Peng et al. Nanoscale Research Letters 2012, 7:559 http://www.nanoscalereslett.com/content/7/1/559 N A N O E X P R E S S Open Access Resistive switching of Au/ZnO/Au resistive memory: an in situ observation of conductive bridge formation Chung-Nan Peng1,3, Chun-Wen Wang2, Tsung-Cheng Chan1,3, Wen-Yuan Chang1,3, Yi-Chung Wang1,3, Hung-Wei Tsai1,3, Wen-Wei Wu2, Lih-Juann Chen1 and Yu-Lun Chueh1,3* Abstract A special chip for direct and real-time observation of resistive changes, including set and reset processes based on Au/ZnO/Au system inside a transmission electron microscope (TEM), was designed. A clear conducting bridge associated with the migration of Au nanoparticles (NPs) inside a defective ZnO film from anode to cathode could be clearly observed by taking a series of TEM images, enabling a dynamic observation of switching behaviors. A discontinuous region (broken region) nearby the cathode after reset process was observed, which limits the flow of current, thus a high resistance state, while it will be reconnected to switch the device from high to low resistance states through the migration of Au NPs after set process. Interestingly, the formed morphology of the conducting bridge, which is different from the typical formation of a conducting bridge, was observed. The difference can be attributed to the different diffusivities of cations transported inside the dielectric layer, thereby significantly influencing the morphology of the conducting path. The current TEM technique is quite unique and informative, which can be used to elucidate the dynamic processes in other devices in the future. Keywords: Real-time observation, Au/ZnO/Au, Conducting bridge, Au nanoparticles Background Resistive random access memory (ReRAM) is one of the most significantly nonvolatile memories because of its fast switching speed, low power consumption, excellent endurance, and easy integration with current device pro- cesses [1,2]. Among the materials for ReRAM applica- tion, metal oxides have attracted an increasing interest in material choice because of controllable compositions. Therefore, making a high-quality metal oxide layer with a bistable resistance state is a key issue in achieving a high- performance ReRAM device. A typical configuration of the ReRAM device usually consists of metal/insulator/ metal structures, and the operation is based on the switching of high resistance state (HRS) and low resist- ance state (LRS) (off and on states) after a larger bias was * Correspondence: ylchueh@mx.nthu.edu.tw 1Department of Materials Science & Engineering, National Tsing Hua University, No. 101, Sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan 3Center For Nanotechnology, Material Science, and Microsystem, National Tsing Hua University, No. 101, Sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan Full list of author information is available at the end of the article applied due to the formation of a conductive bridge/path [3]. In general, the switching behaviors can be classified into two types in terms of current–voltage (I-V) beha- viors, namely bipolar and unipolar switching [4,5]. The bipolar resistive switching shows a directional resistive switching depending on the polarity of the applied volt- age, while the unipolar resistive switching depends on the amplitude of the applied voltage without any polarity. Zinc oxide (ZnO) has many superb characteristics in optics and electronics, such as a direct bandgap of ap- proximately 3.37 eV, adjustable electrical properties by doping with different dopants, and low synthesis temperature [6,7]. ZnO-based thin film ReRAM devices were found to have promising resistive switching charac- teristics with either unipolar or bipolar resistive switch- ing behaviors, while the detailed switching behavior is still not clear. Therefore, unveiling the switching behav- ior of ReRAM based on ZnO system is imperative to shed light on the fundamental understanding of device operation, enabling the further exploration of ReRAM devices. © 2012 Peng et al.; licensee Springer. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.