Investigation of Preexisting and Generated Defects in Nonfilamentary a-Si/TiO2 RRAM and Their Impacts on RTN Amplitude Distribution

An extensive investigation of the preexisting and generated defects in amorphous-Si/TiO
₂
-based nonfilamentary a-vacancy modulated conductive oxide RRAM devices has been carried out in this paper to identify the switching and degradation mechanisms, through a combination of random-telegraph-noise (RTN) and constant-voltage-stress analysis. The amplitude of RTN, which leads to read instability, is also evaluated statistically at different stages of cell degradation and correlated with different defects, for the first time. It is found that the switching between low and high resistance states are correlated with the profile modulation of preexisting defects in the “defect-less” region near the a-Si/TiO
₂
interface. The RTN amplitude observed at this stage is small and has a tight distribution. At longer stress times, a percolation path is formed due to defects generation, which introduces larger RTN amplitude and a significant tail in its distribution.