Novel cell isolation technique for the analysis of CMOS SRAM cell cold failure

CMOS SRAM cell cold failure analysis is not easily performed under a room temperature environment. However, by using the signature analysis method, the transistor failure cell can be identified by directly measuring the transistor parameters from the isolated SRAM cell. The cell isolation technique for signature analysis is sensitive enough to capture the abnormal electrical signature of the SRAM cell cold failure. The technique was used on the analysis of SRAM cell cold failure from a 2-layer metal fab process. The SRAM cell and its transistors were physically and electrically isolated without any problem. The failure signature of the SRAM cell cold failure which failed stuck at "1" at a single bit address during testing, was successfully analyzed. N+ drain junction leakage and threshold voltage degradation was identified as the root cause of the cold failure.