Understanding the dependence of the ohmic drain-source leakage current on gold deposition rate in top-contact pentacene-based thin film transistors

• The influence of the gold deposition rate on the drain-source leakage current in top-contact pentacene-based thin film transistors (TFTs) with different channel lengths was studied.
• For TFTs with channel length of 30 μm, the pentacene grain size influences the leakage current only in the case if high gold deposition rate is employed.
• A physical model has been used to clarify the observed ohmic behavior of the anomalous leakage current, and also provides an explanation for the dependence of the leakage current on the gold deposition rate.

We studied the influence of the gold deposition rate on the drain-source leakage current of top-contact pentacene-based thin film transistors (TFTs) with different channel lengths. It is demonstrated that the anomalous leakage current which occurs only in short-channel TFTs monotonically increases with increasing the gold deposition rate. For TFTs with channel length of 30 μm, we also investigated the dependence of the drain-source leakage current on the pentacene grain size as well as the gold deposition rate. It is shown that the pentacene grain size influences the leakage current only in the case if high gold deposition rate is employed, whereas the anomalous leakage current can be avoided by reducing the gold deposition rate. Finally, due to the observed ohmic character of the anomalous leakage current, we propose that the origin of the current can be attributed to parasitic leakage paths on the surface of the pentacene layers formed by the lateral diffusion of gold clusters from drain/source edges into the channel region during gold deposition. Based on this hypothesis, the observed dependence of the anomalous leakage current on the gold deposition rate can be well explained.

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