Computational study of scaling and radiation effects in nanoscale memory devices

The Earth is continuously being bombarded with radiations from space. The primary space sources are solar flares (very hot plasma of ionized gases ejected from Sun containing high energy sub-atomic particles) and cosmic rays (very high energy charged particles) originating from species within our galaxy. These radiations, while passing through matter, have the property to ionize atoms, i.e, to knock the tightly bound electrons off the atoms, thereby causing a variety of unwanted effects in microelectronics as well as in biological systems. Fortunately, only a small percentage of space radiations can reach terrestrial levels, thanks to Earth’s magnetic shield. The electronics in space missions, satellites, and aircrafts however have to survive much more harsh radiation environments, which is a great concern for their reliability. With the aggressive device scaling, charge that defines a logic state in devices is rapidly decreasing. This has made even the terrestrial radiation environment, which consists of cosmic ray neutrons and alpha particles emitted by radioactive impurities in device packages, a big source of errors for microelectronics. In this thesis, we have studied the initial dynamics of radiation-induced charges in small dimensional memory devices which enabled us to understand many emerging radiation problems. We have used numerical simulations to model the initial energy distributions of radiation-induced carriers and their subsequent energy relaxation to thermal equilibrium. Radiation problems in Floating Body Memory (Z-RAM) and Flash memory cells are studied in detail using these models. Besides, the scaling prospects of Z-RAM – which is perceived as the most dense dynamics memory (DRAM) – are explored using quantum mechanical simulations