Evolution of the conductive filament system in HfO2-based memristors observed by direct atomic-scale imaging

Abstract

The resistive switching effect in memristors typically stems from the formation and rupture of localized conductive filament paths, and HfO2 has been accepted as one of the most promising resistive switching materials. However, the dynamic changes in the resistive switching process, including the composition and structure of conductive filaments, and especially the evolution of conductive filament surroundings, remain controversial in HfO2-based memristors. Here, the conductive filament system in the amorphous HfO2-based memristors with various top electrodes is revealed to be with a quasi-core-shell structure consisting of metallic hexagonal-Hf6O and its crystalline surroundings (monoclinic or tetragonal HfOx). The phase of the HfOx shell varies with the oxygen reservation capability of the top electrode. According to extensive high-resolution transmission electron microscopy observations and ab initio calculations, the phase transition of the conductive filament shell between monoclinic and tetragonal HfO2 is proposed to depend on the comprehensive effects of Joule heat from the conductive filament current and the concentration of oxygen vacancies. The quasi-core-shell conductive filament system with an intrinsic barrier, which prohibits conductive filament oxidation, ensures the extreme scalability of resistive switching memristors. This study renovates the understanding of the conductive filament evolution in HfO2-based memristors and provides potential inspirations to improve oxide memristors for nonvolatile storage-class memory applications.

Improved Performance of the Al2O3-Protected HfO2–TiO2 Base Layer with a Self-Assembled CH3NH3PbI3 Heterostructure for Extremely Low Operating Voltage and Stable Filament Formation in Nonvolatile Resistive Switching Memory

“…It enabled an enhanced ON/OFF ratio of 10 5 for nearly 2 × 10 4 s and an endurance of 3500 cycles at −0.1 V (as shown in Figures g and S29b). The high chemical reactivity of hafnium could attract O 2– ions, leading to the formation of a robust CF, which not only reduces the operating voltage of the device but also maintains the device stability, as the interface quality determines the charge transport and functioning of any optoelectronic devices. − The HfO 2 -TiO 2 /Al 2 O 3 base layer is beneficial for passivating the trap states that would otherwise form in the grain boundaries of the pristine MAPI layer. The charge transport between the layers is enhanced by allowing MAPI to permeate into the dense base layer, thereby forming a pinhole-free dense compact electrolyte layer.…”

A bioinspired configurable cochlea based on memristors

“…The inset depicts the stacked thin films by the high-resolution TEM (HRTEM) images. When different voltage stimuli is applied to the memristor during the set/reset process, the HfO x layer serves as the functional layer because of the changing morphology of the conductive filament ( Zhang et al, 2021 ). The TaO x layer works as a built-in compliance layer, stabilizing the injected current in both forming and programming operation, leading to a uniform LRS distribution ( Lin et al, 2021 ).…”

Nanoscale Networks of Metal Oxides by Polymer Imprinting and Templating for Future Adaptable Electronics

“…As mentioned in the introduction, HfO 2 -based layers attract much interest both in the amorphous phase (as memristive devices) − and in the crystalline form due to the possibility to show a ferroelectric character . In order to investigate this possibility, vector PFM, a PFM measurement in which the piezoresponse of both the in-plane (lateral) and out-of-plane (normal) directions are recorded at the same time, was performed in order to investigate the electromechanical properties of the HfO 2 network (Figure ).…”