Scientists develop ultra-thin semiconductor fibers that turn textiles into wearable electronics
Scientists from Singapore's NTU University have developed ultra-thin semiconductor fibers that can be woven into fabrics, turning them into smart wearable electronics. Their Job published in the journal Nature.
Reliably functioning semiconductor fibers must be flexible and free from defects to ensure stable signal transmission. However, current manufacturing methods subject fibers to stress and produce unstable results, which leads to cracks and deformations in semiconductor cores, negatively affecting their performance and limiting their capabilities.
NTU scientists conducted modeling and simulation to understand how stress and instability arise in the manufacturing process. They concluded that the problem could be solved through careful selection of material and a specific sequence of steps during fiber production.
They improved the mechanical design of the fiber production apparatus and successfully produced thin, defect-free fibers with a length of 100 meters, indicating the possibility of their commercial application. Importantly, the new fibers can be woven into fabrics using existing methods.
To demonstrate the high quality and functionality of its fibers, NTU's research team developed prototypes. These include a smart beanie hat that helps visually impaired people cross the road safely by receiving alerts on their mobile phones; a shirt that receives information and transmits it through an earpiece, like a museum audio guide; and a smartwatch with a strap that functions as a flexible sensor that fits around the user's wrist and can measure heart rate even during physical activity.
The team believes their innovation is a fundamental breakthrough in the development of ultra-long and strong semiconductor fibers, which means they are cost-effective and scalable, as well as superior electrical and optoelectronic (meaning they can detect, transmit and interact with light) characteristics.
NTU Associate Professor Wei Lei from the School of Electrical and Electronics Engineering (EEE) and principal investigator of the study said: “The successful fabrication of high-quality semiconductor fibers was made possible by the interdisciplinary nature of our team's work. The fabrication of semiconductor fibers is a very complex process that requires the know-how of specialists in materials science, mechanics and electrical engineering at different stages of research.”
“The joint team effort allowed us to clearly understand the mechanisms involved in the process, which ultimately helped us open the door to defect-free filaments, overcoming a long-standing challenge in fiber technology.”
Semiconductor fiber development
To develop defect-free fibers, the NTU-led team selected pairs of conventional semiconductor and synthetic materials—a silicon semiconductor core with a quartz glass tube and a germanium core with an aluminosilicate glass tube. The materials were chosen based on their characteristics, which complemented each other. These include thermal stability, electrical conductivity and the ability to pass electric current.
Silicon was chosen for its ability to be heated and manipulated to high temperatures without losing material properties, and for its ability to operate in the visible light range, making it ideal for use in devices designed for extreme environments, such as shielded sensors. clothing for firefighters.
Germanium, on the other hand, allows electrons to travel quickly along the fiber and operates in the infrared, making it suitable for wearable or fabric (e.g. curtains, tablecloth) sensor applications compatible with Light fidelity (“LiFi”) wireless optical networks in indoor environments.
The scientists then placed semiconductor material (the core) inside a glass tube, heating it at high temperatures until the tube and core were soft enough to be pulled into a thin, continuous thread (see image below).
Due to the different melting temperatures and thermal expansion rates of the selected materials, the glass, when heated, functioned like a bottle containing a semiconductor material that, like wine, filled the bottle as it melted.
Study first author Dr Wang Zhixun, a research fellow in the School of Electrical Engineering, said: “Extensive analysis was required before we found the right combination of materials and process to create our fibers. By using the different melting temperatures and thermal expansion rates of our chosen materials, we successfully pulled semiconductor materials into long filaments as they entered and exited a heating furnace, while avoiding defects.”
After the thread has cooled, the glass is removed and connected to a polymer tube and metal wires. After the next heating, the materials are stretched, forming a thin flexible thread.
In laboratory experiments, semiconductor fibers showed excellent performance. When tested for sensitivity, the fibers could detect the entire visible range of light, from ultraviolet to infrared, and reliably transmit signals with a bandwidth of up to 350 kilohertz (kHz), making them the best of their kind. In addition, the fibers turned out to be 30 times stronger than usual.
The fibers were also evaluated for washability: fabric woven from semiconductor fibers was machine washed 10 times and the results showed no significant degradation in the fiber's performance.
Assistant Principal Investigator Emeritus University Professor Gao Huajian, who completed the research while at NTU, said: “Silicon and germanium are two widely used semiconductors that are generally considered to be very fragile and prone to failure. The fabrication of ultra-long semiconductor fiber demonstrates the feasibility and feasibility of creating flexible components using silicon and germanium, opening up broad opportunities for the development of flexible wearable devices in various shapes. Next, our team will work together to apply the fiber fabrication method to other complex materials and discover more scenarios in which fibers play a key role.”
Compatibility with industrial production methods hints at ease of implementation
To demonstrate the feasibility in real-world applications, the team created smart wearable electronics using the semiconductor fibers they created. Among them are a beanie hat, a sweater and a watch that can detect and process signals.
To create a device to help visually impaired people cross busy roads, the NTU team wove fibers into a beanie along with an interface board. In an outdoor experimental test, light signals received by the cap were sent to a mobile phone app, triggering an alarm.
The shirt, woven from fibers, worked as a “smart top” that could be worn in a museum or art gallery to receive information about exhibits and transmit it to an earpiece while the wearer walked through the halls.
The smartwatch with a fiber-integrated wristband worked as a flexible and conformal sensor to measure heart rate, unlike traditional designs where a rigid sensor is mounted on the body of the smartwatch, which can be unreliable in environments where users are very active. and the sensor does not come into contact with the skin.
In addition, fibers have replaced bulky sensors in smartwatch housings, saving space and freeing up the ability to create thinner watch models.
Study co-author Dr Li Dong, a research fellow at the School of Mechanical and Aerospace Engineering, said: “Our method for making the fiber is versatile and easily applicable to industry. The fiber is also compatible with modern textile machinery, meaning it has the potential for large-scale production.”
“By demonstrating the use of fibers in everyday wearable products such as beanies and watches, we prove that our research results can guide the creation of functional semiconductor fibers in the future.”
As next steps, the researchers plan to diversify the types of materials used for the fibers and come up with semiconductors with different hollow cores, such as rectangular or triangular shapes, to expand their applications.
