A universal strategy to improve the mechanical stability of flexible organic thin film transistors†
In flexible electronic systems, mechanical deformation is a key factor that impacts the mechanical stability of flexible devices. In this work, for the first time, a mathematical analysis model was introduced to precisely calculate the position of the bending axis (the strains are zero) in a flexible organic thin film transistor (OTFT) system, which is also broadly applicable for flexible electronic systems. Based on this mathematical analysis model, a universal method was proposed to precisely move the bending axis to different positions in a flexible OTFT by simply adjusting the thickness of the passivation layer. Moreover, the results firstly demonstrated that the flexible OTFT exhibited the best mechanical stability and electrical performance when the bending axis was located at the gate dielectric/semiconductor charge channel interface, as the charge transport was mainly at the charge channel interface, and moving the bending axis to the gate dielectric/semiconductor interface would minimize the impact of mechanical deformation on the charge transport. More importantly, this work definitely demonstrated the importance of the passivation layer, which could not only prevent the damage caused by water and oxygen in the air to flexible devices, but could also tune the position of the bending axis and improve the mechanical stability of flexible devices without sacrificing the electrical performance or increasing the complexity of the fabrication process. Furthermore, this method is also applicable to other flexible electronic systems and has great potential to fabricate flexible electronics with excellent mechanical properties and environmental durability.