A highly bendable thin film encapsulation by the modulation of thermally induced interfacial residual stress

Abstract

Thin film encapsulation (TFE) is an essential component for reliable operation of organic electronic devices. However, the brittleness of inorganic layer in TFE must be resolved to secure the long-term stability of flexible/bendable devices. In this study, the robustness of the TFE in mechanical deformation is improved by harnessing such an interfacial residual stress. During fabrication of TFE by the alternating deposition of the organic layer via initiated chemical vapor deposition (iCVD) and inorganic Al2O3 via atomic layer deposition (ALD), the lower process temperature of iCVD (30 ℃) than that of ALD (90 ℃) generates a residual stress at the organic/inorganic interface, which was optimized by controlling the organic layer thickness, coefficient of thermal expansion (CTE), and elastic modulus. In order to optimize the residual stress, a new type of copolymer layer was suggested in TFE, synthesized from cyclohexyl acrylate (CHA) and 1,3,5-trimethyl-1,3,5-trivinylcyclosiloxane (V3D3) monomers. The water vapor transmission rate (WVTR) of the fabricated TFE was 3.1 × 10-5 g/m2·day, which was fully retained by optimized residual stress after 1000 times of bending cycles with the bending radius of 2.3 R, corresponding to the tensile strain exceeding 1.09%.