E-Textile by Printing an All-through Penetrating Copper Complex Ink

Abstract

Wearable electronics is an emerging field in academics and industry, in which electronic devices, such as smartwatches and sensors, are printed or embedded within textiles. The electrical circuits in electronics textile (e-textile) should withstand many cycles of bending and stretching. Direct printing of conductive inks enables the patterning of electrical circuits; however, while using conventional nanoparticle-based inks, printing onto the fabric results in a thin layer of a conductor, which is not sufficiently robust and impairs the reliability required for practical applications. Here, we present a new process for fabricating robust stretchable e-textile using a thermodynamically stable, solution-based copper complex ink, which is capable of full penetrating the fabric. After printing on knitted stretchable fabrics, they were heated, and the complex underwent an intermolecular self-reduction reaction. The continuously formed metallic copper was used as a seed layer for electroless plating (EP) to form highly conductive circuits. It was found that the stretching direction has a significant role in resistivity. This new approach enables fabricating e-textiles with high stretchability and durability, as demonstrated for wearable gloves, toward printing functional e-textile.

Keywords: copper complex; copper ink; e-textile; printed electronics; wearable electronics.

Figure 1

Illustration of the process starting from (a) screen printing the copper complex ink onto the fabric, (b) heating to induce decomposition and self-reduction to form metallic copper, (c) electroless plating of copper to form dense copper coating along with the fabric of the printed path, and (d) conductive circuits on textile. (Credit: Ehsan Faridi).

Figure 2

SEM images of (a) bare fibers, (b) copper seeds on fibers, and (c) fibers after 1 h electroless plating.

Figure 3

Middle image: a printed copper seed on the fabric is placed on a mirror to show that both sides are coated. Left and right SEM images show copper particles coating the fibers on both the top and bottom sides of the fabric.

Figure 4

(a) Resistance change vs strain in both vertical and horizontal directions. (b) The fabric at 0% strain (top side), and (c) after 110% strain in the horizontal direction (Supporting Movie S1). (d) The fabric at 0% strain (bottom side), and (e) after 220% strain in the vertical direction (Supporting Movie S2).

Figure 5

(a) Normalized resistance change during cyclic 40% strain on V and H directions, (b) SEM image of the fibers before stretching, (c) SEM image of the fibers after 100 cycles in the V direction, and (d) SEM image of the fibers after 1000 cycles in the H direction.

Figure 6

(a) Electrical circuit design on a glove, (b) top view of the glove containing electrical components soldered to the copper circuit, and (c) closing hand for connecting points A and B to close the circuit and turn on light emitting diodes (LEDs).