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 μm 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 × 10 −4 Ωm 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 ( μ ) of 0.50 cm 2 V −1 s −1 , an on‐to‐off current ratio ( I on /I off ) of 5.5 × 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.