Proton mobility in SiO 2 thin films and impact of hydrogen and humidity on the resistive switching effect
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Proton mobility in SiO2 thin films and impact of hydrogen and humidity on the resistive switching effect Stefan Tappertzhofen1,2, Marek Hempel1,2, Ilia Valov1,2,3 and Rainer Waser1,2,3 1 Institut für Werkstoffe der Elektrotechnik II, RWTH Aachen University, Germany 2 JARA – Jülich Aachen Research Alliance, Fundamentals of Future Information Technology 3 Forschungszentrum Jülich GmbH, Jülich, Germany ABSTRACT Silicon dioxide based Electrochemical Metallization (ECM) cells were intensively studied as a promising candidate for CMOS compatible non-volatile memory devices. The resistance of ECM cells can be switched between a high resistive (OFF) state and a low resistive (ON) state by applying a sufficient voltage or current pulse. This resistance transition is attributed to the formation and rupture of a few nanometers in diameter metallic filament. However, the metal ion transport which is believed to be responsible for the filamentary switching mechanism is not understood in detail. In case of SiO2 we suppose protons or humidity may enhance the metal ion transport. In this work we report our studies on the proton incorporation in amorphous SiO2 thin films focused on the impact of hydrogen and humidity on the resistive switching effect. The switching behavior was analyzed by current-voltage measurements performed at different ambient conditions. The incorporation of hydrogen has been confirmed by Time-of-Flight Secondary-Ion-Mass-Spectroscopy (ToF-SIMS). The results led to an expansion of the defect model proposed in the literature. INTRODUCTION Resistive random access memory (ReRAM) is concerned as a promising alternative nonvolatile memory. Devices based on electrochemical metallization cells (type ReRAM) are intensively studied due to the prospect of high scalability and low power consumption [1]. The simple structure of ECM cells consists of a material ensuring a metal ion transport sandwiched between an inert (bottom) electrode and an electrochemically active working (top) electrode. Ag or Cu are typically used as working electrode material. The transition between a high resistive (OFF) and low resistive (ON) state of the ECM cell constituting the logical 0 and 1 states is determined by the process of formation and rupture of a metal filament controlled by the applied voltage [2]. Despite that silicon dioxide is considered as a typical insulator due to the reduced diffusion length (thin film thickness of 30 nm) it is believed to act as a transport media for metal ions supplied by the oxidation process at the active electrode. A schematic presentation of the proposed switching mechanism resulting in a typical current/voltage characteristic for resistive switching devices is shown in figure 1. During the SET process (A)-(D), the cell is short circuited by a metallic filament i.e., switched from a high resistive state to a low resistive state. At the working electrode the anodic dissolution (fig. 1 (B)) of Ag may be written as [13]: Ag → Ag+ + e-
(1)
Figure 1. Schematic of the resistive switching effect of an ECM
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