Sun Yi-Chiang, Boero Giovanni, Brugger Jürgen
Microsystems Laboratory, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
ACS Appl Electron Mater. 2021 Dec 28;3(12):5423-5432. doi: 10.1021/acsaelm.1c00884. Epub 2021 Nov 29.
Embedding liquid metals (LMs) into an elastomer is emerging as a promising strategy for stretchable conductors. Existing manufacturing techniques are struggling between spatial resolution and process complexity and are limited to chemically resistant substrates. Here, we report on a hybrid process combining stencil lithography and centrifugal force-assisted patterning of liquid metal for the development of LM-based stretchable conductors. The selective wetting behavior of oxide-removed eutectic gallium-indium (EGaIn) on metal patterns defined by stencil lithography enables micrometer scale LM patterns on an elastomeric substrate. Stencil lithography allows for defining metal regions without harsh chemical treatments, making it suitable for a wide range of substrates. Microscale LM patterns are achieved by efficiently removing the excess material by the centrifugal forces experienced from spinning the substrate. The proposed approach allows for the creation of LM patterns with a line width as small as 2 μm on a stretchable poly(dimethylsiloxane) (PDMS) substrate. The electrical measurement results show that the fabricated EGaIn devices can endure 40% mechanical strain over several thousands of cycles. Furthermore, a stencil design using microbridges is proposed to address the mechanical stability issue in stencil lithography. An EGaIn conductor with a serpentine structure and an interdigitated capacitor are fabricated and characterized. The results demonstrate that the patterned serpentine conductors retain their functionality with applied mechanical strain up to 80%. The performance of the interdigitated capacitors upon applied strain is in good agreement with the theoretical estimation. Finally, we demonstrate our approach also on poly(octamethylene maleate (anhydride) citrate) (POMaC) substrates to broaden the use of the proposed method to not only flexible and stretchable but also biodegradable substrates, opening a way for in vivo transient microsystem engineering. The work presented here provides a versatile and reliable approach for manufacturing stretchable conductors.
将液态金属（LMs）嵌入弹性体正成为一种制备可拉伸导体的很有前景的策略。现有的制造技术在空间分辨率和工艺复杂性之间面临困境，并且仅限于耐化学腐蚀的基板。在此，我们报告一种结合模板光刻和液态金属离心力辅助图案化的混合工艺，用于开发基于液态金属的可拉伸导体。去除氧化物的共晶镓铟（EGaIn）在通过模板光刻定义的金属图案上的选择性润湿行为，使得在弹性体基板上能够形成微米级的液态金属图案。模板光刻允许在无需苛刻化学处理的情况下定义金属区域，使其适用于广泛的基板。通过旋转基板所产生的离心力有效去除多余材料，从而实现微尺度的液态金属图案。所提出的方法能够在可拉伸的聚二甲基硅氧烷（PDMS）基板上创建线宽小至2μm的液态金属图案。电学测量结果表明，所制备的EGaIn器件在数千个循环中能够承受40%的机械应变。此外，还提出了一种使用微桥的模板设计，以解决模板光刻中的机械稳定性问题。制备并表征了具有蛇形结构的EGaIn导体和叉指电容器。结果表明，图案化的蛇形导体在施加高达80%的机械应变时仍能保持其功能。叉指电容器在施加应变时的性能与理论估计值吻合良好。最后，我们还在聚（马来酸（酐）柠檬酸辛二酯）（POMaC）基板上展示了我们的方法，以将所提出方法的应用范围扩大到不仅适用于柔性和可拉伸基板，还适用于可生物降解基板，为体内瞬态微系统工程开辟了道路。本文所展示的工作为制造可拉伸导体提供了一种通用且可靠的方法。
