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Page 28 of 39 Jeon et al. Soft Sci. 2025, 5, 1 https://dx.doi.org/10.20517/ss.2024.35

APPLICATION
Flexible displays
Flexible MO TFTs have become essential for developing next-generation display technologies, including
VR, AR, and flexible devices. The mechanical flexibility and superior electrical properties of MO
semiconductors have opened new possibilities for flexible, foldable, and rollable display applications.

Recent advancements in high-performance flexible displays involve the integration of ITZO TFTs and air-
stable inverted OLEDs (iOLEDs). For instance, ITZO TFTs fabricated on PI films exhibit high mobility
2
-1 -1
(32.9 cm ·V ·s ) and stability. This technology enables high-resolution displays suitable for next-generation
flexible applications by simplifying the fabrication process through the simultaneous formation of ITZO
[200]
films as both the channel layer in TFTs and electron injection layers in iOLEDs [Figure 10A] .
Additionally, a flexible green AMOLED display with a resolution of 320 × 3 × 240 pixels (80 ppi resolution)
has been developed. The flexible AMOLED display is integrated on the flexible TFT panel on a PEN
substrate. Each pixel driver circuit consists of two TFTs and a storage capacitor, providing an aperture ratio
of 46%. This TFT consists of an Al:Nd gate electrode, an AlOx:Nd gate dielectric, an IGZO channel, ITO S/
D electrodes, and an SU-8 passivation layer. The display achieves 250 cd/m in both flat and bent
2
conditions, maintaining clear image quality without significant luminance degradation or visible defects
[201]
even when bent to a 20 mm bending radius [Figure 10B] .
Flexible circuits
Flexible MO TFTs are also crucial in developing various electronic circuits integrated into flexible devices.
These devices have the ability to fabricate island structure and junctionless TFTs while maintaining high
performance under mechanical stress. Island structure TFTs distribute mechanical stress evenly, preventing
the concentration of mechanical stress in any one area. Junctionless TFTs eliminate source/drain-to-
channel junctions, reducing the risk of performance degradation under mechanical stress.

Innovative research has led to the development of flexible circuits that withstand significant mechanical
deformation. DGTFTs on paper substrates using solution-processed chitosan-based proton conductors as
the gate dielectric have been developed. Employing a dual gate enables precise modulation of the threshold
voltage and facilitates logic operations. DGTFTs exhibited stable performance and switching characteristics.
For the logic function of junctionless DGTFTs, various voltage pulses were applied to the dual in-plane
gates, serving as inputs, while the drain/source current (I ) was used as the output. The voltages of -1 and
DS
0 V represent the low and high inputs, respectively. This operation is characteristic of an AND logic gate,
maintaining a consistent on/off current ratio of approximately 10 without a decrease in on current
6
[194]
[Figure 8B] . Flexible circuits utilizing MO TFTs have achieved significant advancements, combining high
performance with mechanical robustness. Mesa-island structures have enabled the creation of seven-stage
ring oscillators with a-IGZO TFTs, which maintain stable operation even after repeated bending. This
design allows for high-density integration and stress relaxation, making these flexible circuits ideal for
[33]
applications in wearable devices, flexible displays, and portable electronics [Figure 11A] . Another
noteworthy advancement is the hardwired machine learning processing engine fabricated with submicron
metal-oxide TFTs on a flexible substrate. This device integrates AI capabilities into flexible electronics,
offering robust performance and flexibility. It is designed to efficiently handle machine learning tasks,
making it suitable for smart, adaptive wearable devices and flexible AI systems [Figure 11B] . Recent
[37]
developments include a natively flexible 32-bit Arm microprocessor, which integrates complex
computational functionalities into a flexible format. This microprocessor, fabricated on a flexible substrate,
demonstrates operational stability under significant mechanical deformation, showcasing the potential of
flexible electronics in advanced computing applications such as wearable technology and flexible computing
devices [Figure 11C] . Papadopoulos et al. exhibited touchscreen tags utilizing thin-film electronics, aimed
[36]