Inkjet Printing of Polyacrylic Acid-Coated Silver Nanoparticle Ink onto Paper with Sub-100 Micron Pixel Size

Abstract

Printed electronics (PE) technology shows huge promise for the realisation of low-cost and flexible electronics, with the ability to pattern heat- or pressure-sensitive materials. In future developments of the PE market, the ability to produce highly conductive, high-resolution patterns using low-cost and roll-to-roll processes, such as inkjet printing, is a critical technology component for the fabrication of printed electronics and displays. Here, we demonstrate inkjet printing of polyacrylic acid (PAA) capped silver nanoparticle dispersions onto paper for high-conductivity electronic interconnects. We characterise the resulting print quality, feature geometry and electrical performance of inkjet patterned features and demonstrate the high-resolution printing, sub-100 micron feature size, of silver nanoparticle materials onto flexible paper substrate. Printed onto photo-paper, these materials then undergo chemically triggered sintering on exposure to chloride contained in the paper. We investigated the effect of substrate temperature on the properties of printed silver material from room temperature to 50 °C. At room temperature, the resistivity of single layer printed features, of average thickness of 500 nm and width 85 µm, was found to be 2.17 × 10^-7 Ω·m or 13 times resistivity of bulk silver (RBS). The resistivity initially decreased with an increase in material thickness, when achieved by overprinting successive layers or by decreasing print pitch, and a resistivity of around 10 times RBS was observed after overprinting two times at pitch 75 µm and with single pass print pitch of between 60 and 80 µm, resulting in line thickness up to 920 nm. On further increases in thickness the resistivity increased and reached 27 times RBS at print pitch of 15 µm. On moderate heating of the substrate to 50 °C, more compact silver nanoparticle films were formed, reducing thickness to 200 nm from a single pass print, and lower material resistivity approaching five times RBS was achieved.

Keywords: conductive inks; inkjet printing; low-temperature sintering; printed electronics; silver nanoparticles.

Figure 1

(a) TEM image of the solid AgNPs and (b) nanoparticle size distribution.

Figure 2

Optical images of the printed (a) dot arrays, (b) lines at 65 µm print pitch and (c) pads on photo paper with a nozzle diameter 50 µm.

Figure 3

Optical images of (a) printed 2D circuit patterns and pads alongside ruler scale for reference and (b) University of East Anglia logo printed with feature size 85 µm and dot spacing 65 µm with a nozzle diameter 50 µm.

Figure 4

Results from room-temperature printed lines on glossy paper with a 50 µm nozzle diameter (a) Effect of print pitch on line width and resistance and (b) the effect of print pitch on line thickness and resistivity shown relative to resistivity of bulk silver (RBS).

Figure 5

Optical micrograph images showing variation of line width of room-temperature printed lines on photo paper from a 50 µm nozzle by (a) increasing pitch of single pass print from 80 µm to 40 µm and (b) overprinting of layers up to five times at pitch 65 µm.

Figure 6

Properties of room-temperature overprinted features on photo paper from a 50 µm nozzle at 65 µm and 75 µm print pitch, showing the dependence of (a) line width and resistance on number of printed layers and (b) line thickness and resistivity on number of printed layers.

Figure 7

Effect of substrate temperature on (a) line width and resistance and (b) line thickness with varying print pitch.

Figure 8

Effect of substrate temperature on (a) line resistivity with varying dot spacing and (b) line resistivity with number of layers printed.