Patent ID: 8848421
Filing Date: 2014-09-30
Classification: G11C,H01L

Abstract:
1. 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.