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 similar to 2.5 x 10(-4) g/m(2)/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 x 10(-5) g/m(2)/day, representing an order-of-magnitude improvement. OLEDs fabricated on this ultrathin platform preserved J-V-L characteristics and efficiency (similar to 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/m(2) 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.