Researchers from NC State have developed a new technique for directly printing metal circuits, creating flexible, stretchable electronics. The technique can use multiple metals and substrates, and is compatible with existing manufacturing systems that employ direct printing technologies.

Dr. Jingyan Dong

Tech Briefs: What brought you to this project?

Dr. Jingyan Dong: Traditional printing methods are limited by material cost, by the conductivity of the printed feature, or by the printing resolution. That motivated us to try electrohydrodynamic (EHD) printing technology. We use this process to print low-melting-point alloys to achieve high resolution and high conductivity with low-cost material. We can achieve these objectives simultaneously. This is the first time molten metal-based inks have been used for EHD printing.

Tech Briefs: Why did you choose EHD?

Dr. Dong: There are many other printing approaches; for example, inkjet and screen printing. These are very difficult to use with molten metal inks. Moreover, they have lower resolution. For example, inkjet and screen printing can achieve best resolutions of roughly tens to hundreds of microns, while EHD printing can regularly achieve sub-micron to microns. We can achieve a resolution of tens of microns even for high-viscosity molten metal inks with EHD printing.

Tech Briefs: Did you design a new alloy for this process?

Dr. Dong: No. To make this process widely applicable, we just selected existing low-melting-point metals. We tried Field’s metal, Wood’s metal, and solder. We eventually focused on Field’s metal because it is lead-free and environmentally friendly. Although we chose Field’s metal with a melting point of 60 °C for our demonstration, we could also work with other low-melting-point metals like traditional solder.

Tech Briefs: What other applications are there for EHD?

Dr. Dong: Our method can be used to produce wearable devices, since it can bend and stretch without affecting electrical performance. I see applications for wearable sensors and for communication components such as antennas. Solid-state electronics are easy to produce, because there are no requirements for flexibility and stretchability of the electronics features, and it’s relatively easy to print onto glass and silicon wafers.

Basically, we want to further evaluate the capabilities of metal printing for different applications. We’ve demonstrated some simple device designs; for example, touch sensors. We plan to experiment with a pressure sensor and perhaps wearable sensors for healthcare applications.

Tech Briefs: How soon could it be implemented?

Dr. Dong: We feel there are only minor gaps for bridging this printing approach from a laboratory technology to a commercial fabrication method. There might be some work in between, but I would say it’s not too difficult.