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New Stretchy Electronics

Over the past few years, material scientists and electronics engineers have been working together to develop new and innovative materials that can create stretchable and high-performing electronic devices. These devices can be based on different designs such as rigid-island active cells with serpentine-shape/fractal interconnections, neutral mechanical planes, or bunked structures.

Despite the significant advancements in the fabrication of stretchable materials, some challenges have proved difficult to overcome. For instance, materials with wavy or serpentine interconnect designs commonly have a limited area density, and fabricating proposed stretchable materials is often both difficult and expensive. In addition, the stiffness of many existing stretchable materials does not match that of human skin tissue, making them uncomfortable on the skin and thus not ideal for creating wearable technologies.

In order to address these challenges, researchers at Sungkyunkwan University (SKKU), Institute for Basic Science (IBS), Seoul National University (SNU), and Korea Advanced Institute of Science and Technology (KAIST) have recently fabricated a vacuum-deposited elastic polymer for developing stretchable electronics. This new material, introduced in Nature Electronics, could be used to create stretchy field-effect transistors (FETs), which are primary components of most electronic devices on the market today.

“Recently, various approaches for adopting soft materials have been proposed for developing intrinsically stretchable electronics which does not need any specific structural designs owing to their intrinsic deformability,” said Donghee Son, one of the researchers who carried out the study. “However, such devices employed solution-processed dielectric materials and thereby encounter critical challenges in achieving high electrical performances.”

Solution-processed organic gate dielectric materials, materials that can transmit electricity without conducting it (i.e., insulating it), are not particularly suitable for the creation of flexible electronics. Most notably, they have thicknesses in the micrometer-scale, poor insulating performances, chemical instability, and low uniformity. In addition, they are typically incompatible with conventional microfabrication processes, making them difficult to produce on a large scale.

As a result of these limitations, electronic components based on these solution-processed materials are plagued by poor gate controllability and high operation voltages, as well as limited scalability. Son and his colleagues, along with other research teams worldwide, have thus been trying to create ultrathin, stretchable, scalable, and highly performing dielectrics with alternative fabrication strategies.

“In our study, we present a new approach to the design of dielectric materials to resolve the aforementioned challenges in intrinsically stretchable electronic devices,” Son explained. “Our large-scale vacuum-deposited stretchable dielectric enables the scalable fabrication of intrinsically stretchable devices with electrical performances comparable to those fabricated using the non-stretchable inorganic and stretchable organic dielectric materials (e.g., Al2O3 deposited via atomic layer deposition & spin-coated viscoelastic layer).”

To create their polymer-based dielectric, Son and his colleagues first copolymerized two different monomers, namely isononyl acrylate (INA) and 1,3,5-trimethyl-1,3,5-tryvinyl cyclotrisiloxane (V3D3) using a process known as initiated chemical vapor deposition (iCVD). The monomer INA acts as a soft segment, increasing the material’s stretchability, while V3D3 serves as a cross-linkable hard segment, giving the polymer film robust insulating properties.