Oligomer semiconductor/dielectric interface modification for organic thin film transistor hysteresis reduction

Abstract

In this work, we investigate the hydroxyl group effect on hysteresis of the low voltage organic thin film transistor (OTFT). A high k material, hafnium oxide, is utilized as gate dielectric to reduce OTFT operational voltage. By using the hydroxyl-free polymer, polystyrene, the hydroxyl groups on hafnium oxide surface will be shielded. The modification at semiconductor/dielectric interface prevents accumulated charges from trapping in surface states. Such a polymer coverage layer reduces hysteresis and suppresses the off current as low as 10 − 11 A. The interface traps resulted from ambient water absorption significantly decrease according to the hysteresis cancellation. By stacking polystyrene on hafnium oxide, the pentacene-based OTFT shows the threshold voltage of − 2.2 V, on/off current ratio of 10 5, subthreshold swing of 0.34 V/dec, and mobility of 0.24 cm 2/V s under operational voltage of 10 V.