Bending Performance of Flexible Organic Thin-Film Transistors With/Without Encapsulation Layer

Flexible pentacene-based organic thin-film transistors (TFTs) were fabricated and their performance was investigated as a function of the bending radius and the thickness of the polydimethylsiloxane (PDMS) encapsulation layer. The TFTs were fabricated on a flexible polyimide film (film thickness: 75 $\mu \text{m}$ ), and encapsulated by a PDMS layer. Degradation of the device performance during application of a tensile bending stress of 3 mm was minimized by utilizing an encapsulation layer thickness of 75 $\mu \text{m}$ , because the mechanical strain on the pentacene layer was almost off-set (tensile strain was applied to the bottom layer of the pentacene, and compressive strain was applied to the top layer of pentacene). At the tensile bending stress of 3 mm, the performance of the non-encapsulated TFT was degraded, whereas the encapsulated device showed great stability. This flexibility and bending stability were enabled by the use of the 75- $\mu \text{m}$ PDMS encapsulation layer, due to the location of the pentacene active layer in the neutral region position. A mechanical reliability test was performed for 120 min with a bending radius of 3 mm, demonstrating that only the device with the 75- $\mu \text{m}$ thick encapsulation layer showed stable device performance over a stress time of 120 min.