Comprehensive Model of Electron Conduction in Oxide-Based Memristive Devices

Abstract

Memristive devices are two-terminal devices that can change their resistance state upon application of appropriate voltage stimuli. The resistance can be tuned over a wide resistance range enabling applications such as multibit data storage or analog computing-in-memory concepts. One of the most promising classes of memristive devices is based on the valence change mechanism in oxide-based devices. In these devices, a configurational change of oxygen defects, i.e. oxygen vacancies, leads to the change of the device resistance. A microscopic understanding of the conduction is necessary in order to design memristive devices with specific resistance properties. In this paper, we discuss the conduction mechanism proposed in the literature and propose a comprehensive, microscopic model of the conduction mechanism in this class of devices. To develop this microscopic picture of the conduction, ab initio simulation models are developed. These simulations suggest two different types of conduction, which are both limited by a tunneling through the Schottky barrier at the metal electrode contact. The difference between the two conduction mechanisms is the following: for the first type, the electrons tunnel into the conduction band and, in the second type, into the vacancy defect states. These two types of conduction differ in their current voltage relation, which has been detected experimentally. The origin of the resistive switching is identical for the two types of conduction and is based on a modification of the tunneling distance due to the oxygen vacancy induced screening of the Schottky barrier. This understanding may help to design optimized devices in terms of the dynamic resistance range for specific applications.

In-Gap States of HfO2 Nanoislands Driven by Crystal Nucleation: Implications for Resistive Random-Access Memory Devices

“…The here-presented results indicate a way for the fine-tuning of in-gap states based on oxygen defects or carbon doping in smallest nanoislands or NCs. Since the presence of deep or shallow in-gap defect states plays a significant role with respect to electron conduction in memristive devices as well as for the electroforming step, they will directly affect the device resistance. The here-applied growth conditions for HfO 2 nanoislands on HOPG, resulting in carbide-type carbon ( E a3 ) incorporation, can be transferred likewise to HfO 2 NCs on graphene, a substrate which is discussed for ReRAM devices .…”

A Consistent Model for Short-Term Instability and Long-Term Retention in Filamentary Oxide-Based Memristive Devices

“…Oxygen vacancies (V O ·· ) that are of major importance for the current transport in VCM memory devices can be placed at the lattice points of the oxide structure. There, they locally reduce the lattice cations and induce defect states that act as electron traps, which are responsible for electron transport through the initially non-conducting oxide. , …”

Temporal Modulation and Synergistic Current Response of Zinc-Tin Oxide/Gold Nanoparticle Phototransistors Triggered by an Electrical–Optical Hybrid Pulse

“…Similar to the ZTO phototransistor, the gate bias-enhanced charge separation effect contributes to a larger quantity of photogenerated electrons in the channel by applying the light–bias overlapped hybrid pulse with |Δ t | < 0.5 s, as shown in Figure S6. Additionally, the photo-ionized oxygen vacancies ( V o 2+ ) are driven to accumulate at the ZTO/Au NP interface due to the application of V G = −5 V. The Schottky barrier width at the ZTO/Au NP interface decreases with the increasing density of V o 2+ at the interface, which accelerates the electrons to tunnel from Au NPs into the ZTO. , In addition to the gate bias-enhanced charge separation effect, the electron tunneling effect is responsible for the greatly increased Δ I h with |Δ t | < 0.5 s in the ZTO/Au NP phototransistor . Similar to the case of the ZTO phototransistor, when |Δ t | > 0.5 s, the Δ I h depends on the superposition of the current arising from the two stimuli (Figures S7 and S8).…”