Behaviour of injected electrons in high-k dielectric layers

The programming operation in memory device consists of an injection of electrons into the gate dielectric (GD). In many cases, oxide-nitride-oxide (ONO) is used as a GD. A stability of the spatial profile of injected electrons (IE) determines the quality of the memory device. Computer simulations showed that injection of electrons into GD leads to the formation of small charge droplets out of the initial spatial profile of IE. Such a droplet is named as parasitic peak (PP). The simulation of IE redistribution in GD shows that the Coulomb scattering of newly injected carriers on PPs plays an important role in the evolution of the device parameters in conditions of long-term exploitation. The computer model of ONO with high-k layers (HKL) is developed to study the retention parameters of the device in dependence on the type of HKL and on the thickness of GD. The influence of scaling down of the dielectric film with HKL on IE redistribution in GD is investigated. Simulations showed that the possibility of scaling down the thickness of ONO stack with HKL depends not only on the tunnelling effects but also on the multiple scattering processes in ONO with HKL.