Origin of large contact resistance in organic field-effect transistors

Abstract

The large contact resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ) 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> of below 0.1 KΩ cm was successfully achieved in the top-gate OFETs. A field-effect mobility (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FET</sub> ) of 8.3 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V s and near zero threshold voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) were obtained in top-gate devices based on dioctylbenzothienobenzothiophene (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sub> -BTBT).