Forming-free bipolar resistive switching in nonstoichiometric ceria films
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NANO EXPRESS
Open Access
Forming-free bipolar resistive switching in nonstoichiometric ceria films Muhammad Ismail1,3, Chun-Yang Huang1, Debashis Panda1, Chung-Jung Hung2, Tsung-Ling Tsai1, Jheng-Hong Jieng1, Chun-An Lin1, Umesh Chand1, Anwar Manzoor Rana3, Ejaz Ahmed3, Ijaz Talib3, Muhammad Younus Nadeem3 and Tseung-Yuen Tseng1*
Abstract The mechanism of forming-free bipolar resistive switching in a Zr/CeOx/Pt device was investigated. High-resolution transmission electron microscopy and energy-dispersive spectroscopy analysis indicated the formation of a ZrOy layer at the Zr/CeOx interface. X-ray diffraction studies of CeOx films revealed that they consist of nano-polycrystals embedded in a disordered lattice. The observed resistive switching was suggested to be linked with the formation and rupture of conductive filaments constituted by oxygen vacancies in the CeOx film and in the nonstoichiometric ZrOy interfacial layer. X-ray photoelectron spectroscopy study confirmed the presence of oxygen vacancies in both of the said regions. In the low-resistance ON state, the electrical conduction was found to be of ohmic nature, while the high-resistance OFF state was governed by trap-controlled space charge-limited mechanism. The stable resistive switching behavior and long retention times with an acceptable resistance ratio enable the device for its application in future nonvolatile resistive random access memory (RRAM). Keywords: Resistive switching; Space charge-limited conduction (SCLC); Metal-insulator-metal structure; Cerium oxide; Oxygen vacancy
Background A metal-insulator-metal (MIM) structure-based resistive random access memory (RRAM) device has attracted much attention for next-generation high-density and low-cost nonvolatile memory applications due to its long data retention, simple structure, high-density integration, low-power consumption, fast operation speed, high scalability, simple constituents, and easy integration with the standard metal oxide semiconductor (MOS) technology [1]. In addition to transition metal oxide-based RRAMs [2,3], many rare-earth metal oxides, such as Lu2O3, Yb2O3, Sm2O3, Gd2O3, Tm2O3, Er2O3, Nd2O3, Dy2O3, and CeO2 [4-10], show very good resistive switching (RS) properties. Among them, CeO2 thin films having a strong ability of oxygen ion or oxygen vacancy migration attract a lot of attention for RRAM applications [8-10]. CeO2 is a well-known rare-earth metal oxide with a high dielectric constant (26), large bandgap (6 eV), and high refractive * Correspondence: [email protected] 1 Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu 30010, Taiwan Full list of author information is available at the end of the article
index (2.2 to 2.3). The cerium ion in the CeO2 film exhibits both +3 and +4 oxidation states, which are suitable for valency change switching process [11,12]. Forming-free resistive switching and its conduction mechanism are very important for nonvolatile memory applications. In addition, oxygen vacancies
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