Controlling the Oxygen Ion Motion Using a Diffusion Barrier Layer in HfO_x-Based Analog Memory

Oxide-based non-volatile memory devices such as Resistive Random Access Memory (RRAM) have broad applications, particularly in the field of analog neuromorphic computing_.¹ Analog computing requires a linear change in resistance as a function of applied pulses. Resistance change involves the motion of oxygen ions across a conductive filament in filamentary oxide-based memory. However, if the oxygen ion motion is too abrupt with an applied pulse, the resistance change becomes non-linear, degrading the neuromorphic performance.² A diffusion barrier layer with higher activation energy for oxygen ion motion (E_A,O) can be used at the interface (where the filament is expected to reform during the set) to improve the linearity. A previous study showed that HfO_x RRAM with an AlO_x barrier exhibited analog set behavior with an <b>on/off ratio of ~3</b>.³However, SiO_x has a higher diffusion barrier for oxygen ion motion as compared to AlO_x.<br/>In this study, the effect of two different barrier layers, AlO_x (E_A,O= 1.3 eV) and SiO_x (E_A,O= 2.7 eV), on the RRAM switching characteristics and analog temporal responses (e.g., long-term-potentiation and depression, spike-time-dependent-plasticity) of HfO_x based filamentary memory are explored. A thin ~0.8 nm barrier layer was deposited at the HfO_x/BE interface via atomic layer deposition (ALD), followed by a ~4.2 nm HfO_x active layer. A detailed X-ray photoelectron spectroscopy (XPS) depth profile analysis was performed to characterize the composition of the stack. Electrical characterization shows that devices with an AlO_x barrier layer have a comparable forming voltage (~3.1 V) and set-reset behavior than the HfO_x device without a barrier layer. However, the devices with a SiO_x barrier layer show a higher forming voltage (~4.5 V) and an <b>on/off ratio of ~5</b>. The SiO_xbarrier layer devices demonstrate a <b>more</b> <b>gradual set</b>, <b>improved linearity</b> in the potentiation, and significantly <b>less spike-to-spike variation</b> during the analog pulsing compared to HfO_x/AlO_x and HfO_xdevices. A COMSOL Multiphysics^® model is used to develop a fundamental understanding of the observed results. Overall, the experimental results demonstrate that reducing the oxygen ion motion using a SiO_xdiffusion barrier layer at the bottom electrode interface improves the linearity in the analog potentiation of HfO_x-based memory for neuromorphic applications.<br/>1. J. J. Yang, et al., Nature nanotechnology <b>8</b> (1), 13-24 (2013).<br/>2. K. Moon, et al., Faraday discussions <b>213</b>, 421-451 (2019).<br/>3. J. Woo, et al., IEEE Electron Device Lett. <b>37</b> (8), 994-997 (2016).<br/><b>Acknowledgments: </b>This work was supported by the AFOSR MURI under Award No. FA9550-18-1-0024. In part at the Georgia Tech Institute for Electronics and Nanotechnology, a member of the NNCI, which is supported by the NSF (ECCS-2025462). This material is based upon the work supported by the NSF GRFP under Grant No. DGE-1650044.