Impact of Nonuniform Ozone Anneal Treatment on the Resistance Levels in an IGZO-ReRAM Fabricated on ITO-Coated Glass Substrate

Eight-level/cell stable resistance switching (RS) was observed in an indium-gallium-zinc-oxide (IGZO)-resistive random (ReRAM) cell fabricated on ITO-coated glass substrate by providing nonuniform ozone (O
₃
) anneal treatment to its sputtered IGZO films. From electrical measurements, it was observed that the time of O
₃
anneal significantly impacts the low field diffusion coefficient of O
²⁻
, which was reduced by more than 40 times when anneal time was increased from 10 to 30 min. Thus, by sequential stacking of nonuniform O
₃
-annealed IGZO films, it was possible to create a diffusion-resistant medium to O
²⁻
which impacted the rate of current rise due to filamentary conduction. Furthermore, through experiments and numerical modeling, we determined vacancy distribution within the filament in a cell that received nonuniform anneal, which was later correlated with electrical conduction. The anneal scheme had been found feasible to realizing a greater number of non-identical stable resistance states up to a maximum eight-level/cell that were defined by a variable current compliance (CC)-based programming. Endurance and retention characteristics of the said resistance levels demonstrated adequate reproducibility and non-volatility.