Nanoscale 3D Stackable Ag-Doped HfO_x-Based Selector Devices Fabricated through Low-Temperature Hydrogen Annealing

Abstract

Electrochemical metallization-based threshold switching devices with active metal electrodes have been studied as a selector for high-density resistive random access memory (RRAM) technology in crossbar array architectures. However, these devices are not suitable for integration with three-dimensional (3D) crossbar RRAM arrays due to the difficulty in vertical stacking and/or scaling into the nanometer regime as well as the asymmetric threshold switching behavior and large variation in the operating voltage. Here, we demonstrate bidirectional symmetric threshold switching behaviors from a simple Pt/Ag-doped HfO x /Pt structure. While fabricating the Pt/Ag-doped HfO x /Pt film using a 250 nm hole structure, filaments composed of Ag nanoclusters were constructed through a low-temperature (∼200 °C) hydrogen annealing process where the shape of the film in a nanoscale via a hole structure was maintained for integration with 3D stackable crossbar RRAM arrays. Finite Ag filament paths in the HfO x layer led to uniform device-to-device performances. Moreover, we observed that the hydrogen annealing process reduced the delay time through the reduction of the oxygen vacancies in the HfO x layer. Consequently, the proposed Pt/Ag-doped HfO x /Pt-based nanoscale selector devices exhibited excellent performance of high selectivity (∼105), ultralow OFF current (∼10 pA), steep turn-on slope (∼2 mV/decade), and short delay time (3 μs).

Recent Progress in Selector and Self‐Rectifying Devices for Resistive Random‐Access Memory Application

“…However, the intrinsic nature of crossbar arrays (parallel configuration) produces an unwanted selection of memory cells, generally known as the sneak path current. [ 66 ] This can be avoided by integrating the selector element into the memory cell [ 67 ] or by developing self‐selecting memory cells. [ 68 ] In recent years, high‐density RS‐based crossbar arrays have been demonstrated by many research groups, thereby enabling an ultra‐dense memory architecture for data‐intensive applications.…”

Extremely Low Leakage Threshold Switch with Enhanced Characteristics via Ag Doping on Polycrystalline ZnO Fabricated by Facile Electrochemical Deposition for an X-Point Selector

“…One can think of the prudent way to resolve the issues by fabricating a TS device without incorporating the active electrode in it, restricting the amount of Ag ions accessible to the switching layer (SL), thus achieving ideally behaving reliable TS characteristics, as conceptually shown in Figure e. Several research studies have designed the structures to prevent the overinjection of electrochemically active metal ions (Ag or Cu ions) into the solid–electrolyte by modifying the active electrode, − introducing metal doping ,− or by restricting the overdiffusion of metal using highly ordered Ag nanodots . They have demonstrated their outshining performances; however, the devices sometimes require postannealing or involve complex fabrication processes, which hinders further stacking for the scalable cross-point array architecture.…”

Threshold Switching of Ag-Ga2Te3 Selector with High Endurance for Applications to Cross-Point Arrays

“…Therefore, the matrix of the electrolyte material significantly affects the migration of the active metal and switching speed of the selector. The switching speed of a selector based on an oxide-based electrolyte is generally slower than the order of microseconds [ 20 – 22 ], which is relatively slow when compared with that of previously reported OTS [ 23 ] or MIT selector devices [ 24 ]. Meanwhile, defects in chalcogenide films, such as nonbonded Te (NBT), can lower the activation energy for the migration of active metal ions; therefore, chalcogenide materials are preferable for the fast migration of active metal ions [ 18 ].…”