Resistive switching devices have been regarded as a promising candidate of multi-bit memristors for synaptic applications. The key functionality of the memristors is to realize multiple non-volatile conductance states with high precision. However, the variation of device conductance inevitably causes the state-overlap issue, limiting the number of available states. The insufficient number of states and the resultant inaccurate weight quantization are bottlenecks in developing practical memristors. Herein, we demonstrate a resistive switching device based on Pt/LaAlO3/SrTiO3 (Pt/LAO/STO) heterostructures, which is suitable for multi-level memristive applications. By redistributing the surface oxygen vacancies, we precisely control the tunneling of two-dimensional electron gas (2DEG) through the ultrathin LAO barrier, achieving multiple and tunable conductance states (over 27) in a non-volatile way. To further improve the multi-level switching performance, we propose a variance-aware weight quantization (VAQ) method. Our simulation studies verify that the VAQ effectively reduces the state-overlap issue of the resistive switching device. We also find that the VAQ states can better represent the normal-like data distribution and, thus, significantly improve the computing accuracy of the device. Our results provide valuable insight into developing high-precision multi-bit memristors based on complex oxide heterostructures for neuromorphic applications.
This work is supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No. 2021R1C1C1011219 and No. 2021R1A4A1032085). Work at the University of Wisconsin-Madison is funded by the Gordon and Betty Moore Foundation\u2019s EPiQS Initiative, grant GBMF9065 to C.-B.E. and Vannevar Bush Faculty Fellowship (ONR N00014-20-1-2844). Transport measurements and analysis at the University of Wisconsin\u2013Madison was supported by the US Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (BES), under award number DE-FG02-06ER46327 (C.B.E.). J.-Y. P. acknowledges the support from NRF grant funded by the Korea government (MSIT) (No. 2019R1A2C1007913). The work at the KAIST is supported by the NRF grants funded by Korea government (MSIT) (No. 2020R1C1C100623911) and KAIST singularity professor program. C. J. was also partially supported by the KAIST-funded Global Singularity Research Program (M3I3) for 2021. The STEM experiment was conducted using a double Cs corrected Titan cubed G2 60-300 (FEI) equipment at KAIST Analysis Center for Research Advancement (KARA).
