Conductive lines on flexible polymer substrates fabricated by inkjet printing of metal salts solution

Abstract

Recently, printed electronics has attracted lots of attentions because it is a simple processof making a desired conductive pattern on various substrates. In this research, the metal salt was selected as conductive ink because problems of porosity and non-uniform surface on conductive printed pattern can be avoid. The methods to fabricate metal conductive patterns including reactive inkjet printing, reactive sintering and electroless copper plating were investigated. In reactive inkjet printing, the silver line was synthesized by sequentially printing reducing agent and silver nitrate solution. The lowest resistivity of silver line obtained by using 5 M of silver nitrate solution and 15 printing cycles was 4.62×10-4 Ω cm. Alternatively, continuous and smooth patterns of silver lines were fabricated by the reactive sintering process of formic acid vapor and ethylene glycol vapor. The resistivity of the silver line obtained by formic acid vapor reduction at 150ºC for 120 min was 1.86×10-4 Ω cm. The resistivity of the silver line obtained by ethylene glycol vapor reduction at 250ºC for 30 min was 1.20×10-4 Ω cm. As compared to reactive inkjet printing, the reactive sintering process gives more smooth and continuous pattern resulting in lower resistivity. Additionally, the copper line was prepared by electroless copper plating on silver seed layer at room temperature. The resistivity of copper line obtained by electroless plating for 15 min was 1.92×10-5 Ω cm.