Printable Conductive Ink Dispenses with Sintering Step

In a previous Medtech Pulse blog, we reported on a direct-write process for printing electrodes on a polyphenylsulfone spinal-therapy devices. Now, a team of scientists under Shlomo Magdassi from the Institute of Chemistry at the Hebrew University of Jerusalem reports that it has developed a conductive ink for printing electronics that does not require a post-printing sintering step.

According to Nanowerk, the method involves the addition of a latent sintering agent following the printing step. Once the solvent evaporates, the sintering agent concentration increases, leading to the spontaneous sintering of nanoparticles. With the growing importance of electronic devices for a range of medical applications, the medical device industry might welcome the prospect of printing electronic circuits without the need for a separate sintering step.

As described in a paper in ACS Nano, the researchers' 'self-sintering' dispersion is composed of electrosterically stabilized silver nanoparticles together with a low concentration of a destabilizer. Sintering is triggered by changes in the concentration of chloride ions and is accomplished once the dispersion has dried on a substrate. The sintering agent, Magdassi states, can be a simple electrolyte such as sodium chloride, which destabilizes the silver nanoparticles and causes them to come into close contact with one another. The chloride ions replace and detach the anchoring groups of the polymeric stabilizer from the nanoparticles' surface, enabling their coalescence and sintering, Magdassi tells Nanowerk.

The stability of the silver dispersion at a low sodium chloride concentration of <50 mM has enabled the team to test its technology as a conductive inkjet ink that self-sinters at room temperature as water in the dispersion evaporates. Since this technique does not require that printed electronic patterns be heated to elevated temperatures, it opens the door to the formation of conductive patterns on sensitive substrates such as plastic and paper, Magdassi notes.