Crystallization Characteristics Of Phase Change Nanoparticle Arrays Fabricated By Self-Assembly Based Lithography
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Crystallization Characteristics Of Phase Change Nanoparticle Arrays Fabricated By SelfAssembly Based Lithography Yuan Zhang1, Simone Raoux2, Daniel Krebs2, Leslie E. Krupp2, Teya Topuria2, Jean JordanSweet3, Marissa Caldwell4, Philip Rice2, Delia J. Milliron2, and H.-S. Philip Wong1 1 Electrical Engineering, Stanford University, Center for Integrated Systems, 420 Via Palou, Stanford, CA, 94305 2 IBM Almaden Research Center, San Jose, CA, 95120 3 IBM T. J. Watson Research Center, Yorktown Heights, NY, 10598 4 Chemistry, Stanford University, Stanford, CA, 94305 ABSTRACT Phase change nanodot arrays were fabricated using self-assembly diblock copolymer template PS-b-PMMA (polystyrene-poly (methyl-methacrylate)) and studied by time resolved Xray diffraction. The size of the nanodots was less than 15nm in diameter with 40nm spacing. This method is quite flexible regarding the patterned materials, and can be used on different substrates. The crystallization behavior of small scale phase change nanodot arrays was studied for different materials, such as Ge15Sb85, Ge2Sb2Te5 and Ag and In doped Sb2Te. It was found that the nanodots had higher crystallization temperatures compared to their corresponding blanket films and crystallized over a broader temperature range. INTRODUCTION Phase change memory is one of the most promising candidates for non-volatile memory devices because of its high scalability, fast speed and long retention time. [1-3] Due to a difference in either the optical properties or the electrical resistances between the amorphous and crystalline state, information can be stored and read in phase change materials. Materials that can be reversibly switched between the amorphous and crystalline phases are composed mainly of elements from groups IV and VI of the period table. In a phase change memory cell, to reset the device to the amorphous state includes melting and quenching the material; while on the other hand, to set the cell to the polycrystalline state requires heating up the material above its crystallization temperature. To understand the material properties such as melting temperature, crystallization temperature, electrical resistivity as well as thermal resistivity is very important for the development of phase change devices. A high crystallization temperature of the phase change material is preferable which increases thermal stability of the device; and a low melting temperature can be helpful to reduce the reset current. Understanding the scaling behavior of phase change materials is very important for the development of phase change non-volatile memory devices. The scaling properties of ultra-thin blanket films and nanostructures of the of phase change materials Ge2Sb2Te5 (GST) and GeSb have been studied previously using time-resolved X-ray diffraction (XRD). [4-5] It was observed that the minimum film thickness for the appearance of XRD peaks is a function of the phase change material. Electron-beam lithography was used to fabricate arrays of nanodots of amorphous GeSb, which had di
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