Patent ID: 8102696
Filing Date: 2012-01-24
Classification: G11C

Abstract:
1. A nonvolatile memory device comprising: a memory cell array including plural resistance variable elements each of which has a first terminal and a second terminal and is configured to store data based on switching in an electric resistance between the first terminal and the second terminal; an electric pulse application circuit which includes a first output terminal and a second output terminal and is configured to output an electric pulse between the first output terminal and the second output terminal; a select circuit which is configured to select a desired resistance variable element from resistance variable elements in the memory cell array as a selected resistance variable element, electrically connect the first terminal of the selected resistance variable element to the first output terminal, and electrically connect the second terminal of the selected resistance variable element to the second output terminal; a series resistance setting unit configured to set a resistance value of a series current path as desired, the series current path being a current path electrically connecting the first output terminal to a reference node, the reference node being a point on a current path connecting the first output terminal to the first terminal of the selected resistance variable element, a potential between the second output terminal and the reference node being a node potential; and a control circuit configured to control the series resistance setting unit to set the resistance value of the series current path; wherein the node potential is obtained by dividing a voltage between the first and the second output terminals by at least the resistance value of the series resistance setting unit and the resistance value of the selected resistance variable element; wherein each of the resistance variable elements has a characteristic in which the resistance variable element in a low-resistance state switches to a high-resistance state in which a resistance value of the resistance variable element is higher than a resistance value of the resistance variable element in the low-resistance state, when the node potential is higher in absolute value than a first voltage level corresponding to each of the resistance variable elements, and the resistance variable element in the high-resistance state switches from the high-resistance state to the low-resistance state when the node potential is higher in absolute value than a second voltage level which is identical in polarity to the first voltage level, corresponds to each of the resistance variable elements and is higher in absolute value than the first voltage level; and wherein the control circuit is configured to perform control for at least one of: (A) changing the resistance value of the series current path within a predetermined range with time so that the node potential falls within a predetermined range between a lower limit of a variation distribution of the first voltage level in the memory cell array and an upper limit of the variation distribution in a state where the resistance variable element is in the low-resistance state and is lower than the lower limit of the variation distribution of the second voltage level after the resistance variable element has switched to the high-resistance state when the resistance variable element is switched from the low-resistance state to the high-resistance state; and (B) changing the resistance value of the series current path within a predetermined range with time so that the node potential falls within a predetermined range between a lower limit of a variation distribution of the second voltage level in the memory cell array and an upper limit of the variation distribution in a state where the resistance variable element is in the high-resistance state and is lower than the lower limit of the variation distribution of the first voltage level after the resistance variable element has switched to the low-resistance state when the resistance variable element is switched from the high-resistance state to the low-resistance state.