Ivo Godfried Jozef Camps

Ink-jet printing of polymer light-emitting devices

Spin coating is a suitable technique for the fabrication of monochrome light-emitting polymer devices. For color displays, however, it is not the optimal solution when different polymers are applied. In principle, there are several technologies available for patterning light-emitting polymers. In this paper we discuss the advantages of drop-on-demand ink-jet printing over other printing methods. Special attention is given to some fundamental aspects of the printing process, such as drop formation and pixel filling. Examples of both monochrome and full color ink-jet printed passive matrix displays will be discussed.

Passive and active matrix addressed polymer light-emitting diode displays

Polymer LEDs provide a new alternative to LCDs for many display applications, and are particularly attractive because of their high brightness, near-perfect viewing angle, and very fast response time. In this paper, the basic technology used to form the LED structures, and the performance of these devices is presented. Then, the fabrication and driving of passive addressed matrix displays formed using this technology is discussed. Finally, the necessity for active matrix addressing for larger size and higher resolution displays is demonstrated, and it is shown that this is best achieved using low temperature poly-Si technology. The state-of-the-art poly-Si technology used for active matrix addressed LED displays is described, with particular reference to transistor variation, and the resulting non-uniformities in images on displays. A variety of different addressing techniques, and pixel circuits can be used to drive the LEDs in the active matrix, and the performances of these schemes are compared. These include the basic current source circuit; the modified current source circuit; transistor current mirror circuits; and circuits with optical feedback and correction for uniformity variation. Consideration is given both to analogue and to digital drive methods.