Patent ID: 7433222

Claim:
A nonvolatile semiconductor memory device comprising: a variable resistive element having a two-terminal structure wherein a resistive characteristic specified by current-voltage characteristics between two terminals can transit between two resistive characteristics of low resistance state and high resistance state that can be taken stably when voltage is applied to one terminal based on the other terminal with at least one of positive or negative polarities, the variable resistive element including different first threshold voltage and second threshold voltage, the first threshold voltage being the lower limit of an absolute value of applied voltage necessary for the resistive characteristic to transit from the low resistance state to the high resistance state, and the second threshold voltage being the lower limit of an absolute value of applied voltage necessary for the resistive characteristic to transit from the high resistance state to the low resistance state, wherein a memory state of the variable resistive element is determined by whether the resistive characteristic is either in the low resistance state or in the high resistance state, and the memory state can be written as a result of a transition of the resistive characteristic between the low resistance state and the high resistance state by applying voltage between both terminals of the variable resistive element, a load circuit for applying voltage between both terminals of the variable resistive element when the memory state of the variable resistive element is written is provided so as to be electrically connected in series with the variable resistive element to be written, a load resistive characteristic specified by current-voltage characteristics of the load circuit can be switched between two different load resistive characteristics, the two load resistive characteristics of the load circuit is selectively switched depending on whether the resistive characteristic of the variable resistive element to be written transits from the low resistance state to the high resistance state or from the high resistance state to the low resistance state, predetermined voltage for writing applied to both ends of a serial circuit of the variable resistive element to be written and the load circuit allows voltage necessary for transition from one of the two resistive characteristics to the other to be applied between both terminals of the variable resistive element, and after the resistive characteristic of the variable resistive element transits from the one resistive characteristic to the other resistive characteristic, the voltage applied between both terminals of the variable resistive element does not allow the resistive characteristic to return from the other resistive characteristic to the one resistive characteristic depending on the selected load resistive characteristic.