Modeling and validation of mechanical stress in indium tin oxide layer integrated in highly flexible stacked thin films

• Flexible stress of indium tin oxide thin film in multi-stacked films is estimated.
• Nonlinear stress simulation methodology is validated by experimental data.
• Analytical solutions for bending stiffness and stress are derived.
• Better flexible structures are obtained using factorial designs.
• Small bending radius of 1 mm is achieved as polyimide plates are used.

Organic electronic devices with multi-stacked thin films based on polymeric substrates are proposed for use in mainstream flexible organic light-emitting diode displays. To achieve the above-mentioned requirements, indium tin oxide (ITO) thin film, a brittle, inorganic material, is necessary to be utilized as a transparent electrode in flexible electronics. The failure rate of ITO films is of concern when introducing harsh flexural load in terms of reliability. This study utilizes a simulation-based factorial-design approach to determine a suitable combination of mechanical characteristics of ITO film stacked with other films to reduce the neutral plane (NP) impact of stacked films. The results indicate that both Young's modulus and cover plate thickness are major factors that alter the stress magnitude of ITO films. Moreover, the simulated results for stacked structures reveal that the distance between the ITO film and NP is significantly reduced when polyimide materials, rather than steel metal, are used for the cover plate. In the meanwhile, ITO film stress drops in virtue of lower mechanical stiffness and lesser thickness direction between the NP and ITO films in a multi-stacked film structure.