Thin film transistor remains operational upon stretching

January 09, 2017 // By Julien Happich
Publishing the paper "Highly stretchable polymer semiconductor films through the nanoconfinement effect" in the journal Science, an international team of researchers has demonstrated not only flexible but also stretchable transistors made out of a blend of semiconducting polymer DPP-TT within elastomeric polymer SEBS (Styrene Ethylene Butylene Styrene).

The researchers found that by confining small packets of semiconducting polymer within a matrix of elastomer, the nanoconfinement substantially improved the stretchability of the semiconducting polymer, without affecting charge transport mobility.

"The increased polymer chain dynamics under nanoconfinement significantly reduces the modulus of the conjugated polymer and largely delays the onset of crack formation under strain. As a result, our fabricated semiconducting film can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon", they wrote. One explanation put forward is that confinement can prevent crystallization and sometimes give the chains more scope for motion.

The stretchy thin-film transistors they devised using a room-temperature printer were tested to their limits upon bending and stretching. When stretched to twice their length, the transistors only exhibited a relatively small drop in conductivity, from 0.59 cm 2/Vs on average, to just 0.55 cm 2/Vs and cracks did not develop in the polymers even after bending 100 times.

Among the authors of the paper is a researcher at South Korean display manufacturer Samsung which may well be interested in leveraging these finding for novel wearable applications.

A transparent and flexible LED driver worn on a finger, the LED is on the adjacent finger. Credit: J. Xu et al., Science (2016)

In a video, the researchers show the transistors being flexed, stretched and even poked with a sharp object. They also demonstrate a transparent skin-like finger-wearable circuit that remains operational upon finger flexure, driving a light-emitting diode worn on an adjacent finger.