Improvement of Data Retention During Long-Term Use by Suppressing Conductive Filament Expansion in ${\rm TaO}_{x}$ Bipolar-ReRAM

We investigate, for the first time, the expansion of resistive random access memory (ReRAM) conductive filaments during pulse cycles, which may cause retention failure after cycling endurance. We find that filament size becomes larger gradually because of oxygen diffusion from the region surrounding a filament during reset operations. To achieve long-term use of ReRAM while avoiding filament expansion, it is the key to control both an electric power and a pulsewidth input at a switching operation. We successfully demonstrate good data retention even after endurance of 100-k cycles with an optimized reset pulse.