Flexible electrophoretic display driven by solution-processed organic TFT with highly stable bending feature

Abstract

A highly reliable solution-processed organic thin film transistor (OTFT) and its backplane are fabricated for a flexible electrophoretic display (EPD) on a plastic substrate. The all-solution-processed OTFT with an anthradithiophene derivative exhibits excellent bendability for an extreme cyclic bending stress of 100,000 cycles with a radius of 4mm without a significant change in its electrical properties. Process technology using an industrially suitable Cu electrode has also been developed to replace the high work-function material as well as to obtain a low-resistance signal line in the OTFT array. The present TFT exhibits a highly stable threshold-voltage shift (ΔVT) of less than 2V under long-span bias stress exposure with competitive performance to serve as a switching device in an EPD, even if it was fabricated at a low temperature of less than 140°C. An ultra-thin flexible OTFT backplane with Cu electrodes has been successfully achieved via plastic processing technology by releasing a polyimide (PI) substrate from glass without degradation in device performance, which demonstrates a commercially suitable handling process of the thin plastic for flexible device applications. Finally, we demonstrate a 3.5-inch flexible EPD with good bendability, which indicates the great potential of solution-processed organic TFTs as a promising element of flexible electronics as well as a backplane unit from the viewpoint of commercialization.