Abstract
The nanocrystals embedded in memory devices as charge storage nodes, instead of typical semiconductor floating gate, can effectively solve the issue of data losing due to the leaky paths present in the tunneling oxide. All stored charges are not easily lost through the few leaky paths, since the charges are stored in discretely distributed nanocrystals. The specific charges stored in the nanocrystals nearby a leaky path will just flow away, but others are maintained in the independent nanocrystals. Thus, memory function can be effectively retained. In this thesis, the Ni, Co, NiSi2 and CoSi2 nanocrystals have been fabricated as the charge storage nodes for nonvolatile memory. The fabrication temperature of the Ni and Co nanocrystals is 500 °C. On the other hand, the NiSi2 and CoSi2 nanocrystals are formed during thermal oxidation of a-Si/Ni and a-Si/Co structures at 900 °C. The most important advantage using the metal nanocrystals over their semiconductor counterparts is that the metal nanocrystals do not bear a voltage drop from gate voltage. The characteristic means that all the voltages provided from control gate are dropped to tunnel oxide and control oxide. The operating voltages of the memory devices with conventional floating gate and semiconductor nanocrystals embedded in SiO2 are about 7 V and 5 V, respectively. The metal nanocrystals embedded in the different dielectrics were also studied. By changing the dielectric, the lower operating voltage can be obtained.