Investigation and modeling of subthreshold turn-on voltage in bulk and FDSOI MOSFETs at cryogenic temperatures

Conventional physics-based MOSFET models miss the sharp subthreshold turn-on “knee” in the logarithmic dependence of the Id on the Vgs that emerges in MOSFETs at cryogenic temperatures. This oversight results in a fundamental mischaracterization of the MOSFETs' turn-on behavior, compromising the physical accuracy of Cryo-complementary metal–oxide–semiconductor compact models. To address this gap, we define the subthreshold turn-on voltage Vsub,on as the Vgs where Id begins its exponential rise from the leakage floor. Our physics-based model links Vsub,on to the filling of localized band tail states, accurately predicting its temperature dependence and is validated against 40 nm bulk and 22 nm FDSOI data from 300 K down to 4 K, providing a key parameter and framework to enable reliable cryogenic circuit design.