Fabrication of OLED display by an ultrashort laser: selective patterning of thin metal electrode

Organic light emitting diode (OLED) is now in practical use and also a subject of active research and development. In industrial production of OLED displays, one of the key technologies is patterning of electrodes, especially a metal cathode, which is usually made on a thin layer of organic electro-luminescence (OEL) compounds. Difficulties in machining of the OLED come from the fact that the OLED has multi-layered structures consisted from very thin layers of different materials, one of which is a highly heat- and chemical-sensitive organic material. The typical OLED sample has indium tin oxide (ITO) electrode of about 150 nm thick at the bottom. The organic electro-luminescence material of less than 200 nm is deposited on it and the top is aluminum electrode of 100 to 150 nm thickness. We have constructed a fabrication system of the OLED by using an ultrashort fiber laser in the patterning of aluminum electrode and fabricated a display panel successfully. The system has several advantages comparing to other methods currently used. To investigate the process in detail, we have constructed two ultra-fast photography systems, with either subpicoseconds or nanoseconds time resolution, and carried out the time-resolved observation of the process. It is found that the underlying layer affects much to the machinability of the top metal layer. The ITO layer seems to enhance the machining efficiencies of the aluminum electrode: the ablated spot size becomes larger for that on ITO, even though the laser pulse energy is kept constant.