OPTIMIZATION OF LDD DEVICES FOR CRYOGENIC OPERATION

The optimization of lightly doped drain (LDD) devices to maximize hot-carrier device lifetime at cryogenic temperature is studied. The hot-carrier-induced device degradation behavior and mechanisms of the various LDD and conventional devices are investigated. Carefully designed LDD devices can have better device reliability at low temperature compared to the conventional devices. However, the device lifetime is very short at low temperature for all the devices, and the difference in device lifetime between LDD and control device is not appreciably large. Also, the degradation behavior of both LDD and non-LDD devices at 77 K does not follow the simple behavior modeled by substrate current (l(sub)). For a given device, the maximum degradation is not observed at the bias condition for maximum l(sub). Furthermore, the optimum LDD design depends on the specific stressing bias conditions at 77 K.