High Performance OTFTs with CNT/Metal Hybrid Electrodes and Their Application to Amoled Panel

Abstract

The contact resistance is an important factor to significantly affect performance of organic thin film transistors (OTFTs). In this paper, a new carbon nanotube (CNT) based hybrid electrodes are introduced for a low contact resistance of source and drain electrodes of OTFTs. The hybrid electrodes consist of the solution-processed CNTs and a metal (Al; CNT/Al or Au; CNT/Au) evaporated on the CNTs. The contact resistance of CNT/Al and CNT/Au hybrid electrodes was varied depending upon the thickness of Al and Au, as shown in Fig.1. For CNT/Al hybrid electrodes, the contact resistance exhibited the minimum of 2.9 KW∙cm (VGS = -30 V) at the Al thickness of 5 nm, which was smaller than 13 KW∙cm of the bare CNT electrodes and tremendously smaller than 4 MW∙cm of Au electrode. It was noticeable that the minimum contact resistance of CNT/Au was 0.9 KW∙cm at the Au thickness of 5 nm which was the lowest value ever reported. The mobility of OTFTs, which used pentacene as the semiconductor and polyvinylphenol as the gate dielectric, also followed the same metal thickness dependence as the contact resistance. The maximum mobility of OTFTs using CNT/Al and CNT/Au electrodes was 0.78 cm2/V∙sec and 1.0 cm2/V∙sec, respectively, at the same thickness of 5 nm, which was larger than 0.3 cm2/V∙sec of the bare CNT electrodes. A major origin of such enhancements was identified to be the smallest energy difference, which was obtained at the metal thickness of 5 nm, between the work function of the CNT/metal hybrid electrodes and pentacene HOMO (5.1 eV). The CNT/Au electrodes were applied to OTFTs in AMOLED panel. The AMOLED panel consisted of 64 x 64 pixels where each pixel was composed of 2 OTFTs (switching and driving OTFT), 1 capacitor, and 1 OLED. A shown in Fig.2, the AMOLED panel successfully worked to display some patterns. Figure 1