FORMING METHOD OF PERFORMING FORMING ON VARIABLE RESISTANCE NONVOLATILE MEMORY ELEMENT, AND VARIABLE RESISTANCE NONVOLATILE MEMORY DEVICE
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Abstract
A forming method of a variable resistance nonvolatile memory element capable of lowering a forming voltage and preventing variations of the forming voltage depending on variable resistance elements. The forming method is for initializing a variable resistance element, including a step (S24) of determining whether or not a current flowing in a 1T1R memory cell is greater than a reference current; a step (S22) of applying a forming positive voltage pulse having a pulse width (Tp(n)) is gradually increased when it is determined that the current is not greater than the reference current; and a step (S23) of applying a negative voltage pulse having a pulse width Tn equal to or shorter than a pulse width Tp(n). The determining step (S24), the application step (S22), and the application step (S23) are repeated until the forming becomes successful.
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Citations
50 Claims
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1-25. -25. (canceled)
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26. A forming method of performing forming on a variable resistance nonvolatile memory element, by applying a voltage pulse to a memory cell in which the variable resistance nonvolatile memory element is connected in series with a switch element, so as to change a resistance state of the variable resistance nonvolatile memory element from an initial state after manufacturing to a changeable state, the initial state being higher than a high resistance state and having not yet been changed to the changeable state, and the changeable state being a state where the resistance state is reversibly changeable between the high resistance state and a low resistance state according to a polarity of an applied voltage pulse and being lower than the initial state,
the variable resistance nonvolatile memory element including: - a first electrode connected to the switch element;
a second electrode; and
an oxygen-deficient transition metal oxide layer provided between the first electrode and the second electrode,the oxygen-deficient transition metal oxide layer including;
a first transition metal oxide layer in contact with the first electrode; and
a second transition metal oxide layer in contact with the second electrode, the second transition metal oxide layer having an oxygen deficient degree lower than an oxygen deficient degree of the first transition metal oxide layer,the variable resistance nonvolatile memory element having; characteristics by which the resistance state is changed to the low resistance state when a low resistance writing voltage pulse having a positive potential and equal to or higher than a first threshold voltage is applied to the first electrode with reference to the second electrode, and the resistance state is changed to the high resistance state when a high resistance writing voltage pulse having a positive potential and equal to or higher than a second threshold voltage is applied to the second electrode with reference to the first electrode; non-linear current-voltage characteristics in the initial state; and characteristics by which as a current flowing in the variable resistance nonvolatile memory element is increased in the initial state, a time period required for the forming is decreased in an exponential manner, and the forming method comprising; applying a first voltage pulse to the variable resistance nonvolatile memory element when the variable resistance nonvolatile memory element is in the initial state, the first voltage pulse (1) having (1-i) a positive potential at the second electrode with reference to the first electrode and an amplitude equal to or greater than an amplitude of a predetermined voltage higher than the second threshold voltage or (1-ii) a negative potential at the second electrode with reference to the first electrode and an amplitude equal to or greater than an amplitude of a predetermined voltage higher than the first threshold voltage, and the first voltage pulse (2) having a first pulse width; and determining whether or not the forming is successful by the applying of the first voltage pulse, wherein the applying of the first voltage pulse and the determining are repeated until it is determined in the determining that the forming is successful, and in the applying of the first voltage pulse in the repeating, a new first voltage pulse is applied to the variable resistance nonvolatile memory element, the new first voltage pulse having a pulse width longer than a pulse width of the first voltage pulse applied in the applying of the first voltage pulse which is performed immediately prior to the applying of the new first voltage pulse. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37)
- a first electrode connected to the switch element;
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38. A variable resistance nonvolatile memory device including memory cells in each of which a variable resistance nonvolatile memory element is connected in series with a switch element,
the variable resistance nonvolatile memory element including: - a first electrode connected to the switch element;
a second electrode; and
an oxygen-deficient transition metal oxide layer provided between the first electrode and the second electrode,the oxygen-deficient transition metal oxide layer including;
a first transition metal oxide layer in contact with the first electrode; and
a second oxygen-deficient transition metal oxide layer in contact with the second electrode, the second oxygen-deficient transition metal oxide layer having an oxygen deficient degree lower than an oxygen deficient degree of the first transition metal oxide layer,the variable resistance nonvolatile memory element having; characteristics by which a resistance state of the variable resistance nonvolatile memory element is changed to the low resistance state when a low resistance writing voltage pulse having a positive voltage and equal to or higher than a first threshold voltage is applied to the first electrode with reference to the second electrode, and the resistance state is changed to a high resistance state when a high resistance writing voltage pulse having a positive voltage and equal to or higher than a second threshold voltage is applied to the second electrode with reference to the first electrode; non-linear current-voltage characteristics in an initial state after manufacturing where the resistance state is higher than the high resistance sate and has not yet been changed to a changeable state where the resistance state is reversibly changeable between the high resistance state and the low resistance state according to a polarity of an applied voltage pulse and is lower than the initial state; and characteristics by which (i) when a voltage pulse of a voltage equal to or higher than a predetermined voltage is applied in the initial state and is kept being applied for a predetermined time period, forming occurs to change the resistance state from the initial state to the changeable state, and (ii) as a current flowing in the variable resistance nonvolatile memory element is increased, a time period required for the forming is decreased in an exponential manner, and the variable resistance nonvolatile memory device comprising; a memory cell array including the memory cells in each of which the variable resistance nonvolatile memory element is connected in series with the switch element; a selection unit configured to select at least one memory cell from the memory cell array; a forming power source unit configured to generate a forming voltage to perform the forming on the variable resistance nonvolatile memory element included in the at least one memory cell selected by the selection unit; a writing power source unit configured to generate a writing voltage to perform writing to change the resistance state of the variable resistance nonvolatile memory element included in the at least one memory cell selected by the selection unit from the high resistance state to the low resistance state or from the low resistance state to the high resistance state; a variable pulse width writing voltage pulse generation unit configured to generate a writing voltage pulse having a variable pulse width to change the resistance state of the variable resistance nonvolatile memory element to a desired state, when one of the forming and the writing is performed on the variable resistance nonvolatile memory element included in the at least one memory cell selected by the selection unit; and a reading unit including (a) a forming determination unit configured to determine whether or not the forming is successful on the variable resistance nonvolatile memory element included in the at least one memory cell selected by the selection unit and (b) a normal determination unit configured to determine whether or not the variable resistance nonvolatile memory element included in the at least one memory cell selected by the selection unit is in the high resistance state or in the low resistance state, wherein the variable pulse width writing voltage pulse generation unit is configured, for the forming on the variable resistance nonvolatile memory element, to apply a first voltage pulse to the variable resistance nonvolatile memory element, the first voltage pulse (1) having (1-i) a positive potential at the second electrode with reference to the first electrode and an amplitude equal to or greater than an amplitude of a predetermined voltage higher than the second threshold voltage or (1-ii) a negative potential at the second electrode with reference to the first electrode and an amplitude equal to or greater than an amplitude of a predetermined voltage higher than the first threshold voltage, and the first voltage pulse (2) having a first pulse width, the application by the variable pulse width writing voltage pulse generation unit and the determination by the forming determination unit are repeated until the forming determination unit determines that the forming is successful, and in the repetition, the variable pulse width writing voltage pulse generation unit is configured to apply a new first voltage pulse to the variable resistance nonvolatile memory element, the new first voltage pulse having a pulse width longer than a pulse width of the first voltage pulse applied immediately prior to the new first voltage pulse. - View Dependent Claims (39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49)
- a first electrode connected to the switch element;
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50. A variable resistance nonvolatile memory element connected in series with a switch element to form a memory cell, the variable resistance nonvolatile memory element comprising:
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a first electrode connected to the switch element;
a second electrode; and
an oxygen- deficient transition metal oxide layer provided between the first electrode and the second electrode,wherein the oxygen-deficient transition metal oxide layer includes;
a first transition metal oxide layer in contact with the first electrode; and
a second transition metal oxide layer in contact with the second electrode, the second transition metal oxide layer having an oxygen deficient degree lower than an oxygen deficient degree of the first transition metal oxide layer, andthe variable resistance nonvolatile memory element has; characteristics by which a resistance state of the variable resistance nonvolatile memory element is changed to a low resistance state when a low resistance writing voltage pulse having a positive potential and equal to or higher than a first threshold voltage is applied to the first electrode with reference to the second electrode, and the resistance state is changed to a high resistance state when a high resistance writing voltage pulse having a positive potential and equal to or higher than a second threshold voltage is applied to the second electrode with reference to the first electrode; an initial state after manufacturing where the resistance state is higher than the high resistance state and has not yet been changed to a changeable state where the resistance state is reversibly changeable between the high resistance state and the low resistance state according to a polarity of an applied voltage pulse and is lower than the initial state; non-linear current-voltage characteristics in the initial state; characteristics by which (i) when a voltage pulse of a voltage equal to or higher than a predetermined voltage is applied in the initial state and is kept being applied for a predetermined time period, forming occurs to change the resistance state to the changeable state, and (ii) as a current flowing in the variable resistance nonvolatile memory element is increased, a time period required for the forming is decreased in an exponential manner; and characteristics, in the forming, by which as a cumulative pulse application time period of at least one applied voltage pulse is increased, a probability that the forming is successful is increased.
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Specification