Modeling of Composition and Channel Length-Dependent Transient Characteristics in Short-Channel IGZO Field-Effect Transistors

Abstract

In this study, we analyze the characteristics of fast transient drain current (I_D) in IGZO-based field-effect transistors (FETs) with different composition ratios (device O: ratio of 1:1:1 for In, Ga, Zn, device G: ratio of 0.307:0.39:0.303) for reliable operations. Overshoot currents, which can cause device degradation, are caused by fast transients and are attributed to the trapping of electrons in the energy band. As the lateral electric field (E_lat) of the IGZO channel is increased, the overshoot drain current difference (ΔI_OS) is increased for both devices. It is also found that the increase in ΔI_OS with decreasing L is less pronounced in device G compared with that for device O. While device G yields larger ΔI_OS values than device O in long channels (L = 5, 10 μm), it yields smaller ΔI_OS in short channels (L = 0.5, 1 μm). This phenomenon is explained using three physical parameters (n_OS, E_ver, and N_OT), based on Technology Computer-Aided Design (TCAD) simulation modeling. Device G has stronger immunity against ΔI_OS in a short-channel region; this can be attributed to the lower concentration of oxygen vacancies in device G that suppresses dopant diffusion effects within IGZO layer. These results experimentally demonstrate that the short-channel effects on fast-transient I_D can be improved by controlling the Ga composition ratio of IGZO.