Insight Into the Mechanism of Tail Bits in Data Retention of Vacancy-Modulated Conductive Oxide RRAM

The underlying mechanism causing tail bits in data retention for high resistance state (HRS) of vacancy-modulated conductive oxide resistive RAM, consisting of TiN/amorphous-Si/TiO2/TiN structure, was investigated. The tail bits observed in the small size cells with large On/Off ratio were attributed to the current fluctuations in time. The mechanism, in which the current fluctuation is caused by the fragility of the conduction path in a high resistive region determining the cell current in TiO2, was clarified by retention measurement with various conditions of On/Off ratio and cell size. It was found that the total number of defects in the high resistive region is the key to ensure a steady HRS conduction. We, furthermore, demonstrated a way to suppress the tail bits in the small size cells (40 x 40 nm(2)) even with large On/Off ratio (x 10) by process tuning of TiO2 film fabrication.