In a green grassy open space, two researchers from Nanyang Technological University in Singapore displayed a piece of snow-white cloth that was 13.5 meters long, 0.6 meters wide and 1 millimeter thick. This piece of cloth, which looks ordinary, is actually anything but ordinary. It is a piece of photoelectric sensing cloth, "woven" from fiber materials as thin as hair. Hats and clothes made of this fabric are expected to replace smart devices such as mobile phones, tablets, and smart watches.
On February 1, an international joint team led by Professor Wei Lei of Nanyang Technological University published a paper in Nature, introducing how this piece of cloth "woven" with ultra-long continuous high-quality silicon germanium fiber material was created.
Photoelectric sensing cloth 13.5 meters long, 0.6 meters wide, and 1 mm thick. Photo provided by interviewee
Looking for materials that are “flexible and stretchable”
Making brittle materials soft and even able to weave clothes is one of the research directions of Wei Lei's team.
"Today's chip manufacturing for mobile phones, computers, smart watches and other devices is inseparable from silicon materials. Before silicon materials gained favor, germanium was a classic material used to make the first transistor in history." Wang Zhixun, co-first author of the paper and a postdoctoral researcher at Nanyang Technological University, said that these two materials have abundant natural reserves and excellent electrical properties, but they are brittle materials that are "better to be broken than intact", and chips made with them are very easy to break.
Studies have found that although inorganic semiconductor materials represented by silicon and germanium have become indispensable key materials for chip manufacturing, as the electronics industry embraces the new trend of flexibility, the intrinsic brittleness of these semiconductors has brought challenges to materials scientists.
In order to make these semiconductor materials "flexible, stretchable, soft and easy to use", in recent years, international academic circles have proposed some solutions to reduce dimensionality.
Wang Zhe, a professor at Jilin University who participated in the research, explained that reducing the dimensionality means using silicon "dots" (zero-dimensional nano-silicon) with extremely small three-dimensional dimensions and can be considered as zero-dimensional form, distributed in an array on a flexible substrate to form a soft and hard cross-linked network to achieve flexibility of brittle and hard materials; or reducing the thickness of the wafer and passivating mechanical damage to obtain a flat (two-dimensional nano-silicon) silicon film that can be bent.
"Currently, there is relatively little research on one-dimensional (one-dimensional nanosilicon) semiconductor fibers in the academic community. The main reason is that the preparation is extremely difficult." Wei Lei said that how to continuously manufacture crack-free semiconductor fibers with considerable lengths on a large scale and with high yield is a key challenge.
Woven photoelectric sensing fabric comes out
Although scientists have discovered crystal growth methods from melts such as the micro-down-draw method, the preparation of semiconductor fibers still faces some major problems.
Wang Zhixun introduced that the fused core thermal drawing method is a method that slightly changes the method of producing glass optical fibers and is used to manufacture multi-material fibers. This method has the characteristics of low cost, high speed and long fibers. The fiber drawing speed can reach tens or even hundreds of meters per minute, and the drawing length of a single fiber can reach the kilometer level. However, semiconductor fibers produced by melt-core thermal drawing often have defects such as uneven shapes and frequent core fractures, which limit their practical application.
"To solve the production problems of semiconductor fibers, the core hot drawing method is a potential method, but it needs to fundamentally understand the mechanism of defect generation and solve the problem from the source." Zhang Qichong, a researcher at the Suzhou Institute of Nanotechnology and Nanobionics of the Chinese Academy of Sciences who participated in the study, told China Science Journal that the team members combined their respective background advantages and broke through traditional thinking. Starting from basic science and combined with experimental verification, they summarized and summarized different physical and chemical processes in the core hot drawing method in stages, and clarified the key fluid and solid mechanics issues in fiber preparation.
From the establishment of a theoretical model to the successful drawing of semiconductor fibers, this international joint team verified the systematic rules of the melt core thermal drawing method and demonstrated the daily application of woven photoelectric sensing fabrics based on semiconductor fibers. "This kind of sensing cloth can be sewn into a hat, a piece of clothing, or attached to a complex-shaped surface in the form of a single fiber (one-dimensional nanosilicon) to achieve a variety of practical applications in extreme environments such as continuous monitoring of ambient light, indoor optical communications, health management, and even deep-sea wireless communications." said Chen Ming, an associate researcher at the Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, who participated in the research.
Every “hair” has a lot of potential
Silicon and germanium are mature and widely used representative materials in the electronics industry. Semiconductor fibers made from them have an important advantage - they are compatible with existing technology and processes.
Zhang Qichong said that photoelectric sensing is only a small part of the application of this silicon germanium fiber material, and the material has broader application prospects. In the future, solar cells, temperature, pressure and other signal sensing, data storage, and even integrated circuits and microprocessors may all be integrated on these "hairs" and woven into daily clothing to improve people's quality of life.
"Today, we have achieved large-scale production of high-quality silicon and germanium semiconductor fiber materials in the laboratory, but we still face challenges in achieving wider applications." Wei Lei said that from the perspective of fiber morphology, the current shape is single. In actual applications, different devices may require fibers of different shapes or with certain internal structures; from the perspective of the material itself, further exploration of the fiberization preparation of third- and fourth-generation semiconductor materials is needed.
Zhang Qichong revealed that in the future, the joint research team will further study multifunctional fiber materials to jointly solve problems in production and preparation, allowing people to carry smart devices like underwear.