The Effect of Active-Layer Thickness and Back-Channel Conductivity on the Subthreshold Transfer Characteristics of Hf-In-Zn-O TFTs

The effect of active-layer thickness and back-channel conductivity on the subthreshold transfer characteristics of hafnium-indium-zinc-oxide (HIZO) thin-film transistors was studied. Experiments show that subthreshold humps in the transfer curves become more pronounced as the active-layer thickness increases, in the presence of a highly conductive back channel. With a highly conductive thin back channel, subthreshold humps were observed as the total active-layer thickness exceeded 80 nm. The above results can be interpreted as a consequence of a reduction in the effective gate field as the active thickness exceeds the "screening length". The screening length of the HIZO layer is calculated to be approximately 78 nm, and accordingly, as the active thickness exceeds this value, subthreshold humps that are anticipated to originate from the back-channel conduction appear.