Plastic electronics has shown remarkable progress to realize future flexible-image devices. However, there are huge amount of issues to be solved as "nano-scale interface issues" in the plastic electronics, especially in transistor. The nano-scale interface issues are actually serious problems for the transistor operation delay and a future device miniaturization. For example, the interface resistance between the plastic channel and the metal contact dominates the transistor resistance in a short channel transistor, which cannot allow us to control the desirable current switching operation. To investigate these issues, we proposed and established a laser etching method to form a four-terminal device and directly showed gate-dependent contact resistance. Furthermore, an interface between the organic channel and substrate also affects the transistor performance. Controlling these nano-scale interfaces, we integrated a pixel of the organic transistor with the organic light emitting diode, and investigated detail of the operation properties for the future flexible desplay device.