Induced Complementary Resistive Switching in Forming-Free TiO_x/TiO₂/TiO_x Memristors

The undesirable sneak current path is one of the key challenges in high-density memory integration for the emerging cross-bar memristor arrays. This work demonstrates a new heterojunction design of oxide multilayer stacking with different oxygen vacancy contents to manipulate the oxidation state. We show that the bipolar resistive switching (BRS) behavior of the Pt/TiOx/Pt cross-bar structure can be changed to complementary resistive switching (CRS) by introducing a thin TiO2 layer in the middle of the TiOx layer to obtain a Pt/TiOx/TiO2/TiOx/Pt device architecture with a double-junction active matrix. In contrast to the BRS in a single-layer TiOx matrix, the device with a double-junction matrix remains in a high-resistance state in the voltage range below the SET voltage, which makes it an efficient structure to overcome the sneak path constraints of undesired half-selected cells that lead to incorrect output reading. This architecture is capable of eliminating these half-selected cells between the nearby cross-bar cells in a smaller programming voltage range. A simplified model for the switching mechanism can be used to account for the observed high-quality switching performance with excellent endurance and current retention properties.