Papers by Author: Mitsuhisa Ikeda

Abstract: We have studied the effect of 1310 nm light irradiation on the charge distribution of a hybrid floating gate consisting of silicon quantum dots (Si-QDs) and NiSi Nanodots (NiSi-NDs) in MOS capacitors. The light irradiation resulted in reduced flat-band voltage shifts of the MOS capacitors in comparison to the shift in the dark. This result can be interpreted in terms of the shift of the charge centroid toward the gate side in the hybrid floating gate caused by the photoexcitation of electrons in NiSi-NDs and the subsequent electron tunneling to Si-QDs. The capacitance of the MOS capacitors at constant gate biases was modulated with pulsed light irradiation. When the light irradiation was turned off, capacitance recovered to its level in the dark, indicating that the photoexited charges were transferred between the Si-QDs and the NiSi-NDs without being emitted to the Si substrate and gate electrode.

Abstract: We study the sweep speed dependence of electron injection voltage in Si-Nano-Dots (Si-NDs) floating gate MOS Capacitor by using our collective tunneling model, which models the tunneling between two-dimensional electron gas (2DEG) and the Si-NDs. We clarify the sweep speed dependence of electron injection energy with a numerical calculation based on our collective tunneling model, that we developed to emulate the experiment in this system, and obtained a new insight into the origin of sweep speed dependence. We revealed that our model can reproduce the sweep speed dependence of electron tunneling. This insight is useful for designing future nano-electronic devices.

Abstract: Nickel- and Platinum-silicide nanodots with an areal density of the order of ~1011cm-2 were successfully formed on thermally-grown SiO2 through a process of ultrathin metal film formation on self-assembled Si quantum dots (QDs) on SiO2 and subsequent remote H2 plasma exposure. Chemical shifts in photoemission spectra of core lines and changes in valence band spectrum and work function value with the remote H2-plasma treatment show that silicidation of pre-grown Si-QDs is promoted by the remote H2-plasma treatment. Electrical separation among so-prepared nanodots was verified from the surface potential change after applying a dc bias between the AFM tip and the sample surface. From temporal decay in the surface potential after electron injection to the nanodots, we confirmed that silicide nanodots have superior charge retention to that of Si nanodots with almost the same size as expected in a deeper potential well for electrons in silicide dots than pure Si-QDs. In the application of silicide nanodots to a floating gate in MOS capacitors, distinct hysteresis characteristics caused by charging and discharging of several electrons per dot were verified by capacitance-voltage measurements.

Abstract: We demonstrated a new fabrication method of Pt- and Ni-silicide nanodots with an areal density of the order of ~1011 cm-2 on SiO2 through the process steps of ultrathin metal film deposition on pre-grown Si-QDs and subsequent remote H2 plasma treatments at room temperature. Verification of electrical separation among silicide nanodots was made by measuring surface potential changes due to electron injection and extraction using an AFM/Kelvin probe technique. Photoemission measurements confirm a deeper potential well of silicide nanodots than Si-QDs and a resultant superior charge retention was also verified by surface potential measurements after charging to and discharging. Also, the advantage in many electron storage per silicide nanodot was demonstrated in C-V characteristics of MIS capacitors with silicide nanodots FGs.

Abstract: We have formed high density nanodots of nickel silicide (NiSi) on ultrathin SiO2 and characterized their electronic charged states by using an AFM/Kelvin probe technique. Si quantum dots (Si-QDs) with an areal dot density of ~2.5x1011cm-2 were self-assembled on ~3.6nm-thick thermally-grown SiO2 by controlling the early stages of LPCVD using pure SiH4 gas. Subsequently, electron beam evaporation of Ni was carried out as thin as ~1.7nm in equivalent thickness at room temperature and followed by 300°C anneal for 5min in vacuum. XPS and AFM measurements confirm the formation of NiSi dots with an average dot height of ~8nm. After removal of Ni residue on SiO2 by a dilute HCl solution, bias conditions required for electron charging to NiSi dots were compared with those to pure Si-QDs dots and Ni dots. The surface potential changes stepwise with respect to the tip bias due to multistep electron injection and extraction of NiSi nanodots. In addition, it is confirmed that charge retention characteristics of NiSi dots are superior to those of Si-QDs with the almost same size.