Reducing the contact resistance of bottom-contact pentacene thin-film transistors by employing a MoO_x carrier injection layer

We report on the reduced contact resistance in bottom-contact (BC) pentacene thin-film transistors (TFTs) with a molybdenum oxide (MoO_x) carrier injection layer. MoO_x layers were placed between the gate insulator and the source-drain (S-D) electrodes instead of the conventional adhesive layer such as Cr or Ti. The performance of the BC pentacene-TFT with the MoO_x injection layer was significantly improved at low operating voltages. The contact resistance of the MoO_x/Au S-D electrodes, estimated using the gated-transmission line method, was nearly two orders of magnitude smaller than that of conventional Cr/Au electrodes at the gate voltage of -10 V. The highest performance was obtained with a MoO_x injection layer a few nanometers thick, which was comparable to the effective channel thickness of the pentacene-TFT on the gate insulator. This result indicated the importance of the direct connection between the MoO_x injection layer and the effective channel to reduce the contact resistance.