Commercially applicable, solution-processed organic TFT and its backplane application in electrophoretic displays

Abstract

We report a video graphics array (VGA) electrophoretic display (EPD) that adopts commercially applicable process technologies for its solution-processed organic thin-film transistor (OTFT). For source/drain (S/D) engineering, a copper (Cu) electrode was employed instead of high-work-function materials and to obtain a low-resistance signal line on the array that is functionalized by self-assembled monolayer (SAM) treatment on the electrode surface. For gate engineering, a gate electrode with Cu was successfully formed onto the organic gate insulator (OGI) by using sputter deposition, thus providing an industrially suitable technology to replace evaporation processes even on frail organic material. Competitive device performance driving the electrophoretic display was obtained on a TFT derived from anthradithiophene that was fabricated at low temperatures of less than 140°C and that has the stable electrical feature of ΔVT of 3V for induced bias stress with a long time span. Up until now, electrode engineering using low-cost and low-work-function materials has been too problematic for practical use of OTFT backplanes, but we have successfully applied it to produce a 6-in. electrophoretic display based on a large substrate of 370×470mm2 for the backplane process. Thus, as far as mass production is concerned, the solution-processed organic transistor shows promise as a backplane unit with low-temperature processing.