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The radiation hardness of nominally identical SRAM test chips fabricated in five commercial foundries is examined. Large variations in single-event latchup and total dose response are observed. The softest SRAMs fail functionally at ∼200 krad(SiO2) and have a fairly large single-event latchup cross section. This is in contrast to the hardest foundry split which is nearly immune to single-event latchup at room temperature, and remains functional to a total dose of 400 krad(SiO2). Three of the splits show a similar increase in radiation induced leakage current, which is dependent on both the characterization bias as well as the pattern written to the memory array. The other two splits show neither a pattern nor a bias dependence on the leakage current. Heavy-ion microbeam experiments confirm that the most latchup sensitive area of these SRAMs is the peripheral circuitry, not the memory array itself. Qualification and hardened-by-design integrated circuit implications are discussed. [ABSTRACT FROM AUTHOR]

Eliminating radiation-induced parasitic leakage paths in integrated circuits (ICs) is key to improving their total dose hardness. Semiconductor manufacturers can use a combination of design and/or process techniques to eliminate known radiation-induced parasitic leakage paths. However, unknown or critical radiation-induced parasitic leakage may still exist on fully processed ICs and it is extremely difficult (if not impossible) to identify these leakage paths based on radiation induced parametric degradation. We show that light emission microscopy can be used to identify the location of radiation-induced parasitic leakage paths in ICs. This is illustrated by using light emission microscopy to find radiation-induced parasitic leakage paths in partially-depleted silicon on insulator static random-access memories (SRAMs). Once leakage paths were identified, modifications were made to the SRAM design to improve the total dose radiation hardness of the SRAMs. Light emission microscopy should prove to be an important tool for the development of future radiation hardened technologies and devices. [ABSTRACT FROM AUTHOR]