Influence of RF power in the sputter deposition of amorphous InGaZnO film on the transient drain current of amorphous InGaZnO thin-film transistors

The device electrical and transient current characteristics of the amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) are comprehensively investigated according to the radio-frequency (RF) power during the sputter-deposition of IGZO active film. The RF power dependencies of the oxygen vacancy (V_O) concentration in IGZO and the surface morphology of IGZO film are analyzed through X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). According to the RF power change in the range of 100 ∼ 250 W, the optimal point in terms of threshold voltage (V_T), ON current (I_on), field-effect mobility in the linear region (μ_{FE_lin}), hysteresis voltage (V_Hys), and the V_T shift under current stress (ΔV_T) is found to be 200 W. The existence of the optimal power condition originates from the RF-power dependencies of the electron carrier concentration, the density of electron traps in gate insulator (GI), and the interface trap density related to surface roughness.

Furthermore, compared to the direct current (DC) current stress (CS) condition, it is found that when V_GS rises rapidly, a total transient current ΔI_D can be decomposed into three components, i.e., ΔI_OS, ΔI_BOOST, ΔI_DEG. While ΔI_OS is attributed to the non-quasi static Fermi-level rising, ΔI_BOOST and ΔI_DEG result from the donor creation in IGZO and the electron trapping into GI and interface. Noticeably, the occurrence level of each component changes sensitively according to RF power.

Our result suggests that the 200 W device has the least overshoot of transient current and shows the best reliability in terms of deterioration due to transient current characteristics.