Design of Residual Stress-Balanced Transferable Encapsulation Platform Using Urethane-Based Polymer Superstrate for Reliable Wearable Electronics.

Abstract

Wearable and skin-mounted electronics demand encapsulation designs that simultaneously provide strong barrier performance, mechanical reliability, and transferability under ultrathin conditions. In this study, a residual stress-balanced transferable encapsulation platform was developed by integrating a urethane-based copolymer superstrate [p(IEM-co-HEMA)] with inorganic thin films. The polymer, deposited via initiated chemical vapor deposition (iCVD), offered over 90% optical transmittance, low RMS roughness (1-3 nm), and excellent solvent resistance, providing a stable base for inorganic barrier integration. An ALD Al₂O₃/ZnO nano-stratified barrier initially delivered effective moisture blocking, but tensile stress accumulation imposed a critical thickness of 30 nm, where the WVTR plateaued at ~2.5 × 10^-4 g/m²/day. To overcome this limitation, a 40 nm e-beam SiO₂ capping layer was added, introducing compressive stress via atomic peening and stabilizing Al₂O₃ interfaces through Si-O-Al bonding. This stress-balanced design doubled the critical thickness to 60 nm and reduced the WVTR to 3.75 × 10^-5 g/m²/day, representing an order-of-magnitude improvement. OLEDs fabricated on this ultrathin platform preserved J-V-L characteristics and efficiency (~4.5-5.0 cd/A) after water-assisted transfer and on-skin deformation, while maintaining LT80 lifetimes of 140-190 h at 400 cd/m² and stable emission for over 20 days in ambient storage. These results demonstrate that the stress-balanced encapsulation platform provides a practical route to meet the durability and reliability requirements of next-generation wearable optoelectronic devices.