Reliability of thin films: Experimental study on mechanical and thermal behavior of indium tin oxide and poly(3,4-ethylenedioxythiophene)

• An extensive reliability study is performed on the ITO and PEDOT films.
• PEDOT performance is better than ITO under cyclic bending condition.
• Under the cyclic bending, no cracks or deformation were found on the surface for PEDOT film. However, the cracks begun to appear in the center of ITO sample where the stress is highly concentrated then propagated toward the ends of samples.
• Both films are very sensitive to the combination of high temperature and humidity.

In order to improve the performance of various flexible electronic devices, the research on the transparent conductive thin films becomes very intensive in the recent years. In this work, we studied mechanical and thermal behaviors of two types of transparent conductive thin films, Poly(3,4-ethylenedioxythiophene) (PEDOT) as an example on polymer conductive thin film, and indium tin oxide (ITO) as an example on transparent conductive oxide thin film. Both films are deposited on polyethyleneterephthalate (PET) substrate. Two sheet resistances for PEDOT (i.e., 150 Ω/sq and 225 Ω/sq) and one sheet resistance for ITO (i.e., 60 Ω/sq) were involved in the study. PEDOT showed good mechanical properties with a small electrical resistance change and no clear cracks or deformation on the film surface under the condition of cyclic bending. However, the resistance of ITO significantly increased with the cyclic bending and cracks were seen initiated in the center of sample and propagated toward the edges. Further, design of experiment approach was used to study the effect of different cyclic bending parameters, such as bending diameter and frequency. Additionally, damp heat experiment on similar samples was conducted by applying 85 °C temperatures and 85% relative humidity on them for 1000 h. The electrical resistance was dramatically increased for both films. Scanning electronic microscopy (SIM), Energy Dispersive Spectrometry (EDX) and transmission tests were also used to determine the change of films’ compositions and transparencies.