Resistance Controllability of $\hbox{Ta}_{2} \hbox{O}_{5}/\hbox{TiO}_{2}$ Stack ReRAM for Low-Voltage and Multilevel Operation

The controllability of resistance in the set (low resistance) and reset (high resistance) states of Ta
₂
O
₅
/TiO
₂
resistive random access memory (ReRAM) was investigated to achieve low-voltage and multilevel operation. Since resistance in a set state tended to decrease due to the history effect of the lowest resistance, multilevel operation with a controlled set resistance was found to be difficult to achieve. On the other hand, the reset resistance could be controlled accurately by varying the reset voltage. The switching mechanism, the tunnel barrier of which is regenerated to cut off the filament, obtains the high repeatability of the reset resistance. As a result, a four-level storage ReRAM was successfully demonstrated with multireset level operation. In addition, the set voltage was found to strongly depend on reset resistance. Preventing reset resistance from exceeding 1 G¿ achieved a low-set-voltage operation below 5 V.