Stretchable electronics offers unsurpassed mechanical compliance on complex or soft surfaces like the human skin and organs. With uncompromised stretchablility, microfluidic processing offers high possibility to make high performance stretchable electronics. Hence, it is very important to find a good solution to make such kind of stretchable electronics.
Here, with a newly introduced tape transfer printing technique, we present here a new direction to pattern liquid alloys on elastic substrates. By rolling printing or atomized spraying of a liquid alloy onto a soft surface with a tape transferred adhesive mask, a universal fabrication process is provided for high quality patterns of liquid conductors in a meter scale. With this tape transfer printing technique, we can print any pattern on the elastic substrate, which can be done the traditional stencil printing. With the developed technology, we present here an integrated radio frequency identify tag, which showed the robustness of the packaged hybrid integrated system when stretched at 50% in 3,000 cycles. Further developed with a multilayer fabrication technique, a microfluidic stretchable wireless power transfer device with an integrated LED was demonstrated, which could survive cycling between 0% and 25% strain over 1,000 times.
Briefly, the process of tape transfer printing of a liquid alloy is summarized here:
- 1. PDMS substrate was prepared on a rigid support and half-cured on a hot plate.
- 2. A mask for patterning liquid alloy was designed and cut by a cut plotter.
- 3. Then gently, the tape mask on the transfer tape was transferred to the as-prepared half-cured PDMS substrate through the laminated transfer tape after removing the unnecessary patterns.
- 4. The liquid alloy was printed with a sponge head roller by rolling it over several times or atomizing printing with an airbrush scanning.
- 5. The printed liquid alloy patterns were ready, by slowly peeling the tape mask off from the substrate.
- 6. With optional integrating rigid components with so-called localized stiff cells, the liquid alloy circuits were encapsulated with a secondary PDMS layer. This processing can be stacked further for a multilayer fabrication.
This technique is able to pattern high quality, uniform and clear patterns of 500 μm wide lines with lengths near a meter. A microfluidic RFID and wireless power transfer device were successfully demonstrated with excellent mechanical stretchability as well as good performance.
In conclusion, our work demonstrated a versatile liquid alloy patterning technique on soft substrates based on tape transferred adhesive masking, and deposition of a liquid alloy. Further improvement and optimization of this process technique could offer higher resolution and repeatability, and create new opportunities to introduce advanced functions in conformal devices, intelligent systems on the skin or what could be implanted for man-machine communication.
Zhigang WU , 2015.
ASME 2015 International Mechanical Engineering Congress & Exposition, November 13-19, 2015, Houston, Texas