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1250-G01-09

Co/HfO2 Core-Shell Nanocrystal Memory Huimei Zhou1, James A. Dorman2, Ya-Chuan (Sandy) Perng2, Stephanie Gachot2, Jian Huang1, Yuanbing Mao2, Jane P. Chang2 and Jianlin Liu1 1 Department of Electrical Engineering, University of California, Riverside, California 92521 2 Department of Chemical Engineering, University of California, Los Angeles, California 90095 ABSTRACT Metal/high-k dielectric core-shell nanocrystal memory capacitors were demonstrated. This kind of MOS memory shows good performance in charge storage capacity, programming and erasing speed. By using a self-assembled di-block co-polymer, Co/HfO2 core-shell nanocrystals showed uniform size and inter distance between crystals. Compared with traditional metal nanocrystal fabrication process with E-Beam Evaporation followed by RTA (Rapid Thermal Annealing), core-shell nanocrystal memory prepared by the co-polymer process produces a wide memory window of 8.4V at the ±12 V voltage sweep. Co/HfO2 core-shell nanocrystals prepared by the low-temperature co-polymer process ensure high reliability of the devices. INTRODUCTION Nanocrystal (NC) floating gate memory devices have received considerable attention due to its excellent memory performance and high scalability [1-4]. In this kind of memory structure, discrete trapping is used to store charges, which improve charge loss ratio encountered in conventional flash memories. Several approaches, such as deeper well nanocrystals [5,6], dielectric nanocrystals[7,8], and double-layer nanocrystals [9,10] were tried to obtain wider memory window, longer retention time, and faster writing/erasing speed. Metal nanocrystals have larger work function than that of silicon nanocrystals, and are advantageous to reduce the leakage current through the tunneling barrier due to the increased barrier height [12]. These metal particles were demonstrated to achieve better memory performance [10-12]. To avoid reaction between the metal nanocrystal and oxide layer, silicide coated hetero-structure nanocrystals were also proposed, with the goal of prolonging the retention time [13]. At the same time, different high-k materials such as HfO2, Al2O3 were used as the tunneling oxide to improve the retention performance of the memory devices [14-16]. In this paper, we report our novel structure of using core-shell nanocrystals for charge storage, which will improve the retention time, and programming/erasing (P/E) performances. We also demonstrate metal/high-k coreshell nanocrystal memory through a low temperature co-polymer process. EXPERIMENT For comparison, the nanocrystals were prepared in two ways. First, a 5.0-nm-thick thermal oxide was grown in dry oxygen at 8500C. A thin HfO2 layer of around 3nm was then deposited on SiO2 layer by ALD (Atomic Layer Deposition). An ultra-thin (~2nm) blanket Co layer was deposited through e-beam evaporation followed by RTA (Rapid Thermal Annealing)

in N2 at 6500C to form nanocrystals. Another thin HfO2 layer of around 3nm was deposited again on the nanocrystals to create Co/HfO2 core-she