Nonvolatile semiconductor memory device

A nonvolatile semiconductor memory device, comprising:

• a memory cell array including memory cells arranged therein, each of the memory cells being provided between a first line and a second line and including a variable resistor;
• and
• a control circuit configured to apply a voltage to a memory cell through the first and second lines, during a forming operation, the control circuit being configured to repeat an operation of applying a voltage to the memory cell while limiting a value of a current flowing across the memory cell to a current limit value and an operation of changing the current limit value when the current flowing across the memory cell during the forming operation has reached the current limit value,
• wherein
• when the voltage for the forming operation has reached a voltage upper limit value, the control circuit executes an operation of stopping application of the voltage for the forming operation and changing the current limit value, and
• after stopping application of the voltage for the forming operation, the control circuit executes a reading operation in the memory cell, and when a resistance value of the memory cell is higher than a first value, executes an operation of changing the current limit value, whereas when the resistance value of the memory cell is equal to or lower than the first value, completes the forming operation.

A method of forming a nonvolatile semiconductor memory device including memory cells each provided between a first line and a second line and each configured by series connection of a variable resistor and a rectifying element, the method comprising:

• limiting a value of a current flowing across a memory cell during a forming operation to a current limit value;
• applying a voltage for the forming operation by setting the limit value to the current a value;
• and
• applying the voltage for the forming operation again by changing the current limit value when the current flowing across the memory cell during the forming operation has reached the current limit value,
• wherein
• when the voltage for the forming operation has reached a voltage upper limit value, an operation of stopping application of the voltage for the forming operation and changing the current limit value are executed,
• after stopping application of the voltage for the forming operation, a reading operation in the memory cell is executed, and when a resistance value of the memory cell is higher than a first value, an operation of changing the current limit value is executed, and
• when the resistance value of the memory cell is equal to or lower than the first value, the forming operation is completed.