An oxidation process was applied to the fabrication of fluoride resonant tunneling diodes (RTDs) on Si substrates. The oxidation process was carried out after the growth of an ultrathin CaF2 layer on Si, and expected to passivate the Si surface in pinholes generated in the CaF2 layer. Leakage currents of Au/Al/CaF2/Si(111) metal insulator semiconductor (MIS) diodes were extremely reduced by introducing this process. Au/Al/CaF2/CdF2/CaF2/Si(111) double-barrier RTDs were also fabricated by introducing this process, the leakage currents of which were extremely reduced and a very large peak to valley current ratio (PVCR) of 1500 was obtained. It was also shown that the chemical reaction between a CdF2 well layer and the Si substrate was suppressed by the oxidation process. Owing to this effect, high-temperature growth (up to 300°C) of the CdF2 well layer was realized for the first time in the fluoride RTDs, and resulted in the reduction of undesirable current drift.
The relationship between chemical structure (N/Si ratio) or physical structure (bilayer or laminate structure) of Si-rich nitride charge-trapping layer for metal-oxide-nitride-oxide-semiconductor (MONOS) type NAND flash memory and its electrical characteristics (including program/erase V th window, fresh cell data retention and data retention after program/erase cycling stress) are investigated in detail. A bilayer charge-trapping structure formed by two different composite Si-rich nitride films has been developed that can realize a sufficient program/erase window and excellent data retention characteristics for multi-level cell (MLC) operation. #
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