Direct observation of contact and channel resistance in pentacene four-terminal thin-film transistor patterned by laser ablation method

We established a dry-etching patterning process for the channel formation of pentacene thin-film transistor, and fabricated a four-terminal device equipped with a gate electrode. The four-terminal device enabled us to divide two-terminal source–drain resistance into two components of contact resistance and pentacene channel resistance. We obtained direct evidence of a gate-voltagedependent contact resistance change: the gate-induced charge significantly reduced the contact resistance and increased source–drain current. Furthermore, the temperature dependence of the device clearly indicated that the contact resistance was much higher than the channel resistance and was dominated in the two-terminal total resistance of the device below 120 K. An observed activation energy of 80 meV for contact resistance was higher than that of 42 meV for pentacene channel resistance.