Charge loss due to AC program disturbance stresses in EPROMs

Charge loss in interpolyoxide erasable programmable read-only memories (EPROMs) due to program disturbance by alternating current pulses applied to the drain was studied for the first time. It was found that the charge loss due to ac stress is more severe than that due to dc stress. Experimental results reveal that the more positive the floating gate potential, the more severe is the drain ac disturbance observed. The main reason for the charge loss is the displacement current which agitates the charges in the floating gate, creating a leakage path from the floating gate to the drain, in which the drain-to-floating-gate overlapping capacitance C fd plays an important role. The drain dc stresses of interpolyoxide/nitride/oxide (ONO) EPROMs were also measured under different bias conditions and temperatures. The data show that higher dc electric field of the floating gate to the drain results in larger V th shift, which can be accelerated by elevated temperature. In addition, the control gate ac stress-enhanced drain dc disturbance was also measured. We proposed that the dc drain stress is applied during the ac gate stress, which results in a heating effect. The results support the concept of dielectric ac heating.