Characteristics of ZnO Thin Film for the Resistive Random Access Memory
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Characteristics of ZnO Thin Film for the Resistive Random Access Memory Jung Won Seo, Seung Jae Baik, Sang Jung Kang and Koeng Su Lim Department of Electrical Engineering, Korea Advanced Institute of Science and Technology (KAIST), 335 Gwahak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea ABSTRACT We report resistive switching characteristics in Pt/ZnO/Pt devices where ZnO thin film is fabricated at various oxygen conditions. With the increase of oxygen contents in ZnO thin film, the forming voltage is gradually increased while reset and set voltages are almost unchanged. We also investigated the effect of top electrodes on resistive switching of top electrode/ZnO/Pt device. For a Pt/ZnO/Pt device, it exhibits the excellent resistive switching behavior due to high electrical field of the well-defined Schottky barrier. For Al/ZnO/Pt device, little resistive switching phenomena were occurred due to leakage current of the weak Schottky (or Ohmic) contact. INTRODUCTION Currently resistive random access memory (RRAM) is an emerging class of device for next-generation nonvolatile memory device due to its simple structure, good scalability and compatibility with complementary metal oxide semiconductor technology. The resistive switching behavior has been widely observed in ferromagnetic oxide materials (Pr1−xCaxMnO3) [1], doped perovskite oxide materials (SrZrO3) [2], and organic materials (poly-Nvinylcarbazole) [3], as well as in simple binary transition metal oxide materials [4]. Especially, various electrical properties have been reported in metal/ZnO/metal device and explained with resistive switching mechanism such as conducting filament [5], space charge limited conduction (SCLC) [6] and Poole-Frenkel emission model [7]. However, comprehensive understanding for ZnO nature on resistive switching behavior is lacking to fulfill the requirement for the commercialization as a type of next-generation memory application. Therefore, the fundamental analyses such as oxygen contents of ZnO thin film and effects of electrodes on the switching properties must be investigated systematically as an important parameter in order to realize of ZnO thin film RRAM device. In this work, we fabricated ZnO thin film with various oxygen contents (0~50 %) and introduce the resistive switching behavior of Pt/ZnO/Pt device. Also we demonstrated the effect of electrode (Al, Cr, Au and Pt) on resistive switching properties of top metal/ZnO/Pt device. EXPERIMENTAL DETAIL The fabricated Pt/ZnO/Pt device is shown in the inset of Fig. 1(c). About 50 nm ZnO thin films were deposited on Pt/Ti/SiO2/Si substrates by rf magnetron sputtering method at room temperature. During deposition process, the total flow rate of Ar and O2 is fixed to 20 sccm and the O2 contents (Co2) is varied from 0 to 50 % [Co2 (%) = c(O2) / c(Ar+O2)] . The process pressure and rf power were kept at 5 mTorr and 200 W, respectively. As a top electrode, a 100 nm thick Al, Cr, Au and Pt were deposited by dc sputtering with a metal shadow mask and were
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