This article introduces the November 2003 issue of MRS Bulletin on Inkjet Printing of Functional Materials. The issue is devoted to the emerging non-graphic-arts uses of inkjet printing as a technique for depositing and patterning functional materials in the liquid phase onto a substrate. The articles provide an overview of a selected range of representative applications in the field of structural ceramics, polymer electronics, and protein chips, and address some of the key challenges that face the broad scientific and industrial community as it attempts to apply a mature and well-developed graphic arts printing technique to the deposition of functional materials.

Inkjet print heads have become the dominant printing element for home and office printers; they have been a key driver forthe digitization of wide-format graphic arts printing and other printing areas as diverse as addressing and carton coding. In the past few years, inkjet print heads have begun to have an impact in areas outside the graphics arts. In these applications, the inkjet print head may be considered a manufacturing tool; this implies that it will differ in design depending on the application. Also, standards forreliability, consistency, and dependability will differ from those in graphic arts areas. Even though non-graphic-arts applications differ widely in their details, there are general considerations in terms of the systems that are required. Each nontraditional application has specific goals for manufacturing, and a unique inkjet print head designed to meet these goals may be required. This article focuses on a specific piezo-based inkjet print head that has been engineered to meet the manufacturing requirements for flat-panel displays basedon light-emitting polymeric materials.

Inkjet printing is an attractive method for patterning and fabricating objects directly from design or image files without the need for masks, patterns, or dies. In order to achieve this with metals or ceramics, it is often necessary to print them as highly concentrated suspensions of powders in liquids. Such liquid suspensions must have physical properties appropriate to the inkjet delivery mechanism. These properties are presented using a nondimensional formalism to illustrate the requirements for both drop formation and spreading on impact. Further critical issues relevant to inkjet printing of particulate suspensions are discussed and illustrated with experiments on a model alumina-containing colloidal suspension.

Based on the concept of a microliquid process, we have developed an organic electroluminescent display using conductive polymers, including light-emitting polymers. The technology of inkjet printing has progressed enough to be used for the microliquid process. First, we describe the process used to form a patterned thin film. This involves inkjet-related technologies, the self-patterning behavior of a microliquid on the substrate, and the drying process that defines the thickness profile and film properties. Some microliquid behaviors and related phenomena, along with properties of the resulting film, were identified as distinct from those coming from a macroscopic liquid, as a result of size effects. By fully utilizing these unique properties of microliquids, we have succeeded in fabricating color-pixel arrays by direct patterning of polymer solutions. As a result, an organic electroluminescent display with a vivid full-color image has been developed.

We present a process for manufacturing printable thin-film transistors (TFTs) that is based on solution processing and direct inkjet printing of polymer semiconductors, dielectrics, and conductors, as well as inorganic nanoparticle conductors. We show that the high device yield, uniformity, and resolution required for thin-film electronic applications can be achieved by using a substrate that contains a surface energy pattern to control the flow and spreading of inkjet droplets. This technique overcomes many of the limitations of current inkjet printing technology related to its limited droplet placement accuracy. We demonstrate the potential of this printing-based TFT manufacturing process with the fabrication of 50 dpi active-matrix, polymer dispersed liquid-crystal and Gyricon Smartpaper electronic paper displays.

Protein biochips have recently gained a lot of attention as bioanalytical tools in the life sciences. The creation of such biochips has been made possible by the integration of scientific approaches and methodologies in microfabrication, organic interface chemistry, protein engineering, detection physics, and—last but not least—advances in microarrays and microfluidic dispensing technologies. This article reviews some of the current drop-on-demand technologies developed for printing biomolecular arrays, with an emphasis on proteins and the technical challenges associated with them.