Smart Textile

NTU develops wearable electronic garments from ultra-thin semiconductor fibers

Nanyang Technological University scientists have developed ultra-thin semiconductor fibers that can be woven into the fabric, transforming wearable garments into advanced electrical interfaces. This breakthrough not only transforms the concept of smart clothes but also opens up a new universe of possibilities for the Internet of Things, where connectivity and functionality meet in the very threads of wearable garments.

The researchers have used modeling and simulations to understand how stress and instability develop throughout the manufacturing process, and they discovered that the problem could be solved with careful material selection and a sequence of procedures followed during fiber production. To provide steady signal transmission, the semiconductor fibers must be flexible and free of flaws. Conventional production methods induce stress and instability in semiconductor cores, resulting in cracks and deformities that reduce performance and limit progress. So, the researchers have created a mechanical design and produced 100 meters of hair-thin, defect-free fibers, indicating market viability. The fibers can also be woven into fabrics using conventional techniques.

Notable prototype demonstrations of the research

To demonstrate the fibers’ functionality, the researchers created prototypes such as a smart beanie hat that alerts a visually impaired person to cross the road safely via a mobile phone application; a shirt that receives information and transmits it via an earpiece, similar to a museum audio guide; and a smartwatch with a strap that functions as a flexible sensor that conforms to users’ wrists for heart rate measurement during physical activities.

Figure: A prototype of a smartwatch with a semiconductor fibre woven strap that functions as a flexible and conformal sensor. Credit: NTU Singapore

The researchers hope that the invention could help to accelerate the creation of ultra-long and durable semiconductor fibers that are scalable while also providing electrical and optoelectronic (meaning they can sense, transmit, and interact with light) capabilities. attributed the manufacturing of the semiconductor fibers to the research team’s interdisciplinary nature.

“Semiconductor fiber fabrication is a highly complex process, requiring know-how from materials science, mechanical, and electrical engineering experts at different stages of the study. The collaborative team effort allowed us a clear understanding of the mechanisms involved, which ultimately helped us unlock the door to defect-free threads, overcoming a longstanding challenge in fiber technology,”

NTU Associate Professor Lei Wei

Development chronology of the fiber

To develop the fibers, the researchers used couple of typical semiconductor and synthetic materials: a silicon semiconductor core with a silica glass tube, and a germanium core with an aluminosilicate (Al2SiO3) glass tube. The materials were chosen for their complementary properties, such as thermal stability, electrical conductivity, and the capacity to enable electric current to pass (resistivity).

Silicon was chosen because of its ability to be heated to high temperatures and controlled without degrading, making it ideal for use in extreme-condition electronics such as sensors on firefighters’ protective equipment. Germanium, on the other hand, permits electrons to flow swiftly through the fiber and operate in the infrared range, making it ideal for use in wearable fabric-based sensors that are compatible with indoor light-fidelity (LiFi) wireless optical networks.

The researchers then inserted the semiconductor material (core) into the glass tube and heated it to a high temperature until the tube and core were soft enough to be pulled together into a thin continuous filament. Because of the differing melting temperatures and thermal expansion rates, the glass acted like a wine bottle during the heating process, containing the semiconductor material that filled the bottle as it melted.

Figure: A schematic diagram of the semiconductor fiber manufacturing method developed by the NTU research team. Credit: Nanyang Technological University

First author of the study Dr Zhixun Wang said it took extensive analysis to determine the right combination of materials and processes to develop the fibers. “By exploiting the different melting points and thermal expansion rates of our chosen materials, we successfully pulled the semiconductor materials into long threads as they entered and exited the heating furnace while avoiding defects,” Wang said.

After the strand has cooled, the glass is removed and joined with a polymer tube and metal wires. After another round of heating, the components are brought together to form a flexible thread that is as thin as hair.

In laboratory testing, the semiconductor fibers performed admirably. When tested for responsiveness, the fibers were able to detect the full visible light range, from ultraviolet to infrared, and transmit signals with a bandwidth of up to 350 kilohertz (kHz). Furthermore, the fibers were 30 times more durable than ordinary ones.

The fibers were also tested for washability, with a textile woven with semiconductor fibers being washed ten times in a washing machine, and the results revealed no substantial decline in fiber performance.

“Silicon and germanium are two commonly utilized semiconductors that are typically considered highly brittle and prone to fracture”

“The creation of ultra-long semiconductor fiber reveals the capability and feasibility of producing flexible components out of silicon and germanium, leaving plenty of room for the development of flexible wearable gadgets in a variety of shapes.” “Next, our team will work collaboratively to apply the fiber manufacturing method to other challenging materials and to discover more scenarios where the fibers play key roles”

Co-principal investigator, Distinguished University Professor Gao Huajian, who completed the work while at NTU

Figure: The resulting optoelectronic fiber can be woven into large-scale fabrics, enabling a broad scope of applications. Credit: NANYANG TECHNOLOGICAL UNIVERSITY

Convenience for industry adoption and industry practices

Dr. Li Dong, the co-author, stated that the fiber fabrication technology is adaptable and easily implemented by industry. “The fiber is also compatible with existing textile industry gear, indicating that it has the potential for large-scale production. By proving the fibers’ use in daily wearable products such as a beanie, we show that our research discoveries can be used to create functional semiconductor fibers in the future,” Dong added.

To broaden their applicability, the researchers intend to expand the sorts of materials used for fibers and build semiconductors with various hollow core forms, such as rectangular and triangular. To demonstrate the compatibility of the newly developed semiconductor fibers for real-world applications, the researchers designed smart wearable electronics. These include a signal-detecting watch, a beanie, and a sweatshirt.

To make a gadget that helps the vision handicapped traverse busy highways, the NTU team woven fibers into a beanie hat and attached an interface board. When tested outdoors, light signals acquired by the beanie were transmitted to a mobile phone application, resulting in an alert.

Meanwhile, a shirt woven with the fibers served as a “smart top,” allowing the wearer to collect exhibit information and transmit it into an earpiece while walking around the museum or art gallery. A smartwatch with a wristband integrated with fibers served as a flexible and conformal sensor to measure heart rate, as opposed to traditional designs in which a rigid sensor is installed on the smartwatch’s body, which may be unreliable in situations where users are very active and the sensor is not in contact with the skin. Furthermore, the fibers replaced bulky sensors in the smartwatch’s body, freeing up space and allowing for thinner watch designs.

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