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Page 10 of 39 Jeon et al. Soft Sci. 2025, 5, 1 https://dx.doi.org/10.20517/ss.2024.35

the oxide heterointerfaces. This QSL transistor approach could be applied to various oxide materials and
[125]
deposition techniques . Recently, Tang et al. present an eco-friendly, streamlined method for preparing
MO TFTs using a pure water-solution blade-coating process. The process focuses on low-temperature
fabrication and rapid annealing process. Triple-coated indium oxide (3C-TFTs) and indium oxide/zinc
oxide/indium oxide (IZI-TFTs) TFTs on SiO gate dielectric (300 nm) annealed at 300 °C for just 60 s
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exhibit average field-effect mobility of 10.7 and 13.8 cm /V·s, respectively. Flexible MO TFTs on PI
substrates with AlO dielectrics exhibited a field-effect mobility of over 10 cm /V·s at low operating voltages.
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Longer annealing time of 20 min at 300 °C results in high-performance 3C-TFTs (over 18 cm ·V ·s ) and
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IZI-TFTs (over 38 cm ·V ·s ), demonstrating the effectiveness of the method for producing high-mobility,
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stable, and flexible TFTs [Figure 3C] . Bukke et al. fabricated the interface engineering of ZnO-based TFTs
[99]
using nano-scale Ga O . By optimizing the Ga O interface, the work achieved significant enhancements in
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the electrical performance and stability of the ZnO TFTs. The resulting a-Ga O /c-ZnO stack channel TFTs
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exhibit a high field-effect mobility of 41 cm ·V ·s and excellent stability under positive bias temperature
stress. On a PI substrate, a-Ga O /c-ZnO stack channel TFTs show rarely threshold voltage shifts after
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100,000 bending cycles with a 3 mm radius and remain stable under environmental tests. The multiple
layers of a-Ga O and ZnO improve charge transport by enhancing heterointerfaces and reducing defect
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[98]
density [Figure 3D] . Table 1 summarized the innovative materials and multiple-layer MO for high
performance.
Semiconductor layer for flexibility
To maintain electrical performance in flexible devices, the semiconductor layer must be capable of enduring
mechanical stress such as bending and stretching. It is crucial that MO semiconductors endure significant
physical deformation without a degradation of electrical properties. Maintaining flexibility in the
semiconductor layer is therefore essential for the reliable operation of flexible devices under mechanical
stress. Consequently, recent research has focused on increasing the flexibility of MO semiconductors by
synthesizing other materials or forming multiple layers with other materials and MO semiconductors [128-132] .
Initially, by synthesizing MOs with other materials, Liu et al. report on the development of high-
performance transistors based on a composite of single-walled carbon nanotubes (SWNTs) and sol-gel
processed indium zinc oxide (IZO). The SWNTs provide fast tracks for carrier transport, significantly
enhancing the field-effect mobility to as high as 140 cm /V·s while maintaining a high on/off ratio of ~10 .
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The composite thin films also exhibit excellent mechanical flexibility, showing superior stability with only
17% variation in performance at a bending radius of 700 μm and just 8% variation after 300 cycles of
repeated bending [Figure 4A] . As shown in Figure 4B, Divya et al. proposed a new approach using water-
[128]
insoluble and chemically inert polymers to form inorganic/organic composite semiconductors. These
polymers resist intermixing with the oxide lattice, promote crystallization, and maintain the electrical
properties of the oxide semiconductors even in near-equal amounts. As a result, optimized In O and
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25 wt% EC-based composite semiconductor TFTs exhibited linear mobility of 40-45 cm /V·s. TFTs with
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high polymers endure bending tests down to a 1.5 mm bending radius without electrical performance
[129]
deterioration or micro-cracks in the composite semiconductor material . Na et al. and Kim et al.
fabricated flexible phototransistors and flexible TFTs using organic-inorganic hybrid semiconductors based
on IGZO. IGZO:PI and IGZO:PETE (polytetrafluoroethylene) TFTs fabricated by using sputter on the PI
substrate. IGZO:PI phototransistors showed stable optoelectronic characteristics even after 10,000 bending
tests. IGZO:PETE TFTs exhibit a field-effect mobility of 10.27 cm ·V ·s and good mechanical stability with
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a threshold voltage shift of 0.89 V after 10,000 bending cycles at a radius of 5 mm in Figure 4C and D [130,131] .
As shown in Figure 4E, Lee et al. form multiple layers with other materials and MO semiconductors in
flexible MO TFTs. The films consist of an organic aromatic linker and indium oxide, grown using
hydroquinone (HQ) as the organic precursor, bis(trimethylsilyl)amido-diethyl indium (INCA-1) as the
indium precursor, and hydrogen peroxide (H O ) as the oxidant. The hybrid film with semiconductor
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