Study on Floating-Gate Molybdenum Nanocrystals for Nonvolatile Memory Application
Current requirements of nonvolatile memory (NVM) are the high density cells, low-power consumption, high-speed operation and good reliability for the scaling down devices. However, all of the charges stored in the floating gate will leak into the substrate if the tunnel oxide has a leakage path in the conventional NVM during endurance test. Therefore, the tunnel oxide thickness is difficult to scale down in terms of charge retention and endurance characteristics. The nonvolatile nanocrystal memories are one of promising candidates to substitute for conventional floating gate memory, because the discrete storage nodes as the charge storage media have been effectively improve data retention under endurance test for the scaling down device. Many methods have been developed recently for the formation of nanocrystal. Generally, most methods need thermal treatment with high temperature and long duration. This procedure will influence thermal budget and throughput in current manufacture technology of semiconductor industry. In this thesis, an ease fabrication technique of molybdenum nanocrystals was demonstrated for the application of nonvolatile memory. The nonvolatile memory structure of molybdenum nanocrystals embedded in the dielectric layer was fabricated by co-evaporating molybdenum and dielectric which like SiOx, SiNx and AlOx at room temperature. It can be considered that the annealing tamperature plays a critical role during sputter process for the formation of nanocrystal. In addition, the high density (~1011 cm-2) nanocrystal can be simple and uniform to be fabricated in our study. We also proposed a formation of molybdenum nanocrystals embedded in AlOx by co-evaporating molybdenum and AlOx at room temperature. It was also found that high density Mo nanocrystals embedded in theAlOx and larger memory effect. These fabrication techniques for the application of nonvolatile nanocrystal memory can be compatible with current manufacture process of the integrated circuit manufacture.
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