Patrick J. Smith

Inkjet printing as a deposition and patterning tool for polymers and inorganic particles

Inkjet printing is an attractive patterning technology, which has become increasingly accepted for a variety of industrial and scientific applications. This review primarily presents an overview of the investigations that have been conducted since 2003 into inkjet-printing polymers or metal-containing inks and mentions related activities. The first section discusses the droplet-formation process in piezoelectric drop-on-demand printheads and the physical properties that affect droplet formation and the resolution of inkjet-printed features. The second section deals with the issues that arise from printing polymers, such as printability and the output characteristics of devices made by this route. Finally, the challenges and achievements attached to inkjet printing metal-containing inks are discussed before concluding with a few remarks about the future of the field.

Printed electronics: the challenges involved in printing devices, interconnects, and contacts based on inorganic materials

Printed electronics represent an emerging area of research that promises large markets due to the ability to bypass traditional expensive and inflexible silicon-based electronics to fabricate a variety of devices on flexible substrates using high-throughput printing approaches. This article presents a summary of work to date in the field of printed electronics and the materials chemistry involved. In particular, the focus is upon the use of metal- and metal oxide-containing inks in the preparation of contacts and interconnects. The review discusses the challenges associated with processing these types of inks and ways to successfully obtain the desired features.

Geometric control of inkjet printed features using a gelating polymer

When an inkjet printed feature is formed, the behaviour of the ink on the substrate is of great importance. In order to investigate the possibility of increased control over the as-printed feature on a substrate, a TiO2 ink was formulated that gels above a certain temperature. The TiO2 particles in the ink are colloidally stabilised by an adsorbed layer of poly(vinyl methyl ether)-block-poly(vinyloxy-4-butyric acid) diblock copolymer. The thermal gelation, at about 37 °C, is due to the limited solubility of the poly(vinyl methyl ether) buoyant block in the continuous medium of the ink. Drops and lines with improved morphological control and resolution were achieved using the thermal gelation effect. Lines printed using this approach did not display deviations at their starts and ends; and bulges in the line could be avoided. Finally, defect-free straight lines could be printed on very hydrophobic surfaces, which is impossible with regular inks due to the de-wetting nature of such substrates.

Inkjet printing of proteins

This article presents a review of the current status of the use of inkjet technology with protein-related applications. It includes a brief history of inkjet printing, discusses the advantages of employing the technology with proteins, using a number of selected applications as illustration, and concludes with a view of future research directions.

Room temperature preparation of conductive silver features using spin-coating and inkjet printing

Inkjet printing and spin-coating have been used to prepare patterns using a silver-containing metallo-organic decomposition ink. The patterned ink was reduced to silver by exposure to UV light and subsequent treatment with hydroquinone solution. This process, which took less than a minute, was performed at room temperature, which allowed low glass transition temperature polymeric substrates, such as PET, to be used. The conductivity of the silver patterns was found to be 10% that of bulk silver. The mechanical stability was also measured, with a linear increase in resistance seen for increasing strain, and no significant change in resistance seen after 12 000 cyclic deformations.

Terahertz metamaterials fabricated by inkjet printing

Metamaterial layers designed for gigahertz to terahertz (THz)-frequencies have been fabricated by inkjet printing. The spectral response of the structures consisting of periodically arranged metallic split-ring resonators is characterized by THz-time-domain spectroscopy and compared with identical structures produced by conventional photolithography and etching techniques. The broader linewidth of their resonances is shown to originate mainly from structural inhomogeneities. Our study shows that inkjet printing is a viable route for producing metamaterial structures, allowing for rapid processing and flexibility in the choice of substrates.

Reactive inkjet printing

Functional materials can be synthesised at the same time as their final device geometries are patterned.

A Low-Cost Electromagnetic Generator for Vibration Energy Harvesting

This paper reports on a low-cost high-performance generator, which is based on a hybrid approach that uses polymethyl methalcrylate and electrodeposited foil to convert mechanical vibration into electrical power based on Faradays law of magnetic induction. The generator is equipped with four wire-wound micro-coils that can be used separately or connected together depending on the voltage and electrical power requirement of the application. The fabricated generator which has a harvester effectiveness of 55.5% was able to supply a 500-Ω load with 422 μW of electrical power. Investigations have revealed that the utilization factor of the mechanical resonator can be used as an indicator of the lifetime of the generator with respect to fatigue analysis. The reported generator weighs only 12.7 g and is a good candidate for applications where lightweight generators are important.

The preferential deposition of silica micro-particles at the boundary of inkjet printed droplets

The deposition behaviour of uniformly sized silica particles in drying aqueous droplets has been investigated for a range of particle sizes, 0.33, 1, 3 and 5 μm, in order to gain an improved understanding of the coffee drop effect. The droplets were produced by inkjet printing, which allowed multiple droplets of similar volume to be studied. Our observations show that particle size and the contact angle formed by the solvent droplet with the substrate determine how close to the boundary a particle is deposited. After drying, it was found that if the contact angle was less than 90°, smaller particles were located closer to the original droplets periphery than larger particles in similar sized droplets. This deposition of particles can be explained by the wedge shape of the drying droplets edge, which physically limits the movement of particles towards the droplets periphery. In this paper we show that the size of a suspended particle influences the final dried morphology of a printed feature.

Inkjet printing of polyurethane colloidal suspensions

An aqueous 40 wt% dispersion of polyurethane has been successfully printed at room temperature using a piezoelectric inkjet printer. Simple layered structures, as well as dots, were made and subsequently analyzed using white-light interferometry. A single layer was found to have a structure height of 10 µm; a value that suggests that this polyurethane dispersion may be suitable for use in rapid prototyping, since tall structures can be rapidly produced using only a few printing passes. Finally, by the simple addition of a water-soluble dye, colour gradients were produced using this printing technique.