Thursday, May 10, 2012

Study of the relative performance of silicon and germanium nanoparticles embedded gate oxide in metal–oxide–semiconductor memory devices

Maximiliano De La Higuera Macías

     In the present work, we have investigated a comparative performance of the silicon (Si) and germanium (Ge) nanoparticles embedded SiO2  floating gate MOS memory devices. In such devices for low applied fields, the tunneling current is dominated by the direct tunneling mechanism, whereas for higher electric fields, the Fowler–Nordheim tunneling mechanism dominates. As the device dimensions get smaller, problem arises in the conventional MOS memory devices due to the leakage through the thin tunnel oxide. This leakage can be reduced via charge trapping by embedding nanoparticles in the gate dielectric of such devices. Here one objective is to prevent the leakage due to the direct tunneling mechanism and the other objective is to reduce the write voltage, by lowering the onset voltage of the Fowler–Nordheim tunneling mechanism. Our simulations for the current voltage characteristics covered both the low and the high applied field regions.
     Simulations showed that both the Si and the Ge nanoparticles embedded gate dielectrics offer reduction of the leakage current and a significant lowering of the writing or programming onset voltage, compared to the pure SiO2 gate dielectric. In terms of the comparative performance, the Germanium nanoparticles embedded gate dielectric showed better results compared to the silicon nanoparticles embedded one. The results of the simulations are discussed in the light of recent experimental results.
     Here we have presented a simulation study based on a compact, analytical model of a deep submicron MOS structure with a gate dielectric embedded with nanocrystals of Si/Ge. The gate current due to the combination of the direct and the F–N tunneling in such a MOS device has been simulated using the WKB approximation and the Maxwell–Garnett effective medium theory. The study indicated that due to the addition of nanocrystalline Ge/Si the onset voltage of F–N tunneling decreases and the direct tunneling current is slightly lowered compared to a device with pure SiO2 gate dielectric. Consequently the performance of the MOS nonvolatile memory (NVM) device is improved in terms of the lowering of the write voltage and the slight suppression of the leakage. The results of our simulation studies have also been discussed in light of recent experimental reports.

 C. K. Sarkar, et al. "Study Of The Relative Performance Of Silicon And Germanium Nanoparticles Embedded Gate Oxide In Metal-Oxide-Semiconductor Memory Devices." Journal Of Applied Physics 109.6 (2011): 064504. Academic Search Complete. Web. 10 May 2012.

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