Semiconductor science and technology vol:8 issue:3 pages:423-428
In this paper the effects of the application of channel hot-carrier (CHC) stress applied at 4.2 K to SOI nMOS transistors are investigated. As will be shown, a reduction of the threshold voltage is observed for typical stressing conditions, while simultaneously the maximum transconductance increases. Similar changes can be obtained nearly immediately by applying a strong pulse into multiplication, i.e. by pulsing the drain voltage beyond the kink. At 4.2 K this 'low'-threshold-voltage (V(T)) state is metastable. These phenomena can be explained by considering hole trapping in the frozen-out film, yielding a reduction of the depletion charge and an increase in the film potential. This results in a reduction of V(T) and of the transverse electric field. Due to the slow re-emission and to the steep forward diode characteristic, trapped charge will remain for a considerable time in the film, explaining the metastability of the hole-trapping-induced low-V(T) state at 4.2 K.