Electrical conductivity enhancement in inkjet-printed narrow lines through gradual heating

Conductive silver lines of various widths (0.04-40 mm) were fabricated with dilute silver-nanoparticle ink on polyimide films using an inkjet printer. The electrical properties of the lines were found to vary in width. In particular, wider lines (>0.4 mm) exhibited low resistivity (3.6-5.4 mu Omega cm), approaching that of bulk silver (1.6 mu Omega cm). On the other hand, narrower lines (<0.3 mm) exhibited much higher resistivity (14.6-16.5 mu Omega cm), presumably because of the so-called coffee-ring effect. This effect, known to strongly influence nanoparticle deposition, is caused by convection flow, during which nanoparticles segregate at the line edge. However, when the narrower lines were heated slowly from 20 degrees C to 200 degrees C at a heating rate of 3 degrees C min(-1) to reduce convection flow, the nanoparticles redistributed uniformly, after which the lines exhibited low resistivity (3.9-4.2 mu Omega cm). Therefore, gradual heating appears to be an excellent method for enabling inkjet printing technology to yield narrow highly conductive lines.