Low leakage current through zirconium oxide gate fabricated by low temperature solution process in OTFTs on plastic substrate

Abstract

Abstract Zirconium oxide (ZrOx) sol-gel solutions have been used as a high dielectric material for the low voltage operation of organic TFTs (OTFTs). However, ZrOx has disadvantages, including a large off-state current greater than 100 pA and a high annealing temperature above 400 °C, which must be resolved before it can be applied to flexible electronics. In this study, a multiple spin-coating process was used to increase the thickness of the ZrOx gate dielectric layer and reduce the large off-state current. The large off-state current of pentacene TFTs was decreased to 1 pA by a ZrOx gate thickness of 70 nm. Notably, the process was performed at a low temperature of 300 °C and thus was applicable to poly carbonate plastic substrates. In addition, low voltage operation (Ion = 6.4 μA at VGS = −5 V) was also achieved with the thick gate of 70 nm. The mobility was in the range of 0.32–0.43 cm2/V s. An unusual positive off-state current region appeared in the transfer characteristics, likely due to acceptor-like states generated at the interface between a pre-deposited and additional ZrOx layer, spin-coated during the multiple coating process.