Performance and reliability comparison between asymmetric and symmetric LDD devices and logic gates

The performance and reliability of NMOSFET asymmetric lightly doped drain (LDD) devices (with no LDD on the source side) are compared with those of conventional LDD devices. At a fixed V/sub dd/, asymmetric LDD devices exhibit higher I/sub dsat/ and shorter hot-carrier lifetime. To maintain the same hot-carrier lifetime, asymmetric LDD devices must operate at lower V/sub dd/ while higher I/sub dsat/ is retained. For the same hot-carrier lifetime, ring oscillators with NMOSFET asymmetric LDD devices can achieve 5% (10% if PMOSFET also had asymmetric LDD) higher speed and 10% lower power. The hot-carrier reliability of inverter, NAND, and NOR structures with asymmetric and conventional LDD devices is also simulated and compared.