Low-Temperature Solution-Processed ZrO2 Gate Insulators for Thin-Film Transistors Using High-Pressure Annealing

Abstract

A solution-processed ZrO 2 gate insulator was fabricated using high-pressure annealing (HPA). The dehydroxylation process was accelerated and a thin, dense ZrO 2 film was formed at a low annealing temperature of 350 • C using HPA. This resulted in superior dielectric strength of the ZrO 2 films (about 10 −9 A/cm 2 at 2 MV/cm) for use as gate insulators. A low-temperature solution-processed InZnO thin-film transistor with such a ZrO 2 gate insulator had a saturation mobility of 0.10 cm 2 /V · s and an on/off ratio of 1.17 × 10 4 .Since the introduction of thin-film transistors (TFTs) to large-area displays, TFT manufacturing technology has focused on improving performance and reducing cost to achieve commercialization. Transparent oxide TFTs have attracted a great deal of attention because their electrical characteristics are superior to those of hydrogenated amorphous Si TFTs, 1-8 the dominant technology over the past few decades. However, conventional deposition methods that involve vacuum processes, such as sputtering, chemical vapor deposition, pulse laser deposition, and atomic layer deposition, are expensive and have a restricted deposition area. To overcome these limitations, solution processes have been studied as alternative deposition methods. 2-8 Although solution processes have many advantages such as simplicity and low cost, they require a high annealing temperature (400 • C or more) to obtain better performance. This high annealing temperature makes deposition on commercial glass or inexpensive flexible substrates difficult.Many research groups have recently reported results involving lowtemperature solution-processed films, such as ZnO, 4 InSnO, 5 InZnO, 6 and InGaZnO. 7 However, these studies have focused only on active layers; vacuum processes are still used to fabricate gate insulators. Furthermore, solution-processed gate insulators require a high annealing temperature to obtain thin, dense films required for low leakage current density and high breakdown voltage. 3,8,9 In this study, we fabricated low-temperature solution-processed ZrO 2 gate insulators using high-pressure annealing (HPA) and investigated the effects of this method.ZrO 2 solution was synthesized by dissolving 0.2 M ZrCl 2 in 2-methoxyethanol (2ME) solvent and filtering it through a 0.2-μm microfilter. This solution was spin-coated at a speed of 3000 rpm for 30 s on a heavily arsenic (n + )-doped silicon wafer. The ZrO 2 film was pre-annealed at 300 • C for 5 min on a hot plate and then annealed at 350 • C for 30 min in ambient air with a high pressure of 10 atm using a HPA method. The spin-coating and annealing procedures were repeated five times. To confirm the effect of temperature and pressure, other samples were also fabricated by annealing at 500 • C or 350 • C without HPA.Solution-processed InZnO TFTs were fabricated using these ZrO 2 films as gate insulators. The 0.3 M InZnO solution prepared using In(NO 3 ) 3 · xH 2 O and Zn(CH 3 COO) 2 · 2H 2 O in 2ME with the stabilizers was also spin-coated on the ZrO 2 films and ann...

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