Nanoscale thick FDSOI MOSFETs: A simple model of abnormal electrical behavior at low temperature

Two kinds of Fully Depleted Silicon-On-Insulator (FD-SOI) MOSFETs were electrically measured at 300K and at 77K and compared. Both the devices, Ultra-Thin Body (UTB) and Nano Scale Body (NSB), are sharing the same W/L ratio but are having a channel thickness of 46 nm and 2.2 nm respectively. For both the temperatures, the devices' respective linear transfer characteristics were found to be surprisingly different by several orders of magnitude. Moreover, by decreasing the temperature, their behaviors were radically opposite: If for UTB device, the electrical conduction was increased, the opposite effect was observed for NSB. We analyzed the latter result by considering the severe mobility degradation in terms of the influence of a huge voltage dependent series resistance and found it to be more physically coherent. This influence is integrated into a simple but accurate analytical model in order to describe the trends of the transfer characteristics. This new modeling approach may be useful to interpret anomalous electrical behavior of other nano-devices in which series resistance and/or mobility degradation is of a great concern.