Exploring Heteroatomic Layer Structures to Enhance Switching Dynamics of Sub-2 nm Memristors

In oxide memristors composed of a switching layer and an oxygen vacancy reservoir layer (VO layer), both layers are typically made up of homostructures of the same materials. A question arises: how microscopically are the memristor switching dynamics determined by the structure of these two layers? To answer this question, this work reports an exploratory study of the Vo layer in sub-2 nm memristors by stacking 5–7 constituent atomic heterostructured layers (or 0.6–0.8 nm in Vo layer thickness) of Al2O3 (pristine oxide with negligible VO), MgO and Ga2O3 (both containing considerable Vo). The study revealed an intriguing correlation between the atomic layer structure and the memristor switching dynamics, including both switching speed and endurance. Specifically, heterostructured MgO/Ga2O3 Vo layer outperformed its homostructured MgO or Ga2O3 counterparts with higher switching speed up to 2 orders of magnitude, and higher endurance and device yield by a significant margin. An in situ scanning probe spectroscopy study revealed that the heterostructure of MgO and Ga2O3 atomic layers contained comparable VO concentrations but different crystalline structures that can reduce the amount of unintended defects formed at the interface and within the above 2–3 atomic layers. This results in a distinct advantage to facilitate high-speed and high-efficiency VO drift from the VO layer to the switching layer, as illustrated in the high switching speed and endurance. This is however not readily available in homostructured VO layers as unintended defects extend through the entire VO layer, which negatively impacts the switching dynamics of the memristors. This result provides critical insights into the correlation between the atomic-scale device design and switching dynamics of ultrathin memristors for various applications of microelectronics and neuromorphic computing, in which switching dynamics play a vital role.