NAND and NOR gate

Question

Explain why NAND gate is preferred over the NOR gate for fabrication?

Answer 1

NAND gate is preferred over the NOR gate since at the transistor level mobility of electrons is generally three times that of the holes as compared to NOR and therefore the NAND is considered as a faster gate. Moreover, the gate-leakage in the NAND structures is much lower. In case, you consider the t_phl and t_plh delays you might find that it is much more symmetric in case of the NAND, however, in case of NOR, one delay is more higher than other.