Effect of Channel Thickness on Performance of Ultra-Thin Body IGZO Field-Effect Transistors

Abstract

Amorphous indium–gallium–zinc oxide (a-IGZO) is a promising channel material for an upper transistor in monolithic three-dimensional devices. Although the field-effect transistors (FETs) with a rather thick channel thickness >10 nm have been intensively examined, less information is available for the IGZO FETs with an ultra-thin body (< 10 nm). In this study, the FETs with the IGZO channel layer ranging from 2 to 20 nm were investigated in detail. As the channel thickness decreased from 20 to 7 nm, the mobility and subthreshold swing (SS) values were improved. In contrast, the deterioration in mobility and SS occurred when the IGZO thickness was less than 7 nm. The physical rationale for the strong IGZO thickness dependence on performance of the resultant FETs was discussed based on subgap density-of-state distribution and mobility models such as percolation and surface-roughness scattering mechanisms using a technological computer-aided design simulation with a quantum mechanical model. IGZO FET with an IGZO thickness of 7 nm exhibited the best performance, which was attributed to the synergic balance by percolation efficiency and reduction in effective subgap defect density of IGZO.