Thermally Drawn Semiconductor Fibers: Fabrication Strategies and Applications

Wearable electronics enable seamless incorporation of electronics into our daily lives. Consumer-grade wearables, such as smart rings, bands, and watches, have gained popularity in recent years due to their capacity to offer consistent and dependable data collection and assistance for daily activities. Moreover, wearable electronics are emerging in professional medical services, such as continuous glucose monitoring and minimally invasive thrombectomy, to aid healthcare professionals in diagnosing and treating. In addition, the proliferation of the Internet of Things (IoT) has further fueled the demand for wearable electronics, as they are the critical components for an IoT system to support the sharing and analysis of data across multiple devices and platforms. The market for wearable electronics predictably continues to expand in the future. Semiconductors are crucial components of wearable electronics, and especially in fiber form factor, they enable monolithic fiber electronics and smart textiles. Several techniques are developed for fabricating inorganic semiconductor fibers, such as the Czochralski growth method, micropulling-down process, and thermal drawing technique. Thermal drawing of semiconductor fibers is a technique in which semiconductor materials are supported by glassy cladding materials and heated into fluid melts, with the combination drawn to fiber dimensions. Among the various fabrication methods, the thermal drawing technique has the advantages of a high yield rate, feasible integration of multiple materials, the capability of achieving designable sophisticated structures, and an extended single-strand fiber length. The as-drawn semiconductor fibers may serve as the building blocks of wearable electronics directly or subject to postprocessing procedures for on-demand alteration of dimension, geometry, or phase structure before employment. Research efforts within the fundamental understanding of fluid dynamics, rheology, and molecular structure evolution seek to improve the performance and quality of thermally drawn semiconductor fibers such as conductivity, bandgap, electron mobility, thermal stability, and mechanical strength. In this Account, we systematically recapitulate our efforts in developing semiconductor fibers and their application in wearable electronics, including diodes, sensors, energy harvesters, and more. We begin by introducing the three primary thermal drawing methods, highlighting the unique features of each. Next, postprocessing methods to further alter the materials, structures, and geometries of semiconductor fibers are discussed. We then discuss the various devices and applications and conclude with an examination of current challenges and our perspectives on future research directions. This Account aims to inspire further research efforts to expand the scope of fiber materials, the design of in-fiber structures, and configurations of device assembly to achieve widespread adoption of semiconductor fibers in various fields.