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

TL;DR

This paper introduces a new encapsulation design for wearable electronics that improves durability and reliability by balancing residual stress using a urethane-based polymer and inorganic layers.

Contribution

The novel contribution is a stress-balanced encapsulation platform using p(IEM-co-HEMA) and SiO2 to enhance barrier performance and mechanical reliability in ultrathin wearable devices.

Findings

The WVTR was reduced to 3.75 × 10−5 g/m2/day with a stress-balanced design, an order-of-magnitude improvement.

OLEDs on the platform maintained efficiency and stable emission for over 20 days in ambient storage.

The platform achieved LT80 lifetimes of 140–190 h at 400 cd/m2 after water-assisted transfer and on-skin deformation.

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.

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