High voltage transistor degradation in NVM pump application

Aim of this work is to investigate the degradation of n-MOS transistor when stressed at high fields, typical operating condition when used as a pump in non-volatile memory (NVM) application. It is possible to understand where the main degradation occurs studying the degradation in different structures as a function of the stress field. Besides, the impact of different isolation processes is considered, pointing out what is the most critical issue for the degradation. Simulations of the conduction mechanism allow the fitting of the transfer characteristics of virgin transistor, while the stressed one can be described only assuming the localization of oxide positive and negative trapped charge whose amount depends on the field configuration.