Stabilizing Schemes for the Minority Failure Bits in Ta 2 O 5 -Based ReRAM Macro

A low-power 2-Mb Resistance random access memory (ReRAM) macro is developed in a 90-nm CMOS platform with a 3-nm-thick TaO x /Ta 2 O 5 switching layer of the active area of $0.01~\mu \text{m}^{2}$ . Instability of the ON-state minority bits degrades the high-temperature retention lifetime. The oxygen vacancies in the filament are annihilated by oxygen ions, which have been generated mainly by the OFF-write bias repeated in the ON/OFF switching cyclesbefore the retention. This instability is improved by decreasing the oxygen concentration near Ru bottom electrode as well as lowering the OFF-write bias. Instability of the OFF-state minority bits narrows the memory window by random telegraph noise (RTN). Setting a statistically derived guard band with a pulse-modulated verify sequence is able to handle RTN to ensure the memory window. The 2-Mb ReRAMmacro with 1-b error-correcting code is confirmed to ensure ten years’ retention from −40 °C to 85 °C after 1E3 ON/OFF cycles.