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

摘要

Zirconium oxide (ZrO_x) sol-gel solutions have been used as a high dielectric material for the low voltage operation of organic TFTs (OTFTs). However, ZrO_x has disadvantages, including a large off-state current greater than 100 pA and a high annealing temperature above 400 ℃, 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 ZrO_x 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 ZrO_x gate thickness of 70 run. Notably, the process was performed at a low temperature of 300 ℃ and thus was applicable to poly carbonate plastic substrates. In addition, low voltage operation (I_(on) = 6.4 μA at V_(GS) = -5 V) was also achieved with the thick gate of 70 nm. The mobility was in the range of 0.32-0.43 cm~2/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 ZrO_x layer, spin-coated during the multiple coating process.