Scaling Properties of Phase Change Materials


Optical storage based on phase change materials has been so successful because the data density was increased from generation to generation. Phase Change Random Access Memory will only be a viable technology when this trend of increased storage density can continue for several future lithography generations. This chapter reviews the scaling properties of the phase change materials themselves and explores the limit when size effects start to play a role influencing the crystallization temperature, melting temperature, crystallization speed and other material parameters that are vital for this technology.


Phase Change Material Scaling Property Phase Change Memory Threshold Switching Phase Change Random Access Memory 


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  1. [6.1]
    Moore, G.: Cramming more and more components onto integrated circuits. Electronics 38, No. 8, April 19 (1965)Google Scholar
  2. [6.2]
    Kurzweil, R.: The Age of Spiritual Machines. Penguin Books, New York (1999)Google Scholar
  3. [6.3]
    Lloyd, S.: Ultimate physical limits to computation. Nature 406, 1047-1054 (2000)CrossRefGoogle Scholar
  4. [6.4] Accessed 30 November 2007
  5. [6.5]
    Raoux, S., Burr, G. W., Breitwisch, M. J., Rettner, C. T., Chen, Y.-C., Shelby, R. M., Salinga, M., Krebs, D., Chen, S. H., Lung, H.-L., Lam, C. H.: Phase change random access memory —a scalable technology. IBM J. Res. Develop. (2008), in printGoogle Scholar
  6. [6.6]
    Pirovano, A., Lacaita, A. L., Benvenuti, A., Pellizzer, F., Hudgens, S., Bez, R: Scaling analysis of phase-change memory technology. Int. Electron Devices Meeting, Washington, DC (2003)Google Scholar
  7. [6.7]
    Shi, L. P, Chong, T. C.: Nanophase change for data storage applications. J. Nanosci. Nanotechnol. 7, 65-93 (2007)Google Scholar
  8. [6.8]
    Raoux, S., Rettner, C. T., Jordan-Sweet, J. L., Chen, Y.-C., Zhang, Y., Caldwell, M., Wong, H.-S. P., Milliron,. D., Cha, J.: Scaling properties of phase change materials. Non-Volatile Memory Symposium, Albuquerque, pp. 30-34 (2007)Google Scholar
  9. [6.9]
    Chen, Y.-C., Rettner, C. T., Raoux, S., Burr, G. W., Chen, S. H., Shelby, R. M., Salinga, M., Risk, W. P., Happ, T. D., McClelland, G. M., Breitwisch, M., Schrott, A., Philipp, J. P., Lee, M. H., Cheek, R., Nirschl, T., Lamorey, M., Chen, C. F., Joseph, E., Zaidi, S., Yee, B., Lung, H. L., Bergmann, R., Lam, C.: Ultra-thin phase-change bridge memory device using GeSb. Int. Electron Devices Meeting, Technical Digest, San Francisco, CA, pp. 777-780 (2006)Google Scholar
  10. [6.10]
    Raoux, S., Jordan-Sweet, J. L., Kellock, A. J.: Crystallization properties of ultra-thin phase change films. J. Appl. Phys. 103, 114310 (2008)CrossRefGoogle Scholar
  11. [6.11]
    Wei, X., Shi, L., Chong, T. C., Zhao, R., Lee, H. K.: Thickness-dependent nano-crystallization in Ge2Sb2Te5 films and its effect on devices. Jpn. J. Appl. Phys. 46, 2211-2214 (2007)CrossRefGoogle Scholar
  12. [6.12]
    Houle, F. A., Raoux, S., Shelby, R., Kellock, A., Deline, V. A., Chen, Y.-C., Rettner, C. T.: Chemical structure and switching behavior of ultrathin GeSbTe phase change films. Mater. Res. Soc. Spring Meeting, San Francisco (2006)Google Scholar
  13. [6.13]
    Martens, H. C. F., Vlutters, R., Prangsma, J. C.: Thickness dependent crystallization speed in thin phase change layers used for optical recording. J. Appl. Phys. 95, 3977-3983 (2004)CrossRefGoogle Scholar
  14. [6.14]
    Zhou, G.-F., Jacobs, B. A. J.: High performance media for phase change optical recording. Jpn. J. Appl. Phys. 38, 1625-1628 (1999)CrossRefGoogle Scholar
  15. [6.15]
    Zhou, G.-F.: Materials aspects in phase change optical recording. Mater. Sci. Eng. A 304-306, 73-80 (2001)CrossRefGoogle Scholar
  16. [6.16]
    Miao, X. S., Chong, T. C., Huang, Y. M., Lim, K. G., Tan, P. K., Shi, L. P.: Dependence of optical constants on film thickness of phase-change media. Jpn. J. Appl. Phys. 38, 1638-1641 (1999)CrossRefGoogle Scholar
  17. [6.17]
    Zacharias, M., Bläsing, J., Veit, P., Tsybeskov, L., Hirschman, K., Fauchet, P. M.: Thermal Crystallization of amorphous Si/SiO2 superlattices. Appl. Phys. Lett. 74, 2614-2616 (1999)CrossRefGoogle Scholar
  18. [6.18]
    Zacharias, M. and Streitenberger, P.: Crystallization of amorphous superlattices in the limit of ultrathin films with oxide interfaces. Phys. Rev. B 62, 8391-8396 (2000)CrossRefGoogle Scholar
  19. [6.19]
    Williams, G. V. M., Bittar, A., Trodahl, H. J.: Crystallization and diffusion in progressively annealed a-Ge/SiOx superlattices. J. Appl. Phys. 67, 1874-1878 (1990)CrossRefGoogle Scholar
  20. [6.20]
    Honma, I., Hotta, H., Kawai, K., Komiyama, H., Tanaka, K.: The structural stability of reactively-sputtered amorphous multilayer films. J. Non-Cryst. Solids 97/98, 947-950 (1987)CrossRefGoogle Scholar
  21. [6.21]
    Homma, H., Schuller, I. K., Sevenhans, W., Bruynseraede, Y.: Interfacially initiated crystallization in amorphous germanium films. Appl. Phys. Lett. 50, 594-596 (1987)CrossRefGoogle Scholar
  22. [6.22]
    Persans, P. D., Ruppert, A., Abeles, B.: Crystallization kinetics of amorphous Si/SiO2 superlattice structures Source: J. Non-Cryst. Solids 102, 130-135 (1988)CrossRefGoogle Scholar
  23. [6.23]
    Miyazaki, S., Ihara, Y., Hirose, M.: Structural stability of amorphous semiconductor superlattices. J. Non-Cryst. Solids 97/98, 887-890 (1987)CrossRefGoogle Scholar
  24. [6.24]
    Oki, F., Ogawa, Y., Fujiki, Y.: Effect of deposited metals on the crystallization temperature of amorphous germanium film. Jpn. J. Appl. Phys. 8, 1056 (1969)CrossRefGoogle Scholar
  25. [6.25]
    Stiddard, M. H. B.: This films of antimony on metal substrates: crystallite orientation and critical thickness for the occurrence of the amorphous-crystalline phase transition. J. Mater. Sci. Lett. 4, 1157-1159 (1985)CrossRefGoogle Scholar
  26. [6.26]
    Hashimoto, M., Niizeki, T., Kambe, K.: Effect of substrate temperature on crystallization of amorphous antimony film. Jpn. J. Appl. Phys. 19, 21-23 (1980)CrossRefGoogle Scholar
  27. [6.27]
    Hashimoto, M. and Hamano, T.: The stability of the amorphous phase in an Sb layer vacuum deposited on the air-and vacuum-cleaved NaCl and the effects of Sb thickness and overdeposits of Ag, Au, Sn, and Pb. Vacuum 40, 445-448 (1990)CrossRefGoogle Scholar
  28. [6.28]
    Raoux, S., Jordan-Sweet, J. L. and Kellock, A.: Thickness-dependent crystallization behavior of phase change materials. Mater. Res. Soc. Spring Meeting, San Francisco, CA, March 2008Google Scholar
  29. [6.29]
    Ohshima, N.: Crystallization of germanium-antimony-tellurium amorphous thin film sandwiched between various dielectric protective films. J. Appl. Phys. 79, 8357-8363 (1996)CrossRefGoogle Scholar
  30. [6.30]
    Njoroge, W. K., Dieker, H., Wuttig, M.: Influence of dielectric capping layers on the crystallization kinetics of Ag5In6Sb59Te30 films. J. Appl. Phys. 96, 2624-2627 (2004)CrossRefGoogle Scholar
  31. [6.31]
    Alberici, S. G., Zonca, R., Pashmakov, B.: Ti diffusion in chalcogenides: a TooF-SIMS depth profile characterization approach. Appl. Surf. Sci. 231-232, 821-825 (2004)CrossRefGoogle Scholar
  32. [6.32]
    Cabral, Jr, C., Chen, K. N., Krusin-Elbaum, L.: Irreversible modification of Ge2Sb2Te5 phase change material by nanometer-thin Ti adhesion layers in a device-compatible stack. Appl. Phys. Lett. 90, 051908 (2007)CrossRefGoogle Scholar
  33. [6.33]
    Kang, D.-H., Kim, I. H., Jeong, J.-H., Cheong, B.-K., Ahn, D.-H., Lee, D., Kim, H.-M. and Kim, K.-B.: An experimental investigation on the switching reliability of a phase change memory device with oxidized TiN electrode. J. Appl. Phys. 100, 054506 (2006)CrossRefGoogle Scholar
  34. [6.34]
    Matsui, Y., Kurotsuchi, K., Tonomura, O., Morikawa, T., Kinoshita, M., Fujisaki, Y., Matsuzaki, N., Hanzawa, S., Terao., M., Takaura, N., Moriya, H., Iwasaki, T., Moniwa, M. and Koga, T.: Ta2O5 interfacial layer between GST and W plug enabling low power operation of phase change memories. IEDM Tech. Dig., 769-772 (2006)Google Scholar
  35. [6.35]
    Ielmini, D., Lavizzari, S., Sharma, D. And Lacaita, A.: Physical interpretation, modeling and impact on phase change memory (PCM) reliability of resistance drift due to chalcogenide structural relaxation. IEDM Tech. Dig. 939-942 (2007)Google Scholar
  36. [6.36]
    Chen, Y.-C., Rettner, C. T., Raoux, S., Burr, G. W., Shelby, R., Salinga, M.: Crystallization kinetics of as-deposited and melt-quenched phase-change materials. Mat Res. Soc. Spring Meeting, San Francisco (2007)Google Scholar
  37. [6.37]
    Kwon, M.-H., Lee, B.-S., Bogle, S. N., Nittala, L. N., Bishop, S. G., Abelson, J. R., Raoux, S., Cheong, B.-K., Kim, K.-B.: Nanometer-scale order in amorphous Ge2Sb2Te5 analyzed by fluctuation electron microscopy. Appl. Phys. Lett. 90, 021923 (2007)CrossRefGoogle Scholar
  38. [6.38]
    Lee, B.-S., Raoux, S., Shelby, R. M., Rettner, C. T., Burr, G. W., Bogle, S., Bishop, S. G., Abelson, J. R.: Detecting nuclei in phase change materials by Fluctuation Electron Microscopy (FEM): An experimental proof of nucleation theory. Europ. Phase Change and Ovonic Sci. Symp., Zermatt, Switzerland, September 2007Google Scholar
  39. [6.39]
    Voyles, P. M. and Abelson, J. R.: Medium-range order in amorphous silicon measured by fluctuation electron microscopy. Sol. Energy Mater. Sol. Cells 78, 85-113 (2003)CrossRefGoogle Scholar
  40. [6.40]
    Naito, M., Ishimaru, M., Hirotsu, Y., Takashima, M.: Local structure analysis of Ge-Sb-Te phase change materials using high-resolution electron microscopy and nanobeam diffraction. J. Appl. Phys. 95, 8130-8135 (2004)CrossRefGoogle Scholar
  41. [6.41]
    Shelby, R. M., Houlse, F. A., Raoux, S.: Phase-change dynamics of eutectic GeSb alloy. Mat. Res. Soc. Spring Meeting, San Francisco, April 2006Google Scholar
  42. [6.42]
    Reifenberg, J. P., Panzer, M. A., Kim, S.-B., Gibby, A. M., Zhang, Y., Wong, S., Wong, H.-S. P., Pop, E. And Goodson, K. E.: Thickness and stoichiometry dependence of the thermal conductivity of GeSbTe films. Appl. Phys. Lett. 91,111904 (2007)CrossRefGoogle Scholar
  43. [6.43]
    Chong, T. C., Shi, L. P., Qiang, W., Tan, P. K., Miao, X. S., Hu, X.: Superlattice-like structure for phase change optical recording. J. Appl. Phys. 91, 3981-3987 (2002)CrossRefGoogle Scholar
  44. [6.44]
    Wright, D., Armand, M., Aziz, M. M.: Terabit-per-square-inch data storage using phase-change media and scanning electrical nanoprobes. IEEE Trans. Nanotechnol. 5, 50-61 (2006)CrossRefGoogle Scholar
  45. [6.45]
    Hamann, H. F., O’Boyle, M., Martin, Y. C., Rooks, M., Wickramasinghe, H. K.: Ultra-high-density phase-change storage and memory. Nature Mater. 5, 383-387 (2006)CrossRefGoogle Scholar
  46. [6.46]
    Gotoh, T., Sugawara, K., Tanaka, K.: Minimal phase-change marks produced in amorphous Ge2Sb2Te5. Jpn. J. Appl. Phys. 43, L818-L821 (2004)CrossRefGoogle Scholar
  47. [6.47]
    Satoh, H., Sugawara, K., Tanaka, K.: Nanoscale phase changes in crystalline Ge2Sb2Te5 films using scanning probe microscopy. J. Appl. Phys. 99, 024306 (2006)CrossRefGoogle Scholar
  48. [6.48]
    Sun, X., Yu, B., Ng, G., Meyyappan, M.: One-dimensional phase-change nanostructure: Germanium telluride nanowires. J. Phys. Chem C 111, 2421-2425 (2007)CrossRefGoogle Scholar
  49. [6.49]
    Lee, S.-H., Ko, D.-K., Jung, Y., Agarwal, R.: Size-dependent phase transition memory switching behavior and low writing currents in GeTe nanowires. Appl. Phys. Lett. 89, 223116 (2006)CrossRefGoogle Scholar
  50. [6.50]
    Yu, D., Wu, J., Gu, Q., Park, H.: Germanium telluride nanowires and nanohelices with memory-switching behavior. J. Am. Chem. Soc. 128, 8148-8149 (2006)CrossRefGoogle Scholar
  51. [6.51]
    Meister, S., Peng, H., McIlwrath, K., Jarausch, K., Zhang, X. F., Cui, Y.: Synthesis and characterization of phase-change nanowires. Nano Lett. 6, 1514-1517 (2006)CrossRefGoogle Scholar
  52. [6.52]
    Sun, X., Yu, B., Ng, G., Nguyen, T. D., Mayyappan, M.: III-VI compound semiconductor indium selenide (In2Se3) nanowires: Synthesis and characterization. Appl. Phys. Lett. 89, 233121 (2006)CrossRefGoogle Scholar
  53. [6.53]
    Sun, X., Yu, B., Meyyappan, M.: Synthesis and nanoscale thermal encoding of phase-change nanowires. Appl. Phys. Lett. 90, 183116 (2007)CrossRefGoogle Scholar
  54. [6.54]
    Jung, Y., Lee, S.-H., Ko, D.-K., Agarwal, R.: Synthesis and characterization of Ge2Sb2Te5 nanowires with memory switching effect. J. Am. Chem. Soc. 128, 14026-14027 (2006)CrossRefGoogle Scholar
  55. [6.55]
    Lee, S.-H., Jung, Y., Agarwal, R.: Highly scalable non-volatile and ultra-low power phase-change nanowires memory. Nature Nanotechnol. 2, 626-630 (2007)CrossRefGoogle Scholar
  56. [6.56]
    Chattopadhyay, T., Boucherle, J. X., von Schnerig, H. G.: Neutron diffraction study on the structural phase transition in GeTe. J. Phys. C: Solid State Phys. 20, 1431-1440 (1987)CrossRefGoogle Scholar
  57. [6.57]
    Park, G.-S., Kwon, J.-H., Jo, W., Kim, T. K., Zuo, J.-M., Khang, Y.: Crystalline and amorphous structures of Ge-Sb-Te nanoparticles. J. Appl. Phys. 102, 013524 (2007)CrossRefGoogle Scholar
  58. [6.58]
    Choi, H. S., Seol, K. S., Takeuchi, K., Fujita, J. and Ohki, Y.: Sythesis and size-controlled Ge2Sb2Te5 nanoparticles. Jpn. J. Appl. Phys. 44, 7720-7722 (2005)CrossRefGoogle Scholar
  59. [6.59]
    Suh, D.-S., Lee, E., Kim, K. H. P., Noh, J.-S., Shin, W.-C., Kang, Y.-S., Kim, C., Khang, Y.: Nonvolatile switching characteristics of laser-ablated Ge2Sb2Te5 nanoparticles for phase-change memory applications. Appl. Phys. Let.. 90, 023101 (2007)CrossRefGoogle Scholar
  60. [6.60]
    Yoon, H. R., Jo, W., Lee, E. H., Lee, J. H., Kim, M., Lee, K. Y. And Khang, Y.: Generation of phase-change Ge-Sb-Te nanoparticles by pulsed laser ablation. J. Non-Crystalline Solids 351, 3430-3434 (2005)CrossRefGoogle Scholar
  61. [6.61]
    Friedrich, I., Weidenhof, V., Njoroge, W., Franz, P., Wuttig, M.: Structural transformations of Ge2Sb2Te5 films studied by electrical resistance measurements. J. Appl. Phys. 87, 4130-4134 (2000)CrossRefGoogle Scholar
  62. [6.62]
    Raoux, S., Rettner, C. T., Jordan-Sweet, J. L., Deline, V. R., Philipp, J. B., Lung, H.-L.: Scaling properties of phase change nanostructures and thin films. Europ. Phase Change and Ovonic Science Symp., Grenoble, France (2006)Google Scholar
  63. [6.63]
    Raoux, S., Rettner, C. T., Jordan-Sweet, J. L., Kellock, A. J., Topuria, T., Ride, P. M., Miller, D.: Direct observation of amorphous to crystalline phase transitions in nanoparticle arrays of phase change materials. J. Appl. Phys. 102, 094305 (2007)CrossRefGoogle Scholar
  64. [6.64]
    Raoux, S., Rettner, C. T., Jordan-Sweet, J. L., Salinga, M., Toney, M.: Crystallization behavior of phase change nanostructures. Europ. Phase Change and Ovonic Science Symp., Cambridge, UK (2005)Google Scholar
  65. [6.65]
    Zhang, Y., Wong, H.-S. P., Raoux, S., Cha, J. N., Rettner, C. T., Krupp, L. E., Topuria, T., Milliron, D., Rice, P. M., Jordan-Sweet, J. L.: Phase change nanodots arrays fabricated using self-assembly diblock copolymer approach. Appl. Phys. Lett. 91, 013104 (2007)CrossRefGoogle Scholar
  66. [6.66]
    Cha, J., Zhang, Y., Wong, H.-S. P., Raoux, S., Rettner, C., Krupp, L. and Deline, V.: Biomimetic approaches for fabricating high-density nanopatterned arrays. Chem. Mater. 2007, 839-843 (2007)CrossRefGoogle Scholar
  67. [6.67]
    Raoux, S., Zhang, Y., Milliron, D., Cha, J. Caldwell, M. Rettner, C. T., Jordan-Sweet, J. L., Wong, H.-S. P.: X-ray diffraction studies of the crystallization of phase change nanoparticles produced by self-assembly-based techniques. Europ. Phase Change and Ovonic Science Symp., Zermatt, Switzerland (2007)Google Scholar
  68. [6.68]
    Milliron, D. J., Raoux, S., Shelby, R. M., Jordan-Sweet, J.: Solution-phase deposition and nanopatterning of GeSbSe phase-change materials. Nature Mater. 6, 352-356 (2007)CrossRefGoogle Scholar
  69. [6.69]
    Caldwell, M., Raoux, S., Milliron, D. J., Wong, H.-S. P.: Synthesis and characterization of germanium chalcogenide nanoparticles via single-source precursors and coprecipitation. 234th Am. Chem Soc. Meeting, Boston (2007)Google Scholar
  70. [6.70]
    Milliron, D.: Solution-phase deposition of phase change material. Mater. Res. Soc. Spring Meeting, San Francisco (2007)Google Scholar
  71. [6.71]
    Raoux, S., Shelby, R. M., Jordan-Sweet, J., Munoz, B., Salinga, M., Chen, Y.-C., Shih, Y.-H., Lai, E.-K. and Lee, M.-H.: Phase change materials and their application to Random Access Memory Technology. Europ. Mater. Res. Soc. Spring Meeting, Strasbourg, France (2008)Google Scholar
  72. [6.72]
    Ovshinsky, S. R.: Reversible electrical switching phenomena in disordered structures. Phys. Rev. B 21, 1450-1453 (1968)CrossRefGoogle Scholar
  73. [6.73]
    Shi, L. P., Chong, T. C., Zhao, R., Wei, X. Q., Wang, W. J., Li, J. M., Lim, K. G., Yang, H. X., Lee, H. K.: Investigation on high density and high speed phase change random access memory. Non-Volatile Memory Symposium, Albuquerque, pp. 129-130 (2007)Google Scholar
  74. [6.74]
    Rousse, A., Rischel, C., Fourmaux, S., Uschmann, I., Sebban, S., Grillon, G., Balcou, Ph., Förtser, E., Geindre, J. P., Audebert, P., Gauthiers, J. C., Hulin, D.: Non-thermal melting in semiconductots measured at femtosecond resolution. Nature410, 65-68 (2001)CrossRefGoogle Scholar
  75. [6.75]
    Yamada, N., Ohno, E., Nishiuchi, K., Akahira, N., Takao, M.: Rapid-phase transitions of GeTe-Sb2Te3 pseudobinary amorphous thin films for an optical disk memory. J. Appl. Phys. 69, 2849-2856 (1991)CrossRefGoogle Scholar
  76. [6.76]
    Siegel, J., Schropp, A., Solis, J., Alfonso, C. N.: Rewritable phase change optical recording in Ge2Sb2Te5 films induced by picosecond laser pulses. Appl. Phys. Lett. 84, 2250-2252 (2004)CrossRefGoogle Scholar
  77. [6.77]
    Weidenhof, V., Friedrich, I., Ziegler, S., Wuttig, M.: Laser induced crystallization of amorphous Ge2Sb2Te5 films. J. Appl. Phys. 89, 3168-3176 (2001)CrossRefGoogle Scholar
  78. [6.78]
    Solis, J., Afonso, C. N., Hyde, S. C. W., Barry, N. P., French, P. M. W.: Existence of electronic excitation enhanced crystallization in GeSb amorphous thin films upon ultrashort laser pulse irradiation. Phys. Rev. Lett. 76, 2519-2522 (1996)CrossRefGoogle Scholar
  79. [6.79]
    Sokolowski-Tinten, K., Solis, J., Bialkowski, J., Siegel, J., Afonso, C. N., von der Linde, D.: Dynamics of ultrafast phase changes in amorphous GeSb films. Phys. Rev. Lett. 81, 3679-3682 (1998)CrossRefGoogle Scholar
  80. [6.80]
    Solis, J. and Afonso, C. N.: Ultrashort-laser-pulse-driven rewritable phase-change optical recording in Sb-based films. Appl. Phys. A 76, 331-338 (2003)CrossRefGoogle Scholar
  81. [6.81]
    Wiggins, S. M., Bonse, J., Solis, J., Afonso, C. N., Sokolowsi-Tinten, K., Temnov, V. V., Zhou, P., van der Linde, D.: The influence of wavelength on phase transformations induced by picosecond and femtosecond laser pulses in GeSe thin films. J. Appl. Phys. 98, 113518 (2005)CrossRefGoogle Scholar
  82. [6.82]
    Gravesteijn, D. J.: Materials developments for write-once and erasable phase-change optical recording. Appl. Otics 27, 736-738 (1988)CrossRefGoogle Scholar
  83. [6.83]
    Callan, J. P., Kim, A. M.-T., Roeser, C. A. D., Mazur, E., Solis, J., Siegel, J., Afonso, C. N. and de Sande, J. C. G.:. Ultrafast laser-induced phase transitions in amorphous GeSb films. Phys. Rev. Lett. 86, 3550-3653 (2001)CrossRefGoogle Scholar
  84. [6.84]
    Wang, Q. F., Shi, L., Huang, S. M., Mioa, X. S., Wong, K. P. And Chong, T. C.: Dynamics of ultrafast crystallization in as-deposited Ge2Sb2Te5 films. Jpn. J. Appl. Phys. 43, 5006-5008 (2004)CrossRefGoogle Scholar

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© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  1. 1.IBM Almaden Research CenterSan JoseUSA

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