Stretchy transistors suitable for wearable electronics

To date, it has been difficult to design a transistor using inherently stretchable materials that maintains its conductivity upon being stretched. Now, US researchers have created a stretchy transistor that can be elongated to twice its length with only minimal changes in its conductivity.

Writing in the journal Science, Stanford University researcher Jie Xu and his colleagues noted, “Soft and conformable wearable electronics require stretchable semiconductors, but existing ones typically sacrifice charge transport mobility to achieve stretchability. We explore a concept based on the nanoconfinement of polymers to substantially improve the stretchability of polymer semiconductors, without affecting charge transport mobility.”

The team devised a scalable way to confine organic conductors inside a rubbery polymer to create stretchy transistors — they took a semiconducting polymer, called DPPT-TT, and confined it inside another polymer, SEBS, which has elastic properties. As the two polymers don’t like to mix with each other, the DPPT-TT forms thin bundles within the SEBS matrix.

Testing and analysis of this new combination revealed that it works as an effective transistor, even as it is repeatedly stretched up to 100% of its length. While the material demonstrated a normal conductivity of 0.59 cm²/Vs on average, this dropped only slightly to 0.55 cm²/Vs when being stretched to twice its length.

The researchers also demonstrated the potential for the transistors to be used in wearable electronics, fabricating a flexible material that retained its conductive properties when heavily stretched along the surface of a bending finger. Furthermore, they did not observe any visible cracks in the film after 100 cycles of being stretched.