Kinetic Analysis of X-Ray Irradiation Induced Static Refresh Failure Mechanism in DRAM

DRAM products are susceptible to low-dose X-ray irradiation with levels as low as 120 Rad(Si), much lower than previously reported values related to total ionizing dose (TID). A large variance in this susceptibility was observed among DRAM vendors. The key parameter affected by X-ray irradiation was static refresh, where the damage manifested as an increase in junction leakage of the storage node cell. Both junction leakage and gate-induced drain leakage currents (GIDL) were characterized, and results indicated that junction leakage was the dominant mechanism in static refresh (t_ref) degradation. The static refresh of both the extrinsic and intrinsic bit populations were affected by the low-dose ionizing radiation. However, in typical manufacturing X-ray inspection procedures, the tail bits can fall out of spec conditions and render the device a failure. Thermal annealing did lead to some recovery in t_ref; however, a complete recovery was not observed, even at high temperatures that may not be practical for components.