Structures of SiO 2 /SiO x /SiO 2 and SiO 2 /SiO x /SiO 2 /SiO x /SiO 2 have been prepared on Si wafers by ion beam sputtering deposition in ultrahigh vacuum (UHV) and subsequently annealed to form single-layer and doubly stacked Si nanocrystals (NCs). Using these two structures, nonvolatile Si-NC floating-gate nMOSFETs were fabricated at x=1.6 following 1.5-mum CMOS standard procedures. The Fowler-Nordheim tunneling of the electrons through the tunnel oxide, their storage into NCs, retention, and endurance are all investigated by varying the device structure and the thicknesses of the NC and oxide layers. It is shown that charge-retention time is longer, and program/erase (P/E) speeds are faster in doubly stacked devices than in single-layer devices, which seem to result from the optimization of device structure, the exclusion of unwanted defects due to the nature of UHV, and the suppression of charge leakage by the multiple barriers/NC layers in the doubly stacked devices. It is also found that the threshold voltages in the endurance characteristics anomalously increase with the P/E cycles, more strongly in the doubly stacked NC memories
In this paper, we proposes a modified OFDM, CPD-OFDM (Orthogonal Frequency Division Multiplexing with cross polarization diversity structure), system combating the system performance degradation due to the frequency offset. The cross polarization diversity structure composed with 2-pairs cross polarized circular antenna in each transceiver has the characteristic that it can remarkably remove the odd time reflected waves in each receiving end. The cross circular polarization diversity structure can reduce the time delay spread and ICI. Therefore, the proposed CPD-OFDM system can improve the system performance as well as the spectrum efficiency. In order to investigate the performance improvement of OFDM system due to the frequency offset, computer simulation and theoretical analysis were conducted. From this analysis, it can be seen that the CPD-OFDM system performance has been improved by 1～3 [dB] compared to that of the conventional OFDM system.
Most of steam power plant in Korea are heating the feed water system to prevent freezing water flowing in the pipe in winter time. The heating system is operated whenever the ambient temperature around the power plant area below 5 degree Centigrade. But this kind of heat supplying system cause a lot of energy consuming. If we think about the method that the temperature of the each pipe is controled by attaching the temperature measuring sensor like RTD sensor and heat is supplied only when the outer surface temperature of the pipe is under 5 degree Centigrade, then we can save a plenty of energy. In this study, the computer program package for simulation is used to compare the energy consumption load of both systems. Energy saving rate is calculated for the location of Youngweol area using the data of weather station in winter season, especially the January' severe weather data is analyzed for comparison. Various convection heat transfer coefficients for the ambient air and the flowing water inside the pipe was used for the accurate calculation. And also the various initial flowing water temperature was used for the system. Steady state analysis is done previously to approximate the result before the simulation. The result shows that the temperature control system using RTD sensor represents the high energy saving effect which is more than 90% of energy saving rate. Even in the severe January weather condition, the energy saving rate is almost 60%.
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