Origin of large contact resistance in organic field-effect transistors

The large contact resistance (R
_c
) in organic field-effect transistors (OFET) is one of the main limitation factors which prevent the reliable operation and further reduction in device dimensions. In this paper, we report dependence of the R
_c
on the gate dielectric materials, which means that the density of charge traps in access region (from contact to channel) of devices plays a primary role for the large R
_c
rather than energy mismatch between Fermi level of the metal electrode and valence band level of an organic semiconductor. Based on the finding, we fabricated top-gate OFET devices, the structure of which minimizes access region resistance. Very low R
_c
of below 0.1 KΩ cm was successfully achieved in the top-gate OFETs. A field-effect mobility (μ
_FET
) of 8.3 cm
²
/V s and near zero threshold voltage (V
_T
) were obtained in top-gate devices based on dioctylbenzothienobenzothiophene (C
₈
-BTBT).