A Physical Model for Degradation of DRAMs During Accelerated Stress Aging

Charge trapping and interface-state generation at the Si/SiO2 interface have been characterized from the results of pulse-aging and radiation damage experiments conducted on the n-channel Si-Gate MOSFETs. The detailed analysis indicates that it is the intrinsic property of the Si/SiO2 interface to trap holes which act as Qr-like charges. The holes once they are trapped do not redistribute along the interface, but in presence of hydrogen they move toward Si and convert to fast-interface states (Dit). The degradations of the hold-time and the minimum voltage required to operate of a DRAM are related to the densities of Qf and Di, respectively. The ultimate degradation depends on the resultant of the rate of build-up and the rate of annealing of Qf and Dit.