Kentaro Ohhashi

Memory window widening of Pt/SrBi2Ta2O9/HfO2/Si ferroelectric-gate field-effect transistors by nitriding Si

The optimum temperature of rapid thermal nitridation (RTN) of Si substrates was investigated for minimizing an equivalent oxide thickness (EOT) of an interfacial layer (IL) which was grown between HfO2 and Si of Pt/SrBi2Ta2O9(SBT)/HfO2/Si ferroelectric-gate field-effect transistors (FeFETs) during a post-annealing process. The RTN was performed in NH3 gas at various temperatures ranging from 800 ?C to 1190 ?C. As the RTN temperature was raised from 800 ?C to 1080 ?C, memory windows of drain current?gate voltage curves became wider. Large memory windows were obtained at the range from 1020 ?C to 1130 ?C. The maximum was 1.36 V obtained at 1080 ?C. It was 10% larger than the typical values of Pt/SBT/HfO2/Si FeFETs without the RTN. At higher RTN temperatures than 1080 ?C, the memory windows tended to decrease. At 800 ?C and 1190 ?C, all layer boundaries among SBT-HfO2-IL-Si seemed unclear in scanning transmission electron microscopic views probably due to material diffusions. The optimum RTN temperature for minimizing the EOT of the IL and maximizing the memory window of the Pt/SBT/HfO2/SiNx/Si FeFET was 1080 ?C. The FeFET using the Si processed by the RTN at 1080 ?C also showed good retentions without significant degradations over two days.

The effect of electric field on the migration of uranium atoms and spectroscopic studies of uranium glasses

We examined the migration of uranium atoms in uranium glasses after applying the electric field of 5-15kV/mm at RT and at 373K using the technique of Rutherford backscattering (RBS). After applying the electric field of 10kV/mm between the front surface and the back surface of the glasses (1mm in thickness) at 373K for 2 hours, there was neither enhancement nor depression in the concentration of uranium atoms at both surfaces of the negative charge or of the positive charge. In addition, we examined some optical properties such as optical absorption, photoluminescence, photoluminescence excitation and the decay properties of the photoluminescence of the uranium glasses. The optical absorption showed intense absorptions below 345nm and three peaks at 416nm, 482nm and 706nm. The luminescence excited by 416nm light showed four peaks at 512nm, 52Snm, 556nm and 584nm. A decay time determined by the forth harmonic light (266nm) of Nd:YAG laser is about 250 μs.

Preparation of Fullerenes by Arc Discharge between Graphite Anode and Tungsten Cathode--Effects of Arc Temperatures (特集 炭素系機能材料)

(He) arc discharge between two tungsten electrodes. C70 were detected more than C60 in the soot prepared by both vaporizations under He arc discharge between two tungsten electrodes in He gas pressure range of 0.7•~10•¬4 to 8.0 •~ 10•¬4 Pa. In addition, C70 were formed more than C60 near the arc position, that is, at higher temperatures than near the wall of the deposition bowl, that is, at lower temperatures.

Iodine Intercalation of Bi2Sr2Ca(n−1)CunOy(N=2,3) Superconductors by Using Reactants I2 or FeI2

Abstract The change of superconductivity induced by intercalation is very interesting We have investigated on intercalation into Bi2212 single crystal and Bi2223 polycrystalline superconductors using FeI2 or I2 as reactant. The iodine intercalation by using FeI2 as a reactant into Bi2223 phase is reported for first time as long as we know. In iodine intercalation into Bi2212 by using FeI2 as reactant, the critical tem TConset in out-of-plane measurement has suddenly decreased on X=0.95. Similar changes of TConset with higher X have been observed independent of directions and reactants. TConset of IxBi2Sr2CaCu2Oy intercalated by FeI2 is a little lower than one of IxBi2Sr2CaCu2Oy intercalated by I2. This is likely due to the change of hall concentration induced by reduction of host In iodine intercalation into Bi2223, the smaller change of TConset with increasing amount of intercalant is likely due to the number of CuO2 planes between ntercalant layers.