Analyzing hot-carrier effects on cold CMOS devices

The operation of discrete and integrated CMOS ring oscillators was evaluated over the temperature range 77-300 K. Gate delays typically decreased by a factor of two at 77 K. Hot-carrier effects were enhanced by low-temperature operation, and transistor transconductance degradation occurred at low temperatures, which did not occur at room temperature as measured in the forward and inverse transistor curves. In marked contrast to dc stressing, ac stressing caused very little circuit degradation at low temperatures. By modeling the low-temperature phenomena at the MOSFET source junction, both hot-electron and hot-hole carrier effects were analyzed.