Semiconductor storage device

Abstract

When writing ReRAM cells, it is pursued to set the cells in a sufficiently high or low resistance state, while preventing excessive writing. Disclosed is a semiconductor storage device including memory cells, each including a variable resistance element, and control circuitry that executes an Off writing process of applying Off writing pulse to a memory cell to turn it into high resistance state and an On writing process of applying On writing pulse to turn it into low resistance state. The control circuitry, when the memory cell is placed in low resistance state, after applying Off writing pulse, applies a reading pulse for a verify process of reading whether it is placed in high or low resistance state. If the memory cell is not placed in high resistance state as a result of the verify process, the control circuitry applies a reset pulse comprising On writing pulse, applies Off writing pulse with extended pulse width and executes the verify process in mentioned order.