Nonvolatile memory device and method for programming nonvolatile memory element

A nonvolatile memory device comprising:

• a nonvolatile memory element including:
• a first electrode;
• a second electrode;
• and a variable resistance layer having a resistance state which reversibly changes between a high resistance state and a low resistance state in which a resistance value of said variable resistance layer is smaller than the resistance value in the high resistance state, based on electrical signals having different polarities which are given between said first electrode and said second electrode, said variable resistance layer being interposed between said first electrode and said second electrode;
• and
• a control circuit for applying a voltage having a first polarity between said first electrode and said second electrode to change a resistance state of said variable resistance layer from the low resistance state to the high resistance state, and applying a voltage having a second polarity opposite to the first polarity between said first electrode and said second electrode to change the resistance state of said variable resistance layer from the high resistance state to the low resistance state,
• wherein said control circuit:
• determines whether the resistance value of said variable resistance layer in one state between the high resistance state and the low resistance state is equal to or greater than a predetermined threshold value;
• changes the resistance state of said variable resistance layer from the one state between the high resistance state and the low resistance state to the other state on a first write condition if the resistance value of said variable resistance layer is smaller than the threshold value;
• and
• changes the resistance state of said variable resistance layer from the one state to the other state on a second write condition weaker than the first write condition if the resistance value of said variable resistance layer is equal to or greater than the threshold value.

A method for programming a nonvolatile memory device, the nonvolatile memory device comprising:

• a nonvolatile memory element including:
• a first electrode;
• a second electrode;
• and a variable resistance layer having a resistance state which reversibly changes between a high resistance state and a low resistance state in which a resistance value of said variable resistance layer is smaller than the resistance value in the high resistance state, based on electrical signals having different polarities which are given between said first electrode and said second electrode, said variable resistance layer being interposed between said first electrode and said second electrode,
• said method for programming the nonvolatile memory element comprising:
• applying between the first electrode and the second electrode a high resistance writing voltage which has a first polarity to change a resistance state of the variable resistance layer from the low resistance state to the high resistance state;
• determining whether the resistance value of the variable resistance layer in the high resistance state is equal to or greater than a first threshold value;
• applying between the first electrode and the second electrode a first voltage having a second polarity opposite to the first polarity if the resistance value of the variable resistance layer in the high resistance state is smaller than the first threshold value to change the resistance state of the variable resistance layer from the high resistance state to the low resistance state;
• and
• applying between the first electrode and the second electrode a second voltage having a second polarity an absolute value of which is smaller than an absolute value of the first voltage if the resistance value of the variable resistance layer in the high resistance state is equal to or greater than the first threshold value to change the resistance state of the variable resistance layer from the high resistance state to the low resistance state.

A method for programming a nonvolatile memory device, the nonvolatile memory device comprising:

• a nonvolatile memory element including:
• a first electrode;
• a second electrode;
• and a variable resistance layer having a resistance state which reversibly changes between a high resistance state and a low resistance state in which a resistance value of said variable resistance layer is smaller than the resistance value in the high resistance state, based on electrical signals having different polarities which are given between said first electrode and said second electrode, said variable resistance layer being interposed between said first electrode and said second electrode,
• said method for programming the nonvolatile memory element comprising:
• applying a voltage between the first electrode and the second electrode to change a resistance state of the variable resistance layer from one state between the low resistance state and the high resistance state to the other state,
• determining whether the resistance value of the variable resistance layer in the other state is equal to or greater than a first threshold value;
• changing the resistance state of the variable resistance layer from the one state between the high resistance state and the low resistance state to the other state on a first write condition if the resistance value of the variable resistance layer is smaller than a first threshold value;
• and
• changing the resistance state of the variable resistance layer from the one state to the other state on a second write condition weaker than the first write condition if the resistance value of the variable resistance layer is equal to or greater than the first threshold value.