  The extremely low threshold voltage (Vth) of native MOSFETs (Vth~0V@300K) is
conducive to the design of cryogenic circuits. Previous research on cryogenic
MOSFETs mainly focused on the standard threshold voltage (SVT) and low
threshold voltage (LVT) MOSFETs. In this paper, we characterize native MOSFETs
within the temperature range from 300K to 4.2K. The cryogenic Vth increases up
to ~0.25V (W/L=10um/10um) and the improved subthreshold swing
(SS)~14.30mV/dec@4.2K. The off-state current (Ioff) and the gate-induced drain
leakage (GIDL) effect are ameliorated greatly. The step-up effect caused by the
substrate charge and the transconductance peak effect caused by the energy
quantization in different sub-bands are also discussed. Based on the EKV model,
we modified the mobility calculation equations and proposed a compact model of
large size native MOSFETs suitable for the range of 300K to 4.2K. The
mobility-related parameters are extracted via a machine learning approach and
the temperature dependences of the scattering mechanisms are analyzed. This
work is beneficial to both the research on cryogenic MOSFETs modeling and the
design of cryogenic CMOS circuits for quantum chips.
