Probing Band Tail States in MOSFETs at Cryogenic Temperatures through Noise Spectroscopy

Low-frequency noise is one of the main limiting factors for the design of cryogenic electronics and it is also responsible for qubit errors in quantum computers. The high noise levels observed in MOSFETs at cryogenic temperatures have been attributed to band tail states at the Si/SiO
2
interface, also identified as the main cause for the saturation of the subthreshold swing (SS) at low temperatures.In this work, we measured 1/f noise in undoped silicon nMOS-FETs with 12 nm, thermally grown, SiO
2
over a wide range of temperatures and gate voltage overdrives. We show that band tail states contribute to the 1/f noise only at low temperatures, while their effect on noise is not visible at room temperature. Finally, with the help of TCAD simulations, we extract the energy distribution of the defects contributing to 1/f noise from measurements. The results show that the energy distribution of defects at 4 K is compatible with band tail distributions proposed in the literature and with the SS saturation at low temperatures observed in the experiments.