The electrical conduction and bipolar switching properties of resistive random access memory (RRAM) cells with transparent calcium bismuth titanate (CaBi4Ti4O15—CBTi144) thin films were investigated. Experimentally, the (119)-oriented CBTi144 thin films were deposited onto the ITO/glass substrates by RF magnetron sputtering followed by rapid thermal annealing (RTA) at a temperature range of 450–550°C. The surface morphologies and crystal structures of the CBTi144 thin films were examined by using field-emission scanning electron microscopy and X-ray diffraction measurements. The on/off ratio and switching behaviors of the transparent Al/CBTi144/ITO/glass RRAM devices were further discussed in this work. 1. Introduction Recently, various new nonvolatile memory devices were investigated, such as ferroelectric random access memory (FeRAM), resistive random access memory (RRAM), and phase change memory (PCM). Especially, the RRAM that composed of a simple metal-insulator-metal (MIM) structure has the advantages of low power consumption, high speed operation, good retention, and high-density integration capability [1–3]. Recent RRAM research includes perovskite oxides and metal oxides with different electrodes such as VO [4], Pr0.7Ca0.3MnO3 [5], NiO [6], La2O3 [7], Dy2O3 [8], and ZnO [9]. Several perovskite materials, such as SrBi4Ti4O15 (SBT) [10], (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 [11], CaBi4Ti4O15 (CBT) [12, 13], CaBi4？xNdxTi4O15 (CBNT) [14], and Ca1？xLaxBi4(Ti0.9W0.1)4O15 (CLBTW) [15], have been developed and investigated recently. Especially, the CBT film has high Curie temperature and low current density [16, 17]. In this study, we have investigated the bipolar resistive switching properties of the CBTi144 thin films in the metal-insulator-metal (MIM) structure for memory application. 2. Experiment In this study, the CBTi144 thin films were deposited onto the ITO/glass substrates by RF magnetron sputtering with a ceramic CBTi144 target. Ceramic target of CBTi144 was prepared by conventional solid-state reaction technique. First, raw materials of Bi2O3, CaO, and TiO2 were weighted first according to the stoichiometric ratio of CaBi4Ti4O15. After mixing of the raw materials, the mixed material was ball-milled for 5？h. The mixture was then dried and calcined at 1100°C for 4？h. Finally, the CBTi144 target was formed with a diameter of 2 inches. The CBTi144 films of 300？nm thickness were then deposited onto the ITO/glass substrates by RF magnetron sputtering with the CBTi144 target. The preparation conditions of the CBTi144 thin films are summarized in Table 1. To
References
[1]
S.-Y. Wang, C.-H. Tsai, D.-Y. Lee, C.-Y. Lin, C.-C. Lin, and T.-Y. Tseng, “Improved resistive switching properties of Ti/ZrO2/Pt memory devices for RRAM application,” Microelectronic Engineering, vol. 88, no. 7, pp. 1628–1632, 2011.
[2]
A. Prakash, S. Maikap, C. S. Lai et al., “Bipolar resistive switching memory using bilayer TaOx/WOx films,” Solid-State Electronics, vol. 77, pp. 35–40, 2012.
[3]
L.-M. Chen, T.-Y. Lin, C.-C. Chang, S.-C. Chang, and T.-S. Chin, “Electrode effect on resistive switching of Ti-added amorphous SiOx films,” Thin Solid Films, vol. 518, no. 24, pp. 7352–7355, 2010.
[4]
F.-W. Yang, K.-H. Chen, C.-M. Cheng, and F.-Y. Su, “Bipolar resistive switching properties in transparent vanadium oxide resistive random access memory,” Ceramics International, vol. 39, supplement 1, pp. S729–S732, 2013.
[5]
A. Sawa, T. Fujii, M. Kawasaki, and Y. Tokura, “Hysteretic current-voltage characteristics and resistance switching at a rectifying Ti/Pr0.7Ca0.3MnO3 interface,” Applied Physics Letters, vol. 85, no. 18, pp. 4073–4075, 2004.
[6]
S. Seo, M. J. Lee, D. H. Seo et al., “Reproducible resistance switching in polycrystalline NiO films,” Applied Physics Letters, vol. 85, no. 23, pp. 5655–5657, 2004.
[7]
F.-C. Chiu, H.-W. Chou, and J. Y.-M. Lee, “Electrical conduction mechanisms of metal/La2O3/Si structure,” Journal of Applied Physics, vol. 97, no. 10, Article ID 103503, pp. 1–5, 2005.
[8]
F.-C. Chiu, “Electrical characterization and current transportation in metal/Dy2O3/Si structure,” Journal of Applied Physics, vol. 102, no. 4, Article ID 044116, pp. 1–5, 2007.
[9]
F.-C. Chiu, P.-W. Li, and W.-Y. Chang, “Reliability characteristics and conduction mechanisms in resistive switching memory devices using ZnO thin films,” Nanoscale Research Letters, vol. 7, article 178, 2012.
[10]
C.-H. Lu and C.-H. Wu, “Preparation, sintering, and ferroelectric properties of layer-structured strontium bismuth titanium oxide ceramics,” Journal of the European Ceramic Society, vol. 22, no. 5, pp. 707–714, 2002.
[11]
K. H. Chen, C. L. Wu, J. Y. Lin, and C. M. Cheng, “Improvement on oxygen vacancies effect of high dielectric constant (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 thin films using by plasma treatment,” Advanced Materials Research, vol. 239–242, pp. 1002–1005, 2011.
[12]
A. V. Murugan, A. B. Gaikwad, V. Samuel, and V. Ravi, “Preparation of nanocrystalline ferroelectric CaBi4Ti4O15 by citrate gel method,” Ceramics International, vol. 33, no. 4, pp. 569–571, 2007.
[13]
A. Z. Sim？es, C. S. Riccardi, M. A. Ramírez, L. S. Cavalcante, E. Longo, and J. A. Varela, “Synthesis and characterization of CaBi4Ti4O15 thin films annealed by microwave and conventional furnaces,” Solid State Sciences, vol. 9, no. 8, pp. 756–760, 2007.
[14]
R. Z. Hou and X. M. Chen, “Neodymium substituted CaBi4Ti4O15 bismuth layered compound,” Journal of the European Ceramic Society, vol. 26, no. 8, pp. 1379–1383, 2006.
[15]
X. Zheng, X. Huang, and C. Gao, “Study on ferroelectric and dielectric properties of La-doped CaBi4Ti4O15-based ceramics,” Journal of Rare Earths, vol. 25, no. 2, pp. 168–172, 2007.
[16]
A. Z. Simoes, M. A. Ramírez, A. Ries, J. A. Varela, E. Longo, and R. Ramesh, “Electromechanical properties of calcium bismuth titanate films: a potential candidate for lead-free thin-film piezoelectrics,” Applied Physics Letters, vol. 88, no. 7, Article ID 072916, pp. 1–3, 2006.
[17]
K. Kato, D. Fu, K. Suzuki, K. Tanaka, K. Nishizawa, and T. Miki, “Ferro-and piezoelectric properties of polar-axis-oriented CaBi4Ti4O15 films,” Applied Physics Letters, vol. 84, no. 19, pp. 3771–3773, 2004.
[18]
T. F. Chien, J. H. Tsai, K. H. Chen, C. M. Cheng, and C. L. Wu, “The ferroelectric and electrical properties of CaBi4Ti4O15 thin films prepared by sol-gel technology,” Advanced Materials Research, vol. 239–242, pp. 891–894, 2011.
[19]
K. Kato, K. Suzuki, K. Nishizawa, and T. Miki, “Ferroelectric properties of alkoxy-derived CaBi4Ti4O15 thin films on Pt-passivated Si,” Applied Physics Letters, vol. 78, no. 8, pp. 1119–1121, 2001.
[20]
J. Y. Lin and B. X. Wang, “Resistive switching in conductive-bridging random-access memory structure with nanocrystalline silicon films,” Japanese Journal of Applied Physics, vol. 52, no. 4, Article ID 044002, pp. 1–5, 2013.
