High-Viscosity Copper Paste Patterning and Application to Thin-Film Transistors Using Electrohydrodynamic Jet Printing

Direct patterning of copper (Cu) electrodes through a noncontact electrohydrodynamic (EHD) jet printing process is developed to overcome the drawback of printing mechanisms such as high viscosity in inkjet printing. Printed Cu lines with a width of about 40 mu m are obtained from Cu paste with a viscosity of 4000 cPs using an additive. The effect of the operating parameters on jetting modes and printed patterns is investigated. The electrical property of the printed Cu layer shows a low resistivity of 8 x 10(-4) omega m after sintering under vacuum compared with air annealing. Solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs) with vacuum-annealed Cu source and drain (S/D) electrodes are fabricated with comparable characteristics, such as an average effective mobility in the saturation region (mu) of 0.50 cm(2) V-1 s(-1), an on-to-off current ratio (I-on/I-off) of 5.5 x 10(5), and a subthreshold slope (SS) of 3.35 V decade(-1). These results demonstrate the potential of EHD jet-printed Cu for application in electronic devices.