Invited Paper
Comparison of the freeze-out effect in ln and B doped n-MOSFETs in the range 4.2 - 300 K

Abstract
In a first part, the impact of low temperature operation on the classical short channel effects will be discussed critically. Particular attention will be given to the reduction of the threshold voltage V_T with effective device length in the temperature range 4.2 K to 300 K and to the short-channel behaviour of the subthreshold swing 1/S. In a second part, the impact of dopant freeze-out on the static operation of deep submicron n-MOSFETs will be studied. A comparison is made between standard 0.25 µm B doped and exploratory 0.1 µm In doped transistors. Although the experimental threshold voltage behaviour of deep submicron MOSFETs at cryogenic temperatures can be qualitatively described by the standard equations, a significant difference is noted between the measured and the calculated V_T, which is most pronounced in the liquid helium temperature range. Possible additional factors which should be taken into account in a refined modeling will be pointed out, with particular emphasis on the contribution of the interface state charge.