Electrochemical replication and transfer: principle, fabrication, and applications

Abstract

Patterning technique can generate arbitrary micro- and nanopatterns on substrates of choice, which is a fundamental step in a wide range of applications. A wide variety of patterning techniques are used nowadays, such as photolithography, electron beam lithography (EBL), nanoimprint lithography (NIL), inkjet printing, screen printing, etc. High resolution, high throughput, and low cost are three basic requirements for an advanced patterning technique. Photolithography, EBL, and NIL can fabricate high-resolution patterns with nanoscales. However, these high-resolution patterning techniques suffer from limitations of either expensive equipment or low throughput. Inkjet and screen printings can achieve high throughput with relatively low cost. But their resolutions are seriously poor at micrometer scale. A big challenge for existing patterning techniques is the critical tradeoff among the resolution, throughput, and cost. Therefore, it is still of great significance to develop an alternative patterning technique that can achieve high resolution, high throughput, and low cost simultaneously. To address this challenge, an alternative patterning technique, termed electrochemical replication and transfer (ERT), is developed in this thesis. Firstly, ERT process only consists of two steps: 1) electrochemical replication of target materials on pre-patterned template and 2) transfer of replicated pattern onto target substrate. The parallel patterning on large-area substrate allows ERT to fabricate multi-scale patterns with resolutions spanning from sub-100 nm to many cm, which overcomes the tradeoff between resolution and throughput. On the other hand, the cost of ERT is ultralow own to its all-solution process based on ultralow-cost equipment and the nature of additive manufacturing. Furthermore, ERT is suitable for fabricating various materials including metals, semiconductors, metal oxides, and polymers with arbitrary geometric shapes on various flexible substrates including plastics, papers, and textiles. Secondly, the mechanism of ERT process was analyzed. In the step of electrochemical replication, two necessary conditions are the rational structure of Au-patterned template and optimization of current density, which both control the electrodeposited materials to be confined on the region of Au patterns. The success of transfer step is attributed to the surface modification of self-assembled monolayers (SAMs) on template and the use of photo-curable polymer as binder. The SAMs, pre-modified on Au surface, act as the anti-adhesive layers, which not only facilitate the peeling off of target materials, but also improve the reusability of template. The use of photo-curable adhesive as binder could make the transfer easy through its strong interaction with target materials. Thirdly, the applications of ERT technique were demonstrated. ERT technique was used to fabricate three types of typical electrodes (flexible transparent electrodes (FTEs), source/drain (S/D) electrodes, and interdigital electrodes (IDEs)), which were further integrated in the electronic devices. The FTEs show excellent electrical and optical properties, mechanical flexibility, and environmental stability, which were further used in optoelectronic devices, i.e., flexible transparent electrodes, touch screen panels, and organic light-emitting diodes. Furthermore, ERT was used to fabricate S/D electrodes and IDEs, which were successfully integrated in organic electrochemical transistors (OECTs) and micro-supercapacitors (MSCs), respectively. In conclusion, as an alternative patterning technique, ERT combines the advantages of high resolution, high throughput, and low cost. It can fabricate arbitrary geometric patterns with various materials on various flexible/wearable substrates. The mechanism of ERT process are relevant to the template structure, electrodeposition parameter, surface modification, and photo-curable binder. The applications of ERT for demonstration include flexible transparent electrodes, source/drain electrodes, and interdigital electrodes and their integrations in the electronic devices.