Transmission electron microscopy measurements of the injection distances in nanocrystal-based memories

The characteristics of nonvolatile memories making use of Si nanocrystals as charge storage elements buried in the gate oxide of regular metal–oxide–semiconductor transistors strongly depend on the distances between the nanocrystals and two electrodes, the channel and the gate. In this letter, we compare two transmission electron microscopy methods that can be used to extract such distances. We demonstrate by using image simulations that conventional electron microscopy under out-of-Bragg and strongly underfocused conditions is the fastest and most efficient technique to be used for routine measurements at a subnanometer resolution. Finally, we show that the injection oxide thickness of nanocrystal devices obtained by low-energy Si implantation into thin SiO2 layers and subsequent annealing can be precisely tuned from 8 to 5 nm by adjusting the implantation energy from 0.65 to 2 keV.