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

VARIOUS SUBSTRATE OF FLEXIBLE MO TFT
To create flexible devices, it is essential to prepare bendable substrate materials, and oxide TFTs, which can
be manufactured at low temperatures, are well-suited for use with flexible substrates. Many studies have
explored flexible oxide-based TFTs, classified by the type of substrate material, such as polymer plastics,
paper, and metal foils. In the development of flexible devices, the use of bendable substrate materials is a key
requirement, as these substrates must maintain their structural integrity under mechanical deformation
such as bending or stretching. Oxide TFTs processed at relatively low temperatures are particularly
advantageous for integration with such flexible substrates. This compatibility with a low-temperature
process allows oxide-based TFTs to be effectively utilized in various flexible electronic applications. Much
research has been conducted on flexible oxide TFTs with the primary focus on the types of substrate
materials that enable these devices to achieve high flexibility and performance. These studies often classify
the substrates into three main groups: polymer plastics, paper sheets, and metal foils.

Polymeric materials
Polymeric materials offer numerous advantages, such as being flexible, stretchable, bendable, lightweight
and highly transparent, making them appropriate materials for use in flexible substrates in various
electronic applications [14,68,69] . These properties enable polymeric materials to support the development of
advanced flexible electronics, including displays, sensors, and wearable devices. Amorphous oxide TFT
technology, which can be processed at relatively low temperatures, is highly compatible with polymeric
[12]
materials, allowing for scalable and cost-effective manufacture . Among these materials, polyimide (PI)
stands out as the most commonly used substrate for flexible oxide TFTs due to its excellent thermal
stability, mechanical flexibility, and processability [70-73] . Other frequently used polymeric materials include
polyethylene terephthalate (PET) [74-76] , polyethylene naphthalate (PEN) [77-79] , poly(vinyl alcohol) (PVA) ,
[80]
[82]
polydimethylsiloxane (PDMS) [52,81] , polycarbonate (PC) , and polyether sulfone (PES) [83,84] , each offering
unique mechanical and chemical properties suitable for different applications. In addition, glass-fabric
reinforced composite films are used as flexible plastic substrates, providing additional mechanical strength
and stability while maintaining the flexibility needed for next-generation flexible electronics . These
[85]
materials combined with advancements in oxide-based TFT technology are driving innovation in flexible,
lightweight, and durable electronics that can conform to various shapes and surfaces.

Paper sheets
Paper is an attractive alternative substrate for flexible electronics due to its low cost, renewable nature, and
biodegradability. These substrates offer an eco-friendly solution compared to traditional plastics. Employing
paper sheets in flexible oxide TFTs has potential in applications such as disposable electronics and smart
packaging [86,87] . However, the rough surface and moisture absorption tendency of paper sheets create
challenges to reliable fabrication and performance limiting their direct application in high-performance
devices. To address these issues, surface treatments such as thin layers of silicon dioxide (SiO ) deposited via
2
plasma-enhanced chemical vapor deposition (PECVD) or epoxy acrylate copolymer coatings are
[88]
applied . These coatings smooth surface of paper and act as moisture barriers improving suitability for
[89]
flexible electronics. This allows paper-based devices to combine environmental sustainability with enhanced
performance and durability.

Metal foils
Metal foils, including those made from gold, silver, copper, Hastelloy or aluminum, offer significant
advantages in flexible electronics due to their excellent mechanical strength, ductility, and high thermal
resistance. Unlike polymer plastics, metal foils can withstand a higher temperature process allowing for a
broader range of fabrication techniques . Their ability to bend with very small curvature radii makes them
[90]
[91]
ideal for high-strain applications such as sensors integrated into advanced systems such as artificial skin .