SEPIA: a new isolation structure for soft-error-immune LSIs

A new isolation structure for soft-error immunity has been developed. This structure, SEPIA (soft-error-preventing isolation by charge absorption), is suitable for advanced ULSIs such as 256-kb bipolar SRAMs. The SEPIA structure combines charge absorption and trench isolation. Experiments and simulations show that SEPIA reduces the amount of alpha-particle-induced charge collected in transistors. Electrons which diffuse in the substrate are absorbed by SEPIA. The collected charge is reduced to 20-30 fC, which is about 1/5 of the charge collected with the conventional structure. With SEPIA the amount of charge collected decreases as the transistor size is scaled down. SEPIA is thus more effective in the small transistors that will be used in advanced ULSIs