Mechanochemical and Thermal Treatment for Surface Functionalization to Reduce the Activation Temperature of In-Ga-Zn-O Thin-film Transistors

Abstract

Amorphous indium-gallium-zinc oxide (a-IGZO) films, which are widely regarded as a promising material for the channel layer in thin-film transistors (TFTs), require a relatively high thermal annealing temperature to achieve switching characteristics through the formation of metal–oxygen (M–O) bonding (i.e., the activation process). The activation process is usually carried out at a temperature above 300 °C; however, achieving activation at lower temperatures is essential for realizing flexible display technologies. Here, a facile, low-cost, and novel technique using cellophane tape for the activation of a-IGZO films at a low annealing temperature is reported. In terms of mechanochemistry, mechanical pulling of the cellophane tape induces reactive radicals on the a-IGZO film surface, which can give rise to improvements in the properties of the a-IGZO films, leading to an increase in the number of M–O bonds and the carrier concentration via radical reactions, even at 200 °C. As a result, the a-IGZO TFTs, compared to conventionally annealed a-IGZO TFTs, exhibited improved electrical performances, such as mobility, on/off current ratio, and threshold voltage shift (under positive bias temperature and negative bias temperature stress for 10,000 s at 50 °C) from 8.25 to 12.81 cm2/(V·s), 2.85 × 107 to 1.21 × 108, 6.81 to 3.24 V, and −6.68 to −4.93 V, respectively.

Defect Passivation and Carrier Reduction Mechanisms in Hydrogen-Doped In-Ga-Zn-O (IGZO:H) Films upon Low-Temperature Annealing for Flexible Device Applications

“…A slight difference in the shape of the peaks before and after annealing was found in the higher binding energy region. Three clear distinguishable Gaussian–Lorentzian curves after the O 1s spectra deconvolution were assigned to 530.7 eV, 531.2 eV and 532.0 eV, corresponding to the metal-oxygen bonds ( M–O ), oxygen vacancies ( V O ) and oxygen-hydrogen ( OH ), respectively [ 21 , 36 , 37 ]. Table 2 is a summary of the relative area ratio of the obtained peaks.…”

“…This limitation requires the development of new approaches to achieve comparable electrical properties at a relatively low temperature. Several methods have already been proposed (these methods are referred to as “activation process of IGZO”), such as active IGZO layer oxidation at low temperatures by O 2 wet and O 3 annealing [ 15 , 16 ], high-pressure O 2 and N 2 gas annealing [ 17 ], hydrogen injection and oxidation for low-temperature aqueous solution-processed IGZO TFT [ 18 ], microwave and e-beam annealing [ 19 ], capacitive coupled plasma-assistant IGZO magnetron sputtering [ 20 ], and mechanochemical and thermal treatment [ 21 ]. Our research group has recently reported that adding hydrogen to the sputtering atmosphere can effectively reduce the activation temperature of IGZO films [ 22 , 23 , 24 ].…”

High-Performance ZnO Thin-Film Transistors on Flexible PET Substrates With a Maximum Process Temperature of 100 °C

“…Using low-temperature processes, the state-of-the-art oxide TFTs achieve a mobility higher than 10 cm 2 V -1 s -1 at a bending radius of 10 mm [8]. However, the oxide TFTs need to be subject to a post-annealing treatment at a temperature equal to or higher than 300 ℃ to optimize electrical properties and stability [9], [10], which limits the fabrication of them on cost-effective flexible substrates like PET, PEN, and PC [11], [12]. Thereby, it is urgently in need to develop process methods for fabricating the high-performance oxide TFTs at a low temperature.…”

Impact of Photo-Excitation on Leakage Current and Negative Bias Instability in InSnZnO Thickness-Varied Thin-Film Transistors

“…In the last two decades, thin-film transistors (TFTs) based on metal oxide semiconductors are one of encouraging low-input voltage electronic devices in transparent and flexible flat panel display (FPD) applications where traditional silicon-related TFTs are hard to match [ 1 , 2 , 3 ]. Among various metal oxide active layers, amorphous InGaZnO (a-IGZO)-dependent transistors have rapidly developed because they easily achieve high mobility ( μ ) of ~10 cm 2 V −1 s −1 and long-term stability through creative approaches [ 4 , 5 , 6 ], including interface modification, doping engineering, and device structure adjustment. Nevertheless, their mobility is insufficient to satisfy the requirement of driving integrated circuits in ultra- and super-high-definition FPDs.…”