Charge Storage Properties of Nickel Silicide Nanocrystal Layer Embedded in Silicon Dioxide
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1160-H04-04
Charge Storage Properties of Nickel Silicide Nanocrystal Layer Embedded in Silicon Dioxide
Yoo-Sung Jang and Jong-Hwan Yoon
Department of Physics, College of Natural Sciences, Kangwon National University, Chuncheon, Gangwon-do 200-701, Republic of Korea
ABSTRACT
Memory properties of nickel silicide nanocrystal monolayers embedded in silicon dioxide have been investigated. The nanocrystal layers were produced by thermal annealing of a sandwich structure comprised of ultrathin Ni film (0.2 nm) sandwiched between two silicon-rich oxide (SiO1.57) layers. Average diameter and areal density is about 2.9 nm and 1.3×1012 cm-2, respectively. Capacitance-voltage (C-V) measurements are shown to have C-V characteristics suitable for nonvolatile memory applications, including large memory window (~ 10 V), long retention time ( > 107 s), and excellent endurance ( > 106 program/erase cycles).
INTRODUCTION
The demand for nonvolatile memory (NVM) devices with smaller size, faster operating speed and larger storage capacity is rapidly rising and as a consequence there is considerable research efforts devoted to realizing such devices. One approach is to use a floating-gate transistor where the floating-gate consists of nanocrystal (NC) charge traps. This method enables the tunneling oxide thickness of memory cells to be thinner, which makes NVM devices smaller and faster. On the other hand, multibit cell is another approach to enhance the storage capacity of NVM devices. Previous studies have demonstrated that multibit cells can be achieved by employing a multilayered NC floating gate [1, 2] or an extremely large memory window [3]. These can be realized by fabricating a well-defined NC monolayer with large charge storage capacity Metal nanocrystals have received particular attention because they have additional advantages over those of semiconducting nanocrystals, namely, an enhancement in charge storage capacity and retention time [4-7]. These suggest that NVM devices satisfying the present demands might be realized by employing the floating gates based on metallic nanocrystal monolayers. Recently, we demonstrated a simple method that produced a well-defined nickel silicide (NiSi) NC monolayer, which has also physical properties similar to those of pure nickel, by thermal annealing of a sandwich structure comprised of an ultrathin Ni film sandwiched between two silicon-rich oxide layers [8]. In this work, we reports memory properties of NiSi NC monolayer fabricated by the same method as suggested in our previous work [8]. Despite thin tunnel oxide layer (~ 5 nm) the NC layer is shown to exhibit characteristic memory
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properties suitable for multibit NVM applications, including large memory window, long-term retention, and excellent endurance.
EXPERIMENTAL DETAILS
NiSi NC monolayers were formed by thermal annealing of a sandwich structure comprised of a thin Ni film sandwiched between two silicon-rich oxide (SiO1.57) layers. SiO1.57 films were deposited on (100) oriented p-type silicon wafers at a substrate t
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