Formation of high density TiN nanocrystals and its application in non-volatile memories

Non-volatile memory based on TiN nanocrystal (TiN--NC) charge storage nodes embedded in SiO_2 has been fabricated and its electrical properties have been measured. It was found that the density and size distribution of TiN--NCs can be controlled by annealing temperature. The formation of well separated crystalline TiN nano-dots with an average size of 5 nm is confirmed by transmission electron microscopy and x-ray diffraction. x-ray photoelectron spectroscopy confirms the existence of a transition layer of TiN_xO_y/SiON oxide between TiN--NC and SiO_2, which reduces the barrier height of tunnel oxide and thereby enhances programming/erasing speed. The memory device shows a memory window of 2.5 V and an endurance cycle throughout 10^5. Its charging mechanism, which is interpreted from the analysis of programming speed (dV_\rm th/dt) and the gate leakage versus voltage characteristics (I_\rm g vs V_\rm g), has been explained by direct tunnelling for tunnel oxide and Fowler--Nordheim tunnelling for control oxide at programming voltages lower than 9V, and by Fowler--Nordheim tunnelling for both the oxides at programming voltages higher than 9 V.