Elucidating Dynamic Conductive State Changes in Amorphous LLTO for Resistive Switching Devices

Resistive random-access memory (ReRAM) is one of the promising memory devices to achieve neuromorphic computing that is a novel system to mimic human brain. ReRAM has a simple metal-insulator-metal structure and has advantages such as low power consumption and low manufacturing cost. Recently, our group has developed amorphous lithium lanthanum titanate (Li3xLa2/3-xTiO3, LLTO) thin film as a solid-state electrolyte for all solid-state thin-film batteries by using pulsed laser deposition, which has high ionic conductivity (≈10-3 S/cm) [1]. Beyond its application to energy storage devices, we found that the amorphous LLTO (a-LLTO) demonstrates a resistive switching response under the stimuli of an external electric field, where LLTO becomes high resistance state (HRS) at pristine state and switches to low resistance state (LRS) by external electric field. However, despite its unique feature, the resistive switching mechanism of a-LLTO is poorly understood. Thus, in this work, we demonstrate successful observation of LLTO resistive switching behavior and optimize voltage range to achieve both resistive switching and cycling stability. Furthermore, electronic conductivity changes that provoke the LLTO switching are investigated through the comparison of thin films with different oxygen composition, under an hypothesis that oxygen vacancy plays a role in changing local LLTO conductivity. First-principles analysis also supports such conductivity change mechanism due to the local composition changes under electrical bias. Based on these experimental and computational results, the switching mechanisms are discussed with a simplified LLTO model. At last, in-situ testing of LLTO nano device under focused ion beam (FIB) setup, which aims for scanning transmission electron microscopy (STEM)-electron energy loss spectroscopy (EELS) to fully elucidate the switching mechanisms of LLTO at nanoscale. Reference [1] Lee, J. Z.; Wang, Z.; Xin, H. L.; Wynn, T. A.; Meng, Y. S. Amorphous Lithium Lanthanum Titanate for Solid-State Microbatteries. J. Electrochem. Soc. 2016, 164 (1), A6268. Figure 1