WO2012001944A1 - 不揮発性記憶装置及びその駆動方法 - Google Patents
不揮発性記憶装置及びその駆動方法 Download PDFInfo
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- WO2012001944A1 WO2012001944A1 PCT/JP2011/003670 JP2011003670W WO2012001944A1 WO 2012001944 A1 WO2012001944 A1 WO 2012001944A1 JP 2011003670 W JP2011003670 W JP 2011003670W WO 2012001944 A1 WO2012001944 A1 WO 2012001944A1
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Definitions
- the present invention relates to a nonvolatile memory device and a driving method thereof, and in particular, a resistance change element that reversibly transitions between a low resistance state and a high resistance state having a higher resistance value than the low resistance state by application of a voltage pulse.
- the present invention relates to a nonvolatile memory device having a diode and a driving method thereof.
- the resistance change element refers to an element that has a property that the resistance value reversibly changes by an electrical signal and that can store information corresponding to the resistance value in a nonvolatile manner.
- the resistance value changes due to a change in crystal state due to heat generated by electrical stimulation.
- a resistance change element changes the resistance value of an element by changing the oxidation-reduction state of a resistance change material directly, that is, through transfer of electrons. Change.
- a cross-point type semiconductor memory device is known as an example of a large-capacity semiconductor memory device equipped with this variable resistance element.
- a diode is inserted in series with respect to the nonvolatile memory element of each memory cell (see, for example, Patent Document 1).
- the current flowing through the non-selected memory element can be avoided.
- FIG. 10 is a diagram showing a semiconductor memory device equipped with a conventional variable resistance element.
- the semiconductor memory device shown in FIG. 10 is a cross-point memory cell array having a bit line 210, a word line 220, and memory cells 280 formed at their intersections.
- a memory cell 280 is formed by serially connecting a resistance change element 260 that stores information by a change in electric resistance caused by an electrical stress and a two-terminal diode 270 having a nonlinear current-voltage characteristic that allows a current to flow bidirectionally. Is formed.
- the bit line 210 serving as the upper wiring is electrically connected to the diode 270
- the word line 220 serving as the lower wiring is electrically connected to the resistance change element 260.
- FIG. 11 is a block diagram showing a relationship among a resistance change element, a load circuit, and a peripheral circuit of a selected memory cell of a conventional semiconductor memory device.
- the semiconductor memory device shown in FIG. 11 can stabilize the high resistance state and the low resistance state in data rewriting of the memory cell by changing the resistance value of the load circuit.
- the memory cell When such a defect occurs in a certain memory cell, the memory cell is substantially short-circuited (a state having a very low resistance value, hereinafter referred to as an excessively low resistance state). As a result, all currents when accessing another memory cell in the same row or column as the defective memory cell flow to the defective memory cell that is substantially short-circuited. As a result, there is a problem that writing or reading cannot be correctly performed on all other memory cells in the same row or the same column as the defective memory cell.
- a predetermined load resistance is connected in series with the resistance change element in advance in order to suppress an excessive current generated due to a sudden low resistance phenomenon.
- resistance is changed by connecting.
- the memory cell is in an excessively low resistance state as described above, even if a rewrite voltage is applied to the memory cell, most of the applied voltage is applied to the load resistance, so the resistance change A voltage necessary for rewriting cannot be effectively applied to the element. As a result, there was a problem that it was not possible to recover from the excessively low resistance state.
- the present invention has been made to solve the above-described problem. Even when a defect occurs in a certain nonvolatile memory element, the nonvolatile memory element in the same row or column as the defective nonvolatile memory element is used.
- An object of the present invention is to provide a nonvolatile memory device and a driving method thereof that can effectively prevent writing or reading from being disabled.
- a method for driving a nonvolatile memory device includes a diode having nonlinear current-voltage characteristics, and a resistance change element connected in series to the diode.
- a non-volatile memory device driving method comprising: a plurality of memory cells including: a plurality of memory cells; and a variable load resistor connected in series to the plurality of memory cells, the memory cell and the variable load resistor having a first resistance value;
- the resistance change element is changed from the first high-resistance state to the first low-resistance state by applying a first low-resistance electrical pulse to the series circuit configured by: By applying an electric pulse, the variable resistance element is changed from the first low resistance state to the first high resistance state, and between the first low resistance state and the first high resistance state.
- a detecting step of detecting an excessively low resistance cell including a resistance change element in a second low resistance state having a resistance value lower than that of the first low resistance state among the plurality of memory cells; and a resistance value of the variable load resistor.
- the first variable resistance value changing step for changing the first resistance value to a second resistance value lower than the first resistance value, the excessively low resistance cell, and the variable of the second resistance value
- a second high-resistance electrical pulse to a series circuit composed of a load resistor
- the variable resistance element included in the excessive low-resistance cell is moved from the second low-resistance state to the first
- a second high resistance writing step for setting a second high resistance state having a resistance value higher than that of the low resistance state.
- the driving method of the nonvolatile memory device detects a memory cell (excessive low resistance cell) in which a failure has occurred due to the diode being substantially short-circuited. Furthermore, the driving method increases the resistance of the memory cell by applying a voltage pulse to the detected excessively low resistance cell after reducing the resistance value of the variable load resistance. Thereby, most of the voltage applied to the excessively low resistance cell for increasing the resistance is applied not to the variable load resistor but to the resistance change element, so that the resistance change element can be increased in resistance. Therefore, since the excessive low resistance cell can escape from the excessive low resistance state, when a current is passed through the same row or the same column as the defective memory cell, an excessive current flows through the defective memory cell. Can be prevented. Thereby, other memory cells can be operated normally.
- “when the diode is substantially short-circuited” means that the diode has a resistance value lower than the resistance value of the diode in the normal state due to dielectric breakdown. .
- the resistance value in the second high resistance state may be higher than that in the first high resistance state.
- the driving method of the nonvolatile memory device can further reduce the current flowing through the defective memory cell, another nonvolatile memory device in the same row or the same column as the defective nonvolatile memory element. Further, it is possible to further prevent the writing or reading from being performed on the volatile memory element.
- the second high-resistance electrical pulse is applied to a series circuit including the excess low-resistance cell and the variable load resistor having the second resistance value.
- the driving method of the nonvolatile memory device is applicable even when the resistance of the defective memory cell cannot be increased by increasing the resistance using the variable load resistor having the second resistance value.
- the resistance of a defective memory cell can be increased.
- the variable load resistor includes a transistor.
- the resistance value of the variable load resistor may be changed to a lower resistance value by changing a gate voltage of the transistor. Good.
- the driving method of the nonvolatile memory device can easily change the resistance value of the load resistor connected to the memory cell.
- the resistance value of the variable load resistor is changed from the resistance value lower than the first resistance value to the first resistance value.
- the driving method of the nonvolatile memory device can perform normal writing and reading operations in the subsequent processing.
- the memory cell stores only binary data of a first logical value corresponding to the first high resistance state and a second logical value corresponding to the first low resistance state. May be.
- a nonvolatile memory device includes a plurality of first wirings arranged in a first direction at a predetermined interval in parallel to the main surface of the substrate, and parallel to the main surface of the substrate. And a plurality of second wirings arranged at predetermined intervals in a second direction so as to form a three-dimensional intersection with the first wirings, the plurality of first wirings, and the plurality of second wirings
- Each terminal of a plurality of memory cells having two terminals each including a diode having a nonlinear current-voltage characteristic and a resistance change element connected in series to the diode.
- a nonvolatile memory device comprising: a column selection circuit / driver; a sense amplifier for reading a resistance value of the selected memory cell; and a variable load resistance circuit connected in series to the memory cell array, The resistance change element included in the selected memory cell applies a first high-resistance electrical pulse to a series circuit including the selected memory cell and the variable load resistor having the first resistance value.
- the nonvolatile memory device includes a resistance change element in a second low-resistance state having a resistance value lower than that of the first low-resistance state among the plurality of memory cells. Detect resistance cell The resistance value of the variable load resistor is changed from the first resistance value to a second resistance value lower than the first resistance value, and the excess low resistance cell and the second resistance value of the second resistance value are changed.
- the resistance change element included in the excessive low-resistance cell has a resistance value higher than that of the first low-resistance state.
- a control circuit for setting the second high resistance state is further included.
- the nonvolatile memory device detects a memory cell (excessive low resistance cell) in which a failure has occurred due to a diode being substantially short-circuited. Further, the nonvolatile memory device increases the resistance of the memory cell by applying a voltage pulse to the detected excessively low resistance cell after reducing the resistance value of the variable load resistance. Thereby, most of the voltage applied to the excessively low resistance cell for increasing the resistance is applied not to the variable load resistor but to the resistance change element, so that the resistance change element can be increased in resistance. Therefore, since the excessive low resistance cell can escape from the excessive low resistance state, when a current is passed through the same row or the same column as the defective memory cell, an excessive current flows through the defective memory cell. Can be prevented. Thereby, other memory cells can be operated normally.
- the nonvolatile memory device can be applied to another nonvolatile memory element in the same row or the same column as the defective nonvolatile memory element even when a defect occurs in a certain nonvolatile memory element.
- the nonvolatile memory device further includes a recording unit that records an address of the excessive low-resistance cell in the second high-resistance state, and at least one spare memory cell, and the control circuit includes a second It has a function of recording the address of the excessive low resistance cell in the high resistance state and controlling to access the address of the spare memory cell when the address of the excessive low resistance cell is designated in the subsequent memory operation. Also good.
- the resistance value in the second high resistance state may be higher than that in the first high resistance state.
- the nonvolatile memory device can further reduce the current flowing through the defective memory cell, so that other nonvolatile memory in the same row or the same column as the defective nonvolatile memory element. It can be further prevented that writing to or reading from the element cannot be performed.
- the control circuit may control the variable load resistance circuit to return the resistance value of the variable load resistance circuit to the first resistance value after setting the excessive low resistance cell to the second high resistance state. Good.
- the nonvolatile memory device can perform normal write and read operations in the subsequent processing.
- the present invention can be realized not only as a driving method of such a nonvolatile memory device but also realized as a nonvolatile memory device using characteristic steps included in the driving method.
- the present invention can also be realized as a program that causes a computer to execute characteristic steps included in the driving method. Needless to say, such a program can be distributed via a recording medium such as a CD-ROM and a transmission medium such as the Internet.
- the present invention can be realized as a semiconductor integrated circuit (LSI) that realizes part or all of the functions of such a nonvolatile memory device.
- LSI semiconductor integrated circuit
- FIG. 1A is a schematic diagram of a memory cell according to the first embodiment of the present invention.
- FIG. 1B is a schematic diagram of the semiconductor memory device according to the first embodiment of the present invention.
- FIG. 2 is a top view of the semiconductor memory device according to the first embodiment of the present invention.
- FIG. 3 is a cross-sectional view of the semiconductor memory device according to the first embodiment of the present invention.
- FIG. 4 is a graph showing current-voltage characteristics of the diode according to the first embodiment of the present invention.
- FIG. 5A is a schematic diagram showing a connection relationship between the memory cell and the load resistor according to the first embodiment of the present invention.
- FIG. 5B is an equivalent circuit diagram showing a connection relationship between the memory cell and the load resistor according to the first embodiment of the present invention.
- FIG. 6 is a graph showing a resistance change state according to the first embodiment of the present invention.
- FIG. 7 is a block diagram of a nonvolatile memory device according to the second embodiment of the present invention.
- FIG. 8A is a diagram illustrating an example of a load resistor according to the second embodiment of the present invention.
- FIG. 8B is a diagram illustrating an example of a load resistance according to the second exemplary embodiment of the present invention.
- FIG. 9 is a flowchart of a driving method by the nonvolatile memory device according to the second embodiment of the present invention.
- FIG. 10 is a diagram showing a semiconductor memory device equipped with a conventional variable resistance element.
- FIG. 11 is a block diagram showing a relationship among a conventional variable resistance element, a load circuit, and a peripheral circuit.
- each of the embodiments described below shows a preferred specific example of the present invention.
- the numerical values, shapes, materials, constituent elements, arrangement positions and connecting forms of the constituent elements, steps, order of steps, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention.
- the invention is limited only by the claims. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims indicating the highest concept of the present invention are not necessarily required to achieve the object of the present invention. It will be described as constituting a preferred form.
- FIG. 1A is a schematic circuit diagram showing a memory cell 11 according to the first embodiment of the present invention.
- FIG. 1B is a schematic circuit diagram showing the semiconductor memory device (memory cell array) 10 according to the first embodiment of the present invention.
- FIG. 2 is a schematic plan view showing the configuration of the semiconductor memory device 10 shown in FIG. 1B in plan view.
- FIG. 3 is a schematic cross-sectional view of the XX plane shown in FIG.
- the memory cell 11 As shown in FIG. 1A, the memory cell 11 according to the first embodiment of the present invention has a configuration in which a diode 112 and a resistance change element 105 are connected in series.
- the semiconductor memory device 10 includes a plurality of memory cells 11 arranged in a matrix. One end of each memory cell 11 is connected to the first wiring (word line) 101, and the other end is connected to the second wiring (bit line) 119.
- the semiconductor memory device 10 has a cross point structure.
- the word line WL1 and the bit line BL1 are short-circuited by the memory cell 11, and other memory cells (M10, M12) and other memory cells (M01, M21) in the same column cannot be normally written and read.
- the semiconductor memory device 10 includes a substrate 100 and a main surface of the substrate 100 that are parallel to each other and in a first direction (the horizontal direction in FIGS. 2 and 3). And a plurality of first wirings (word lines) 101 disposed so as to extend in parallel to each other in a plane parallel to the main surface of the substrate 100 above the plurality of first wirings 101.
- a plurality of second wirings (bit lines) arranged so as to extend in a second direction (a direction perpendicular to the paper surface in FIG. 3 and a vertical direction in FIG. 1B) that three-dimensionally intersects the first wiring 101 of FIG.
- Nonvolatile memory having nonvolatile memory element 11 It includes an element array.
- the resistance change element 105 includes a lower electrode (first electrode) 106, an upper electrode (second electrode) 108, and a resistance change layer 107 interposed between the lower electrode 106 and the upper electrode 108. ing.
- the lower electrode 106 and the resistance change layer 107 are in physical contact, and the upper electrode 108 and the resistance change layer 107 are in physical contact.
- the diode 112 includes a lower electrode (third electrode) 113, an upper electrode (fourth electrode) 115, and an insulator layer or semiconductor layer 114 interposed between the lower electrode 113 and the upper electrode 115.
- the lower electrode 113 and the insulator layer or semiconductor layer 114 are in physical and electrical contact to form a Schottky junction, and the upper electrode 115 and the insulator layer or semiconductor layer 114 are physically and electrically in contact. Contact to form a Schottky junction.
- a first interlayer insulating layer 102 is formed on the substrate 100 so as to cover the first wiring 101.
- a plurality of resistance change elements 105 are arranged on the first interlayer insulating layer 102 so as to be arranged at equal intervals on the first wiring 101 when viewed from the main surface side of the substrate 100 (upward direction in FIG. 3). Is formed.
- the first wiring 101 and the lower electrode 106 of the resistance change element 105 located thereabove are connected by a first contact plug 103 formed so as to penetrate the first interlayer insulating layer 102.
- a second interlayer insulating layer 109 is formed on the first interlayer insulating layer 102 so as to cover the variable resistance element 105.
- a plurality of diodes 112 are formed at positions overlapping the resistance change element 105 when viewed from the main surface side of the substrate 100.
- the upper electrode 108 of the variable resistance element 105 and the lower electrode 113 of the diode 112 are in direct contact with both the variable resistance layer 107 of the variable resistance element 105 and the semiconductor layer 114 of the diode 112 by the second contact plug 110. Connected without.
- a third interlayer insulating layer 116 is formed on the second interlayer insulating layer 109 so as to cover the diode 112.
- a second wiring 119 is formed on the third interlayer insulating layer 116 so as to be orthogonal to the first wiring 101 and overlap the resistance change element 105 and the diode 112 when viewed from the main surface side of the substrate 100. ing.
- the second wiring 119 and the upper electrode 115 of the diode 112 below the second wiring 119 are connected by a third contact plug 117 formed so as to penetrate the third interlayer insulating layer 116.
- the memory cell 11 includes the first contact plug 103 that is provided between the first wiring 101 and the lower electrode 106 of the resistance change element 105 and that conducts them, and the upper electrode 108 of the resistance change element 105. And a second contact plug 110 provided between the upper electrode 115 of the diode 112 and the second wiring 119 provided between the upper electrode 115 of the diode 112 and the second wiring 119. 3 contact plugs 117.
- a lead-out wiring 120 extending in the second direction is formed in parallel with the second wiring 119 outside the region where the memory cells 11 are arranged as viewed from the thickness direction.
- the first wiring 101 and the lead-out wiring 120 are fourth contact plugs 118 formed so as to penetrate the first interlayer insulating layer 102, the second interlayer insulating layer 109, and the third interlayer insulating layer 116, respectively. Connected by.
- the first wiring 101, the second wiring 119, and the lead-out wiring 120 are made of a conductive material such as aluminum or copper.
- the first interlayer insulating layer 102, the second interlayer insulating layer 109, and the third interlayer insulating layer 116 are made of an insulating material such as silicon oxide, for example.
- the second contact plug 110, the third contact plug 117, and the fourth contact plug 118 excluding the first contact plug 103 are made of a conductive material such as tungsten or copper.
- the memory cell 11 is provided at each of the three-dimensional intersections of the first wiring 101 and the second wiring 119 that intersect each other.
- a semiconductor memory device 10 including a cross-point type memory cell array is realized.
- the resistance change layer 107 of the resistance change element 105 in this embodiment includes an oxygen-deficient transition metal oxide.
- the oxygen-deficient transition metal oxide is a transition metal oxide having a lower oxygen content [atomic ratio: ratio of the number of oxygen atoms to the total number of atoms] compared to the stoichiometric oxide.
- the transition metal is tantalum (Ta)
- the stoichiometric oxide composition is Ta 2 O 5 and the ratio of the number of atoms of Ta and O (O / Ta) is 2.5. . Therefore, in the oxygen-deficient tantalum oxide, the atomic ratio of Ta and O is larger than 0 and smaller than 2.5.
- the resistance change layer 107 may be composed of an oxygen-deficient oxide of tantalum (TaO x : 0 ⁇ x ⁇ 2.5) or an oxygen-deficient oxide of hafnium (HfO x : 0 ⁇ x ⁇ 2.0).
- an oxygen-deficient oxide of tantalum or the oxygen-deficient oxide of hafnium instead of the oxygen-deficient oxide of tantalum or the oxygen-deficient oxide of hafnium, other transition metal oxides such as an oxygen-deficient oxide of zirconium may be used.
- the resistance change layer made of an oxygen-deficient transition metal oxide may have a laminated structure made of transition metal oxides having different oxygen contents.
- a high oxygen content resistance variable layer (high resistance layer) is disposed on the upper electrode side, and a low oxygen content resistance variable layer (low resistance layer) is disposed on the lower electrode side.
- the resistance change layer becomes highly resistive and a negative voltage pulse whose absolute value is greater than or equal to the second threshold is applied.
- the resistance change layer is lowered in resistance.
- the current may be limited by a predetermined current value.
- a transistor or a load resistor may be connected in series to the variable resistance element.
- the resistance value of the resistance change element 105 is switched by electric pulses having different polarities.
- a positive voltage positive electrical signal
- current flows from the upper electrode 108 to the lower electrode 106.
- electrons are taken from the variable resistance layer 107 to the electrode on the upper electrode side, so that the material of the variable resistance layer 107 is oxidized and its resistance value increases.
- a negative voltage negative electrical signal
- current flows from the lower electrode 106 to the upper electrode 108.
- electrons are applied from the electrode to the resistance change layer 107 on the upper electrode side, whereby the material of the resistance change layer 107 is reduced and the resistance value thereof decreases.
- the upper electrode 108 is made of a material having a higher standard electrode potential than the metal constituting the resistance change layer, such as platinum (Pt) or iridium (Ir), and the lower electrode 106 is made of a material having a lower standard electrode potential than the upper electrode material.
- a material having a higher standard electrode potential than the metal constituting the resistance change layer such as platinum (Pt) or iridium (Ir)
- the lower electrode 106 is made of a material having a lower standard electrode potential than the upper electrode material.
- tantalum nitride (TaN) is used.
- the film thickness of the resistance change layer 107 can be set to, for example, 50 to 200 nm.
- the thickness of the high resistance layer can be 1 to 10 nm. By setting it as such a film thickness, a resistance change can be stably caused at a low voltage of 5 V or less.
- the resistance value of the resistance change element 105 is switched by applying an electric pulse having an absolute value different in polarity with a certain threshold value or more between both electrodes of the resistance change element 105. Therefore, in the memory cell 11, a current needs to flow in either direction between both electrodes. Therefore, a bidirectional diode 112 having a function of flowing a current bidirectionally through the resistance change element 105 when the memory cell is selected and not flowing a current through the resistance change element 105 when the memory cell is not selected is applied.
- the diode 112 is an element having non-linear current-voltage characteristics. When the absolute value of the applied voltage is less than the critical voltage, the resistance value is large (off state), and the absolute value of the applied voltage is positive or negative. In the above, the element has an extremely small resistance value (ON state).
- the diode 112 in this embodiment includes, for example, a lower electrode 113 made of tantalum nitride, a semiconductor layer 114 made of a nitrogen-deficient silicon nitride film having a nitrogen content smaller than that of Si 3 N 4 , and tantalum.
- An MSM diode including an upper electrode 115 made of nitride is formed.
- the thickness of the semiconductor layer 114 can be set to 3 to 20 nm, for example.
- the silicon nitride film can be formed to have semiconductor characteristics by reducing the nitrogen content, and the diode 112 configured as an MSM diode can be manufactured by a simple manufacturing process.
- the nitrogen-deficient silicon nitride film (SiN z : 0 ⁇ z ⁇ 1.33) can be formed, for example, by reactive sputtering using a Si target in a nitrogen gas atmosphere.
- the chamber pressure may be 0.1 Pa to 1 Pa and the Ar / N 2 flow rate may be 18 sccm / 2 sccm at room temperature.
- FIG. 4 shows the IV curve (current-voltage characteristics) on the positive side of the bidirectional diode 112 manufactured by the method as described above (the negative side is not shown because it is the same except that the sign is reversed).
- IV curve of the diode 112 also varies due to processing variations during manufacture.
- IV curves 21 and 22 shown in FIG. 4 show examples of such variations.
- the maximum voltage before breakdown (maximum voltage that can be applied to the diode 112) and maximum current (maximum current that can be passed through the diode 112) are 3.2V, 180 ⁇ A for the IV curve 21, and 3, 4V for the IV curve 22. 250 ⁇ A.
- the diode 112 is an example of an MSM (Metal Semiconductor Metal) diode here, the diode 112 is an MIM (Metal Insulator Metal) diode having an insulating layer between the lower electrode 113 and the upper electrode 115. It may be. In that case, SiO 2 , Si 3 O 4 , Ta 2 O 5 , or the like can be used as a material for the insulator layer. Note that the MSM diode is more advantageous when it is desired to flow a larger current in the on state.
- MSM Metal Semiconductor Metal
- a resistance change element 105 using tantalum oxygen-deficient oxide (film thickness: about 30 nm) as the resistance change layer 107 and a diode 112 using nitrogen-deficient silicon nitride as the semiconductor layer 114 are connected in series. The characteristics will be described.
- FIG. 5A is a schematic diagram of the memory cell 11 according to the present embodiment.
- FIG. 5B is an equivalent circuit diagram of the memory cell 11 according to the present embodiment.
- FIG. 6 is a graph showing a change in resistance value when a voltage pulse is applied to the memory cell.
- the memory cell 11 is constituted by a series connection of a diode 112 and a resistance change element 105. Further, a load resistor 121 is connected in series with the memory cell 11 in order to stabilize the resistance change operation.
- the resistance change element 105 has a resistance value higher than that of the first low resistance state (LR state) and the first low resistance state when an electric pulse is applied to a series circuit including the memory cell 11 and the load resistor 121. Transition reversibly between the first high resistance state (HR state) having a high.
- the memory cell 11 including the resistance change element 105 in the LR state is referred to as the memory cell 11 in the LR state
- the memory cell 11 including the resistance change element 105 in the HR state is referred to as the memory cell 11 in the HR state.
- the load resistor 121 is composed of, for example, a polysilicon resistor, an impurity diffusion layer resistor, or an ON resistance of a transistor.
- the load resistor 121 may be realized by various methods as shown in Patent Document 2.
- FIG. 5B shows an equivalent circuit diagram of the configuration shown in FIG. 5A.
- the voltage Vw (first high resistance) is applied to both ends of the series circuit composed of the memory cell 11 and the load resistor 121.
- the first low resistance are different in polarity and absolute value).
- Vw Vd + Vr + Vx.
- Vd is a voltage across the diode 112
- Vr is a voltage across the resistance change element 105
- Vx is a voltage across the load resistor 121.
- Vd is about 3 V from the IV curve 21 of the diode 112 shown in FIG.
- Vw 6.5V
- Vw Vr + Vx (Vd ⁇ 0 V). That is, the rewrite voltage Vw is divided between the resistance change element 105 and the load resistor 121.
- the voltage Vr that is effectively applied to the resistance change element 105 is further reduced.
- a voltage value is applied as a first high-resistance voltage pulse between the lower electrode 106 and the upper electrode 115, with the lower electrode 106 as a reference.
- a voltage pulse having a pulse width of 500 ns at +6.5 V and a voltage pulse having a voltage value of ⁇ 5.5 V and a pulse width of 500 ns are alternately applied as the first low-resistance voltage pulse.
- the resistance value on the vertical axis in FIG. 6 is the sum of the resistance values of the memory cell 11 and the load resistor 121 including the resistance change element 105 and the diode 112.
- the resistance value becomes the first high-resistance state (for example, about 500 k ⁇ ).
- the resistance value becomes the first low resistance state (for example, about 100 k ⁇ ).
- a first operating current for example, about ⁇ 100 to 200 ⁇ A
- the resistance change element 105 for example, 5000 ⁇ .
- the resistance change range shifts downward, and the resistance change element 105 has an excessively low resistance state (second low resistance state) in which the resistance value is lower than that of the first low resistance state (LR level). Become.
- a second high resistance voltage is applied to the memory cell 11 in order to increase the resistance of the memory cell 11 in an excessively low resistance state.
- the load resistor 121 is switched to a load resistor having a lower resistance value than that during normal operation.
- the resistance value of the load resistor 121 is changed from 5000 ⁇ to 0 ⁇ , and a second high resistance voltage (for example, +10 V) is applied.
- a second high resistance voltage for example, +10 V
- the memory cell 11 remains low. It has been confirmed that it does not become resistive.
- the resistance value of the load resistor 121 is set to 0 ⁇ during the second high resistance process, but the resistance value of the load resistor 121 obtains an effective voltage sufficient for the high resistance process. Therefore, it is not necessary to be 0 ⁇ . That is, the resistance value of the load resistor 121 may be lower than that during normal operation during the high resistance process.
- +10 V is applied as the high resistance voltage, but other voltage values may be used.
- load resistance such as wiring resistance and contact resistance from the voltage pulse generation circuit to the memory cell 11 is often about several hundred to 1,000 ⁇ .
- the resistance increasing process is performed to an extremely high level. However, if the resistance is increased to at least a level higher than the LR level during normal operation, the same row as the defective memory cell, or The operation of other memory cells existing in the same column is not hindered.
- an excessively low resistance defective memory cell caused by diode destruction can be increased in resistance.
- the current flowing through the defective memory cell is reduced, and the operation of other memory cells existing in the same row and the same column as the defective memory cell is not hindered.
- the address of the defective memory cell in the second high resistance state as described above is recorded separately, and is controlled by the peripheral circuit of the memory device so that the address of the defective memory cell is not selected in the subsequent memory operation.
- An example of this will be described in the second embodiment below.
- FIG. 7 shows a schematic configuration diagram of a non-volatile memory device (hereinafter simply referred to as “memory device”) 200 including a plurality of memory cells 11.
- memory device hereinafter simply referred to as “memory device”
- FIG. 8A and 8B are diagrams illustrating an example of the load resistor 121.
- FIG. 8A and 8B are diagrams illustrating an example of the load resistor 121.
- FIG. 9 is a flowchart of a process for increasing the resistance of a defective bit in an excessively low resistance state.
- the memory device 200 includes the memory cell array 10 in which a plurality of (for example, 256) memory cells 11 having the structure described in the first embodiment are arranged.
- the memory device 200 includes a memory main body 201.
- the memory body 201 includes a memory cell array 10, a row selection circuit / driver 203, a column selection circuit / driver 204, a write circuit 205 for writing information, and a sense amplifier that amplifies the potential of the bit line 119. 206, a data input / output circuit 207 that performs input / output processing of input / output data via a terminal DQ, and a variable load resistance circuit 211.
- the memory device 200 further includes an address input circuit 208 that receives an address signal input from the outside, and a control circuit 209 that controls the operation of the memory body 201 based on a control signal input from the outside. Yes.
- the memory cell array 10 includes the nonvolatile memory elements described in the first embodiment arranged in a matrix as memory cells 11.
- the memory cell array 10 includes a plurality of word lines 101 (WL0, WL1, WL2,%) Formed in parallel with each other on a semiconductor substrate, and a main portion of the semiconductor substrate above the plurality of word lines 101.
- a plurality of memory cells 11 (M00, M01, M02,..., M10, M11, M12) provided in a matrix corresponding to the solid intersections of the plurality of word lines 101 and the plurality of bit lines 119. ,..., M20, M21, M22,.
- the memory cell 11 corresponds to the nonvolatile memory element (memory cell 11) according to the first embodiment, and includes a resistance variable layer including an oxygen-deficient tantalum oxide on a semiconductor substrate.
- a change element 105 is formed, and a bidirectional diode (here, MSM diode 112) is connected in series to the resistance change element 105.
- the address input circuit 208 receives an address signal from an external circuit (not shown), outputs a row address signal to the row selection circuit / driver 203 based on the address signal, and outputs a column address signal to the column selection circuit / driver.
- the address signal is a signal indicating the address of a specific memory cell 11 to be selected among the plurality of memory cells 11.
- the row address signal is a signal indicating a row address among the addresses indicated by the address signal
- the column address signal is a signal indicating a column address among the addresses indicated by the address signal.
- the control circuit 209 In the information write cycle, the control circuit 209 outputs a write signal instructing application of a write voltage to the write circuit 205 according to the input data Din input to the data input / output circuit 207. On the other hand, in the information read cycle, the control circuit 209 outputs a read signal instructing application of the read voltage to the column selection circuit / driver 204.
- the row selection circuit / driver 203 receives the row address signal output from the address input circuit 208, selects one of the plurality of word lines 101 in accordance with the row address signal, and selects the selected word line. A predetermined voltage is applied to 101.
- the column selection circuit / driver 204 receives the column address signal output from the address input circuit 208, selects one of the plurality of bit lines 119 in accordance with the column address signal, and selects the selected one. A write voltage or a read voltage is applied to the bit line 119.
- These row selection circuit / driver 203 and column selection circuit / driver 204 constitute a selection circuit that selects at least one memory cell 11 from the memory cell array 10.
- the write circuit 205 When the write circuit 205 receives the write signal output from the control circuit 209, the write circuit 205 outputs a signal instructing the row selection circuit / driver 203 to apply a voltage to the selected word line 101, and the column selection circuit. / Outputs a signal instructing the driver 204 to apply a write voltage to the selected bit line 119.
- the write circuit 205 when the write circuit 205 receives the write signal output from the control circuit 209, the write circuit 205 connects the load resistor 121 having the first resistance value to the selected word line 101 with respect to the variable load resistor circuit 211. A signal instructing to do is output.
- the variable load resistance circuit 211 includes a load resistor 121 whose resistance value can be changed, as exemplified in FIGS. 8A and 8B.
- the variable load resistance circuit 211 connects the load resistance 121 to the selected word line 101. Further, the variable load resistance circuit 211 changes the resistance value of the load resistor 121 to, for example, a first resistance value, a second resistance value smaller than the first resistance value, and a second resistance value smaller than the second resistance value. It is also possible to switch between the three resistance values in multiple stages.
- the load resistor 121 can be configured using a transistor 130.
- the variable load resistance circuit 211 changes the on-resistance of the transistor 130 by changing the gate voltage of the transistor 130.
- the variable load resistance circuit 211 changes the resistance value of the load resistance 121.
- the load resistor 121 may include a transistor 131 and a resistor 132 connected in parallel.
- the variable load resistance circuit 211 changes the resistance value of the load resistance 121 by switching the transistor 131 on and off.
- the sense amplifier 206 amplifies the potential of the bit line 119 to be read in the information read cycle.
- the output data DO obtained as a result is output to an external circuit via the data input / output circuit 207. That is, in the sense amplifier 206, the resistance change element 105 included in the memory cell 11 selected by the selection circuit (row selection circuit / driver 203 and column selection circuit / driver 204) is in either the high resistance state or the low resistance state. Is determined.
- the MSM diode 112 is in an ON state to which a high applied voltage is applied during writing. Therefore, since a large voltage is efficiently applied to the resistance change element 105, stable writing can be performed on the memory cell 11.
- an applied voltage lower than the applied voltage for writing is applied to the MSM diode 112.
- an applied voltage lower than the applied voltage for writing is applied to the MSM diode 112.
- the MSM diode 112 can efficiently prevent noise and crosstalk from affecting the variable resistance element 105, so that the malfunction of the memory cell 11 can be prevented.
- the memory device 200 according to the present embodiment is configured using the memory cell 11 shown in the first embodiment of the present invention.
- the memory device 200 further includes an excessive low resistance cell address recording unit that records the address of the excessive low resistance cell in the second high resistance state, and at least one spare memory cell (not shown). ),
- the control circuit 209 records the address of the excessive low resistance cell in the second high resistance state in the excessive low resistance cell address recording unit, and the address of the excessive low resistance cell is designated in the subsequent memory operation.
- a function of controlling access to the address of the spare memory cell may be provided.
- FIG. 9 is a flowchart of the high resistance write process for the memory cell 11 in the excessively low resistance state (hereinafter, excessively low resistance cell) by the memory device 200.
- control circuit 209 sets the resistance value of the load resistor 121 to the first resistance value. Further, the control circuit 209 applies the voltage pulse to the series circuit including the memory cell 11 and the load resistor 121 having the first resistance value during the normal write process, thereby setting the resistance change element 105 to the LR state. Transition reversibly between HR states.
- control circuit 209 detects an excessively low resistance cell which is a defective bit (S101).
- the control circuit 209 measures the resistance value in a state where the load resistor 121 having the first resistance value is connected to the memory cell 11.
- the control circuit 209 determines whether or not the resistance value measured above is lower than the LR level by a predetermined value or more. For example, if the resistance value measured above is LR level ⁇ 70% or less, the control circuit 209 determines that the cell is an excessively low resistance cell.
- the step S101 is performed, for example, during a verify operation during normal write processing.
- the step S101 is specifically performed by the control circuit 209 controlling the sense amplifier 206.
- control circuit 209 determines that the memory cell 11 to be processed is normal and ends the processing.
- the control circuit 209 controls the variable load resistance circuit 211 to thereby load the memory cell 11.
- the resistance value of the resistor 121 is switched from the first resistance value to a second resistance value smaller than the first resistance value (S103).
- the first resistance value is 5000 ⁇ and the second resistance value is 1000 ⁇ . This is because the voltage applied to the resistance change element 105 is effectively increased as described above.
- control circuit 209 applies a voltage pulse to a series circuit including the excessively low resistance cell and the load resistor 121 having the second resistance value, so that the resistance value of the excessively low resistance cell is lower than that of the LR state. A high second high resistance state is established.
- control circuit 209 controls the write circuit 205 to thereby execute the second high resistance write on both ends of the series circuit including the memory cell 11 and the load resistor 121 having the second resistance value.
- a voltage pulse for example, +6 to 10 V and a pulse width of 500 ns are applied (S104).
- control circuit 209 determines whether or not the excessive low-resistance cell has entered the second high-resistance state in step S104 by controlling the sense amplifier 206 (S105). For example, it is determined whether or not the resistance value of the memory cell 11 after the pulse application is higher than the LR level.
- the control circuit 209 controls the variable load resistance circuit 211 to further reduce the resistance value of the load resistance 121. Switching to the third resistance value (S109). Then, the control circuit 209 controls the writing circuit 205 to apply a voltage pulse to a series circuit including the excessively low resistance cell and the load resistor 121 having the third resistance value. The process of setting the cell to the second high resistance state (S104) is repeated.
- the third resistance value is 100 ⁇ .
- the control circuit 209 By controlling the variable load resistance circuit 211, the load resistance 121 is returned again to the first resistance value (5000 ⁇ ) (S107).
- the determination level after the high resistance write processing in step S105 may be set to a higher resistance value such as HR level (HR state resistance value) or higher, or +1 digit or higher from the HR level.
- HR level HR state resistance value
- the resistance value in the second high resistance state may be higher than the HR level, or may be one digit higher than the HR level.
- control circuit 209 determines the memory cell 11 having a high resistance as described above as a defective bit. In addition, the control circuit 209 stores information specifying the defective bit in a redundant circuit (not shown), and replaces the defective bit with a normal memory cell (S108).
- the nonvolatile memory device 200 detects the memory cell 11 (excessive low resistance cell) in which a failure has occurred due to the diode 112 being substantially short-circuited. Further, the nonvolatile memory device 200 reduces the resistance value of the load resistor 121 to a second resistance value lower than the first resistance value used during normal operation for the detected excessively low resistance cell. The voltage of the memory cell is applied to increase the resistance of the memory cell.
- the nonvolatile memory device 200 even when a failure occurs in a certain memory cell 11, another memory cell in the same row or the same column as the defective memory cell 11 is used. 11 can be effectively prevented from being unable to write to or read from.
- the present invention is not limited to this embodiment.
- the memory cell 11 stores only binary data of a first logical value corresponding to the first high resistance state and a second logical value corresponding to the first low resistance state.
- the memory cell 11 may store data of three or more values.
- the resistance change element 105 has a plurality of resistance states corresponding to the plurality of logical values.
- the excessive low resistance state (second low resistance state) described above is a state in which the resistance value is lower than the lowest resistance value among the resistance values of the plurality of resistance states.
- each processing unit included in the nonvolatile memory device is typically realized as an LSI which is an integrated circuit. These may be individually made into one chip, or may be made into one chip so as to include a part or all of them.
- circuits are not limited to LSI, and may be realized by a dedicated circuit or a general-purpose processor.
- An FPGA Field Programmable Gate Array
- reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.
- nonvolatile memory device may be realized by a processor such as a CPU executing a program.
- the present invention may be the above program or a recording medium on which the above program is recorded.
- the program can be distributed via a transmission medium such as the Internet.
- MOS transistor an example using a MOS transistor is shown, but another transistor such as a bipolar transistor may be used.
- the present invention can be applied to a nonvolatile memory device and a driving method thereof.
- the present invention is useful for various electronic devices such as digital home appliances, memory cards, portable telephones, and personal computers using a nonvolatile storage device.
- Memory cell array (semiconductor memory device) 11,280 Memory cell (nonvolatile memory element) 21, 22 IV curve 100 Substrate 101, 220 Word line (first wiring) 102 First interlayer insulating layer 103 First contact plug 105, 260 Resistance change element 106 Lower electrode 107 Resistance change layer 108 Upper electrode 109 Second interlayer insulating layer 110 Second contact plug 112, 270 Diode 113 Lower electrode 114 Semiconductor layer 115 Upper electrode 116 Third interlayer insulating layer 117 Third contact plug 118 Fourth contact plug 119, 210 Bit line (second wiring) 120 Lead-out wiring 121 Load resistance 130, 131 Transistor 132 Resistance 200 Non-volatile memory device (memory device) DESCRIPTION OF SYMBOLS 201 Memory body part 203 Row selection circuit / driver 204 Column selection circuit / driver 205 Write circuit 206 Sense amplifier 207 Data input / output circuit 208 Address input circuit 209 Control circuit 211 Variable load resistance circuit
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Abstract
Description
[概略構成]
図1Aは、本発明の第1の実施の形態に係るメモリセル11を示す概略回路図である。
本実施の形態における抵抗変化素子105の抵抗変化層107は、酸素不足型の遷移金属酸化物を含む。ここで、酸素不足型の遷移金属酸化物とは、化学量論的な酸化物と比較して酸素の含有量[原子比:総原子数に占める酸素原子数の割合]が少ない遷移金属酸化物をいう。例えば遷移金属がタンタル(Ta)の場合には、化学量論的な酸化物の組成はTa2O5であって、TaとOの原子数の比率(O/Ta)は2.5である。したがって、酸素不足型のタンタル酸化物は、TaとOの原子比は0より大きく、2.5より小さいことになる。
本実施の形態においては、前述のように、絶対値がある閾値以上の極性の異なる電気パルスを抵抗変化素子105の両電極間に印加することで抵抗変化素子105の抵抗値を切り換える。したがって、メモリセル11では両電極間にいずれの方向にも電流が流れる必要がある。よって、メモリセルが選択されたときに抵抗変化素子105に双方向に電流を流し、メモリセルが非選択のときに抵抗変化素子105に電流を流さない機能を有する双方向のダイオード112が適用される。ダイオード112は、非線形の電流-電圧特性を有する素子であり、印加電圧の絶対値が臨界電圧未満では抵抗値が大きく(オフ状態)、印加電圧の絶対値が正又は負の臨界電圧の絶対値以上では抵抗値が極端に小さくなる(オン状態)素子である。
以下では、抵抗変化層107としてタンタルの酸素不足型酸化物(膜厚:約30nm)を用いた抵抗変化素子105と、半導体層114として窒素不足型窒化シリコンを用いたダイオード112とを直列接続したときの特性について説明する。
図6に示す「ダイオード破壊」点以降は、メモリセル11のダイオード112が絶縁破壊して短絡を起こしている状態である。
次に、第2の実施の形態では、第1の実施の形態で説明した半導体記憶装置(メモリセルアレイ)10を有する不揮発性記憶装置について説明する。
11、280 メモリセル(不揮発性記憶素子)
21、22 IVカーブ
100 基板
101、220 ワード線(第1の配線)
102 第1の層間絶縁層
103 第1のコンタクトプラグ
105、260 抵抗変化素子
106 下部電極
107 抵抗変化層
108 上部電極
109 第2の層間絶縁層
110 第2のコンタクトプラグ
112、270 ダイオード
113 下部電極
114 半導体層
115 上部電極
116 第3の層間絶縁層
117 第3のコンタクトプラグ
118 第4のコンタクトプラグ
119、210 ビット線(第2の配線)
120 引き出し配線
121 負荷抵抗
130、131 トランジスタ
132 抵抗
200 不揮発性記憶装置(メモリ装置)
201 メモリ本体部
203 行選択回路/ドライバ
204 列選択回路/ドライバ
205 書き込み回路
206 センスアンプ
207 データ入出力回路
208 アドレス入力回路
209 制御回路
211 可変負荷抵抗回路
Claims (10)
- 非線形の電流-電圧特性を有するダイオードと、当該ダイオードに直列に接続されている抵抗変化素子とを含む複数のメモリセルと、
前記複数のメモリセルに直列に接続される可変負荷抵抗とを備える不揮発性記憶装置の駆動方法であって、
前記メモリセルと第1の抵抗値の前記可変負荷抵抗とで構成される直列回路に、第1の低抵抗化電気パルスを印加することにより、前記抵抗変化素子を第1の高抵抗状態から第1の低抵抗状態に変化させ、第1の高抵抗化電気パルスを印加することにより、前記抵抗変化素子を前記第1の低抵抗状態から前記第1の高抵抗状態に変化させて前記第1の低抵抗状態と第1の高抵抗状態との間を可逆的に遷移させ、
前記複数のメモリセルのうち、前記第1の低抵抗状態より抵抗値が低い第2の低抵抗状態の抵抗変化素子を含む過剰低抵抗セルを検出する検出ステップと、
前記可変負荷抵抗の抵抗値を、前記第1の抵抗値から、前記第1の抵抗値より低い第2の抵抗値に変更する第1可変抵抗値変更ステップと、
前記過剰低抵抗セルと、前記第2の抵抗値の前記可変負荷抵抗とで構成される直列回路に第2の高抵抗化電気パルスを印加することにより、前記過剰低抵抗セルに含まれる前記抵抗変化素子を、前記第2の低抵抗状態から、前記第1の低抵抗状態より抵抗値が高い第2の高抵抗状態にする第2の高抵抗化書き込みステップとを含む
不揮発性記憶装置の駆動方法。 - 前記第2の高抵抗状態の抵抗値は、前記第1の高抵抗状態より高い
請求項1に記載の不揮発性記憶装置の駆動方法。 - 前記第2の高抵抗化書き込みステップは、
前記過剰低抵抗セルと、前記第2の抵抗値の前記可変負荷抵抗とで構成される直列回路に前記第2の高抵抗化電気パルスを印加する第1印加ステップと、
前記第1印加ステップ後に、前記過剰低抵抗セルの抵抗値を読み出すステップと、
前記読み出しステップにより前記過剰低抵抗セルに含まれる前記抵抗変化素子が前記第2の高抵抗状態になったか否かを判定する判定ステップと、
前記判定ステップにおいて前記過剰低抵抗セルが前記第2の高抵抗状態になっていないと判定された場合、前記可変負荷抵抗の抵抗値を前記第2の抵抗値より低い第3の抵抗値にする第2可変抵抗値変更ステップと、
前記過剰低抵抗素子と、前記第3の抵抗値の前記可変負荷抵抗とで構成される直列回路に第2の高抵抗化電気パルスを印加することにより、前記過剰低抵抗素子を前記第2の高抵抗状態にする第2印加ステップとを含み、
前記判定ステップにおいて前記過剰低抵抗セルに含まれる前記抵抗変化素子が前記第2の高抵抗状態になるまで前記各ステップが繰り返される
請求項1又は2に記載の不揮発性記憶装置の駆動方法。 - 前記可変負荷抵抗は、トランジスタを含み、
前記第1可変抵抗値変更ステップでは、前記トランジスタのゲート電圧を変化させることにより、前記可変負荷抵抗の抵抗値をより低い抵抗値に変化させる
請求項1~3のいずれか1項に記載の不揮発性記憶装置の駆動方法。 - 前記不揮発性記憶装置の駆動方法は、さらに、
前記第2の高抵抗化書き込みステップの後、前記可変負荷抵抗の抵抗値を、前記第1の抵抗値よりも低い抵抗値から前記第1の抵抗値に変更する第2可変抵抗値変更ステップを含む
請求項1~4のいずれか1項に記載の不揮発性記憶装置の駆動方法。 - 前記メモリセルは、前記第1の高抵抗状態に対応する第1の論理値と、前記第1の低抵抗状態に対応する第2の論理値との、2値のみのデータを記憶する
請求項1~5のいずれか1項に記載の不揮発性記憶装置の駆動方法。 - 基板の主面に平行に、第1の方向に所定の間隔で配置された複数の第1の配線と、
前記基板の主面に平行にかつ前記第1の配線と立体交差するように、第2の方向に所定の間隔で配置された複数の第2の配線と、
前記複数の第1の配線と、前記複数の第2の配線との交差点に配置され、非線形の電流-電圧特性を有するダイオードと、当該ダイオードに直列に接続されている抵抗変化素子とを含む2端子の複数のメモリセルの各端子がそれぞれ前記複数の第1の配線と前記複数の第2の配線に接続されたメモリセルアレイと、
前記メモリセルアレイに含まれる前記メモリセルを選択し所定の書き込み及び読み出し電圧を前記選択されたメモリセルに印加するための行選択回路/ドライバ及び列選択回路/ドライバと、
前記選択されたメモリセルの抵抗値を読み出すためのセンスアンプと、
前記メモリセルアレイに直列に接続される可変負荷抵抗回路と、を備える不揮発性記憶装置であって、
前記選択されたメモリセルに含まれる前記抵抗変化素子は、前記選択されたメモリセルと第1の抵抗値の前記可変負荷抵抗とで構成される直列回路に、第1の高抵抗化電気パルスが印加されることにより、第1の低抵抗状態から第1の高抵抗状態に変化し、第1の低抵抗化電気パルスが印加されることにより、前記第1の高抵抗状態から前記第1の低抵抗状態に可逆的に変化し、
前記不揮発性記憶装置は、
前記複数のメモリセルのうち、前記第1の低抵抗状態より抵抗値が低い第2の低抵抗状態の抵抗変化素子を含む過剰低抵抗セルを検出し、
前記可変負荷抵抗の抵抗値を、前記第1の抵抗値から、前記第1の抵抗値より低い第2の抵抗値に変更し、
前記過剰低抵抗セルと、前記第2の抵抗値の前記可変負荷抵抗とで構成される直列回路に第2の高抵抗化電気パルスを印加することにより、前記過剰低抵抗セルに含まれる前記抵抗変化素子を、前記第1の低抵抗状態より抵抗値が高い第2の高抵抗状態にする制御回路をさらに備える
不揮発性記憶装置。 - 前記不揮発性記憶装置は、第2の高抵抗状態にした過剰低抵抗セルのアドレスを記録する記録部と、少なくとも1つの予備のメモリセルとをさらに備え、
前記制御回路は、第2の高抵抗状態にした過剰低抵抗セルのアドレスを記録し、以降のメモリ動作時において前記過剰低抵抗セルのアドレスが指定された場合、予備のメモリセルのアドレスにアクセスするよう制御する機能を備える
請求項6に記載の不揮発性記憶装置。 - 前記第2の高抵抗状態の抵抗値は、前記第1の高抵抗状態より高い
請求項7又は8に記載の不揮発性記憶装置の駆動方法。 - 前記制御回路は、過剰低抵抗セルを第2の高抵抗状態にした後、前記可変負荷抵抗回路の抵抗値を前記第1の抵抗値に戻すよう前記可変負荷抵抗回路を制御する
請求項7~9のいずれか1項に記載の不揮発性記憶装置。
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