Origin of Low-Frequency Noise in Si n-MOSFET at Cryogenic Temperatures: The Effect of Interface Quality

This study investigates the origin of low-frequency (LF) 1/
$f$
noise in Si n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs) under cryogenic operation. The fluctuation of the drain current increased with decreasing temperature, exhibiting LF 1/
$f$
noise of more than two orders of magnitude higher at 2.5 K compared with that at 300 K. As revealed by the temperature dependence of the normalized current spectral density, the LF 1/
$f$
noise at 2.5 K is primarily governed by carrier number fluctuations. To obtain insight into the carrier trapping centers under cryogenic operation, we investigate the effect of oxide/Si interface states on the LF 1/
$f$
noise by utilizing Si n-MOSFETs with different surface orientations, i.e., different interface trap densities (
$\text{D}_{\mathrm {it}}$
). The LF 1/
$f$
noise is comparable between the surface orientations at 300 K, whereas excess noise was observed at 2.5 K for the surface orientation with higher
$\text{D}_{\mathrm {it}}$
in the order of (100)< (120)
$\le $
(110)-orientations. This indicates that the LF 1/
$f$
noise at cryogenic temperatures originates from oxide/Si interface defects and disorders, that is, the interface states and band tail states. These states are localized at the conduction-band edge, which contributes to noise generation as the Fermi level approaches the conduction-band edge at cryogenic temperatures. This study demonstrates the significance of the oxide/Si interface quality in suppressing the LF 1/
${f}$
noise in Si MOS devices operated at cryogenic temperatures.