Variable resistance nonvolatile memory device and method for writing into the same

摘要

In a method for writing into a variable resistance nonvolatile memory device according to one aspect of the present disclosure, a verify write operation of newly applying a voltage pulse for changing a resistance state is performed on a variable resistance element which does not satisfy a determination condition for verifying that the resistance state has been changed despite application of a voltage pulse for changing the resistance state, and the determination condition in the verify write operation is relaxed when an average number of times of verify write operation, having already been performed on all or part of a plurality of variable resistance elements that are targets for write operation, exceeds a predetermined number of times.

主权项

1. A method for writing information into a variable resistance nonvolatile memory device including a variable resistance element, the method comprising:
(A) applying an initial voltage pulse to the variable resistance element for changing a resistance value of the variable resistance element; (B) performing a first verify operation at least once after applying the initial voltage pulse, the first verify operation including
(b1) reading the resistance value of the variable resistance element,(b2) determining whether or not the read resistance value satisfies a first determination condition, and(b3) applying a voltage pulse to the variable resistance element when the read resistance value does not satisfy the first determination condition; (C) stopping the first verify operation when a number of times of the first verify operation exceeds a predetermined number; and (D) performing a second verify operation at least once when the number of times of the first verify operation exceeds the predetermined number, the second verify operation including
(d1) reading the resistance value of the variable resistance element,(d2) determining whether or not the read resistance value satisfies a second determination condition that is looser than the first determination condition, and(d3) applying the voltage pulse to the variable resistance element when the read resistance value does not satisfy the second determination condition.