Floating nanodot gate memory fabrication with biomineralized nanodot as charge storage node

Abstract

We have demonstrated floating nanodot gate memory (FNGM) fabrication by utilizing uniform biomineralized cobalt oxide (Co3O4) nanodots (Co-BNDs) which are biochemically synthesized in the vacant cavity of supramolecular protein, ferritin. High-density Co-BND array (>6.5×1011cm−2) formed on Si substrate with 3-nm-thick tunnel SiO2 is embedded in metal-oxide-semiconductor (MOS) stacked structure and used as the floating gate of FNGM. Fabricated Co-BND MOS capacitors and metal-oxide-semiconductor field effect transistors show the hysteresis loop due to the electron and hole confinement in the embedded Co-BND. Fabricated MOS memories show wide memory window size of 3–4V under 10V operation, good charge retention characteristics until 104s after charge programming, and stress endurance until 105 write/erase operation. Observed charge injection thresholds suggest that charge injection through the direct tunneling from Si to the energy levels in the conduction and valence bands of Co3O4 and long charge retention characteristics implies prompt charge confinement to the deeper energy level of metal Co which is formed during the annealing in the device processing.