A 8 K×8 radiation hardened SRAM

Describes a 64 K (8 K×8) radiation hardened SRAM and the process modifications which contribute to achieve a satisfactory immunity to worst case heavy ion environments. This 64 K SRAM incorporates polysilicon feedback resistors in the memory cell to provide SEU immunity. These resistors, obtained by selected polysilicon silicidation, allow an access time of 55 ns in some process and temperature worst case conditions. Besides, one can significantly reduce leakage current degradations due to total dose effects by removing or biasing `off´ the parasitic transistors which exist in addition to `real´ transistors. Circuit simulations indicate a total dose immunity of 100 krads (Si)