PDMS-metal oxide nanocomposites as transparent encapsulants for flexible electronic devices

Abstract

Encapsulation is integral to electronic devices for maintaining long-term functionality and stability. While a variety of materials and solutions are available for conventional silicon-based electronics, not all of them are suitable for flexible optoelectronic devices. Typically, these devices require materials with low processing temperature, while maintaining both the optical and electrical functionality. Simple deposition and low cost are added advantages. In this work, we show that pure polydimethylsiloxane (PDMS), and its composites with metal oxide nanoparticles such as zinc oxide (ZnO) and titanium dioxide (TiO2) are suitable encapsulants for flexible electronics. These coatings are electrically and thermally insulating, optically transparent (controllable by the amount of metal oxides), hydrophobic (contact angle 114∘), and offer good environmental protection. The coatings can be prepared by a simple spin coating process and annealed at temperatures less than 150 ∘C. The performance of pure PDMS and PDMS-metal oxides were evaluated using different characterisation techniques. These coatings were also tested on printed silver nanowire patterns and commercial flexible NFC (near field communication) tags. The addition of up to 2 wt.% ZnO and TiO2 nanoparticles was found to improve the properties of PDMS, improving the environmental protection (showing a Bode impedance of the order of 10-), without significantly affecting the optical transparency (73% transmittance).