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Titanium dioxide thin films for next-generation memory devices

  • Seong Keun Kim (a1), Kyung Min Kim (a2), Doo Seok Jeong (a3), Woojin Jeon (a4), Kyung Jean Yoon (a4) and Cheol Seong Hwang (a4)...


The synthesis, structure, and electrical performances of titanium dioxide (TiO2 and also doped TiO2) thin films, a capacitor dielectric for dynamic random access memory (DRAM) and a resistance switching material in resistance switching RAM (ReRAM), are reviewed. The three-dimensionality of these structures and the extremely small feature sizes (<20 nm) of these memory devices require the synthesis method of TiO2-based layers to exhibit high degree of conformality. Atomic layer deposition is, therefore, the method of choice in respect of film growth for these applications. The unique arrangement of the TiO6-octahedra in the rutile structure, which results in the value for dielectric constant of the dielectric layer, εr (>100), makes the material especially attractive as the capacitor dielectric layer in DRAM. Removing some of the oxygen ions from the rutile structure and arranging the resulting oxygen vacancies on a specific crystallographic plane results in the so called Magnéli phase materials, which show distinctive conducting semiconductor or metallic characteristics. External electrical stimuli can cause the repeated formation and rupture of conducting channels that consist of these Magnéli phase materials in the insulating TiO2 matrix, and this aspect makes the material a very feasible choice for applications in ReRAM. This article reviews the material properties, fabrication process, integration issues, and prospect of TiO2 films for these applications.


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1.Tanaka, H., Kido, M., Yahashi, K., Oomura, M., Katsumata, R., Kito, M., Fukuzumi, Y., Sato, M., Nagata, Y., Matsuoka, Y., Iwata, Y., Aochi, H., and Nitayama, A.: Bit-cost scalable technology with punch and plug process for ultrahigh density flash memory. VLSI Symp. Tech. Dig. 14 (2007).
2.Wilk, G.D., Wallace, R.M., and Anthony, J.M.: High-κ gate dielectrics: Current status and materials properties considerations. J. Appl. Phys. 89, 5243 (2001).
3.Sawa, A.: Resistive switching in transition metal oxides. Mater. Today 11(6), 28 (2008).
4.Waser, R., Dittmann, R., Staikov, G., and Szot, K.: Redox-based resistive switching memories—Nanoionic mechanisms, prospects, and challenges. Adv. Mater. 21, 2632 (2009).
5.Choi, B.J., Jeong, D.S., Kim, S.K., Rohde, C., Choi, S., Oh, J.H., Kim, H.J., Hwang, C.S., Szot, K., Waser, R., Reichenberg, B., and Tiedke, S.: Resistive switching mechanism of TiO2 thin films grown by atomic layer deposition. J. Appl. Phys. 98, 033715 (2005).
6.Fujimoto, M., Koyama, H., Konagai, M., Hosoi, Y., Ishihara, K., Ohnishi, S., and Awaya, N.: TiO2 anatase nanolayer on TiN thin film exhibiting high-speed bipolar resistive switching. Appl. Phys. Lett. 89, 223509 (2006).
7.Tsunoda, K., Fukuzumi, Y., Jameson, J.R., Wang, Z., Griffin, P.B., and Nishi, Y.: Bipolar resistive switching in polycrystalline TiO2 films. Appl. Phys. Lett. 90, 113501 (2007).
8.Lee, M-J., Seo, S., Kim, D-C., Ahn, S-E., Seo, D.H., Yoo, I-K., Baek, I-G., Kim, D-S., Byun, I-S., Kim, S-H., Hwang, I-R., Kim, J-S., Jeon, S-H., and Park, B.H.: A low-temperature-grown oxide diode as a new switch element for high-density, nonvolatile memories. Adv. Mater. 19, 73 (2007).
9.Baek, I.G., Park, C.J., Ju, H., Seong, D.J., Ahn, H.S., Kim, J.H., Yang, M.K., Song, S.H., Kim, E.M., Park, S.O., Park, C.H., Song, C.W., Jeong, G.T., Choi, S., Kang, H.K., and Chung, C.: Realization of vertical resistive memory (VRRAM) using cost effective 3D process. IEEE Int. Electron Devices Meeting 31.8.1 (2011).
10.Yang, J.J., Strachan, J.P., Miao, F., Zhang, M-X., Pickett, M.D., Yi, W., Ohlberg, D.A.A., Medeiros-Ribeiro, G., and Williams, R.S.: Metal/TiO2 interfaces for memristive switches. Appl. Phys. A 102, 785 (2011).
11.Kofstad, P.: Thermogravimetric studies of the defect structure of rutile (TiO2). J. Phys. Chem. Solids 23, 1579 (1962).
12.Balachandran, U. and Eror, N.G.: Electrical conductivity in nonstoichiometric titanium dioxide at elevated temperatures. J. Mater. Sci. 23, 2676 (1988).
13.Marucco, J-F., Gautron, J., and Lemasson, P.: Thermogravimetric and electrical study of nonstoichiometric titanium dioxide TiO2-x, between 800 and 1100 C. J. Phys. Chem. Solids 42, 363 (1981).
14.Meis, C. and Fleche, J.L.: Study of the solubility limit of oxygen vacancies in TiO2-x using molecular dynamics. Solid State Ionics 101103(Part 1), 333 (1997).
15.Baumard, J.F., Panis, D., and Anthony, A.M.: A study of Ti-O system between Ti3O5 and TiO2 at high temperature by means of electrical resistivity. J. Solid State Chem. 20, 43 (1977).
16.Hasiguti, R.R.: The structure of defects in solids. Ann. Rev. Mater. Sci. 2, 69 (1972).
17.Andersson, P.O., Kollberg, E.L., and Jelenski, A.: Charge compensation in iron-doped rutile. J. Phys. C: Solid State Phys. 7, 1868 (1974).
18.Banus, M.D. and Reed, T.B.: The Chemistry of Extended Defects in Nonmetallic Solids (North-Holland, Amsterdam, 1970).
19.Bursill, L.A. and Hyde, B.G.: Crystallographic shear in the higher titanium oxides: Structure, texture, mechanisms and thermodynamics. Prog. Solid State Chem. 7, 177 (1972).
20.Jeong, D.S., Schroeder, H., and Waser, R.: Mechanism for bipolar switching in a Pt/TiO2/Pt resistive switching cell. Phys. Rev. B 79, 195317 (2009).
21.Kim, G.H., Lee, J.H., Seok, J.Y., Song, S.J., Yoon, J.H., Yoon, K.J., Lee, M.H., Kim, K.M., Lee, H.D., Ryu, S.W., Park, T.J., and Hwang, C.S.: Improved endurance of resistive switching TiO2 thin film by hourglass-shaped Magnéli filaments. Appl. Phys. Lett. 98, 262901 (2011).
22.Kwon, D-H., Kim, K.M., Jang, J.H., Jeon, J.M., Lee, M.H., Kim, G.H., Li, X-S., Park, G-S., Lee, B., Han, S., Kim, M., and Hwang, C.S.: Atomic structure of conducting nanofilaments in TiO2 resistive switching memory. Nat. Nanotechnol. 5, 148 (2010).
23.Strachan, J.P., Pickett, M.D., Yang, J.J., Aloni, S., David Kilcoyne, A.L., Medeiros-Ribeiro, G., and Williams, R.S.: Direct identification of the conducting channels in a functioning memristive device. Adv. Mater. 22, 3573 (2010).
24.Kim, S.K., Lee, S.W., Han, J.H., Lee, B., Han, S., and Hwang, C.S.: Capacitors with an equivalent oxide thickness of <0.5 nm for nanoscale electronic semiconductor memory. Adv. Funct. Mater. 20, 2989 (2010).
25.Seok, J.Y., Kim, G.H., Kim, J.H., Kim, U.K., Chung, Y.J., Song, S.J., Yoon, J.H., Yoon, K.J., Lee, M.H., Kim, K.M., and Hwang, C.S.: Resistive switching in TiO2 thin films using the semiconducting In-Ga-Zn-O electrode. IEEE Electron Device Lett. 33, 582 (2012).
26.Leskelä, M. and Ritala, M.: Atomic layer deposition chemistry: Recent developments and future challenges. Angew. Chem. Int. Ed. 42, 5548 (2003).
27.Suntola, T.: Atomic layer epitaxy. Mater. Sci. Rep. 4, 261 (1989).
28.Leskelä, M. and Ritala, M.: Atomic layer deposition (ALD): From precursors to thin film structures. Thin Solid Films 409, 138 (2002).
29.Kuesters, K.H., Beug, M.F., Schroeder, U., Nagel, N., Bewersdorff, U., Dallmann, G., Jakschik, S., Knoefler, R., Kudelka, S., Ludwig, C., Manger, D., Mueller, W., and Tilke, A.: New materials in memory development sub 50 nm: Trends in Flash and DRAM. Adv. Eng. Mater. 11, 241 (2009).
30.Gordon, R.G., Hausmann, D., Kim, E., and Shepard, J.: A kinetic model for step coverage by atomic layer deposition in narrow holes or trenches. Chem. Vap. Deposition 9, 73 (2003).
31.Kim, S.K., Kim, K-M., Kwon, O.S., Lee, S.W., Jeon, C.B., Park, W.Y., Hwang, C.S., and Jeong, J.: Structurally and electrically uniform deposition of high-k TiO2 thin films on a Ru electrode in three-dimensional contact holes using atomic layer deposition. Electrochem. Solid-State Lett. 8(12), F59 (2005).
32.Kim, W.D., Hwang, G.W., Kwon, O.S., Kim, S.K., Cho, M., Jeong, D.S., Lee, S.W., Seo, M.H., Hwang, C.S., Min, Y-S., and Cho, Y.J.: Growth characteristics of atomic layer deposited TiO2 thin films on Ru and Si electrodes for memory capacitor applications. J. Electrochem. Soc. 152(8), C552 (2005).
33.Kim, S.K., Hoffmann-Eifert, S., and Waser, R.: High growth rate in atomic layer deposition of TiO2 thin films by UV irradiation. Electrochem. Solid-State Lett. 14(4), H146 (2011).
34.Kim, S.K., Hoffmann-Eifert, S., Mi, S., and Waser, R.: Liquid injection atomic layer deposition of crystalline TiO2 thin films with a smooth morphology from Ti(O-i-Pr)2(DPM)2. J. Electrochem. Soc. 156(8), D296 (2009).
35.Aarik, J., Aidla, A., Mändar, H., and Uustare, T.: Atomic layer deposition of titanium dioxide from TiCl4 and H2O: Investigation of growth mechanism. Appl. Surf. Sci. 172, 148 (2001).
36.Diebold, U.: The surface science of titanium dioxide. Surf. Sci. Rep. 48, 53 (2003).
37.Lee, C., Ghosez, P., and Gonze, X.: Lattice-dynamics and dielectric properties of incipient ferroelectric TiO2 rutile. Phys. Rev. B 50, 13379 (1994).
38.Aarik, J., Aidla, A., Uustare, T., Kukli, K., Sammelselg, V., Ritala, M., and Leskelä, M.;: Atomic layer deposition of TiO2 thin films from TiI4 and H2O. Appl. Surf. Sci. 193, 277 (2002).
39.Schuisky, M., Aarik, J., Kukli, K., Aidla, A., and Hårsta, A.: Atomic layer deposition of thin films using O2 as oxygen source. Langmuir 17, 5508 (2001).
40.Kim, S.K., Kim, W-D., Kim, K-M., Hwang, C.S., and Jeong, J.: High dielectric constant TiO2 thin films on a Ru electrode grown at 250 °C by atomic layer deposition. Appl. Phys. Lett. 85(18), 4112 (2004).
41.Kim, S.K., Hwang, G.W., Kim, W-D., and Hwang, C.S.: Transformation of the crystalline structure of an ALD TiO2 film on a Ru electrode by O3 pretreatment. Electrochem. Solid-State Lett. 9(1), F5 (2006).
42.Kim, S.K., Lee, S.Y., Seo, M., Choi, G-J., and Hwang, C.S.: Impact of O3 feeding time on TiO2 films grown by atomic layer deposition for memory capacitor applications. J. Appl. Phys. 102, 024109 (2007).
43.Green, M.L., Gross, M.E., Papa, L.E., Schnoes, K.L., and Brasen, D.: Chemical vapor deposition of ruthenium and ruthenium dioxide films. J. Electrochem. Soc. 132, 2677 (1985).
44.Han, J.H., Han, S., Lee, W., Lee, S.W., Kim, S.K., Gatineau, J., Dussarrat, C., and Hwang, C.S.: Improvement in the leakage current characteristic of metal-insulator-metal capacitor by adopting RuO2 film as bottom electrode. Appl. Phys. Lett. 99, 022901 (2011).
45.Fröhlich, K., Aarik, J., Ťapajna, M., Rosová, A., Aidla, A., Dobročka, E., and Hušková, K.: Epitaxial growth of high-kappa TiO2 rutile films on RuO2 electrodes. J. Vac. Sci. Technol., B 27, 266 (2009).
46.Kim, S.K., Han, S., Han, J.H., Lee, W., and Hwang, C.S.: Atomic layer deposition of TiO2 and Al-doped TiO2 films on Ir substrates for ultralow leakage currents. Phys. Status Solidi RRL 5, 262 (2011).
47.Kim, S.K., Choi, G-J., Lee, S.Y., Seo, M., Lee, S.W., Han, J.H., Ahn, H-S., Han, S., and Hwang, C.S.: Al-doped TiO2 films with ultralow leakage currents for next generation DRAM capacitors. Adv. Mater. 20, 1429 (2008).
48.Seo, M., Kim, S.K., Han, J.H., and Hwang, C.S.: Permittivity enhanced atomic layer deposited HfO2 thin films manipulated by a rutile TiO2 interlayer. Chem. Mater. 22, 4419 (2010).
49.Seo, M., Rha, S-H., Kim, S.K., Han, J.H., Lee, W., Han, S., and Hwang, C.S.: The mechanism for the suppression of leakage current in high dielectric TiO2 thin films by adopting ultrathin HfO2 films for memory application. J. Appl. Phys. 110, 024105 (2011).
50.Hwang, C.S.: Thickness-dependent dielectric constants of (Ba, Sr)TiO3 thin films with Pt or conducting oxide electrodes. J. Appl. Phys. 92, 432 (2002).
51.Black, C.T. and Welser, J.J.: Electric-field penetration into metals: Consequences for high-dielectric-constant capacitors. IEEE Trans. Electron Devices 46, 776 (1999).
52.Stengel, M. and Spaldin, N.A.: Origin of the dielectric dead layer in nanoscale capacitors. Nature 443, 679 (2006).
53.Jeong, D.S., Schroeder, H., and Waser, R.: Coexistence of bipolar and unipolar resistive switching behaviors in a Pt/TiO2/Pt stack. Electrochem. Solid-State Lett. 10(8), G51 (2007).
54.Kim, K.M., Choi, B.J., Lee, M.H., Kim, G.H., Song, S.J., Seok, J.Y., Yoon, J.H., Han, S. and Hwang, C.S.: A detailed understanding of the electronic bipolar resistance switching behavior in Pt/TiO2/Pt structure. Nanotechnology 22, 254010 (2011).
55.Rohde, C., Choi, B.J., Jeong, D.S., Choi, S., Zhao, J-S., and Hwang, C.S.: Identification of a determining parameter for resistive switching of TiO2 thin films. Appl. Phys. Lett. 86, 262907 (2005).
56.Shin, Y.C., Lee, M.H., Kim, K.M., Kim, G.H., Song, S.J., Seok, J.Y., and Hwang, C.S.: Bias polarity dependent local electrical conduction in resistive switching TiO2 thin films. Phys. Status Solidi RRL 4(5–6), 112 (2010).
57.Kim, K.M. and Hwang, C.S.: The conical shape filament growth model in unipolar resistance switching of TiO2 thin film. Appl. Phys. Lett. 94, 122109 (2009).
58.Kim, K.M., Choi, B.J., Shin, Y.C., Choi, S., and Hwang, C.S.: Anode-interface localized filamentary mechanism in resistive switching of TiO2 thin films. Appl. Phys. Lett. 91, 012907 (2007).
59.Kim, K.M., Choi, B.J., and Hwang, C.S.: Localized switching mechanism in resistive switching of atomic-layer-deposited TiO2 thin films. Appl. Phys. Lett. 90, 242906 (2007).
60.Kim, K.M., Jeong, D.S., and Hwang, C.S.: Nanofilamentary resistive switching in binary oxide system: A review on the present status and outlook. Nanotechnology 22, 254002 (2011).
61.Kim, K.M., Kim, G.H., Song, S.J., Seok, J.Y., Lee, M.H., Yoon, J.H., and Hwang, C.S.: Electrically configurable electroforming and bipolar resistive switching in Pt/TiO2/Pt structures. Nanotechnology 21, 305203 (2010).
62.Yoon, K.J., Lee, M.H., Kim, G.H., Song, S.J., Seok, J.Y., Han, S.R., Yoon, J.H., Kim, K.M., and Hwang, C.S.: Memristive tristable resistive switching at ruptured conducting filaments of a Pt/TiO2/Pt cell. Nanotechnology 23, 185202 (2012).
63.Yang, J.J., Pickett, M.D., Li, X., Ohlberg, D.A.A., Stewart, D.R., and Williams, R.S.: Memristive switching mechanism for metal/oxide/metal nanodevices. Nat. Nanotechnol. 3, 429 (2008).


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Titanium dioxide thin films for next-generation memory devices

  • Seong Keun Kim (a1), Kyung Min Kim (a2), Doo Seok Jeong (a3), Woojin Jeon (a4), Kyung Jean Yoon (a4) and Cheol Seong Hwang (a4)...


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