Electrical Properties of TaO x Thin Films for ReRAM Prepared by Reactive RF Magnetron Sputtering Method
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Electrical Properties of TaOx Thin Films for ReRAM Prepared by Reactive RF Magnetron Sputtering Method Natsuki Fukuda, Hidenao Kurihara, Kazumasa Horita, Yoshiaki Yoshida, Yutaka Kokaze, Yutaka Nishioka, and Koukou Suu Institute of Semiconductor and Electronics Technologies, ULVAC, Inc. 1220-1 Suyama, Susono, Shizuoka, 410-1231, Japan [email protected] ABSTRACT TaOx thin films were fabricated by O2 reactive Radio Frequency (RF) magnetron sputtering on 8inch substrate using a Ta metal target at room temperature for mass-production of ReRAM. The TaOx thin films had good uniformity (±1%), excellent stability(±1%) at the sputtering process. Ta/TaOx(10nm)/Pt-ReRAM cell was confirmed the bipolar switching and excellent endurance property to 7×108 cycles with large on/off resistance ratio above 1,000 at high speed operation (50nsec, ±3V). INTRODUCTION Recently NAND Flash memory will be scaling limit under 25nm technical node [1], so the next generation non-volatile memory is actively researched. Resistive Random Access Memories (ReRAM) has advantages of scaling, high speed and low power operation in comparison with the other non-volatile memories. The first report of resistance switching was due to T. W. Hickmott et al. in 1962, the materials are SiO2, Al2O3, Ta2O5, ZrO2 and TiO2, it’s the preparation methods were evaporation and anodization [2]. 64kbit-array for memory application were reported by W. W. Zhuang in 2002, (Pr,Ca)MnO3 (PCMO) deposited on Si substrate by Metal Organic Deposition (MOD) and Pulse Laser Deposition (PLD) methods [3]. The materials for ReRAM are classified into the perovskite oxides and the binary oxides. The perovskite oxides such as PCMO are fabricated at high temperature over 700℃ [3], [4], [5]. On the other hand, the binary oxides such as NiOx [6], TiOx [7] and HfOx [8] are fabricated at low temperature under 400 ℃ . Moreover, binary oxides are highly compatible with a conventional CMOS process. So binary oxides have many advantage for mass-production. The sputtering method has many advantages of throughput, thickness uniformity for large substrate, stability of deposition, low temperature and low cost for ReRAM mass-production compare with the other preparation method. In this study, we prepared TaOx thin films by O2 reactive RF magnetron sputtering and evaluate the uniformity, stability and resistive switching performance.
EXPRIMENT Cluster type sputtering tool (ULVAC, CERAUS ZX-1000, [9], [10]) used in this experiment is illustrated in figure 1. TaOx thin films were prepared by O2 reactive RF magnetron sputtering on 8inch-Pt (100nm)/Si substrate using a Ta metal target at room temperature. The properties of TaOx film, thickness, refractive index, particle, and crystal phase were evaluated by ellipsometor (ESM-1AT, ULVAC), particle counter (SP1, KLA tencore) and X-ray diffraction meter (MRD, PANalytical). After deposited TaOx thin film, 100nm-thick Ta or Pt top electrode were formed by DC magnetron sputtering method through a shadow mask with dots of 50 μ m in diameter.
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