Stretchable Electronics Jumping to the Next Level

Integration of solid-state microchips into soft-matter electronics has been the biggest challenge against their scalable fabrication. We introduce, Pol-Gel, Reversible Polymer-Gel transition of Block Co Polymers, for self-soldering, self-encapsulation, and self-healing highly stretchable circuits.

Like Comment
Read the paper

In my group, we have been working in the field of stretchable electronics for many years. However, i was always getting dissapointed that many times we cannot realy apply the circuits in real-world applications, because it is pretty difficult to integrate microchips into these circuits. The traditional soldering techniques does not work for printed and stretchable electroncis, and conductive adhesives require high temperature curing, and selective deposition. We could see clearly that Microchip integration is now the biggerst chanllenge in the field, and takes many fabrication steps. So we were looking for a magical solution that allows us easily integrate microchips into stretchable cirucuits in one single step! But none of the traditional techniques could be further optimized. We had to think out of  the box!

One day, we noticed that Block Co Polymers get soft, when they are exposed to the solvent vapour. So we thaught, maybe we can use this property to "solder" the composnents to the circuit. We did a few tests, and we were surprised by the results. It works!!

We then designed a simple,  3 step process. Printing, Pick and Place, and Chip Integration through Vapor Exposure. Everything is performed at the room temperature.  The process is very simple,  scalable, and compatible with heat-sesnitive susbtrates.

This of course required some optimziation on the materials, and design of fabrication process. We designed a novel ink that contains Liquid Metal and SIS Block Co Polymers, that is highly stretchable. We then adjusted the ink to be digitally printable, and we optimized the process parameters for Microchip Integration. The mechanism of action is simples. BCPs melt, and the chips penetrate into them, due to the gravity. It is simple isn´ t it?

We then found that the same mechanism heals the substrate and the ink. Sometimes there are microcracks on the substrate, which reduce the maximum strain tolerance, and when exposed to the vapor, they are gone. Becasue of this, we got a record breaking max. strain values: 1200% for printed circuits, and 500-800%  for chip integrated circuits.

Even if you cut the circuit, this proces heals it effectively, so that it can be stretched again. 

Another problem that this process solves, is the need for encapsulation. The process of vapor exposure, results in the ink penetration i nto the substrate, and self-encapsulate it. That is why we call this single-step process: Self-Soldering, Self-Healing, and Self-Encapsulation. To make it more interesting, this process increases the conductivity of the ink, though making the ink more compact, and improving its percolation. Image below shows the cross section of the ink, before and after treatment, which shows clearly that the percolation is improved. 

Many steps of fabrication are eliminated with this simple process. We have as well filed a patent, and are looking for partners for commercizlization of this technology.

We as well showed some applications. For instance a miniaturized circuit for continious on-body temperature monitoring, with integrated bluetooth. 

These circuits are as well transferable to the textile. So they can be used for e-textile for wearble computing.

Make sure to read full details, and watch the videos in the article.

Lopes, P.A., Santos, B.C., de Almeida, A.T. et al. Reversible polymer-gel transition for ultra-stretchable chip-integrated circuits through self-soldering and self-coating and self-healing. Nat Commun 12, 4666 (2021). https://doi.org/10.1038/s41467-021-25008-5

Mahmoud Tavakoli

Professor, Unvirsity of Coimbra