28-nm FDSOI nMOSFET RF Figures of Merits and Parasitic Elements Extraction at Cryogenic Temperature Down to 77 K

Abstract

This paper presents detailed RF characterization of 28-nm FDSOI nMOSFETs at cryogenic temperatures down to 77 K. Two main RF figures of merit (FoM), i.e., current gain cutoff frequency ( $f_{T}$ ) and maximum oscillation frequency ( $f_{\max }$ ), as well as elements of small-signal equivalent circuit are extracted from the measured S-parameters. Increases of $f_{\textit T}$ and $f_{\max }$ by about 85 GHz and about 30 GHz, respectively, are demonstrated at 77 K. The observed behavior of RF FoMs versus temperature is discussed in terms of small-signal equivalent circuit elements, both intrinsic and extrinsic (parasitics). This paper suggests 28-nm FDSOI as a good candidate for future cryogenic applications.