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Huater University of Science and Technology Professor Tao Guangming's team "Mater. Today": the new frontier of flexible electronics-heat-drawn advanced functional fiber
2020-01-04 Source: Polymer Technology

Electronic devices are evolving from rigid to flexible stretchable structures, which enables electronic products to integrate seamlessly into everyday life. The integration of various electronic materials in hot-drawn fibers has become a universal platform for manufacturing advanced functional fiber electronic products. An extremely important platform. This method utilizes the hot drawing of macroscopic preforms, where functional materials or prefabricated devices are placed in a specific location, in a very simple and scalable way to produce kilometers of electronic fibers with complex architectures and functions. Combines different electronic, optoelectronic, thermomechanical, rheological and acoustic properties of electronic materials with monofilament fibers to produce functions that perceive stimuli, communicate, store and convert energy, regulate temperature, monitor health and dissect the brain.

Professor Tao Guangming's team at Huazhong University of Science and Technology collaborated with several top international research teams to publish a review paper entitled “Thermally drawn advanced functional fibers: new frontier of flexible electronics” in Materials Today (IF: 25), a top journal of materials science. The article reviews the development of thermally drawn fiber optic electronic technology, focusing on its research fields such as communication, sensing, energy, artificial muscle, 3D printing, healthcare, neuroscience, nanoscience and manufacturing, and basic science of fiber optic materials. The unique opportunities and broad application prospects summarize the prospects for implementing similar to "Moore's Law" in fibers and fabrics and the challenges facing future research, laying the foundation for fabrics to become the next frontier of computing and artificial intelligence. This technology assembles electronic materials or high-performance micro-state devices with different electronic, optoelectronic, thermomechanical, rheological and acoustic properties into a single fiber in one step, and then integrates it into the fabric using traditional textile technology , Laying the foundation for fabric to become the next frontier of computing and artificial intelligence.

Figure 1 Electronic schematic of multi-functional smart fabric integrated multi-material fiber

It is challenging to prepare optical fiber electronic fiber devices with integrated multi-materials and complex structures. The typical industrial production method with hot drawing as its core came into being. The article lists the representative works of the historical development of hot drawn fiber. This method integrates different materials with different optical, electronic, and optoelectronic characteristics, designs the structure in the macro preform, and then heat-draws the preform into fibers, so that the fibers maintain the complex structure and function of the preform, thereby obtaining High-density devices and various functional fibers.

In order to meet the requirements of flexibility and low loss in sensing and material processing, hollow-core microstructured optical fibers have been developed , which confine light to the hollow core of a photonic bandgap mirror consisting of alternating layers. The main influencing factors of photonic band gap are the thickness and refractive index of each layer, which determine the optical characteristics of the Bragg fiber. Compared with other photonic band-gap fibers, Bragg fibers are easier to manufacture, and their photonic band gaps are easier to control, and their transmission losses are lower. They are therefore widely used in laser scalpels, optical resonators, and self-testing high-power transmission.

Figure 2 Preparation process of mid-infrared transmission medium and photon band gap fiber

The electronic fiber used to modulate laser emission can be used to make a cylindrically symmetric laser emitting omnidirectional laser with a transverse plane of the fiber axis. It has important application value in omnidirectional imaging, biomedical detection and photodynamic therapy, because it provides It has a larger laser emitting surface area than ordinary fiber. The research of new laser materials is arousing great interest and provides a broad prospect for the development of the next generation of all-fiber optical subsystems.

Fig. 3. Cylindrical symmetrical radial emission omnidirectional laser with microfluid in fiber.

Stretchable flexible fibers for strain sensing are used in a wide range of applications. On the one hand, it needs to realize the assembly of conductive materials and insulating materials in a specific structure; on the other hand, it is also developing to achieve a hot drawing process about stretchable or soft fibers, but due to the rheological properties of the material, This has also become a challenge. There is increasing interest in the development of such fibers, and electronic fiber products have demonstrated their ability to conform to human skin, biological tissues, flexible robots and fabrics.

Fibrous energy harvesters have unique advantages in portable and wearable electronic systems. Although such piezoelectric-based fibers have made great progress in the fields of acoustic sensing and solar cells, the output performance is still far lower than that of planar structures. Therefore, while maintaining the unique mechanical advantages of the fiber structure, further research is needed to improve the output of fiber power generation.

Figure 4 Schematic diagram of super-elastic stretchable fibers

Microfluidic fibers have complex microchannel shapes that can be used to study the focusing behavior of inertial particles in the channels to achieve cell separation and microfluidic sensing. These microfluidic devices open up new possibilities for the application of laboratory fiber technology in the fields of chemistry, biochemistry and medicine. Integrating electrodes and dielectric materials in fibers can also be used to make capacitive fiber devices, enabling touchpad sensors without crosstalk between channels.

Bidirectional memory switch fibers and field effect transistor fibers benefit from materials that exhibit reversible amorphous / crystalline phase transitions under the action of an electric field. The processability of this material enables the complex circuits of long fibers to further promote crossbar array flexible electronics development of.

Figure 5 (a) Microfluidic fiber for cell separation (b) Fiber-based heat flow sensor (c) Capacitor fiber (d) Bidirectional memory switch fiber (e) Field effect transistor fiber

Thermal sensors reveal important information about the dynamics of many chemical, physical, and biological phenomena, and are one of the most commonly used sensors in industrial processing, medical diagnostics, and military defense , as shown in Figure 6. The fibers used for thermal sensing, positioning, and cooling can be further woven into fabrics, making them particularly suitable for use in green buildings, industrial energy management, wearable electronics, smart fabrics, and large-scale sustainable energy production systems.

Figure 6 Fibers for thermal sensing, positioning, and cooling

Fibers used for radiation detection have important application values in many fields such as nuclear monitoring, geophysical exploration, radiation therapy, and high-energy physics. The fibers can also be arranged in an array detector, where each fiber can be regarded as a separate pixel, which is expected to study the spatial distribution of radiation while suppressing signal crosstalk.

Figure 7 Schematic diagram of fiber artificial muscle

Transforming electrical, chemical, or thermal energy into mechanically deformed artificial muscles has broad application prospects in robotics, haptics, and prosthetics. Fiber artificial muscle has unique strength and responsiveness , and its retractable feature size opens a new path for the application of robots and artificial limbs (see Figure 7).

It has been found through research that the sensitivity of thin-film structured optical fibers used in photosensitive optoelectronic fibers is better than that of solid-core fibers. Since the original semiconductor cores were amorphous, the disordered atomic structure is harmful to the electronic and optoelectronic properties of the device. Therefore, different annealing strategies are usually used to change the semiconductor atomic structure, such as directly annealing the amorphous core. Laser heating, the use of phase changes in chemical solutions, etc. Figure 8 shows the optoelectronic fibers prepared by different processes.

Figure 8 Photosensitive photoelectronic fibers prepared by different processes

Non-interference lensless imaging and fluorescence imaging are typical applications of optoelectronic fibers in lensless imaging. Non-interference lensless imaging mainly stretches preforms out of tough polymer photodetection fibers and then weaves them into lightweight, low-density two-dimensional and three-dimensional structures for measuring the amplitude and phase of large-area electromagnetic fields. For fluorescence imaging, a single optical fiber and several photodetectors are integrated to measure the photocurrent intensity, thereby achieving lensless imaging.

Figure 9 Fiber drawing process diagram of the electrical connection diode

The use of high-pressure chemical vapor deposition to prepare semiconductor diodes in multiple materials is not scalable, so a new method was developed: a fiber stretching process that electrically connects the diodes, and a stretchable preform to fiber stretching process Combined with high-performance prefabricated semiconductor devices (see Figure 9), the resulting optoelectronic fibers can be used in optical communications.

Figure 10 Various applications of different neural interfaces based on optical fibers

Fibers and neurons have many things in common. Establishing a connection between neurons and electronic communication networks will develop a new type of neuron-integrated electronic device that is used in the fields of basic science and medical equipment. Significant advances have been made in fiber-based neural interfaces over the past few decades. According to the interface method, optical fiber devices can be basically divided into optical interfaces, electrical interfaces, chemical interfaces, and stent-type optical fibers for nerve repair and regeneration (see Figure 10).

Figure 11 Schematic diagram of 1-dimensional fibers to 0-dimensional particles

Multi-material fibers can be used in micro-nano manufacturing, such as laser recombination of high-temperature semiconductor core fibers, synthesis of new materials in the fiber, preparation of nanowires, and preparation of micro-nano particles. As an unprecedented micro and nano-processing platform, hot drawing, melt spinning The silk and electrospinning methods can achieve a span from 1 to 0 dimensions (fiber to particles) to prepare uniform micro-nano particles (see Figure 11). The particle preparation method is scalable, and the preparation of micro-nano particle arrays will open a new path for the next generation of functional devices.

Figure 12 Multi-material fiber for 3D printing

In addition, multi-material fibers can also be used as 3D printed inks. Materials with different physical properties can be well combined and printed into the device (see Figure 12). In this way, any form of three-dimensional structure can be constructed to demonstrate the functions of the device.

Fabrics are everywhere, but their function has not changed for thousands of years. Combining multi-material fibers with electronic fabrics mainly includes the direct integration of electronic fibers, or other typical technologies such as electronic devices embedded in fabric substrates, and directly functionalized textile surfaces. In addition, combining intelligent fabrics with artificial intelligence (AI), electronic fibers and fabrics may evolve into smarter systems with powerful data processing and analysis capabilities . Compared with rigid equipment, fabrics with intelligent fabric technology make the data collection process more transparent and accurate, and the data quality is more reliable and authentic.

Figure 13 Combination of intelligent fabric and artificial intelligence (AI)

This advanced functional fiber, which combines electronic and optoelectronic functions, has a wide range of potential application prospects in many technical fields such as sensing, communication, energy, robotics, smart fabrics, bioengineering and neuroscience. Fundamental sciences offer tremendous opportunities in many areas of research, including material processing, structural control and optimization of properties at the atomic and microscopic levels, the combination of materials with different physical and chemical properties, rheology and interface science, and multifunctional coupling. The combination of electronic fibers and traditional fabrics may revolutionize textile technology and industry.

When the article summarized this work, it also put forward the remaining challenges and future directions : the preparation process of the preform is incompatible with the existing electronic technology, and it is necessary to develop more advanced and comprehensive technology; it can be integrated into the hot drawing platform Functional materials are limited, and new technologies need to be developed to integrate incompatible functional materials with the hot-drawing process; research on the interaction between material structure and performance has just begun. In order to achieve complex functions and avoid manufacturing complex structures, materials need to be controlled The microstructure of fibers; the function of fibers will be gradually upgraded in a predictable way, forming a similar "Moore's Law" in fibers and fabrics. In the next few years, fibers with multiple functions will be able to see, hear, and feel To, communicate, store and convert energy, regulate temperature, monitor health and change color. The results of these efforts will have the potential to fundamentally change our perception of fibers and fabrics. Fibers and fabrics are evolving from a single function, a single material, to highly integrated electronics with complex structures and functions. Multifunctional fibers and fabrics have broad application prospects in the next generation of intelligent, flexible and wearable electronic products.

Thanks

All authors thank Professor Zhu Meifang, Professor Zhang Xinliang and Professor Zhou Jun for their support. Professor Tao Guangming especially thanked the National Natural Science Foundation of China (approval number 61875064), WNLO Joint Laboratory for Human-Computer Interaction, WNLO Innovation Project, and HUST Innovation Fund (approval number 2172018KFYXKJC021) for funding. Professor Hu Run thanked the National Natural Science Foundation of China (Grant No. 51606074) for funding. Professor Wei Lei would like to thank the Ministry of Education's Academic Research Fund II (MOE2015-T2-2-010) and the Singapore's Ministry of Education Academic Research Fund (T1-001-103 and MOE2019-T1-001-111) for their funding. Professor Zhou Shifeng especially thanked the National Key R & D Project (2018YFB1107200), the National Natural Science Foundation of China (Grant Nos. 51622206, 51972113), and the Guangzhou Key Research Project (201904020013) for funding. Xiaoting Jia thanked the National Science Foundation (1847436) for funding. Professor Tao Xiaoming thanked the Hong Kong Special Administrative Region Government Research Grants Council (152110 / 16E and 152009 / 17E) and the Innovation and Technology Commission (ITS / 306/17). Fabien Sorin is especially grateful to the Swiss CCMX Materials Challenge funding program, the Swiss National Science Foundation (approval number 200021_146871) and the European Research Council (ERC launch approval number 679211 "FLOWTONICS").

Original link http://www.sciencedirect.com/science/article/pii/S1369702119308697

DOI: 10.1016 / j.mattod.2019.11.006

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