On the Origin of Improved Charge Transport in Double-Gate In–Ga–Zn–O Thin-Film Transistors: A Low-Frequency Noise Perspective

Low-frequency noise (LFN) in double-gate (DG) In-Ga-Zn-O (IGZO) thin-film transistors (TFTs) is studied to investigate the origin of performance improvement. We found that thinning down the IGZO film enhances such improvements. With 7-nm IGZO, the mobility is raised by a factor of 3.77, and the subthreshold slope is reduced to 0.17 V/decade from single-gate to DG mode. Device simulations show that bulk transport inside IGZO film emerges as the two gates field effects get coupled. The LFN results reveal a transport transition from surface to bulk and disclose the superior bulk transport that experiences slight phonon scattering with a small Hooge parameter α_H = 4.44 × 10^-3 whereas the surface transport undergoes serious charge trapping with surface trap densities about 2 × 10¹¹ eV^-1cm^-2.