High‐performance HfO ₂ /ZrO ₂ /IGZO thin‐film transistors deposited using atmospheric pressure plasma jet

Abstract

An atmospheric pressure plasma jet (APPJ) deposition technology that is employed for the preparation of transparent oxide semiconductors film using an eco-friendly water-based metal salt solution as a precursor is presented. Through the use of APPJ indium-galliumzinc-oxide (IGZO) film as the channel material and a high-k dielectric HfO 2 /ZrO 2 gate stack, IGZO-based transparent thin-film transistors (TFTs) were fabricated and characterised. The HfO 2 /ZrO 2 /IGZO-TFTs by APPJ demonstrated excellent electrical characteristics, including a low V th of 0.63 V, a small subthreshold swing of 0.37 V/dec, a high mobility of 40 cm 2 /V-s and a large I on /I off ratio of 7 × 10 8 .Introduction: Amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs) are of considerable interest for backplanes of the next-generation flat-panel displays, such as active matrix liquid crystal displays and active matrix organic light-emitting diode displays, owing to their better field-effect mobility (>10 cm 2 /V-s), larger I on /I off ratio (>10 6 ), smaller subthreshold swing and better stability against electrical stress in comparison with traditional amorphous Si-based TFTs [1-3]. Conventionally, a-IGZO films are deposited by vacuum technologies, such as radio-frequency or direct-current magnetron sputtering and pulsed laser deposition. Recent researches have focused on the nonvacuum techniques, such as solution-processed IGZO films [3-5] and atmospheric pressure plasma jet (APPJ)-deposited IGZO films [6,7]. Compared to the vacuum techniques, the APPJ has lower apparatus cost since it does not need a vacuum chamber and associated pumping systems. The APPJ also has better suitability for large-scale applications among the other deposition technologies. We have reported that IGZO TFTs prepared by an APPJ with a gate dielectric of Al 2 O 3 exhibited good electrical performance on mobility, I on /I off ratio, subthreshold swing and threshold voltage [6]. As well as the deposition technologies, researches on the compositional effects on the indium, gallium and zinc atomic (mole, molar) ratio have also been carried out extensively in the previous reports. However, they were based on vacuum-processed [2] or solution-processed [3] IGZO films. Owing to the different deposition mechanism, it may have a different optimal composition condition on the APPJ-processed IGZO films. In the work reported in this Letter, we prepared the IGZO films with three kinds of In:Ga:Zn composition ratio by an APPJ, to further investigate the compositional effects of this technique. In addition, HfO 2 /ZrO 2 high-k gate dielectric stacks annealed at various temperature conditions were also investigated, to improve the electrical performance of the TFT device.

Design of a voltage‐programmed V TH compensating pixel circuit for AMOLED displays using diode‐connected a‐IGZO TFT

“…Out of all these oxide TFTs, amorphous‐indium–gallium–zinc oxide (a‐IGZO) TFTs have gained considerable traction because of the presence of several sought after properties like transparency [6], high electron mobility, good uniformity, high on‐to‐off current ratio, sharp threshold swing and low processing temperature [7]. Some fabrication techniques for high‐performance a‐IGZO TFTs have also been proposed like deposition using atmospheric pressure plasma jet [8, 9] etc. However, threshold voltage instability under gate bias stress still remains an issue for a‐IGZO pixel circuits resulting in OLED current degradation with time, thus limiting the lifetime of the OLED panel.…”