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We report high-performance homojunction amorphous-indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with low-resistive a-IGZO source/drain (S/D) electrodes. The a-IGZO S/D electrodes are selectively treated with high-power NF 3 plasma, which reduces their resistivity from ∼16 to 5.5×10 −3 · cm. X-ray photoelectron spectroscopy indicates an increase in weakly bonded oxygen and a substantial amount of indium-fluorine and zinc-fluorine bonds at the a-IGZO top surface (extending to ∼7 nm into the bulk) after plasma treatment. Temperature-dependent conductivity measurements show metallic behavior of the a-IGZO after treatment. It is concluded that fluorine atoms substitute for oxygen atoms-generating free electrons in the process and/or occupy oxygen vacancy sites-eliminating electron trap sites. As a result, the homojunction TFTs show good ON-state characteristics with typical field-effect mobility, subthreshold gate-voltage swing, and turn-ON voltage of 19 ± 1 cm 2 /V · s, 178 ± 30 mV/decade, and −3.2 ± 1.5 V, respectively. Good stability at high temperature and under bias and light stress are also exhibited by the homojunction TFTs, verifying a stable doping effect by the NF 3 plasma treatment. IndexTerms-Amorphous-indium-gallium-zinc-oxide (a-IGZO), fluorine, homojunction, thin-film transistor (TFT).

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Owing to their unique device structures, amorphous oxide semiconductor (AOS)-based thin-film transistors (TFTs) often exhibit non-ideal dependencies on channel width (W) and channel length (L) variations. In particular, two abnormalities are common; 1) the TFT threshold-voltage (VTH) shifts to the negative gate voltage (VGS) direction as L decreases for fixed W; and 2) the TFT field-effect mobility (µFE) dramatically increases as W decreases for fixed L. This paper therefore seeks to explain the origin of these non-ideal behaviors and present device topologies that can be utilized to minimize them. The abnormal negative VTH shift (ΔVTH) is attributed to unintentional doping of the intrinsic channel region from n+ doped source/drain regions, whereas the large increase in µFE is due to spreading current, which effectively increases W. It is found that the former can be minimized by reducing the source/drain to active layer contact area, whereas the latter is solved by employing device topologies in which the source and drain electrodes extend over the active layer along the W direction. This paper furthers our knowledge and understanding of the physical topology of TFT designs and its impact to TFT performance.

The use of a Corbino thin-film transistor (TFT) as the driving-TFT in large-area active-matrix organic light-emitting diode (AMOLED) display pixels is reported. Given the infinite output resistance exhibited by the Corbino TFT beyond pinch-off, the same drive (diode) currents are maintained, even with voltage (IR) drop-related variations in the supply voltage (V DD ).