a) at the upper right of the plane divided by the curve (a), that is, at a certain pulse width, with respect to the curve (a) indicating the write characteristics at low temperature. It is a current value, and at a certain current value, the pulse width is larger than that of the curve (a). On the other hand, reading according to the second example is performed with the current value B and the writing pulse width P2. The current value B and the write pulse width P2 are smaller than the curve (b) at the lower left of the plane divided by the curve (b), that is, at a certain pulse width, with respect to the curve (b) indicating the write characteristics at high temperature. It is a current value, and the pulse width is smaller than the curve (b) at a certain current value.

  The low temperature and high temperature shown in FIG. 2 are also values related to the minimum temperature and the maximum temperature guaranteed in the operating temperature range of the memory cell shown in the product specifications, for example. Therefore, according to the second example, by setting the current value B at the time of reading smaller than the current value A at the time of writing, a state in which the read disturb is smaller than that of the first example described above can be realized, and the product specification Stable writing and reading can be performed in all temperature ranges. With this feature, a highly reliable semiconductor memory device with small disturbance and stable operation can be realized.

  Next, a third example of the operation method of the memory cell according to the first embodiment will be described with reference to FIG. FIG. 3 is a graph illustrating the relationship between the write current or read current flowing through the memory cell and the pulse width, as in FIG. 1 described above. The difference from the first example and the second example described above is that the write pulse width and the read pulse width are equal.

  In the third example, the write pulse width P1 and the read pulse width P2 are equal to each other, writing is performed with the current value A, and reading is performed with the current value B. The current value A is larger than the curve (a) indicating the characteristics at low temperature, which is inherently larger than the curve (b) indicating the characteristics at high temperature, so that reliable writing can be performed in all temperature ranges. It can be carried out. The current value B is smaller than the curve (b) showing the characteristics at high temperature, which is inherently smaller than the curve (a) showing the characteristics at low temperature, so that the readout disturbance is small in all temperature ranges. Reading can be performed. Thus, in the third example, writing and reading can be stably performed with one kind of pulse width in a wide temperature range.

  Next, a fourth example of the operation method of the memory cell according to the first embodiment will be described with reference to FIG. FIG. 4 is a graph for explaining the relationship between the write current or read current flowing in the memory cell and the pulse width, as in FIG. 1 described above. The difference from the first example and the second example described above is that the write pulse width and the read pulse width are set to the same value, and the current value at the time of reading is set according to the operating temperature.

  In the fourth example, the write pulse width P1 and the read pulse width P2 are equal. The write pulse width P1 is a pulse width necessary for writing at the current value A in the curve (a) showing the characteristics at low temperature, as in the first example. On the other hand, the read pulse width P2 is equal to the write pulse width P1, but the current value at the time of reading is changed according to the temperature at the time of reading. That is, when the reading time is relatively low, the current value is B1, which is smaller than the curve (a) indicating the characteristics at low temperature and larger than the curve (b) indicating the characteristics at high temperature. When the reading time is relatively high, the current value is B2, which is smaller than the curve (b) indicating the characteristics at high temperature.

  Even if the maximum temperature guaranteed in the operating temperature range of the memory cell indicated by the product specifications is the characteristic indicated by the curve (b), the actual reading operation temperature of the memory cell is indicated by the curve (b). May be lower. In such a case, the current value and read pulse width at the time of reading can be set with reference to a temperature lower than the characteristic at the low temperature indicated by the curve (b) (actual memory cell read operation temperature). . As described above, in the fourth example, it is possible to obtain an optimum read current in which read disturb is suppressed at the current temperature.

  Next, a memory cell operation circuit using magnetoresistance change according to the first embodiment will be described.

  FIG. 5 shows a main configuration example of the memory chip circuit included in the semiconductor memory device according to the first embodiment. In this figure, the word driver is selected by the address buffer and decoder based on the address signal Ai. Each memory cell SC1, SCn is controlled by a word driver. Memory cells SC1 and SCn are composed of select MIS transistors M1 and Mn and tunnel magnetoresistive elements T1 and Tn, and are connected to word lines W1 and Wn, bit line BL, and source line SL. Reference sign PC is a drive signal for a MIS transistor that connects the bit line BL and the source line SL to the ground potential Vs.

  The write circuit includes a latch circuit composed of two stages of inverter circuits that output latch outputs LTP and LTA. The information of this latch is set by the column selection signal Y1 and the first write control signal power WE in accordance with information from the input / output line I / O. When the MIS transistor connected to the second write control signal power WE1 is turned on, the bit line BL and the source line SL are electrically connected to the high potential voltage Vd or the low potential voltage Vs depending on the values of the latch outputs LTP and LTA. Will be connected. At this time, when the bit line BL is electrically connected to the high potential voltage Vd (when the latch output LTP is high potential and the latch output LTA is low potential), the source line SL is electrically connected to the low potential voltage Vs. Connected. The potential of the latch circuit is set higher than the high potential voltage Vd.

  At the time of reading, the signal of the bit line BL precharged by the MIS transistor driven by the signal PP1 is read into the sense amplifier AMP by the read control signals RE1 and RE, and the value is compared with the reference voltage VR to thereby read from the memory cell. The signal of the sense amplifier AMP can be output to the input / output line I / O through the MIS transistor controlled by the column selection signal Y1. The input / output line I / O is connected to the signal terminal DOj / DIj via the input / output circuit.

  The symbol Sk is a signal for designating functions such as reading and writing, and may be a dedicated signal or may be combined with other signals, which are decoded and set by a command decoder. In the first embodiment, there are a write pulse generation circuit and a read pulse generation circuit, and the necessary pulse width is generated in the first embodiment. These circuits are controlled by a control circuit from a command decoder. The current required for writing is controlled by the word line voltage, the bit line voltage, and the source line voltage. FIG. 5 shows a word line voltage generation circuit, in which a plurality of voltages are supplied as necessary. Generate and switch according to operation. This control is also performed by a control circuit controlled by a command decoder. By using the circuit configuration shown in FIG. 5, the memory cell according to the first embodiment and the memory cell according to another embodiment described later can be operated.

  6 and 7 are operation timing charts for explaining an operation example of the memory chip circuit of FIG. 5 described above. FIG. 6 shows an example of the read operation timing, and FIG. 7 shows an example of the write operation timing.

  As shown in FIG. 6, initially, the drive signal PC is at a high level, and the bit line BL and the source line SL are grounded to the low potential voltage Vs. Next, the drive signal PC becomes low level, the signal PP1 becomes low level, the read control signal RE1 becomes high level, and the source line SL continues to be grounded to the low potential voltage Vs. Precharge starts to BL. The bit line BL is precharged from the high level of the read control signal RE1 to a voltage that drops the threshold voltage of the MIS transistor.

When the precharge is completed, the signal PP1 returns to the high level, the word line W1 is selected and becomes the high level. This level is also determined by the value of current (current value A or current value B) that flows through the selection MIS transistor M1 of the memory cell SC1. The value of the current is also related to the potential of the bit line BL. This word line W1 is at a high level only during the period indicated by the symbol _tP2 , and this is the read pulse width P2. As a result, a potential corresponding to the stored information of the memory cell SC1 appears on the bit line BL. That is, if the resistance of the tunnel magnetoresistive element T1 in the memory cell SC1 is high, the potential change of the bit line BL, which corresponds to the information “0” here, becomes small. On the other hand, if the resistance of the tunnel magnetoresistive element T1 is low, the potential change of the bit line BL, which corresponds to the information “1” here, becomes large. These two states are shown together in the figure.

  Even if the word line W1 is closed, these two states remain in the bit line BL. This voltage and the reference voltage VR are detected by the sense amplifier AMP. The value of the reference voltage VR is an intermediate value between two types of bit line voltages corresponding to information “0” and information “1” as shown in FIG. Thereby, the state of the memory cell can be read by the sense amplifier AMP. When the column selection signal Y1 is switched, the signal of the sense amplifier AMP is output to the input / output line I / O. Thereafter, the drive signal PC and the read control signals RE and RE1 are switched to return to the initial state. Thus, in the first embodiment, reading using the pulse width P2 can be performed with a desired current value.

As shown in FIG. 7, information writing is performed by fetching write data from the input / output line I / O. It is assumed that the input / output line I / O is initially at a low level and is at a high level as write data. This is taken into the latch circuit by setting the column selection signal Y1 and the first write control signal power WE to a high level. As a result, the latch output LTP is switched from the low level to the high level, and the latch output LTA is switched from the high level to the low level. Since the drive signal PC at this time is at a high level, both the bit line BL and the source line SL are at the low potential voltage Vs. When the second write control signal power WE1 is switched, the source line SL can be electrically connected to the high potential voltage Vd, and the bit line BL can be electrically connected to the low potential voltage Vs. Thereafter, the drive signal PC becomes a low potential, and the bit line BL and the source line SL are electrically disconnected from the low potential voltage Vs. Thereafter, the second write control signal power WE1 becomes high level, and the source line SL is electrically connected to the high potential voltage Vd, and the bit line BL is electrically connected to the low potential voltage Vs. Here, the word line W1 is switched, and a write current is supplied to the memory cell. The time (pulse width) during which the word line W1 is at the high level is the symbol t _P1 shown in FIG. 7, and this is the write pulse width P1. The levels of the word line W1, the source line SL, and the bit line BL are set so that the current flowing through the tunnel magnetoresistive element T1 of the memory cell SC1 becomes the current value A. In the first embodiment, in this way, writing using the pulse width P1 can be performed with a desired current value.

  Next, a method for producing a voltage and a pulse width according to temperature will be described with reference to an example of a pulse generation circuit diagram for generating a pulse width according to temperature according to the first embodiment shown in FIG.

  As shown in FIG. 8, the pulse generation circuit is a circuit that determines from which position in the delay circuit row the pulse is extracted based on the result of the temperature sensor. The temperature sensor has a configuration in which a tunnel magnetoresistive element TMR in an antiparallel state and a resistor R1 for taking out a voltage that is easy to detect are connected in series between a high potential Vdd and a low potential Vss. Output voltage. The tunnel magnetoresistive element TMR may be embedded in a normal memory cell array as a dummy cell. The voltage corresponding to this temperature and the output of the reference voltage generation circuit Vref are input to the amplifier AM1. The output O is input to a conversion circuit ADCConv that converts an analog signal into a digital signal. The output of the conversion circuit ADCConv is the output BO.

  On the other hand, there is a circuit in which a plurality of delay circuits DLY are connected in series and a necessary delay time can be taken out by a selector, and each delay circuit DLY is adjusted by a signal VT1 that reduces the influence of temperature. Although a generation circuit for VT1 is not shown, it includes a temperature sensor using a MIS transistor constituting the delay circuit DLY and a circuit for generating a voltage capable of controlling the current based on the result. The output BO of the conversion circuit ADCConv is input to a selector that determines from which position in the delay circuit row the signal is extracted. The output BO of the conversion circuit ADCConv changes depending on the result of the temperature sensor. For example, the output BO is 3-bit information, and thus, a number of delay circuits DLY (four delay circuits are shown as an example in FIG. 8). A signal corresponding to the temperature can be taken out from the eight positions of the delay circuit array configured as described above. A timing signal is generated from this signal.

  FIG. 9 is a schematic diagram for explaining the temperature characteristics of the tunnel magnetoresistive element. The horizontal axis in FIG. 9 is the current flowing through the tunnel magnetoresistive element, and the vertical axis is the resistance of the tunnel magnetoresistive element when the current is passed. The solid line shows the characteristics at low temperature, and the broken line shows the characteristics at high temperature.

  When the initial state is a parallel state (the spin direction of the fixed layer PL and the spin direction of the free layer FL are the same), the tunnel magnetoresistive element TMR at this time has a low resistance, and its resistance value is shown in FIG. This is the resistance range Rp shown. When the current is increased in the right direction in this figure, when the amount of current in this direction becomes larger than a certain current value, the state of the tunnel magnetoresistive element TMR changes and becomes an antiparallel state (the spin of the fixed layer PL). The direction and the spin direction of the free layer FL are opposite). In this state, the resistance of tunneling magneto-resistance element TMR is high, and the resistance value is in the resistance range Rap shown in FIG. After this high resistance state is reached, the flowing current is increased in the opposite direction. When the amount of current in the reverse direction becomes larger than a certain current value, the state of tunnel magnetoresistive element TMR changes and returns to the original parallel state.

  This characteristic varies with temperature. First, the resistance value Rap in the anti-parallel state, which is a high resistance state, is large at low temperatures but small at high temperatures. In addition, the magnitude of the current at which the state is switched is large at low temperatures but small at high temperatures in absolute values in the respective directions. On the other hand, the resistance value Rp in the parallel state, which is a low resistance state, hardly depends on the temperature. In the first embodiment, the temperature characteristics of the tunnel magnetoresistive element TMR are utilized.

(Embodiment 2)
The operation method of the memory cell using the magnetoresistance change according to the second embodiment will be described.

  FIG. 10 is a graph for explaining the relationship between the write current and the read current and the processing rule for producing the memory cell. The horizontal axis shows the processing rule for manufacturing the memory cell, and the processing rule becomes smaller as it goes to the right, that is, the state where scaling has advanced. For example, in the 90 nm rule, the planar dimension of the tunnel magnetoresistive element can be 90 nm × 180 nm. The processing size of the MIS transistor and the processing size of the tunnel magnetoresistive element may be different. For example, even in a memory cell using a MIS transistor with a rule of 90 nm, the planar dimension of the tunnel magnetoresistive element may be 180 nm × 180 nm.

  As shown in FIG. 10, in the spin injection RAM, the current required for writing decreases as the scaling progresses and the memory cell becomes fine. On the other hand, the read current generally needs to be smaller than the write current in order to avoid read disturb. However, this causes a problem that the value of the read current becomes too small in a region where the write current is small. Therefore, in the second embodiment, reading is performed with the same current as writing, and unlike the first embodiment described above, destructive reading and rewriting each time reading is performed. As a result, the influence of the read disturb can be extremely reduced.

  FIG. 11 is an operation timing chart for explaining the operation of the memory cell according to the second embodiment. FIG. 11 shows an operation example of the word line and the bit line / source line.

  As shown in FIG. 11, destructive read and rewrite are performed with a single word line selection. Further, the driving time (pulse width) of the word line can be set as the write pulse width. Thus, even when the read operation and the write operation are symmetric and the read current is large, the read operation is hardly affected.

  When burst reading is performed, this rewriting can be performed during the operation of outputting data from the sense amplifier to the outside of the chip. With this method, the rewrite time can be completely invisible. This is because, for example, the bit line can be amplified to a large amplitude for rewriting in DRAM (Dynamic RAM), and then the speed can be increased to the same level as that required for transition to an intermediate potential. Speed can be realized.

  12A and 12B show a circuit diagram of the memory cell according to the second embodiment and a schematic diagram of its current operation waveform, respectively. In FIG. 12B, the vertical axis represents the current flowing through the tunnel magnetoresistive element, and the horizontal axis represents time.

  As shown in FIG. 12B, when the current value K1 is applied, the amount of current does not change during the first drive time t1, but then decreases to the current value K2. This indicates that writing (destruction of information) occurred and the resistance changed when the current value decreased. In other words, the state of the tunnel magnetoresistive element does not change during the first drive time t1, and a current corresponding to this state flows. Therefore, if read information is taken out in the region of the driving time t1, this information can be rewritten. Here, a case is shown in which current is passed with a pulse width of the drive time t2 as rewriting. Exactly in this case, the current changes in the actual operation, but is omitted. Even if the direction of the current to be applied first is the state of the memory cell opposite to the example shown in FIG. 12A, the direction of change is different, but information can be written and rewritten in the same manner. In the second embodiment, destructive reading is performed by this method, and further rewriting is performed. Thereby, information can be read with a large current while the influence of the read disturb remains small.

  FIG. 13 is a graph for explaining the relationship between the pulse width and the current value in destructive readout using the temperature as a parameter according to the second embodiment. In the second embodiment, when operating at a low temperature, destructive reading and writing are performed under the condition at the upper right of the characteristic plane divided by the curve (a) indicating the characteristics at low temperature. That is, the pulse width for writing and reading is the pulse width P1, and the current value is the current value A1. On the other hand, when operating at a sufficiently high temperature, destructive reading and writing are performed under the conditions at the upper right of the characteristic plane divided by the curve (b) indicating the characteristics at the high temperature. That is, the pulse width for writing and reading is the pulse width P2, and the current value is the current value A2. Since a similar curve can be defined even at an intermediate temperature, the measurement is performed under the condition at the upper right of the characteristic plane divided by the curve. Thereby, in the second embodiment, it is possible to perform the operation at the minimum current and the fastest speed according to the temperature.

  FIG. 14 shows an example of a circuit diagram for obtaining a pulse width and a current value corresponding to the temperature during operation. The current value is changed according to the voltage value of the word line. The mechanism for detecting the temperature and the mechanism for generating the pulse width corresponding to the mechanism are the same as those described in the first embodiment (FIG. 8 described above). The tunnel magnetoresistive element for detecting temperature can be embedded in a normal memory cell array as a dummy cell. As shown in FIG. 14, the second embodiment is characterized in that a mechanism for changing the word line voltage by the output of the amplifier according to the temperature of the tunnel magnetoresistive element is provided. That is, the word line voltage is generated based on the output of the amplifier corresponding to the temperature of the tunnel magnetoresistive element. Thereby, a desired word line voltage corresponding to the temperature can be obtained.

  FIG. 15 shows an example of a circuit configuration diagram according to the second embodiment for performing destructive reading and rewriting. FIG. 15 shows only the peripheral circuit of the memory cell. Between the bit lines BLL and BLR and the source lines SLL and SLR, memory cells SCL1 and SCR1 driven by the word lines WL1 and WR1 are arranged. In practice, a large number of memory cells, for example 512, are arranged for a set of bit lines and source lines, and a large number of bit line and source line pairs having such a large number of memory cells are arranged on the chip. Yes. Reference numerals DCL and DCR denote dummy memory cells, which are driven by dummy word lines DWL and DWR, and the currents flow in two states corresponding to information “0” and “1” that can be taken by the memory cells. For example, the voltage DCG is controlled so as to be in the middle of the current value. The voltage DCG has temperature characteristics so that the dummy memory cells DCL and DCR have temperature characteristics following the temperature characteristics of the tunnel magnetoresistive element described in the first embodiment (FIG. 9 described above). Keep it. Reference numeral RE denotes a read control signal for connecting the bit lines BLL and BLR and a sense amplifier at the time of reading, and this sense amplifier is activated by a signal SA. The outputs are outputs SAL and SAR, which are connected to a latch circuit controlled by the first write control signal power WE. The latch output is electrically connected to the bit lines BLL and BLR and the source lines SLL and SLR for rewriting by MIS transistors controlled by the left array and right array write control signals WEL and WER. This is also used for normal writing. In FIG. 15, the MIS transistor that lowers the source line during reading controlled by the read control signal RE, and the bit lines and source lines on both sides of the sense amplifier controlled by the left array and right array precharge signals PCL and PCR. MIS transistors having low potentials for both are disposed. By using such a circuit, the operation of the memory cell shown in FIGS. 10 to 12 can be realized.

  FIG. 16 is an operation timing chart showing an operation example of the circuit shown in FIG.

  First, reading is performed. When the drive signal PC changes from the high level to the low level, the read control signal RE rises and the word line WR1 is selected. At the same time, the dummy word line DWR to be paired with this is selected. As a result, a change corresponding to the information of the memory cell appears on the bit line BLR, and a change corresponding to the dummy memory cell appears on the bit line BLL. Here, by starting the sense amplifier by changing the signal SA, a large amplitude signal is generated at the outputs SAR and SAL. Since the read control signal RE is input to the gate of the MIS transistor, the bit line BLR / BLL does not become a potential higher than the threshold voltage drop of the MIS transistor from the high level of the read control signal RE. Thereafter, the read control signal RE is changed, and the drive signal PC is changed to set the bit line and the source line to the same low potential voltage Vs. Reading is completed in this state, and the sensing operation is completed at a high speed with a large reading current.

  Next, rewriting is started. Here, first, the right array precharge signal PCR is set to a low level to make the bit line BLR and the source line SLR floating. Here, the first write control signal power WE and the right array write control signal WER are changed. Thus, the latch information is connected to the bit line BLR and the source line SLR, the potential relationship between the bit line BLR and the source line SLR is determined according to the rewrite information, and writing starts. When the writing is finished, the word line WR1 is closed, the first write control signal power WE and the right array write control signal WER are restored, and the right array precharge signal PCR is raised to raise the bit line BLR and the source line SLR. Are set to the low potential voltage Vs. This is the initial state. By such an operation example, the destructive read and rewrite operations according to the second embodiment are completed.

(Embodiment 3)
The structure of the memory cell according to the third embodiment will be described with reference to FIGS. FIG. 17 is an example of a layout diagram of the memory cell array according to the third embodiment, and the area of the memory cell is 8F ² when the wiring pitch of word lines or bit lines is 2F. 18 is a cross-sectional view of the main part taken along the line AA ′ of FIG. 17 and the main part of the peripheral circuit. FIG. 19 is a cross-sectional view of the main part taken along the line BB ′ of FIG. FIG.

  The memory cell MC includes one n-channel type selection MIS transistor and a tunnel magnetoresistive element TMR. The word line WL is connected to the gate GP of the selected MIS transistor. The gate material is made of p-type polysilicon. Further, the gate material may be composed of a low resistance laminated film in which silicide or tungsten is laminated on top of p-type polysilicon. The selection MIS transistor is formed in the p-type semiconductor region PWEL. The p-type semiconductor region PWEL is formed in the n-type semiconductor region DWEL, and the n-type semiconductor region DWEL is formed in the p-type semiconductor substrate PSsub.

  A source line contact SLC is disposed on one side of the diffusion layer LN of the selection MIS transistor. By sharing the source line contact SLC between adjacent memory cells MC, the area of the memory cell MC is reduced. A source line SL is wired on the source line contact SLC in a direction orthogonal to the word line WL. In the diffusion layer LN where the source line contact SLC is not disposed, the lower electrode contact BEC connected to the tunnel magnetoresistive element TMR is disposed. The lower electrode contact BEC is connected to the lower electrode BE where the tunnel magnetoresistive element TMR is disposed. A tunnel magnetoresistive element TMR including a plurality of magnetic films and a tunnel barrier film is disposed on the lower electrode BE. The tunnel magnetoresistive element TMR includes at least one tunnel barrier film TB, and a fixed layer PL and a free layer FL disposed above and below the tunnel barrier film TB. In the magnetic fixed layer PL, the direction of spin of electrons inside is fixed in a fixed direction. On the other hand, in the free layer FL of magnetic material, the direction of spin of electrons inside is in one of two states, a parallel state and an antiparallel state with respect to the fixed layer PL. In this configuration, the free layer FL is disposed between the tunnel barrier film TB and the lower electrode BE, and the fixed layer PL is provided between the bit line BL and the tunnel barrier film TB wired above the tunnel magnetoresistive element TMR. Be placed. The bit line BL is wired perpendicular to the word line WL and parallel to the source line SL. Tunneling magneto-resistance element TMR has a rectangular or elliptical shape in which the bit line wiring direction is longer than the word line wiring direction. Thereby, there is an advantage that the retention characteristic in the spin direction of the free layer FL is improved.

  In the peripheral circuit, for example, various elements such as a CMIS (Complementary Metal Insulator Semiconductor) device, a resistor element, a capacitor element, or an inductor element are formed. FIG. 18 is a cross-sectional view of a principal part of a part of the CMIS device.

  The CMIS device includes an n-channel MIS transistor nMIS and a p-channel MIS transistor pMIS. The n-channel MIS transistor nMIS is formed in the p-type semiconductor region PWEL formed in the p-type semiconductor substrate PSsub, and includes a gate insulating film, a gate GN made of n-type polysilicon, and a source / drain made of an n-type diffusion layer LN. Composed. Similarly, the p-channel type MIS transistor pMIS is formed in the n-type semiconductor region NWEL formed in the p-type semiconductor substrate PSub, and includes a gate insulating film, a gate GP made of p-type polysilicon, and a source made of a p-type diffusion layer LP. -Consists of drains.

  FIG. 20 is a fragmentary cross-sectional view of another example of the memory array according to the third embodiment and a fragmentary cross-sectional view of a peripheral circuit, and shows a portion corresponding to FIG. 18 described above. The memory cell shown in FIG. 18 is different from the memory cell shown in FIG. 20 in that an assist word line AW running in parallel with the word line WL is arranged below the lower electrode BE. A magnetic field can be generated by passing a current through the assist word line AW, which can affect the operation of the tunnel magnetoresistive element TMR.

  FIG. 21 is a circuit diagram of the memory cell shown in FIG. The word line WL and the assist word line AW are arranged in parallel, and the assist word line AW can affect the tunnel magnetoresistive element T1 by the magnetic field generated by the current flowing through the assist word line AW. This is indicated by the arrows in the figure. As this operation example, two operations (1) and (2) are performed. That is, in the first operation (1), only the assist word line AW is turned on to pass a current. As a result, the spin direction inside the tunnel magnetoresistive element T1 can be easily changed by the generated magnetic field. In the subsequent operation (2), the word line WL is turned on to allow a write current to flow. Since the spin is already easily reversed by the operation of the assist word line AW, writing can be performed with a smaller current. Note that the spin is easily reversed only by passing a current through the assist word line AW, but it immediately returns to the initial state.

FIG. 22 is a fragmentary cross-sectional view of another memory cell according to the third embodiment. The selected MIS transistor is a vertical MIS transistor, and the memory cell area can be reduced to 4F ² . Symbol PL is a fixed layer, symbol FL is a free layer, symbol TB is a tunnel barrier film, and constitutes a tunnel magnetoresistive element TMR. In FIG. 22, the fixed layer PL is at the top, but the fixed layer PL may be below the free layer FL. Further, the order of arrangement of the tunnel magnetoresistive element TMR and the vertical MIS transistor in the height direction may be different from that shown in FIG. A source / drain SD composed of n ⁺ regions is provided above and below the gate GA, and operates in the same manner as a normal lateral MIS transistor depending on the voltage applied to the gate GA. The gate GA may wrap the p-type region in a ring shape, or may control the surface of the vertical structure from two directions or from three directions. FIG. 22 illustrates an n-channel MIS transistor as the vertical MIS transistor, but a vertical MIS transistor may be configured by a p-channel MIS transistor.

  FIG. 23 is a cross-sectional view of a main part of another memory cell according to the third embodiment, in which a heating element HEATER is added to the tunnel magnetoresistive element TMR in FIG. 22 described above. The heating element HEATER has a property of generating heat when a current or voltage is applied, and at the time of writing, the heating element HEATER is activated to heat the tunnel magnetoresistive element. As described in the first embodiment, the current required for writing can be reduced at high temperatures. For this reason, there is a feature that writing can be performed with low power. FIG. 24 shows an operation timing chart for explaining the operation example. When writing is performed by spin injection by selecting the word line WL and the bit line BL / source line SL, a signal is applied to the heating element HEATER to generate heat.

  FIG. 25 is a diagram schematically showing a tunnel magnetoresistive element of another memory cell array according to the third embodiment. In this tunnel magnetoresistive element, the directions of the electron spins of the free layer FL and the fixed layer PL are not horizontal but perpendicular to the tunnel barrier film TB. By selecting such a material, the two states (parallel and antiparallel) of the tunnel magnetoresistive element can be made stable against thermal disturbance. When the above-described temperature control method according to the first embodiment and the above-described destructive read method according to the second embodiment are applied to this, a memory operation that stably operates in a wide temperature range is achieved even if scaling progresses. Can be realized.

  FIG. 26 schematically shows a tunnel magnetoresistive element of another memory cell array according to the third embodiment. In this tunnel magnetoresistive element, the free layer FL has a laminated structure. In other words, the non-magnetic layer MB is sandwiched between magnetic material layers that are antiparallel to each other, and this forms a free layer FL as a unit. This laminated structure may be further multilayered. Even with such a structure, a memory element in which the state of the tunnel magnetoresistive element is stable against disturbance due to heat can be obtained.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

  The present invention can be applied to a mixed memory or a single product memory in which a nonvolatile memory cell having a large number of writing operations, which is desired to operate stably over a wide temperature range, is mounted.

FIG. 6 is a graph of a first example illustrating a relationship between a write current or read current flowing through a memory cell according to the first embodiment and time (pulse width). FIG. 10 is a graph of a second example illustrating the relationship between the write current or read current flowing through the memory cell according to the first embodiment and time (pulse width). FIG. 10 is a graph of a third example illustrating the relationship between the write current or read current flowing through the memory cell according to the first embodiment and time (pulse width). It is a graph of the 4th example explaining the relationship between the write current or read current which flows into the memory cell by this Embodiment 1, and time (pulse width). 2 is a main configuration example of a memory chip circuit included in the semiconductor memory device according to the first embodiment; FIG. 6 is a read operation timing diagram illustrating an operation example of the memory chip circuit of FIG. 5. FIG. 6 is a write operation timing diagram illustrating an operation example of the memory chip circuit of FIG. 5. It is an example of the pulse generation circuit diagram which generates the pulse width according to the temperature by this Embodiment 1. FIG. It is a schematic diagram explaining the temperature characteristic of the tunnel magnetoresistive element by this Embodiment 1. FIG. It is a graph explaining the relationship between the processing current which produces the write-in electric current and read-out electric current by this Embodiment 2, and a memory cell. FIG. 10 is an operation timing diagram illustrating an operation of a memory cell according to the second embodiment. (A) And (b) is the circuit diagram of the memory cell by this Embodiment 2, respectively, and the schematic diagram of the electric current operation waveform. It is a graph explaining the relationship between the pulse width and the current value in destructive readout with temperature as a parameter according to the second embodiment. FIG. 10 is an example of a circuit diagram for obtaining a pulse width and a current value corresponding to a temperature during operation according to the second embodiment. It is an example of the circuit block diagram by this Embodiment 2. FIG. FIG. 16 is an operation timing chart illustrating an operation example of the circuit illustrated in FIG. 15. FIG. 14 is a layout diagram of an example of a memory cell array according to the third embodiment. FIG. 18 is a fragmentary sectional view taken along line AA ′ in FIG. 17 and a fragmentary sectional view of peripheral circuits. (A) is principal part sectional drawing of the BB 'line of FIG. 17, (b) is principal part sectional drawing of CC' line of FIG. FIG. 16 is a fragmentary cross-sectional view of another example of the memory array according to the third embodiment and a fragmentary sectional view of a peripheral circuit. FIG. 10 is a circuit diagram of a memory cell according to a third embodiment. It is principal part sectional drawing of the other memory cell by this Embodiment 3. FIG. It is principal part sectional drawing of the other memory cell by this Embodiment 3. FIG. FIG. 10 is an operation timing diagram illustrating an operation example of a memory cell according to the third embodiment. It is the figure which showed typically the tunnel magnetoresistive element of the other memory cell array by this Embodiment 3. FIG. It is the figure which showed typically the tunnel magnetoresistive element of the other memory cell array by this Embodiment 3. FIG. It is the figure which showed typically the tunnel magnetoresistive element which the present inventors examined. It is the figure which showed typically operation | movement of the tunnel magnetoresistive element which the present inventors examined.

Explanation of symbols

A current value ADCConv conversion circuit Ai address signal AM1 amplifier AMP sense amplifier AW assist word line B, B1, B2 current value BE lower electrode BEC lower electrode contact BL, BLL, BLR bit line BO output DCG voltage DCL, DCR dummy memory cell DLY Delay circuit DOj / DIj Signal terminal DWEL n-type semiconductor region DWL, DWR Dummy word line FL Free layer GA, GN, GP Gate HEATER Heating element I / O Input / output lines K1, K2 Current value LN Diffusion layer LP Diffusion layers LTA, LTP Latch output M1, Mn Select MIS transistor MB Nonmagnetic layer MC Memory cell nMIS n-channel MIS transistor NWEL n-type semiconductor region O Output P1 Write pulse width P2 Read pulse width PC Drive signal PCL, PCR Left array and Array precharge signal PL Fixed layer pMIS p channel type MIS transistor PP1 signal PSsub p type semiconductor substrate PWEL p type semiconductor region R1 resistance Rap, Rp resistance range RE, RE1 read control signal SA signal SAL, SAR output SC1, SCn, SCR1, SCL1 Memory cell SD Source / drain Sk Signal SL, SLL, SLR Source line SLC Source line contact t1, t2 Drive time T1, Tn, TMR Tunnel magnetoresistive element TB Tunnel barrier film Vd High potential voltage Vdd High potential VR Reference voltage Vref Reference Voltage generation circuit Vs Low potential voltage (ground potential)
Vss low potential VT1 signal Y1 column selection signal W1, Wn, WL, WL1, WR1 word line WE first write control signal power WE1 second write control signal power WEL, WER left array and right array write control signal

Claims (21)

Multiple word lines,
A plurality of bit lines wired in a direction orthogonal to the plurality of word lines;
A plurality of memory cells including a MIS transistor and a tunnel magnetoresistive element disposed at a predetermined intersection of the plurality of word lines and the plurality of bit lines, each including a fixed layer, a tunnel barrier film, and a free layer; Have
The fixed layer is a magnetic body in which the direction of electron spin is fixed in a predetermined direction, and is disposed adjacent to one surface of the tunnel barrier film,
The free layer is a magnetic material in which the direction of electron spin takes either a parallel state or an antiparallel state with respect to the direction of electron spin of the fixed layer, and is adjacent to the other surface of the tunnel barrier film. Arranged,
A gate of the MIS transistor is electrically connected to the word line;
The drain of the MIS transistor is electrically connected to the bit line through the tunnel magnetoresistive element,
The memory cell information write operation is performed according to a desired first current value and a first time, and the memory cell information read operation is performed by a pulse generation circuit including a temperature sensor that detects the temperature of the memory cell. 2. The semiconductor memory device according to claim 1, wherein the semiconductor memory device is operated according to a second current value and a second time set in accordance with an operating temperature of the memory cell.   2. The semiconductor memory device according to claim 1, wherein the first current value and the first time are constant regardless of an operating temperature of the memory cell.   2. The semiconductor memory device according to claim 1, wherein the first current value and the first time are a current value at a minimum temperature at which an electron spin direction of the free layer guaranteed in an operating temperature range of the memory cell is reversed. The second current value and the second time are set to the same value as or larger than the time, respectively, and the direction of the electron spin of the free layer guaranteed in the operating temperature range of the memory cell is reversed. A semiconductor memory device characterized in that the current value at the highest temperature and a value smaller than the time are respectively set. 2. The semiconductor memory device according to claim 1, wherein the first current value and the first time are a current value at a minimum temperature at which an electron spin direction of the free layer guaranteed in an operating temperature range of the memory cell is reversed. The second current value and the second time are set to the same value as or larger than the time, respectively, and the direction of the electron spin of the free layer guaranteed in the operating temperature range of the memory cell is reversed. Is set to a value smaller than the current value and time at the maximum temperature to be
The semiconductor memory device, wherein the second current value and the first current value are the same, and the second time is shorter than the first time. 2. The semiconductor memory device according to claim 1, wherein the first current value and the first time are a current value at a minimum temperature at which an electron spin direction of the free layer guaranteed in an operating temperature range of the memory cell is reversed. The second current value and the second time are set to the same value as or larger than the time, respectively, and the direction of the electron spin of the free layer guaranteed in the operating temperature range of the memory cell is reversed. Is set to a value smaller than the current value and time at the maximum temperature to be
The semiconductor memory device, wherein the second current value is smaller than the first current value, and the second time is shorter than the first time. 2. The semiconductor memory device according to claim 1, wherein the first current value and the first time are a current value at a minimum temperature at which an electron spin direction of the free layer guaranteed in an operating temperature range of the memory cell is reversed. The second current value and the second time are set to the same value as or larger than the time, respectively, and the direction of the electron spin of the free layer guaranteed in the operating temperature range of the memory cell is reversed. Is set to a value smaller than the current value and time at the maximum temperature to be
The semiconductor memory device, wherein the second current value is smaller than the first current value, and the second time and the first time are the same. 2. The semiconductor memory device according to claim 1, wherein the first current value and the first time are a current value at a minimum temperature at which an electron spin direction of the free layer guaranteed in an operating temperature range of the memory cell is reversed. The second current value and the second time are set to the same value as or larger than the time, respectively, and the direction of the electron spin of the free layer guaranteed in the operating temperature range of the memory cell is reversed. Set to a value smaller than the current value and time at the lowest temperature to be
The semiconductor memory device, wherein the second current value is smaller than the first current value, and the second time and the first time are the same. Multiple word lines,
A plurality of bit lines wired in a direction orthogonal to the plurality of word lines;
A plurality of memory cells including a MIS transistor and a tunnel magnetoresistive element disposed at a predetermined intersection of the plurality of word lines and the plurality of bit lines, each including a fixed layer, a tunnel barrier film, and a free layer; Have
The fixed layer is a magnetic body in which the direction of electron spin is fixed in a predetermined direction, and is disposed adjacent to one surface of the tunnel barrier film,
The free layer is a magnetic material in which the direction of electron spin takes either a parallel state or an antiparallel state with respect to the direction of electron spin of the fixed layer, and is adjacent to the other surface of the tunnel barrier film. Arranged,
A gate of the MIS transistor is electrically connected to the word line;
The drain of the MIS transistor is electrically connected to the bit line through the tunnel magnetoresistive element,
The memory cell information write operation is performed with a first current value and a first time set to values that can reverse the direction of electron spin of the free layer, and the memory cell information read operation is performed. The second current value is the same as the first current value and the second time is the same as the first time. After the read operation, the information destroyed by the read operation is rewritten,
The first and second current values and the first and second times are set according to the operating temperature of the memory cell by a pulse generation circuit including a temperature sensor for detecting the temperature of the memory cell. A semiconductor memory device.   9. The semiconductor memory device according to claim 8, wherein the direction of electron spin in the free layer is reversed by the read operation and the write operation.   2. The semiconductor memory device according to claim 1, wherein a tunnel magnetoresistive element having the same structure as the tunnel magnetoresistive element constituting a part of the memory cell is used as the temperature sensor for detecting the temperature of the memory cell. A semiconductor memory device.   2. The semiconductor memory device according to claim 1, wherein the direction of electron spin of the free layer and the direction of electron spin of the fixed layer are parallel to the direction of current flowing through the tunnel magnetoresistive element. apparatus.   2. The semiconductor memory device according to claim 1, wherein the free layer is composed of two layers of magnetic bodies whose electron spin directions are antiparallel to each other.   2. The semiconductor memory device according to claim 1, wherein a wiring for generating a magnetic field by flowing a current is disposed in the vicinity of the free layer.   2. The semiconductor memory device according to claim 1, wherein means for heating the free layer is disposed in the vicinity of the free layer.   2. The semiconductor memory device according to claim 1, wherein the first time is 10 ns or more.   9. The semiconductor memory device according to claim 8, wherein a tunnel magnetoresistive element having the same structure as the tunnel magnetoresistive element constituting a part of the memory cell is used as the temperature sensor for detecting the temperature of the memory cell. A semiconductor memory device.   9. The semiconductor memory device according to claim 8, wherein the direction of electron spin of the free layer and the direction of electron spin of the fixed layer are parallel to the direction of current flowing through the tunnel magnetoresistive element. apparatus.   9. The semiconductor memory device according to claim 8, wherein the free layer is composed of two layers of magnetic bodies whose electron spin directions are antiparallel to each other.   9. The semiconductor memory device according to claim 8, wherein a wiring for generating a magnetic field by flowing a current is disposed in the vicinity of the free layer.   9. The semiconductor memory device according to claim 8, wherein means for heating the free layer is disposed in the vicinity of the free layer.   9. The semiconductor memory device according to claim 8, wherein the first time is 10 ns or more.

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