Enhanced Fail Rate Projections Using Negative Design Assist in Automotive Grade SRAMs

SRAMs used in automotive grade applications are required to meet stringent fail rate criteria through End-of-Life (EOL) operation. Current fail rate projections often involve Vmin testing at low voltages which introduce uncertainties due to the large fail rate extrapolations involved. We propose complementary Vmin testing with negative read assist as a way to improve EOL fail rate estimates through the use of triangulation with constrained regression. The use of design assist is also shown to be an effective way of time-zero (TO) product screening without the use of very low voltages that are often not possible during product testing.