Effects of Active Layer Thickness on the Electrical Characteristics and Stability of High-Mobility Amorphous Indium–Gallium–Tin Oxide Thin-Film Transistors

Abstract

Herein, we investigated the effects of active layer thickness (tS) on the electrical characteristics and stability of high-mobility indium–gallium–tin oxide (IGTO) thin-film transistors (TFTs). IGTO TFTs, with tS values of 7 nm, 15 nm, 25 nm, 35 nm, and 50 nm, were prepared for this analysis. The drain current was only slightly modulated by the gate-to-source voltage, in the case of the IGTO TFT with tS = 50 nm. Under positive bias stress (PBS), the electrical stability of the IGTO TFTs with a tS less than 35 nm improved as the tS increased. However, the negative bias illumination stress (NBIS) stability of these IGTO TFTs deteriorated as the tS increased. To explain these phenomena, we compared the O1s spectra of IGTO thin films with different tS values, acquired using X-ray photoelectron spectroscopy. The characterization results revealed that the better PBS stability, and the low NBIS stability, of the IGTO TFTs with thicker active layers were mainly due to a decrease in the number of hydroxyl groups and an increase in the number of oxygen vacancies in the IGTO thin films with an increase in tS, respectively. Among the IGTO TFTs with different tS, the IGTO TFT with a 15-nm thick active layer exhibited the best electrical characteristics with a field-effect mobility (µFE) of 26.5 cm2/V·s, a subthreshold swing (SS) of 0.16 V/dec, and a threshold voltage (VTH) of 0.3 V. Moreover, the device exhibited robust stability under PBS (ΔVTH = 0.9 V) and NBIS (ΔVTH = −1.87 V).