Relation between thehot carrier lifetime of transistors and CMOS SRAM products

The hot-carrier degradation of static RAMs is discussed. During the stress, an increase of the access times, the minimum operating voltage, and the write times is observed. The latter two can be directly related, even quantitatively, to the degradation of the access transistor of the memory cell. Comparison of product and transistor lifetimes show that their voltage dependence is the same, but that the product lifetime is significantly (about a factor 50) larger. The discrepancy is caused by the small sensitivity of the SRAM to transistor degradation, and by duty cycle effects It is concluded that the product lifetime is severely underestimated if it is straightforwardly derived from static transistor lifetime data only. The true product lifetime should be obtained from stressing the product.<>