Impact Ionization and Hot-Carrier Degradation in Saddle-Fin and Buried-Gate Transistor of Dynamic Random Access Memory at Cryogenic Temperature

Impact ionization and hot-carrier degradation (HCD) in buried-channel-array transistors (BCATs), which are used as the cell transistor, were investigated using sub-30 nm DRAM technology. The impact ionization rate was calculated by measuring the substrate current at different measurement conditions and modeled using an energy-driven model, which is suitable for short-channel transistors. In addition, HCD in BCAT under various operation conditions was analyzed. A multitrap-based approach, in which both interface- and oxide-trap generation were considered, was used to fit the experimental results. Our analysis and modeling results are useful in understanding and predicting the reliability of dynamic random access memory.