Modification of Ge 2 Sb 2 Te 5 by the Addition of SiO x for Improved Operation of Phase Change Random Access Memory
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Modification of Ge2Sb2Te5 by the Addition of SiOx for Improved Operation of Phase Change Random Access Memory Jin-Seo Noh1, Dong-Seok Suh1, Sang Mock Lee1, Kijoon H. P. Kim1, Woong-Chul Shin1, Eunhye Lee1, Youn-Seon Kang1, Ju-Cheol Park2, Ki-Hong Kim2, and Yoonho Khang1 1 Materials Center, 2AE Center, Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, Korea ABSTRACT Conventional Ge2Sb2Te5 (GST) was modified by adding up a small amount of SiOx, using co-sputtering technique from multiple targets. The SiOx content was gradually increased by increasing the power applied to SiOx target, up to 8 volume percent. The sheet resistance of SiOx-containing GST exponentially increased, when the room-temperature-deposited samples were annealed at 300 oC. Transmission electron microscopy images revealed that no SiOx particulates were formed, which was confirmed by Gattan image filtering. It was indicated by xray diffraction patterns that the grain size of SiOx-containing GST is smaller than normal GST with lattice locally distorted at its crystalline state, suggesting that molecular SiOx is homogeneously distributed throughout the GST matrix. We observed that the crystallization temperature of SiOx-containing GST is gradually elevated by increasing the SiOx content, while the melting point decreased. These observations led to the reset current reduction, which is a critical requirement for the high density PRAM. INTRODUCTION Phase change random access memory (PRAM) has been rapidly emerging due to its advantages over other competing next generation memories, which include high density, low cost, good compatibility with standard CMOS process, and relatively fast writing speed [1-3]. However, some material issues are yet to be resolved for the successful launch of the memory. Writing current reduction is on top of the list, because the PRAM is a current-driven device and its scaling is controlled by the switching transistor width [4]. To resolve this issue, both devicestructural and materialistic approaches have been taken by various research groups. Structurewise approaches focus on confinement of phase change area [5,6], while material-wise ones on development of new materials showing phase change at low energy input [7,8]. The former techniques have a certain difficulty in either making a confined memory node or reducing the contact size, although they can be used for whatever phase change materials employed. Likewise, the latter methodology is troubled by few chance of finding a phase change material better than GST. In this work, we harmoniously combined the two approaches aforementioned. GST as a matrix material was subject to modification by adding up a small amount of dielectric, SiOx. The dielectric can be incorporated in form of either particulates or finer ones like molecular interstitials. Well-dispersed dielectric particulates in GST matrix may confine the current path into inter-particulate regions, causing localized and elevated current density around them. If the particulate become
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