Abstract
Flexible electronics have attracted extensive interest due to their wide range of remarkable applications, including wearable devices, foldable displays, healthcare monitoring systems, and soft robotics. These innovative applications have been made possible through technological advancements in materials and fabrication techniques, enabling the creation of electronics that are lightweight, flexible, and adaptable to various forms. These innovations are paving the way for unobtrusive devices that seamlessly integrate into everyday objects, transforming how we interact with technology. Among the cutting-edge advancements, metal oxide semiconductors, particularly amorphous InGaZnO (IGZO), have proven highly attractive. Known for their high electron mobility (ranging from 10 cm2 V−1 s −1 to 100 cm2 V−1 s −1 ), low-cost and low-temperature processability, compatibility with large-area substrates, and optical transparency, IGZO expands the possibilities for flexible and transparent electronics, addressing limitations of traditional silicon technology in these emerging fields. However, while progress in semiconductor materials is vital, the choice of substrate materials plays an equally critical role in enabling flexible and stretchable electronics. The substrate serves as the foundation for these technological advancements in device fabrication. For electronics to be scalable, lightweight, flexible, stretchable, and compatible with modern fabrication techniques, the substrate material must meet rigorous requirements. Polymers such as polyimide (PI), with thicknesses ranging from 1.5 µm to 50 µm and a high glass transition temperature of 360 ◦C, are widely used due to their high thermal stability, flexibility, chemical resistance, and low surface roughness. Additionally, the growing need for environmentally sustainable materials, including biodegradable ones, adds complexity to the substrate selection. Achieving all these properties in a single material remains a significant challenge that necessitates ongoing research. To contribute to the advancement of flexible electronics, this thesis explores a diverse range of unconventional materials as potential substrates for electronic fabrication. While the primary focus is on lightweight and flexible materials, it also examines natural rigid substrates to enhance the understanding of a broader spectrum of material properties. The material selection process begins with identifying and evaluating substrates based on key factors such as solubility and compatibility with standard fabrication processes. Among the materials investigated, self-fusing silicone tape was chosen to fabricate a self-healable piezoresistive strain sensor, for which a novel piezoresistive self-healing composite material was also utilized. This sensor exhibited a high gauge factor of 34.6±0.26 under strains of up to 50 %, and its self-healing capability was demonstrated by restoring functionality after being fully cut, while maintaining reliable operation post-healing. Following this, stone-based materials—including marble, brick, stone paper, and Limex—along with animal-based substrates like buffalo horn and mother of pearl, were utilized to fabricate temperature sensors. Among the stone-based thermistors, the marble thermistor demonstrated the highest sensitivity of −11.54 % ◦C −1 , while among the animal-based thermistors, the buffalo horn thermistor showed the highest sensitivity of 0.22 % ◦C −1 . Both types of thermistors operated reliably within the temperature range 25 ◦C to 80 ◦C. Additionally, the feasibility of fabricating thin-film transistors (TFTs) on these unconventional substrates was explored. To establish a reference point, a preliminary study on TFTs fabricated on conventional polyimide substrates was conducted to evaluate different TFT geometries and identify the optimal configuration for achieving the fastest transistor performance. All devices were thoroughly characterized, both electrically and mechanically, demonstrating the potential of these substrates for flexible electronics and their suitability for transient devices when used in combination with dissolvable materials. Furthermore, the demonstrated dissolvability of IGZO, used to realize IGZO thermistors, in water highlights the fabrication of transient electronics based on this remarkable IGZO semiconductor.