White Paper: 256 Megabit SDRAM Single Event Effects and Total Ionizing Dose Testing

By G. Williamson, P. Layton, C. Thibodeau, L. Longden and R. Hillman
Maxwell Technologies

Abstract
256 Megabit SDRAMs are advanced memories with internal state machines and functions that make testing and understanding the resultant radiation effects complicated. In this paper, we present results and methodologies for single event effects (SEE) and total ionizing dose (TID) testing.

The SEL threshold is greater than 85 MeV-cm²/mg at room temperature (25°C) and decreases to 55 MeV-cm²/mg at 85°C. This corresponds to a Single Event Latchup (SEL) rate in a geosynchronous orbit (worst-case environment for heavy ions) of one latchup in 20,000 years operating at 85°C. The Single Event Functional Interrupt (SEFI) saturated cross-section is approximately 4 E-4 cm²/device with a threshold around 20 MeV-cm²/mg. The SEFI rate in a geosynchronous orbit (worst case environment for heavy ions) is once every 8 years. Parts programmed in the inverse bleed down pattern have the highest probability of Single Event Upsets (SEUs). The inverse bleed down SEU saturated cross-section is 2 E-9 cm²/bit, with a SEU threshold of approximately 2.7 MeV-cm²/mg. The proton cross-section at 92.5 MeV is approximately 3 E18 cm²/bit. This device is not subject to Multiple Bit Upsets (MBUs), SEL or SEFIs from protons.

Packaged parts were tested for TID up to 50 krad(Si). Every part passed all parametric tests, with the exception of one part that experienced a functional failure at 42 krad(Si).

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