부산대학교 도서관

The sub-threshold swing (SS) of Si n-MOSFETs is experimentally and systematically evaluated in a temperature range of 300 to 4 K with varying substrate impurity concentrations ($N_{sub}$) from ~1×10 16 to ~1×10 18 cm −3 , in order to obtain a physical understanding of SS at cryogenic temperatures. The saturated SS at low temperatures is found to increase with increasing $N_{sub}$. It is confirmed that the temperature and drain current dependencies of SS are well represented by the conventional model composed of mobile band tail states and localized interface states. On the other hand, the densities of the band tail states and the interface states, assumed in the model, are found to increase with increasing $N_{sub}$. Almost no change in SS with substrate bias suggests that these states can be generated by impurity-induced potential fluctuation.