| Author: | Chen, Zijian |
| Title: | A study on electrochemical replication and transfer for flexible electronics |
| Advisors: | Zheng, Zijian (SFT) |
| Degree: | Ph.D. |
| Year: | 2025 |
| Subject: | Wearable technology Flexible electronics Electrochemistry Electrocrystallization Hong Kong Polytechnic University -- Dissertations |
| Department: | School of Fashion and Textiles |
| Pages: | xxxii, 220 pages : color illustrations |
| Language: | English |
| Abstract: | With the rapid progress of science and technology, the concept of the Internet of Things (IoT) has gained significant prominence. The field of wearable electronics has become an essential part of the Internet of Things (IoT) and has sparked a great deal of curiosity and thorough investigation. The basic fabrication technical core of electronic devices on untraditional flexible and stretchable substrates largely relies on patterning techniques. Traditional methods of patterning, such as photolithography, electron beam lithography (EBL), and nanoimprinting lithography (NIL), serve as effective instruments in creating high-resolution integrated circuits on semiconductor substrates. However, they are not suitable for the direct patterning process on flexible substrates due to various problems including rough surfaces with low wettability, poor resistance to chemical solvents, and unstable to thermal treatment. In just the past few decades, miscellaneous advanced patterning techniques have been proposed to satisfy the requirements of fabricating electronic devices with different materials on arbitrary substrates, including transfer printing, 3D printing, inject printing and so on. However, there is still no one patterning technique that could satisfy most of the applications while achieving a great balance in the aspects of resolution, throughput and cost. Recently, electrochemical replication and transfer (ERT), an advanced patterning technique had evolved. By combining the traditional patterning methods with the electroplating process, the high-resolution pattern could be easily replicated and peeled off by a UV-curable binder. The electrodeposited pattern could be therefore transferred to various flexible substrates like fibers, papers, and polymers. Furthermore, it could achieve a great balance between resolution, throughput and cost. However, the fabrication of nanoscale patterns is still a challenge. The fabrication of stretchable electronics and the construction of 3D structures have not been demonstrated. Therefore, to tackle the challenges and enhance the capability of ERT, various modifications to the template and binder material were proposed in this thesis. The applicability and potential applications of each template were demonstrated. Firstly, a thin layer of SiO2 was added to the original Si substrate which has the same thickness as the Au pattern in the following thermal evaporation process. By combining the photolithography and drying etching methods, the Au pattern could be embedded into the SiO2 layer and protected by it. Therefore, during the next electrodeposition process, the target materials will only be deposited onto the up surface of the Au pattern. The adhesion force between the Au pattern and the target materials will be greatly reduced because of the decreasing contact area. This SiO2-protecting template could be efficient in improving the robustness of the Au template and the resolution limits of ERT. Nanoscale patterns with various materials reaching sub-100 nm could be successfully fabricated with this template. Secondly, the rigid UV-curable binder was replaced by a PVA solution. After drying, the PVA layer could serve as a strong adhesion layer to peel off and transfer the electrodeposited pattern. It is still applicable for large-area transfer of various materials patterns. Additionally, the dissolvability of the PVA layer allows an arbitrary transfer of the replicated pattern to any substrates including hard surfaces, curved surfaces and stretchable substrates. The production of diverse stretchable electronic devices was showcased. Thirdly, through conducting photolithography and drying etching process on a SiO2/Si substrate, a 3D patterned Si template with different aspect ratios could be successfully fabricated. The electroplating process will be directly conducted on the Si substrate without deposition of the Au pattern. Instead of using PFDT, a silylating reagent will be used to conduct the surface modification of the template to minimise the interfacial adhesion force between the template and the electrodeposited substances. Both continuous and isolated patterns with different aspect ratios could be replicated and transferred to flexible substrates. Additionally, the growth of the target materials will be restricted to the 3D groove area, which mitigates the diminution of the resolution of the replicated pattern attributable to the isotropic deposition inherent in the electroplating process. This 3D architecture presents a significant advantage in the production of transparent electrodes. Finally, we investigated the application prospect of ERT in the field of energy and biomedical engineering. Taking the fabrication of triboelectric nanogenerator (TENG) electrodes by ERT as an example, we conceived the idea of setting up the production line of ERT and characterize the performance of the devices in the view of electrochemical performance, stability and flexibility. The potential consumption of energy and money was evaluated using LCA in the aspect of sustainable production. We also explored the biocompatibility of electrodes fabricated by ERT and showed the relating application of an electronic bandage in accelerating wound recovery. In summary, this work focuses on the shortcomings of the original ERT methods, and proposed target improvements for each challenge through modification of the template and binder material. The applicability of each modification was detailly studied, and the related applications were demonstrated. The improved ERT method has great potential in the large-scale fabrication of diverse wearable electronic apparatuses and become an indispensable part of patterning techniques in the near future. |
| Rights: | All rights reserved |
| Access: | open access |
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