Atomic-scale oxygen-vacancy engineering in Sub-2 nm thin Al2O3/MgO memristors

Ultrathin (sub-2 nm) Al _2 O _3 /MgO memristors were recently developed using an in vacuo atomic layer deposition (ALD) process that minimizes unintended defects and prevents undesirable leakage current. These memristors provide a unique platform that allows oxygen vacancies (V _O ) to be inserted into the memristor with atomic precision and study how this affects the formation and rupture of conductive filaments (CFs) during memristive switching. Herein, we present a systematic study on three sets of ultrathin Al _2 O _3 /MgO memristors with V _O -doping via modular MgO atomic layer insertion into an otherwise pristine insulating Al _2 O _3 atomic layer stack (ALS) using an in vacuo ALD. At a fixed memristor thickness of 17 Al _2 O _3 /MgO atomic layers (∼1.9 nm), the properties of the memristors were found to be affected by the number and stacking pattern of the MgO atomic layers in the Al _2 O _3 /MgO ALS. Importantly, the trend of reduced low-state resistance and the increasing appearance of multi-step switches with an increasing number of MgO atomic layers suggests a direct correlation between the dimension and dynamic evolution of the conducting filaments and the V _O concentration and distribution. Understanding such a correlation is critical to an atomic-scale control of the switching behavior of ultrathin memristors.