Page 176 - Read Online

Page 6 of 39 Jeon et al. Soft Sci. 2025, 5, 1 https://dx.doi.org/10.20517/ss.2024.35

One example is the work by Tang et al. who developed flexible MO TFT using GaO TFTs on 50-μm-thick
x
[92]
metal foils . These devices demonstrated impressive performance, uniformity, and stability. This study
exhibits the potential of metal foil substrates in next-generation flexible device technologies, particularly in
applications requiring flexibility and durability.

MATERIALS OF HIGH-PERFORMANCE FLEXIBLE MO TFT
High-performance flexible MO TFTs necessitate the use of sophisticated materials to simultaneously
achieve superior electrical performance and exceptional mechanical stability. The active semiconductor
layer is a charge transport layer, where charge carriers are generated and modulated. MOs such as indium
oxide (In O ), IGZO, and zinc oxide (ZnO) are widely used due to their high electron mobility, optical
2
3
transparency, and environmental stability [11,93,94] . These materials can be doped with various elements to their
electrical properties, improve carrier concentration, and enhance electrical performance. For example,
doping with tin (Sn) in In O [forming indium-tin-oxide (ITO)] increases carrier concentration, while
3
2
doping with gallium (Ga) and zinc (Zn) in IGZO optimizes semiconductor properties and improves
stability [55,95-97] . Multiple layers improved the performance of flexible MO TFTs. They are formed by
combining different semiconductor materials to create interfaces that enhance efficient charge carrier
transport. Selecting materials with complementary properties and multiple layers can significantly improve
carrier mobility and reduce off-current, thereby enhancing electrical device performance. This approach
minimizes energy loss and ensures that electronic devices operate with high efficiency and reliability over
time [61,95,98-100] . The flexibility of the semiconductor layer is essential for maintaining device performance
under mechanical stress such as bending and stretching. In flexible electronic devices, the semiconductor
layer must withstand significant physical stress without degrading its electrical properties. MO
semiconductors are inherently brittle due to their crystalline or amorphous structures. This brittleness
makes them susceptible to cracking and fracture under mechanical deformation such as bending or
stretching, which can severely degrade their electrical performance. Under repeated mechanical stress, MO
thin films are susceptible to cracking and delamination from the flexible substrate and other layer such as
source-drain electrodes. This led to interruptions of the conductive path, leading to increased resistance,
device failure, and loss of functionality. Additionally, mechanical deformation induces strain-induced
defects and dislocations in the MO layer. These defects act as trap sites for charge carriers, reducing
mobility and causing instability in the electrical properties of the devices [33,61,101,102] .

Dielectric materials are crucial for isolating different components within the TFT and enabling proper gate
modulation. High-k dielectric materials, such as aluminum oxide (Al O ), zirconium oxide (ZrO ), and
2
3
2
hafnium oxide (HfO ), are preferred due to their high dielectric constants, which enhance capacitance and
2
reduce operating voltage. These materials must also be deposited with low-temperature processing to be
suitable for flexible substrates. Polymers and copolymers are also used for their flexibility and high dielectric
constraints [103-106] .
Each of these components must be carefully selected and engineered to ensure that the flexible TFTs can
achieve high electrical performance while enduring the mechanical demands of bending, stretching, and
other forms of deformation. The use of these advanced materials is important in developing next-generation
flexible electronic devices that are not only efficient and reliable but also versatile and robust in various
applications.