Liquid Helium Temperature Operation of Graded-Channel SOI nMOSFETs

This work reports, for the first time, the operation of Graded-Channel SOI nMOSFETs at liquid helium temperature. As expected, for all measured devices it has been observed that at 4.2K the transconductance increases with respect to room temperature as a consequence of the mobility rise. On the opposite hand, all the studied devices demonstrated a degradation of the output conductance with temperature reduction. However, this degradation is attenuated below 90K. As a consequence, an increase of the Early voltage and of the intrinsic voltage gain were obtained, in contrast to the data reported in the literature, for devices operating down to 100K. It is demonstrated that GC SOI presented larger Early voltage increase at 4.2K than at room temperature. The rise of the voltage gain promoted by GC architecture has shown to be constant with temperature down to 4.2K.