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Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II

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A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "E：Engineering and Technology".

Deadline for manuscript submissions: closed (30 June 2024) | Viewed by 14817

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Prof. Dr. Rui Li

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Department of Engineering Mechanics, Dalian University of Technology, Dalian 116024, China
Interests: flexible and stretchable electronics; bioelectronic implants; thin films; transfer printing; mechanics of soft matter
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Flexible and stretchable electronics represent a class of promising technology that involves stretchable/bendable/twistable components such that unprecedented properties are achieved over conventional rigid/brittle semiconductor-based electronics. Wide applications of flexible and stretchable electronics have been explored to yield many emerging devices, such as flexible displays, conformable sensors, epidermal electronics and implantable transient electronics for daily use or healthcare purposes. Rapid development in the field has attracted a great deal of interest in the modeling, design and fabrication of relevant materials, structures, components and devices.

This Special Issue seeks contributions on different aspects of flexible and stretchable electronics, with a focus on mechanical analyses and structural designs toward various component-level or device-level applications. Research papers and review articles are both welcome. The topics include, but are not limited to:

Mechanical analysis methods of flexible/stretchable electronics on either the device or component level;
Structural optimization and design theories toward providing better related performance;
Experimental studies on various properties of flexible/stretchable electronics;
Novel flexible/stretchable structures with extraordinary mechanical or electrical properties;
Design of materials, structures, and components for special application scenarios, such as bioelectronics and implantable electronics.

Prof. Dr. Rui Li
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

flexible electronics
stretchable electronics
wearable electronics
bioelectronics
implantable electronics
flexible/stretchable electronic materials
flexible/stretchable electronic structures
flexible/stretchable electronic components
structural analyses
structural designs
structural optimization

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Related Special Issues

Structural Analyses and Designs for Flexible/Stretchable Electronics in Micromachines (17 articles)
Structural Analyses and Designs for Flexible/Stretchable Electronics, 3rd Edition in Micromachines (2 articles)

Published Papers (10 papers)

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Research

17 pages, 5340 KiB

Open AccessArticle

An Optimal Design Method for Lightweight Heating Film of Anisotropic Heat Conduction Substrate Based on Surrogate Model

by Zheng Deng, Qingkui Yu, Jingyu Liu, Yanan Wang, Shoubing Yan, Nana Huai, Jingze Zhang and Huaxing Gao

Micromachines 2024, 15(8), 970; https://doi.org/10.3390/mi15080970 - 29 Jul 2024

Viewed by 636

Abstract

In space missions, heating films are crucial for uniformly heating onboard equipment for precise temperature control. This study develops an optimization method using surrogate models for lightweight anisotropic substrate thermal conductive heating films, meeting the requirements of uniform heating in thermal control for space applications. A feedforward neural network optimized by particle swarm optimization (PSO) was employed to create a surrogate model, mapping design parameters to the temperature uniformity of the heating film. This model served as the basis for applying the NSGA-II algorithm to quickly optimize both temperature uniformity and lightweight characteristics. In this study, the PSO-BP surrogate model was trained using heating film thermal simulation data, and the surrogate model demonstrated an accurate prediction of the mean square error (MSE) of the predicted temperature difference within 0.0168 s. The maximum temperature difference in the optimal model is 1.188 ℃, which is 30.5 times lower than before optimization, and the equivalent density is only increased by 3.9%. In summary, this optimization design method effectively captures the relationships among various parameters and optimization objectives. Its superior computational accuracy and design efficiency offer significant advantages in the design of devices such as heating films. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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12 pages, 4738 KiB

Open AccessArticle

Assessing the Effect of Twisting and Twisting Fatigue on ZnO:Al Thin Film Performance on PEN and PET Substrates

by Dilveen W. Mohammed, Rayan M. Ameen, Rob Waddingham, Andrew J. Flewitt, James Bowen and Stephen N. Kukureka

Micromachines 2024, 15(7), 853; https://doi.org/10.3390/mi15070853 - 29 Jun 2024

Viewed by 736

Abstract

This study examines the electromechanical characteristics of aluminium-doped zinc oxide (AZO) films. The films were produced using the RF magnetron sputtering process with a consistent thickness of 150 nm on various polymer substrates. The study focuses on assessing the electro-mechanical failure processes of coated segments using flexible substrates, namely polyethylene naphthalate (PEN) and polyethylene terephthalate (PET), with a specific emphasis on typical cracking and delamination occurrences. This examination involves conducting twisting deformation together with using standardised electrical resistance measurements and optical microscope monitoring instruments. It was found that the crack initiation angle is mostly dependent on the mechanical mismatch between the coating and substrate. Higher critical twisting angle values are observed for the AZO/PEN film during twisting testing. Relative to the perpendicular plane of the untwisted sample, it was found that cracks initiated at a twist angle equal to 42° ± 2.1° and 38° ± 1.7° for AZO/PEN and AZO/PET, respectively, and propagated along the sample length. SEM images indicate that the twisting motion results in deformation in the thin film material, leading to the presence of both types of stress in the film structure. These discoveries emphasise the significance of studying the mechanical properties of thin films under different stress conditions, as it can impact their performance and reliability in real-world applications. The electromechanical stability of AZO was found to be similar on both substrates during fatigue testing. Studying the electromechanical properties of various material combinations is important for selecting polymer substrates and predicting the durability of flexible electronic devices made from polyester. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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17 pages, 3139 KiB

Open AccessArticle

Light-Responsive Soft Robot Integrating Actuation and Function Based on Laser Cutting

by Ben Jia, Changbo Liu, Yi Zhang, Yujin Tan, Xuecheng Tian, Yuanyuan Cui and Yuan Deng

Micromachines 2024, 15(4), 534; https://doi.org/10.3390/mi15040534 - 16 Apr 2024

Viewed by 3643

Abstract

Soft robots with good deformability and adaptability have important prospects in the bionics and intelligence field. However, current research into soft robots is primarily limited to the study of actuators and ignores the integrated use of functional devices and actuators. To enrich the functions of soft robots and expand their application fields, it is necessary to integrate various functional electronic devices into soft robots to perform diverse functions during dynamic deformation. Therefore, this paper discusses methods and strategies to manufacture optical stimuli-responsive soft actuators and integrate them into functional devices for soft robots. Specifically, laser cutting allows us to fabricate an optically responsive actuator structure, e.g., the curling direction can be controlled by adjusting the direction of the cutting line. Actuators with different bending curvatures, including nonbending, can be obtained by adjusting the cutting depth, cutting width, and the spacing of the cutting line, which makes it easy to obtain a folded structure. Thus, various actuators with complex shape patterns can be obtained. In addition, we demonstrate a fabrication scheme for a worm-like soft robot integrated with functional devices (LEDs are used in this paper). The local nonbending design provides an asymmetric structure that provides driving power and avoids damage to the functional circuit caused by the large deformation during movement. The integration of drive and function provides a new path for the application of soft robots in the intelligence and bionics field. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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16 pages, 6667 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Temperature Prediction Model for Flexible Electronic Devices Based on GA-BP Neural Network and Experimental Verification

by Jin Nan, Jiayun Chen, Min Li, Yuhang Li, Yinji Ma and Xuanqing Fan

Micromachines 2024, 15(4), 430; https://doi.org/10.3390/mi15040430 - 23 Mar 2024

Cited by 2 | Viewed by 1403

Abstract

The problem that the thermal safety of flexible electronic devices is difficult to evaluate in real time is addressed in this study by establishing a BP neural network (GA-BPNN) temperature prediction model based on genetic algorithm optimisation. The model uses a BP neural network to fit the functional relationship between the input condition and the steady-state temperature of the equipment and uses a genetic algorithm to optimise the parameter initialisation problem of the BP neural network. To overcome the challenge of the high cost of obtaining experimental data, finite element analysis software is used to simulate the temperature results of the equipment under different working conditions. The prediction variance of the GA-BPNN model does not exceed 0.57 °C and has good robustness, as the model is trained according to the simulation data. The study conducted thermal validation experiments on the temperature prediction model for this flexible electronic device. The device reached steady state after 1200 s of operation at rated power. The error between the predicted and experimental results was less than 0.9 °C, verifying the validity of the model’s predictions. Compared with traditional thermal simulation and experimental methods, this model can quickly predict the temperature with a certain accuracy and has outstanding advantages in computational efficiency and integrated application of hardware and software. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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22 pages, 16248 KiB

Open AccessArticle

A Study on the Reliability Evaluation of a 3D Packaging Storage Module under Temperature Cycling Ultimate Stress Conditions

by Shuai Zhou, Kaixue Ma, Yugong Wu, Shizhao Wang and Nian Cai

Micromachines 2024, 15(4), 428; https://doi.org/10.3390/mi15040428 - 23 Mar 2024

Viewed by 962

Abstract

Based on the theory of reliability enhancement testing technology, this study used a variety of testing combinations and finite element simulations to analyze the stress–strain properties of 3D packaging storage modules and then evaluated its operating and destruction limits during temperature cycling tests (−65 °C~+150 °C) for the purpose of identifying the weak points and failure mechanisms affecting its reliability. As a result of temperature cycling ultimate stress, 3D packaging storage devices can suffer from thermal fatigue failure in the case of abrupt temperature changes. The cracks caused by the accumulation of plastic and creep strains can be considered the main factors. Crack formation is accelerated by the CTE difference between the epoxy resin and solder joints. Moreover, the finite element simulation results were essentially the same as the testing results, with a deviation occurring within 10%. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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21 pages, 19252 KiB

Open AccessArticle

Methods to Improve Accuracy of Electronic Component Positioning in Thermoformed Electronics

by Behnam Madadnia, Jan Vanfleteren and Frederick Bossuyt

Micromachines 2023, 14(12), 2248; https://doi.org/10.3390/mi14122248 - 16 Dec 2023

Viewed by 1366

Abstract

Three new methods for accurate electronic component positioning for thermoformed electronics are presented in this paper. To maintain the mechanical and electrical properties of printed-ink tracks, prevent deformation and stretching during thermoforming, and ensure reproducibility, the component positioning principle for all three proposed methods is based on keeping the temperature of some regions in the thermoplastic substrate less than the glass transition temperature of the thermoplastic carrier, to keep those regions resistant to plastic deformation. We have verified the accuracy of the different approaches by implementing these methods in a semi-sphere mold for positioning seven LEDs and one printed capacitive touch sensor. We compared the result of our fabrication processes with the typical fabrication process of in-mold electronics (direct printing on a thermoplastic foil and followed by a thermoforming step) and noticed that the sample produced by the typical process had tracks that were randomly stretched, tracks were not in a straight path after thermoforming and they were not electrically conductive. Furthermore, the final 3D position of the components was not reproducible sample by sample. However, with our proposed fabrication methods, the tracks and pads do not deform or expand during thermoforming and are electrically conductive after. Moreover, the round shape of the touch sensor remains the same as in the 2D design. Based on the results of the experiments, it appears that the proposed methods are capable of positioning electronic components with high precision in thermoformed electronics. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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10 pages, 5386 KiB

Open AccessArticle

Electrically Doped PNPN Tunnel Field-Effect Transistor Using Dual-Material Polarity Gate with Improved DC and Analog/RF Performance

by Chan Shan, Ying Liu, Yuan Wang, Rongsheng Cai and Lehui Su

Micromachines 2023, 14(12), 2149; https://doi.org/10.3390/mi14122149 - 24 Nov 2023

Cited by 2 | Viewed by 1026

Abstract

A new structure for PNPN tunnel field-effect transistors (TFETs) has been designed and simulated in this work. The proposed structure incorporates the polarity bias concept and the gate work function engineering to improve the DC and analog/RF figures of merit. The proposed device consists of a control gate (CG) and a polarity gate (PG), where the PG uses a dual-material gate (DMG) structure and is biased at −0.7 V to induce a P⁺ region in the source. The PNPN structure introduces a local minimum on the conduction band edge curve at the tunneling junction, which dramatically reduces the tunneling width. Furthermore, we show that incorporating the DMG architecture further enhances the drive current and improves the subthreshold slope (SS) characteristics by introducing an additional electric field peak. The numerical simulation reveals that the electrically doped PNPN TFET using DMG improves the DC and analog/RF performances in comparison to a conventional single-material gate (SMG) device. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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13 pages, 2108 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

An Analytical Thermal Buckling Model for Semiconductor Chips on a Substrate

by Guangping Gong, Dian Xu, Sijun Xiong, Fangyu Yi, Chengbo Wang and Rui Li

Micromachines 2023, 14(11), 2025; https://doi.org/10.3390/mi14112025 - 30 Oct 2023

Viewed by 1381

Abstract

Semiconductor chips on a substrate have a wide range of applications in electronic devices. However, environmental temperature changes may cause mechanical buckling of the chips, resulting in an urgent demand to develop analytical models to study this issue with high efficiency and accuracy such that safety designs can be sought. In this paper, the thermal buckling of chips on a substrate is considered as that of plates on a Winkler elastic foundation and is studied by the symplectic superposition method (SSM) within the symplectic space-based Hamiltonian system. The solution procedure starts by converting the original problem into two subproblems, which are solved by using the separation of variables and the symplectic eigenvector expansion. Through the equivalence between the original problem and the superposition of subproblems, the final analytical thermal buckling solutions are obtained. The SSM does not require any assumptions of solution forms, which is a distinctive advantage compared with traditional analytical methods. Comprehensive numerical results by the SSM for both buckling temperatures and mode shapes are presented and are well validated through comparison with those using the finite element method. With the solutions obtained, the effects of the moduli of elastic foundations and geometric parameters on critical buckling temperatures and buckling mode shapes are investigated. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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13 pages, 2902 KiB

Open AccessArticle

Customised Implant for Temporomandibular Joint: New Technique to Design and Stress Analysis to Balance the Loading at Both Ends

by Anubhav Tiwari, Ishfaq A. Ahmed, Vijay Kumar Gupta, Rakesh Kumar Haldkar and Ivan A. Parinov

Micromachines 2023, 14(8), 1646; https://doi.org/10.3390/mi14081646 - 20 Aug 2023

Cited by 1 | Viewed by 1610

Abstract

The temporomandibular joint (TMJ) is a critical joint for the opening and closing of the mouth. The generation of customised TMJs according to individuals’ dental anatomy is needed. Currently, the implants available on the market lack consideration of the patient’s dental anatomy. This leads to the creation of an imbalance in the reaction forces on both ends of the TMJ. This requires a slight structural change in the design parameters to give a solution. The purpose of this study is to propose a new design that includes the geometry and materials for a TMJ implant. Stress analysis was carried out on the TMJ to balance the reaction forces at both TMJ ends. A static analysis was performed using ANSYS Workbench, to compare the results of two customised designs of TMJ implants, in order to better balance the reaction forces at both ends. The model in the study showed that the reaction forces for both the patient-specific TMJ implants were nearly balanced. The reaction forces were better balanced, and almost equivalent to the intact conditions. The stresses in the mandible were more uniformly distributed in the customised design of the TMJ implant. The two types of design showed that the custom design took up less space in the patient’s region of surgery, making it a better option compared to a stock TMJ implant. The custom implant would allow faster patient rehabilitation, as the reaction forces would be close to those in intact conditions. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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11 pages, 2760 KiB

Open AccessArticle

Impact of Through-Hole Defects on the Electro-Explosive Properties of Exploding Foil Transducers

by Kexuan Wang, Jiangxu Wang, Xinyu Li, Dangjuan Li, Junxia Cheng, Jia Wang and Shenjiang Wu

Micromachines 2023, 14(8), 1499; https://doi.org/10.3390/mi14081499 - 26 Jul 2023

Viewed by 988

Abstract

This study examines the impact of surface defects on the electro-explosive properties of metal explosive foil transducers. Specifically, it focuses on the effects of defects in the bridge foil and their influence on the electrical explosion time and transduction efficiency. To analyze these effects, a current-voltage simulation model is developed to simulate the behavior of a defective bridge foil. The simulation results are validated through experimental current-voltage measurements at both ends of the bridge area. The findings reveal that the presence of through-hole defects on the surface of the bridge foil leads to an advancement in the electrical explosion time and a reduction in the transduction efficiency of the bridge foil. A performance comparison is made between the defective bridge foil and a defect-free copper foil. As observed, a through-hole defect with a radius of 20 μm results in a 1 ns advance in the blast time and a 1.52% decrease in energy conversion efficiency. Similarly, a through-hole defect with a radius of 50 μm causes a 51 ns advancement in the blast time and a 13.96% reduction in the energy conversion efficiency. These findings underscore the detrimental effects of surface defects on the electro-explosive properties, emphasizing the importance of minimizing defects to enhance their performance. Full article

(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)

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