Material scientists and electronics engineers have been attempting to generate new flexible inorganic materials in order to construct stretchy and high-performance electronic devices for many years. These devices may be built in a variety of ways, including rigid-island active cells with serpentine-shape/fractal linkages, neutral mechanical planes, and bunked structures.
Despite substantial progress in the production of stretchy materials, several obstacles have proven difficult to overcome. Materials having wavy or serpentine connecting patterns, for example, often have a restricted area density, and producing suggested stretchy materials is frequently both difficult and costly. Moreover, the stiffness of many current stretchy materials differs from that of human skin tissue, making them unpleasant to wear and hence unsuitable for developing wearable devices.
Sungkyunkwan University (SKKU), the Institute for Basic Science (IBS), Seoul National University (SNU), and the Korea Advanced Institute of Science and Technology (KAIST) have created a vacuum-deposited elastic polymer for the development of stretchy electronics. This material, described in Nature Electronics, might be used to make stretchable field-effect transistors (FETs), which are key components in the majority of electronic products on the market today.
“Recently, numerous ways for using soft materials have been presented for constructing intrinsically stretchy electronics that do not need any special structural designs due to their inherent deformability,” Donghee Son, one of the study’s authors, told Tech Xplore. “Unfortunately, such devices used solution-processed dielectric materials, posing key obstacles in obtaining good electrical performances.”
Organic gate dielectric materials, which may transport electricity without conducting it (i.e., insulating it), are not well suited for the fabrication of flexible electronics. They exhibit micrometer-scale thicknesses, weak insulating properties, chemical instability, and poor homogeneity. Moreover, they are often incompatible with normal microfabrication procedures, making large-scale production challenging.
Because of these constraints, electronic components based on these solution-processed materials suffer from poor gate controllability, high operating voltages, and restricted scalability. Son and his colleagues, as well as other research teams across the globe, have therefore attempted to build ultrathin, stretchy, scalable, and highly performing dielectrics using various manufacturing processes.
“In this work, we provide a novel method to dielectric material design to address the aforementioned issues in inherently stretchable electrical devices,” Son added. “Our large-scale vacuum-deposited stretchable dielectric enables the scalable fabrication of intrinsically stretchable devices with electrical performances comparable to those fabricated using non-stretchable inorganic and stretchable organic dielectric materials (e.g., Al2O3 deposited via atomic layer deposition & spin-coated viscoelastic layer,” the researchers write.
Son and his colleagues used started chemical vapour deposition to copolymerize two distinct monomers, isononyl acrylate (INA) and 1,3,5-trimethyl-1,3,5-tryvinyl cyclotrisiloxane (V3D3), to construct their polymer-based dielectric (iCVD). The monomer INA functions as a soft segment, boosting the material’s stretchability, while V3D3 functions as a cross-linkable hard segment, providing the polymer film with strong insulating characteristics.
“The monomer mixing ratio (INA and V3D3) was tuned to accomplish both insulating and stretching performance of the device,” Son said. “Our vacuum-deposited polymer dielectric with a dielectric constant of 3.59 and a breakdown field of 2.3 MV/cm demonstrated the lowest equivalent oxide thickness (EOT) value among the stretchy dielectric layers reported to date.”
To illustrate the material’s potential, the researchers utilised it to make transistors, which were then used to make stretchable inverters and logic gates. These components performed well in preliminary testing.
They could be stretched up to 40% strain while maintaining their insulating function, in addition to having a high dielectric constant and a low EOT value. The researchers also discovered that their material has good chemical and thermal resilience throughout microfabrication operations and is very homogenous over broad regions.
“This is the first report of a vacuum-deposited stretchable dielectric, as well as its application to inherently stretchy electrical devices,” Son added. “In other words, as compared to traditional thick polymer dielectrics, a stretchy vacuum-deposited nanometer-thick layer (around 160 nm) exhibits superior electrical, mechanical, and chemical capabilities. Our vacuum-deposited methodology’s remarkable benefits might aid in the creation of high-performance wafer-scalable wearable devices. The findings of our research would change the current paradigm of soft electronics.”
In the future, the team’s material might be used to create new inherently stretchable and high-performance transistors and logic circuits that use less electricity. These transistors and circuits have the potential to be utilised to produce a wide range of soft electronics, including wearable and implantable devices.
“I believe the most critical difficulty in the long-term development of trustworthy wearables will be attaining an energy-efficient performance in stretchy electronic devices,” Son stated. “As a result, the thickness of vacuum-deposited insulating layers should become thinner in order to increase gate controllability while retaining stretchability. Additionally, its dielectric constant would be increased to beyond 10, making it equivalent to high-k inorganic dielectrics.”
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