Impact of AlO_x layer on resistive switching characteristics and device-to-device uniformity of bilayered HfO_x-based resistive random access memory devices

An AlO_x layer was deposited on HfO_x, and bilayered dielectric films were found to confine the formation locations of conductive filaments (CFs) during the forming process and then improve device-to-device uniformity. In addition, the Ti interposing layer was also adopted to facilitate the formation of oxygen vacancies. As a result, the resistive random access memory (RRAM) device with TiN/Ti/AlO_x (1 nm)/HfO_x (6 nm)/TiN stack layers demonstrated excellent device-to-device uniformity although it achieved slightly larger resistive switching characteristics, which were forming voltage (V_Forming) of 2.08 V, set voltage (V_Set) of 1.96 V, and reset voltage (V_Reset) of %1.02 V, than the device with TiN/Ti/HfO_x (6 nm)/TiN stack layers. However, the device with a thicker 2-nm-thick AlO_x layer showed worse uniformity than the 1-nm-thick one. It was attributed to the increased oxygen atomic percentage in the bilayered dielectric films of the 2-nm-thick one. The difference in oxygen content showed that there would be less oxygen vacancies to form CFs. Therefore, the random growth of CFs would become severe and the device-to-device uniformity would degrade.