Complementary and bipolar regimes of resistive switching in TiN/HfO2/TiN stacks grown by atomic-layer deposition

Atomic‐layer deposition (ALD) technique in combination with in vacuo X‐ray photoelectron spectroscopy (XPS) analysis has been successfully employed to obtain fully ALD‐grown planar TiN/HfO2/TiN metal–insulator–metal structures for resistive random access memory (ReRAM) memory elements. In vacuo XPS analysis of ALD‐grown TiN/HfO2/TiN stacks reveals the presence of the ultrathin oxidized layers consisting of TiON (∼0.5 nm) and TiO2 (∼0.6 nm) at the bottom TiN/HfO2 interface (i); the nonoxidized TiN at the top HfO2/TiN interface (ii); the oxygen deficiency in the HfO2 layer does not exceed the XPS detection limit (iii). Electroformed ALD TiN/HfO2/TiN stacks reveal both conventional bipolar and complementary types of resistive switching. In the complementary resistive switching regime, each programming sequence is terminated by a reset operation, leaving the TiN/HfO2/TiN stack in a high‐resistance state. The observed feature can avoid detrimental leaky paths during successive reading operation, which is useful in the passive ReRAM arrays without a selector element. The bipolar regime of resistive switching is found to reveal the gradual character of the SET and RESET switching processes. Long‐term potentiation and depression tests performed on ALD‐grown TiN/HfO2/TiN stacks indicate that they can be used as electronic synapse devices for the implementation of emerging neuromorphic computation systems.