Synthesis of Nickel Disilicide Nanocrystal Monolayers for Nonvolatile Memory Applications
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Synthesis of Nickel Disilicide Nanocrystal Monolayers for Nonvolatile Memory Applications Jong-Hwan Yoon1, and Robert G. Elliman2 1 Department of Physics, College of Natural Sciences, Kangwon National University, Chuncheon, Gangwon-do, 200-701, Korea, Republic of 2 Department of Electronic Materials Engineering, Research School of Physical Science and Engineering, The Australian National University, Canberra, ACT, 0200, Australia ABSTRACT Nickel silicide nanocrystals (NCs) were formed by thermally annealing SiOxNy films either implanted with Ni or coated with an evaporated Ni film. It is observed that the NCs grow into well-defined single crystalline structures embedded in a SiOxNy matrix, and that their size can be directly controlled by adjusting the concentrations of either silicon or nickel in the SiOxNy layer. The formation of well-defined NC monolayers was also demonstrated by depositing an ultra-thin Ni layer between two SiOxNy layers. These structures are shown to exhibit characteristic capacitance-voltage hysteresis suitable for nonvolatile memory applications.
INTRODUCTION The demand for nonvolatile memory (NVM) devices, such as memory sticks in digital cameras, is rising rapidly and as a consequence there is considerable research effort devoted to realizing devices with smaller size, faster operating speed and larger storage capacity. One such approach is to use a floating-gate transistor where the floating-gate consists of discrete charge traps (nanocrystals) instead of a continuous conducting layer as used in many conventional devices [1]. Discrete charge storage offers many advantages over conventional floating gate structures. The charge trapped in a nanocrystal floating gate is more stable than in a conventional floating gate as the latter can lose trapped charge through a single leakage path in the gate oxide. As a consequence nanocrystal floating gate memory is expected to have a longer retention time than the conventional devices. The reduced susceptibility to gate oxide failure also means that devices can be scaled to smaller dimensions by reducing the tunnel oxide thickness. The properties of NVM with floating gates based on semiconducting [2-4] or metallic nanocrystals [5-7] have been extensively studied. A comparison of these studies suggests that there are additional advantages in using metallic nanocrystals instead of semiconducting nanocrystals, namely, a reduction in spurious effects caused by traps at the nanocrystals/oxide interface and an enhancement in charge storage capacity and retention time. As a result, floating gates based on various metal nanocrystals, such as Au, Ag, Pt [8] and Co [9], have received particular attention. As metal silicides have been shown to have physical properties similar to those of pure metals [10] they are also clearly worthy of investigation. In this study we report the direct growth of crystalline nickel silicide nanocrystal monolayers (NCs) in silicon-rich silicon oxide (SiOxNy) layers and the memory properties of Ni-based nanocrystal floa
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