Germanium Nanostructures with Hafnium Oxide as the Tunnel Dielectric for Non-Volatile Electronic Memory Application

The widespread proliferation and increasing use of wearables and portable electronic devices have fueled the requirement for high-density and low-voltage nonvolatile memories. Nanocrystal memories, which make use of the Coulomb blockade effect, can potentially result in scaling of the tunnel dielectric to a very small thickness. Since the nanocrystals are isolated electrically, potential charge leakage paths via localized defects in the thin tunnel oxide can be substantially decreased. The equivalent oxide thickness (EOT) of the tunnel dielectric layer can be further reduced by using high dielectric constant materials to replace silicon dioxide, thus giving rise to a better charge retention performance and faster program/erase during device operation. A physically thicker but high dielectric constant hafnium oxide, with a small EOT, employed as the tunnel dielectric layer in a trilayer gate structure to minimize charge leakage is presented in this work. Investigations into the electrical performance and charge storage mechanism of germanium (Ge) nanocrystal memory devices are shown. Traps/defects within the Ge nanocrystals play important roles in the charge storage and retention mechanism. This work also shows how the trap energy level could be modulated using a high dielectric constant material in the tunnel dielectric and cap oxide layers for improved device performance. Finally, the use of scanning capacitance spectroscopy/microscopy, a scanning probe microscope-based nanocharacterization method, to analyze carrier charging in Ge nanodots and the passivation of hole and electron traps after forming gas annealing are shown.