Charge Storage and Optical Response of Hybrid Nanodots Floating Gate For Functional Memories
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1208-O12-05
Charge Storage and Optical Response of Hybrid Nanodots Floating Gate for Functional Memories Seiichi Miyazaki, Naoya Morisawa, Sho Nakanishi, Mitsuhisa Ikeda and Katsunori Makihara Graduate School of Advanced Sciences of Matter, Hiroshima University Kagamiyama 1-3-1, Higashi-Hiroshima 739-8530 Japan ABSTRACT We have proposed and fabricated a hybrid nanodots floating gate (FG), in which Si quantum dots (QDs) as charge injection/emission nodes and NiSi nanodots as charge storage nodes are stacked with an ultrathin SiO2 interlayer, to satisfy both large memory window and multivalued capability. In this study, Si-QDs with an areal density of ~3x1011cm-2 were formed on ultrathin SiO2 layer by controlling SiH4 chemical vapor deposition (CVD) and NiSi nanodots were prepared by full-silicidation of Si-QDs promoted with remote H2-plasma exposure after Ni evaporation. From capacitance-voltage(C-V) characteristics of MOS capacitors with a NiSi nanodots/Si-QDs hybrid FG, stable storage of many charges in the deep potential well of each NiSi nanodot was confirmed. Also, by applying pulsed gate biases, stepwise charge injection to and emission from NiSi nanodots through discrete energy states in Si-QDs were demonstrated. In addition, by 1310nm (~0.95eV) light irradiation, a distinct optical response in C-V characteristics was detected, which can be interpreted in terms of the shift of charge centroid in the hybrid FG stack due to transfer of photoexcited electrons from NiSi-nanodots to the Si-QDs.
INTORDUCTION The application of high density nanometer-sized dots to a floating gate (FG) has been attracting much attention because of several advantages over a conventional single planar FG [1-6]. Essentially, the charge storage in individual nanodots leads to superior charge retention against gate oxide degradation. In addition, for semiconducting nanodots, their well-discrete charged states due to quantization and charging energies can provide multivalued capability. On the other hand, for metallic nanodots, charge storage capacity depends on metal work function and spin dependent charging characteristics is also expected. Considering the impact of metal diffusion on oxide reliability, nanodots made of metal silicides showing higher thermal stability than elemental metals are thought to be preferable alternatives for the floating gate application. To satisfy both multiple valued capability and charge storage capacity for a sufficient memory window, we have proposed and fabricated a hybrid stack structure in which Si quantum dots (QDs) and NiSi nanodots are stacked with a very thin SiO2 interlayer [7]. In this paper, recent achievements on the hybrid nanodots FG consisting of Si-QDs and Ni-silicide nanodots have been demonstrated, and charge storage characteristics of such hybrid nanodots FG MOS devices and their optical response have also been shown.
SAMPLE PREPARATION The Si(100) wafers used in this work were p-type with a resistivity of 8 -12Ωcm and n-type with 0.19Ωcm. Hemispherical Si-QDs with an areal density of
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