Low-Power and Highly Uniform 3-b Multilevel Switching in Forming Free TiO2–x-Based RRAM With Embedded Pt Nanocrystals

Multilevel capability is greatly desired in order to attain high effective memory density. Here, we demonstrate that 3-b per memory cell storage capacity can take place by incorporating small (~3 nm diameter) Pt nanocrystals (NCs) within 45-nm TiO
_2-x
-based resistive random access memory. Seven low-resistance states as well one high-resistance state were achieved by setting proper compliance current (I
_cc
) limit between 2 and 200 μA. In striking contrast, the reference sample without NCs exhibited 2-b multilevel switching at higher operating voltages. The enhanced performance of the Pt NCs embedded sample is ascribed to the preferable creation of small conducting filaments around the NCs with high density of oxygen vacancies, due to the concentrated electric field effect, which improves the uniformity of the switching characteristics regardless of the random nature of switching effect.