Direct tunneling from source to drain in nanometer-scale silicon transistors

Direct tunneling from the source to the drain in a nanometer-scale silicon metal-oxide-semiconductor field-effect transistor (MOSFET) was investigated in terms of subthreshold currents in electrically variable shallow junction MOSFETs (EJ-MOSFETs) with gate lengths ranging from 8 to 52 nm at 25 less than or equal to T less than or equal to 300 K. Electrical transport in the nanometer-scale EJ-MOSFETs was studied by one-dimensional numerical analysis incorporating tunneling effects. The calculated results not only well reproduced subthreshold currents but also reveal that the weak temperature dependence of the current at low temperature is caused by direct tunneling from the source to the drain ("direct SD tunneling"). The scaling limit of MOSFETs in the direct SD-tunneling scheme was estimated by applying the same calculation technique to the simplified channel potential distribution of MOSFETs.