Enhancement of electrical performance in indium-zinc oxide thin-film transistors with HfO2/Al2O3 gate insulator deposited via low-temperature ALD

Abstract

Several studies have been conducted on amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) with the aim of applying them to the next-generation low-power displays. To improve the electrical performance of conventional AOS TFTs, which are known for their poor switching characteristics, we fabricated indium-zin oxide (IZO) TFTs with HfO2/Al2O3 gate insulator deposited via low-temperature atomic layer deposition (ALD). We optimized the electrical performance of the fabricated TFTs by varying the thickness of the IZO channel and Al2O3 insulator, respectively. Compared to the samples with a thermally grown 150 nm thick SiO2 gate insulator, the samples with a 10 nm thick IZO channel and a 10/70 nm thick HfO2/Al2O3 gate insulator exhibited the subthreshold swing of 0.24 V/dec, saturation carrier mobility of 7.49 cm2/V∙s and on–off current ratio of 1.09 × 107, which were improved by more than 47 %, 64 % and 5 times, respectively. Also, the threshold voltage shift in positive and negative bias stress conditions were improved to + 0.90 and – 1.75 V, respectively.