Total dose radiation effects on DRAM performance

Abstract

Dynamic RAMS (DRAMs) subjected to accelerated radiation testing techniques with a 5 MeV alpha particle source produce soft errors. The soft error rate (SER) increases with the total dose. Investigation of total dosing shows an accumulated soft error rate (ASER) which is pattern-dependent and contains static and dynamnic charge-dependent elements. Total dosing initiates two principal mechanisms within the SiO2 and at the Si-SiO2 interface which serve to increase the bit line capacitance and simultaneously modify the device threshold voltages (V T). The two mechanisms, however, occur at different rates and have differing influences on the NMOS device operation. Each mechanism has its own dominating effect on the ASER but is dependent on its location within the NMOS device structure. Changes in V T characteristics are most significant in their effects on dummy cells in determining SER performance. The dominant mechanisms in the NMOS DRAM are: the reduction in V T by the drift of trapped oxide charge, and the...