Effects of the Ag content on the geometrical and electrical characteristics of the screen-printed etched gate electrodes of OTFTs using Ag ink

During the fabrication of gate electrodes by Ag ink screen-printing combined with a wet-etching process, the effects of the Ag content on the geometrical and electrical characteristics such as the thickness and surface roughness of gate electrode, step coverage with the gate dielectric, leakage current associated with the step coverage, and the electrical performance of organic thin film transistors (OTFTs) were investigated. An increase of Ag content resulted in the thick and densely-packed Ag electrode, which had a stable and excellent conductivity. But, the large thickness of Ag electrode caused the worse step coverage of PVP (polyvinylphenol) dielectric layer on the edge of the Ag gate electrode, therefore, for Ag contents more than 40 wt.%, MIM (metal–insulator–metal) devices and OTFTs with the Ag gate electrodes had very large leakage current (>10−4 A/cm2) and off-state current (>∼19 pA/μm) due to the poor step coverage of PVP dielectric layers, respectively. Finally, we found that an Ag content of 20–30 wt.% was suitable for the screen-printed etched gate electrode of OTFTs using Ag ink. This range generated a mobility of 0.18 cm2/V s, an on/off current of 5 × 106, and an off-state current of 0.002 pA/μm, which are suitable to drive e-paper.