Analysis of resistance switching and conductive filaments inside Cu-Ge-S using in situ transmission electron microscopy
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Masashi Arita and Yasuo Takahashia) Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan
Ichiro Fujiwara Semiconductor Technology Academic Research Center, Yokohama 222-0033, Japan (Received 25 July 2011; accepted 27 November 2011)
In situ transmission electron microscopy (TEM) was carried out to investigate the dynamics of resistance switching in a solid electrolyte, Cu-Ge-S. By applying voltage to Pt-Ir/Cu-Ge-S/Pt-Ir, where Pt-Ir constituted the electrodes, a deposit containing conductive filaments composed mainly of Cu was formed around the cathode. As voltage continued to be applied, the deposit grew and finally narrow conductive filaments made contact with the anode. This corresponded to resistance switching from high- to low-resistance states (HRS and LRS). By alternating the voltage, the deposit contracted toward the cathode and detached from the anode. The resistance immediately changed from LRS to HRS. By applying voltage, the deposit containing Cu-based filaments grew and shrank, and resistance switching occurred at the electrolyte-anode interface. This conductive filament-formation model, which was recently reported, was experimentally confirmed with TEM through dynamic observations of the deposit-containing filaments. I. INTRODUCTION
A wide range of products has made use of semiconductor memories and the demand for them is expected to expand. However, they suffer from several problems such as size reduction, access speed, and power consumption. Conceptually new nonvolatile memory devices need to be fabricated to accomplish the high performance that is expected. Resistance random access memories (ReRAMs) have been actively investigated in the research field of nonvolatile memories as a likely candidate for universal memories. They have the potential of yielding high functionality with a large change in resistance as well as highspeed access and nonvolatility.1–5 As ReRAMs have a simple capacitor structure that is metal/insulator/metal, they are scalable to nanometer size. The resistance switching of ReRAMs between two stable conditions of a highresistance state (HRS) and a low-resistance state (LRS) is operated by simply applying voltage. The current-voltage (I-V) feature exhibits hysteresis characteristics that can be exploited as nonvolatile resistance switching. ReRAMs are expected to use multivalued or logic memories in the future. Many materials have been applied to ReRAMs such as perovskite-type oxides (Pr0.7Ca0.3MnO3 (PCMO),1–3
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Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2011.437 886
J. Mater. Res., Vol. 27, No. 6, Mar 28, 2012
SrTiO35), binary-type oxides (NiO,4–7 TiO2,8 and CuO9), and solid electrolytes (Ag-Ge-S,10–13 Cu-Ge-S,11 Cu2S,14 Ag2S15,16) to find the best set of materials to use. The switching characteristics of these materials can be classified into several categories. For example, resistance switching is caused by alternating or n
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