International Conference on Solid State Devices and Materials

We performed drain current–gate voltage (I_D–V_G) characterization of bulk Si n-MOSFETs at deep cryogenic temperatures down to 15 mK to clarify the role of band-edge states. From the temperature-dependent subthreshold swing (SS) characterization, we found that the saturated SS at a few Kelvins decreased again in the milli-Kelvin range in proportion to temperature. Theoretical analysis of the temperature-dependent SS revealed that the exponentially distributed localized immobile states at the band-edge govern I_D–V_G characteristics at cryogenic temperatures, in which the occupancy of band-edge states is a key parameter for cryogenic MOSFETs. This study provides deep insights into the physical understanding of Si MOS-based devices under cryogenic operation, that is, both cryogenic CMOS and silicon qubits.