Low-temperature CMOS-a brief preview

The advantages of operating CMOS at liquid nitrogen temperature (LN) are attributed to increased carrier mobility, reduced subthreshold swing, increased conductivity, reduced leakage, an improved device and circuit reliability such as electromigration ionic migration, and latchup. The gain in performance compared to room temperature (RT), however, begins to erode as the channel length is decreased below one micrometer, where increased lateral field causes the drift velocity to approach its scattering limited value along a large fraction of the channel. In the limit when saturation velocity is reached along the entire channel, the improvement at LN does not exceed a factor of approximately=2, after all other enhancements are considered. This gain must justify the added inconvenience and cost of operating the system at LN temperatures. As the channel length is reduced to deep submicrometer, below approximately=0.15 mu m, operating at low temperature could become a necessity rather than mere improvement over RT, because of the lack of a room-temperature process and device design point. >