Inkjet printing is one of the key technologies behind the direct writing revolution, spanning an ever-increasing number of applications. During recent years, print-head technology has turned academic research into a viable manufacturing solution. Modern inkjet technology allows accurate printing to form functional components through additive deposition of a variety of materials, including ceramics, conductive polymers and now, metal oxides.
Transparent Conducting Oxides

Patterning Technologies Ltd (PTL), a company at the forefront of several direct writing technologies, is using its know-how to enable the direct patterning of transparent conducting oxide (TCO) films and circuits. These metal oxides are already used for making a broad range of advanced products, including flat panel displays, energy conserving architectural windows, and de-fogging windows for cars and aircraft. Patterned transparent conducting oxides are increasingly being used in displays for making the interconnections between the electronics and the pixel pad.
Transparent Conducting Oxide in Thin Film Transistor (TFT) Flat Panel Displays

Transparent conducting oxide interconnections can be used with any thin film transistor (TFT), including the type being developed by Plastic Logic for plastic electronics. In liquid crystal displays, a transistor switches the liquid crystals off and on by the creation of an electric field around the transparent conducting oxide pixel pad. Display applications such as this typically require a transparent conducting oxide sheet resistance of 125 ohms/sq.
Advantages of Using Inkjet Technology over More Conventional Techniques

In current processing methods, indium oxide doped with tin oxide (ITO) is deposited using sputter coating technology, and so covers the whole area of the substrate. While this is suitable for some applications, others require the patterning of pads and electrical interconnects. Creating a patterned layer is a time-consuming, costly, multi-stage process, involving lithographic masking and etching away of unwanted material. In contrast, the new approach being developed by PTL offers cheaper patterned transparent conducting oxide layers in less time. By using inkjet technology, not only is the processing cheaper, but the materials themselves are less expensive, requiring a much lower concentration of the doping element.
Indium Tin Oxide Circuit Deposition and Properties

Until now, sputtering has been the dominant technology for producing transparent conducting oxide films and circuits, although ITO has been much used to produce circuits, partly because it is etched. The mechanism for conduction in these films requires a high number of available charge carriers, in the form of free electrons and oxygen lattice vacancies. However, this high density of charge carriers also results in an increase in light absorption, which reduces optical transmission. Although the resistance of a sheet of material can be as low as 10 ohms/sq, visible transmission would only be 80% at best. For transmission rates greater than 90%, the resistance would typically be 100 ohms/sq or greater. These and other properties of ITO films are dependent on the deposition parameters and starting composition of the sputter target used.