Patent ID: 8902629
Filing Date: 2014-12-02
Classification: G11C,H01L

Abstract:
1. A forming method of performing forming on a variable resistance nonvolatile memory element, by applying a forming voltage pulse to memory cells in each of which a 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 to an operable state, the initial state being a state where no voltage has yet been applied after manufacturing, and the operable state being a state where a resistance value of the variable resistance nonvolatile memory element is smaller than a resistance value of the variable resistance nonvolatile memory element in the initial state and the resistance state is changeable between a high resistance state and a low resistance state according to a polarity of a voltage pulse which is applied in a normal operation, the variable resistance nonvolatile memory element including: a first electrode; a second electrode; and a transition metal oxide layer provided between the first electrode and the second electrode, the transition metal oxide layer including: a first oxygen-deficient transition metal oxide layer connected to 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 smaller than an oxygen deficient degree of the first oxygen-deficient transition metal oxide layer, the variable resistance nonvolatile memory element having: in the normal operation, characteristics by which the resistance state is changed to the low resistance state when a positive voltage having a first writing voltage pulse which is 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 positive voltage having a second writing voltage pulse which is equal to or higher than a second threshold voltage is applied to the second electrode with reference to the first electrode; in the initial state, characteristics by which when a first forming voltage having an amplitude equal to or greater than a first absolute value is applied between the first electrode and the second electrode so that a cumulative time period during which the first forming voltage is applied exceeds a first predetermined time period, first forming occurs to change the resistance state of the variable resistance nonvolatile memory element from the initial state to a first operable state where the resistance state is changeable between the high resistance state and the low resistance state according to application of a normal operation voltage, and the first predetermined time period decreases as a current flowing in the variable resistance nonvolatile memory element increases in the application of the first forming voltage; and in the first operable state after the first forming, characteristics by which when a second forming voltage is applied between the first electrode and the second electrode so that a cumulative time period during which the second forming voltage is applied exceeds a second predetermined time period, second forming occurs to change the resistance state of the variable resistance nonvolatile memory element from the first operable state to a second operable state where the resistance state is changeable to a low resistance state having a resistance value lower than a resistance value of the low resistance state in the first operable state, and said forming method comprising: applying the first forming voltage between the first electrode and the second electrode in the initial state, until the first forming occurs; and applying the second forming voltage between the first electrode and the second electrode in the first operable state after the first forming, until the second forming occurs.