Physical meaning of σ value estimated with VTH-mismatch evaluation circuit

A new test chip is developed for clarifying the quantity corresponding to the standard deviation of the threshold voltage, σ_TC, which is extracted using the test circuit proposed previously (Terada, K. and Eimitsu, M., Proc. IEEE Int. Conf. on Microelectronic Test Structures, p.227-31, 2003; Terada and Fukeda, K., Proc. IEEE Int. Conf. on Microelectronics Test Structure, p.155-59, 2004). Comparing σ_TC with the standard deviation calculated from the many data for individual MOSFETs, it is considered that σ_TC is a good approximation to the standard deviation of the threshold voltage.