Dynamic Evolution of Conducting Nanofilament in Resistive Switching Memories

Chen, Jui-Yuan, Cheng-Lun Hsin, Chun- Wei Huang, Chung-Hua Chiu, Yu-Ting Huang, Su-Jien Lin, Wen-Wei Wu and Li-Juann Chen, 2013

Image courtesy of Nano Letters

Abstract

Resistive random access memory (ReRAM) has been considered the most promising next-generation nonvolatile memory. In recent years, the switching behavior has been widely reported, and understanding the switching mechanism can improve the stability and scalability of devices. We designed an innovative sample structure for in situ transmission electron microscopy (TEM) to observe the formation of conductive filaments in the Pt/ZnO/Pt structure in real time. The corresponding current–voltage measurements help us to understand the switching mechanism of ZnO film. In addition, high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) have been used to identify the atomic structure and components of the filament/disrupted region, determining that the conducting paths are caused by the conglomeration of zinc atoms. The behavior of resistive switching is due to the migration of oxygen ions, leading to transformation between Zn-dominated ZnO1–x and ZnO.

Impact Statement

Using the electrical biasing features of the Fusion 300 system, a resistive RAM (ReRAM) device was analyzed in the TEM. By applying a voltage to a metal-insulator-metal stack, in this case Pt-ZnO-Pt, the electrical behavior of the device was visualized in real time in the TEM while simultaneous current-voltage measurements were taken. The researchers used a combination of bright and dark field and high resolution imaging, diffraction and EELS to determine the behavior of the device. It was found that a metallic filament is created as the voltage is increased, until the filament bridges the gap between the Pt electrodes creating a low resistance path for electrical current. This process is reversible and the device can be reset.