Printed Electronics as Prepared by Inkjet Printing

Abstract

Inkjet printing has been used to produce a range of printed electronic devices, such as solar panels, sensors, and transistors. This article discusses inkjet printing and its employment in the field of printed electronics. First, printing as a field is introduced before focusing on inkjet printing. The materials that can be employed as inks are then introduced, leading to an overview of wetting, which explains the influences that determine print morphology. The article considers how the printing parameters can affect device performance and how one can account for these influences. The article concludes with a discussion on adhesion. The aim is to illustrate that the factors chosen in the fabrication process, such as dot spacing and sintering conditions, will influence the performance of the device.

Keywords: adhesion; droplet behavior; electrical conductivity; ink; inkjet printing; laser sintering; printed electronics.

Figure 1

Illustration of the three printing techniques. (a) represents the positive contact printing similar to stamping, (b) represents the negative contact printing similar to screen printing, and (c) represents non-contact printing similar to inkjet printing, where ink is ejected from a nozzle.

Figure 2

(a) Picture of a sessile drop in equilibrium on a polymer substrate. (b) Representation of the interfacial forces acting on a droplet on a substrate. The contact angle, θ, is less than 90°, indicating a partial wetting of the substrate.

Figure 3

Representation of the various scenarios which can occur when a droplet is deposited onto a dry solid surface, illustrating the possible wetting states.

Figure 4

Illustration of the different angles formed by a droplet on a substrate.

Figure 5

(a–e) Illustration showing the relationship between dot spacing and print morphology. Reprinted (adapted) with permission from [80]. Copyright (2019) American Chemical Society.

Figure 6

SEM of an inkjet-printed silver nanoparticle ink. The micrograph to the left represents the ink as printed, and the one to the right represents the ink after thermal sintering at 200 °C for 60 min.

Figure 7

A four-point probe technique for measuring the resistivity of a sample under load.

Figure 8

Comparison of the adhesion of particles on a rough surface and a smooth surface. The zoomed-in views show the formation of voids during the post–deposition processing, especially when the surface is rough.

Figure 9

Illustration of the three-step process for visually assessing the cross-cut test.

Figure 10

Schematic of the assembly for the pull-off test method.

Figure 11

Illustration of a simple bending test for printed electronics. One plate is kept stationary while the other slides along the graduated bed, the distance of which is according to the test radius. The encoder is used to automate the process.