In the past decade, the rapid development of stretchable inorganic flexible electronic technology has enabled a large number of functional devices (such as stretchable batteries, cardiac activity sensors, stretchable light emitting diodes, optogenetics platforms and strain sensors) to complex surfaces, such as the surface of human skin and organs, as well as flexible device surfaces. Mechanical-guided structural designs are often used to integrate traditional hard inorganic semiconductor components and geometrically structured interconnected wires onto soft substrates, which ensures that electronic systems can withstand great deformation without failure. So far, various strategies based on wave structures, island bridge structures (such as arc-shaped interconnection wires, snake-shaped interconnection wires, two-dimensional spiral interconnection wires and three-dimensional spiral interconnection wires), fractal structures, paper-cutting structures, etc. have been adopted into the most advanced stretchable inorganic flexible electrons.
Accuracy and robustness are crucial for the large-scale commercial use of stretchable inorganic flexible electrons to improve people's medical conditions and quality of life. On this topic, there is a common and important problem: this type of device is usually designed and calibrated under free interface conditions. However, in practical applications, the interface conditions between the device and the human body/object are relatively complex, including interface conditions such as free, slipperable, and consolidation, and can switch between them (Figure 1). The actual deformation mode and strain distribution may differ from the initial design objectives and experimental calibration results under free interface conditions, which may further lead to changes in electrical properties and non-rosity, and even failure after long-term fatigue. Such an effect will greatly limit the actual use of the device and further commercialization. Ideally, mechanical and electrical properties (such as stretchability, durability, electrical conductivity and sensing properties) should be insensitive to interface conditions, so as to ensure that the device can operate accurately and robustly, not only in theoretical or FEA models and calibration tests of laboratory free interface conditions, but also in complex interface conditions such as human skin/other organ surfaces/flexible industrial equipment surfaces. So is there any general design principle of stretchable inorganic flexible electronics to achieve this goal?
Recently, a team of researchers at the Institute of Mechanics of the Chinese Academy of Sciences has studied the influence of the interface conditions of stretchable inorganic flexible electrons in different configurations of on their mechanics and electrical properties. In order to reveal the law theoretically, the wave-like structure was first studied, showing the relationship between its mechanical properties and packaging thickness under different interface conditions (Figure 2). For stretchable inorganic flexible electrons of different configurations, a general qualitative analysis was conducted based on the superposition principle and the St. Venen's principle, giving conclusions similar to the wave structure (Figure 3). Based on the above research, a general and simple stretchable inorganic flexible electronic size design principle is proposed to ensure consistency between mechanical and electrical properties under different interface conditions. , that is, the device/interconnection wire cycle length should be on the same order of magnitude as the package thickness or less. The applicability of this design principle has been verified through FEA and experiments of serpentine structure stretchable electrons (Figure 4). In order to ensure the comfort of human skin/organs, according to the above design principles, epidermal stretchable electronic devices require micron-scale geometric design. This discovery is of great significance to ensure the accuracy and robustness of stretchable inorganic flexible electrons in practical applications.
This research result is recently published in the academic journal Advanced Functional Materials (doi.org/10.1002/adfm.202210880). The first author of the paper is Li Shuang , a doctoral student at the Institute of Mechanics, Chinese Academy of Sciences, and the corresponding author is Su Yewang , a researcher at the Institute of Mechanics, Chinese Academy of Sciences. Also involved in this work are doctoral students of the Institute of Mechanics Lan Yuqun , Huazhong University of Science and Technology Huang Yongan and Beihang University of Aeronautics and Astronautics Professor Chen Yuli . In addition, doctoral students from the Institute of Mechanics Zhang Maoyi and Zhao Yang also provided technical support for this work.This work has been supported by projects such as the National Natural Science Foundation of China, the original innovation plan of the Chinese Academy of Sciences from 0 to 1, the interdisciplinary innovation team of the Chinese Academy of Sciences, and the WRQB talent plan of the Organization Department of the CPC Central Committee.
Figure 1. Tensile inorganic flexible electrons under different interface conditions (a) stretchable electronic wristbands as examples; (b) Work consistency requirements for electronic devices under complex interface conditions (free, slipperable or consolidated)
Figure 2. Analysis of wavy structure stretchable electrons under different interface conditions (a) Three interface conditions for free, slipperable and consolidated; (b) The change curve of the maximum main strain of wavy stretchable electrons with applied strain under three interface conditions; (c) The FEA results of the strain distribution of wavy stretchable electrons under three interface conditions; (d) The change curve of the tensileability of wavy stretchable electrons with package thickness under three interface conditions
Figure 3. General stress analysis of stretchable inorganic flexible electrons (a) Infinite thickness stretchable inorganic flexible electrons; stress decomposition under (b) free, (c) slipable and (d) consolidation interface conditions
Figure 4. The application of the principle of interface insensitive design to verify the application of serpentine structures (a) three interface conditions for free, slip and consolidation; (b) the change curve of the tensileability of serpentine structures with packaging thickness under three interface conditions; (c) the strain distribution FEA result of thin/thick packaged serpentine structures under three interface conditions; (d) the change curve of the maximum interface stress between serpentine structures and packaging materials with packaging thickness under three interface conditions; (e) the FEA result of the interface stress distribution between serpentine structures and packaging materials under three interface conditions; (f) Design drawing of the serpentine structure with off-axis Conco foil; (g) Tensile specimens of thin/thick encapsulated serpentine structures used for free interface conditions and consolidation interface conditions; (h) Change curve of the relative resistance change of thin/thick encapsulated serpentine structures under free/consolidation interface conditions with applied strain
Corresponding author of this article, Researcher Su Yewang, returned from , , Northwestern University, to the Institute of Mechanics, Chinese Academy of Sciences in 2015, and has been committed to the research on flexible structure and device mechanics . Selected in National Youth Talent Program and Chinese Academy of Sciences BR Program ; served as the head of the innovation cross-team team of the Chinese Academy of Sciences ; won the second prize of the Chinese Academy of Sciences in 2017 (2/3); published JMPS (3 articles), IJSS (5 articles), PNAS, Nature Com. (3 articles), Adv. Mat., Adv. Func. Mat. (4 articles), ACS Nano (3 articles), Nano Energy (3 articles), Small and other SCI papers; wrote 2 chapters in English; applied for invention patent 30 , has authorized 13 , has submitted 2 international patent PCT applications, and developed flexible sensors are used in Mars engineering ; served as composite material international authoritative journal Composite Editorial Committee of Structures; presided over a number of projects such as the Foundation's project , the Chinese Academy of Sciences from 0 to 1 original innovation project , the Beijing Municipal Science and Technology Commission's major special project Huairou Science City results implementation special project , and the application project of the research results of the aerospace and medical enterprises. Researcher Su Yewang’s research team is now recruiting postdoctoral and long-term cooperative positions (assistant/assistant researcher/researcher) from professional backgrounds such as mechanics, machinery, materials and electronics. Those interested, please send your resume (pdf) to Researcher Su Yewang’s email address [email protected]. Please indicate “Intent Position + Name + Graduation School” in the title of the email.
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Original link:
https://doi.org/10.1002/adfm.202210880
Source: Frontiers in Polymer Science
