Recovery Effects in the Distributed Cycling of Flash Memories

Dielectric damage caused by program/erase cycling partially recovers during the delays between cycles. This paper characterizes the effect of these delays on the charge-detrapping data-retention mechanism. Delay effects are temperature accelerated with an activation energy of 1.1 eV. Using this activation energy, qualification cycling temperature and time can be chosen to emulate the rate of cycling expected in field use. Retention lifetime can be more than an order of magnitude greater after cycling with realistic delays than with the minimal delays common in qualification stresses. For purposes of extrapolating from one cycling rate or temperature to another, an empirical accelerated reliability model is proposed, based on a "unified detrapping metric" or UDM. The UDM comprehends the effects of cycle count, cycle rate, cycling temperature, retention time, and retention temperature