Long term charge loss in EPROMs with ONO interpoly dielectric

Charge loss through ONO dielectric is limited by the oxide conductivity. The leakage current is too large to be explained by pure electron injection from the floating gate through the bottom oxide. A trap-assisted model is proposed wherein electrons tunnel to oxide traps and are then emitted. The coupling of the trap level to oxide phonons results in virtual energy levels in the oxide which allow more effective tunneling paths. Holes do not participate, because they are blocked by the top oxide. It has been verified that charge loss is not due to mobile ions.<>