Patent ID: 8432720
Filing Date: 2013-04-30
Classification: G11C,H01L

Abstract:
1. A nonvolatile semiconductor memory device comprising a memory cell array provided in such a manner that nonvolatile variable resistive elements each having a variable resistor formed of a metal oxide film having resistance changing depending on an oxygen concentration in the film, an insulation film having contact with the variable resistor, a first electrode connected to the variable resistor through the insulation film, and a second electrode directly connected to the variable resistor without passing through the insulation film, are arranged in at least row and column directions in the form of a matrix, wherein the variable resistive element is provided in such a manner that an oxygen depletion layer having an oxygen concentration lower than a stoichiometric composition, in the metal oxide film serving as the variable resistor, is formed at an interface between the variable resistor and the first electrode on the side of the variable resistor, connection between the first electrode and the variable resistor is rectifier junction with the insulation film interposed therebetween, connection between the second electrode and the variable resistor is ohmic junction, oxygen reversibly moves between the insulation film and the variable resistor when a voltage having an absolute value of a first threshold value or more is applied across the first and second electrodes in a forward direction of the rectifier junction, the oxygen depletion layer narrows, and resistance characteristics of the variable resistive element shifts to a low resistance state, oxygen reversibly moves between the insulation film and the variable resistor when a voltage having an absolute value of a second threshold value or more is applied across the first and second electrodes in a reverse direction of the rectifier junction, the oxygen depletion layer widens, and the resistance characteristics of the variable resistive element shifts to a high resistance state, and each of the resistance characteristics of the low resistance state and the resistance characteristics of the high resistance state has asymmetric characteristics such that when a predetermined voltage is applied across the first and second electrodes, a current amount flowing in the variable resistive element is large in the case where the voltage is applied in the forward direction of the rectifier junction, and small in the case where the voltage is applied in the reverse direction of the rectifier junction.