Formation and Characterization of Hybrid Nanodots Floating Gate for Optoelectronic Application
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Formation and Characterization of Hybrid Nanodots Floating Gate for Optoelectronic Application Seiichi Miyazaki, Department of Electrical Engineering and Computer Science, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, Japan ABSTRACT We have fabricated a hybrid nanodots floating gate (FG) in which Si quantum dots (QDs) and silicide nanodots (NDs) are stacked with a very thin SiO2 interlayer in order to satisfy both multiple valued capability and charge storage capacity for a sufficient memory window and to open up novel functionality for optoelectronic application. In electron charging and discharging characteristics measured with application of pulsed gate biases to MOS capacitors with a hybrid NDs FG, stepwise changes in the rates for electron injection and emission were revealed with increasing pulse width at room temperature. Also, nMOSFETs with a hybrid NDs FG show unique hysteresis with stepwise changes in the drain current - gate voltage characteristics. The observed characteristics can be interpreted in terms that the electron injection and storage into silicide-NDs proceed through the discrete charged states of Si-QDs. For MOS capacitors with a triple-stacked hybrid NDs FG fabricated by adding another Si-QDs, by subgap light irradiation from the back side of the Si substrate, a distinct infrared optical response in C-V characteristics was detected at room temperature. The result is attributable to the shift of charge centroid in the hybrid NDs FG as a result of transfer of photoexcited electrons from silicide NDs to Si-QDs. INTRODUCTION The application of silicon quantum dots (Si-QDs) and metallic nanodots (NDs) to a floating gate (FG) in MOS devices has attracted much attention because of their potential advantages over conventional FG MOS memories. In fact, multi-valued memory capability can be provided by discrete charged states of Si-QDs originating from the quantum confinement energy as demonstrated in a unique stepwise shift in the threshold voltage of MOSFETs with a Si-QDs floating gate [1-4]. On the other hand, enlarged and stabilized memory window can be achieved by a FG made of metallic NDs with an appropriate work function to form a deep potential well [5, 6]. Recently, we have proposed and fabricated hybrid stacked structures consisting of metallic NDs, Si-QDs and ultrathin interlayer SiO2 to satisfy both multiple valued capability and charge storage capacity for a sufficient memory window and to open up novel functionality [7]. To realize such hybrid NDs stacks, the control of formation of high density metal silicide nanodots is one of key issues. In this paper, we reviewed recent achievements on the formation of a functional hybrid NDs FG consisting of Si-QDs, silicide NDs and an ultrathin SiO2 interlayer, and demonstrated infrared optical response of hybrid NDs FG as well as their charge injection/storage
characteristics. FABRICATION OF HYBRID NANODOTS FLOATING GATE After conventional wet-chemical cleaning steps of Si(100) wafer, ultrathin SiO2 la
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