Patent ID: 9251898
Filing Date: 2016-02-02
CPC Classification: G11C,H01L

Claim Text:
1. A method for programming a nonvolatile memory element which includes a variable resistance element that is nonvolatile and a bidirectional diode that is connected in series with the variable resistance element, wherein the nonvolatile memory element further includes a load resistor which is connected in series with the variable resistance element and whose resistance value can be changed, and the variable resistance element includes: a first transition metal oxide layer comprising a first transition metal; and a second transition metal oxide layer comprising a second transition metal and having a lower degree of oxygen deficiency than the first transition metal oxide layer, the method comprising: decreasing a resistance value of the variable resistance element to be lower than a resistance value of the variable resistance element in an initial state, by applying an initialization voltage pulse to a series circuit in which the variable resistance element, the bidirectional diode, and the load resistor are connected in series, the resistance value of the variable resistance element in the initial state being higher than a resistance value of the variable resistance element in a high resistance state, and the load resistor having a first resistance value; causing, after the decreasing, the variable resistance element to change from the high resistance state to a low resistance state in which the resistance value of the variable resistance element is lower than the resistance value of the variable resistance element in the high resistance state, by applying a write voltage pulse to the series circuit after a resistance value of the load resistor is changed to a second resistance value lower than the first resistance value, the write voltage pulse having a first polarity; and causing, after the decreasing, the variable resistance element to change from the low resistance state to the high resistance state by applying an erase voltage pulse to the series circuit after a resistance value of the load resistor is changed to a third resistance value lower than the first resistance value, the erase voltage pulse having a second polarity opposite to the first polarity, wherein in the decreasing, a divided voltage applied to the load resistor varies according to a current flowing through the bidirectional diode.