Large Improvement of Data Retention in Nanocrystal-Based Memories on Silicon Using InAs Quantum Dots Embedded in $\hbox {SiO}_{2}$

We have investigated the electrical properties of InAs nanocrystals (nc-InAs) embedded in SiO₂ for nonvolatile-memory (NVM) applications. Memory structures with 3.5-nm-thick tunnel oxide and 6-7-nm-diameter nc-InAs were studied electrically. It is possible to reach the write/erase long-term ITRS requirements for NVMs with a tunnel-oxide thickness of around 4 nm. Indeed, a 1-mus programming time is obtained for gate voltages that are lower than 15 V, while an erasing time of 100 mus is obtained for gate voltages of 11 V. The nc-InAs/ SiO₂ system was compared with the nc-Si/ SiO₂ system in terms of data retention. We measured a strong increase of retention properties (about two orders of magnitude) for nc-InAs. Moreover, our best structure retains 80% of the charge after four months, which is a record when using 3.5-nm-thick tunnel oxides in nanocrystal-based NVMs. We have also shown that the ten-year retention time can be reached using nc-InAs with diameters that are larger than 8 nm and at least 4-nm-thick tunnel oxides.