Pixel activation

To assure the best pixel formation and maximum luminosity, the Ink Jet Printing of PLED Displays requires a very specific surface condition. This surface preparation is performed with PVA TePla’s direct microwave plasma technology, producing precisely the desired surface energy (hydrophilic or hydrophobic). The direct microwave plasma technology is safe and scalable to next generation mother glass sizes.

Electroluminescent devices using organic light emitting diodes (OLED’s) are fast becoming the mainstream display technology. Their basic structure consists of one or more layers of luminescent material sandwiched between two electrodes. One electrode must be transparent (ITO) and is normally supported on a glass substrate. For polymer OLED devices (PLED’s), reservoirs are structured onto the ITO using organic photo-patternable material. The PLED material is then dispensed into the reservoirs from solution by inkjet printing. Surface properties of the ITO electrode are critical to both the electrical and optical performance of the PLED device. Surface cleanliness is essential for intimate contact of the hole transport layer (e.g. PEDOT) or light emitting polymer (LEP), with the ITO. To ensure complete pixel filling and uniform coverage the ITO surface must also be very wettable (hydrophilic). Additionally, increasing the ITO work-function prior to LEP deposition greatly improves the efficiency of charge transport into the organic layers.

Bank structures of the pixel reservoirs need to be surface conditioned to avoid overflow of the LEP to the neighboring pixels after inkjet dispensation. In this case the bank walls need to be non-wettable, or hydrophobic. The difficulty here is the task of selectively making the ITO hydrophilic, while at the same time making the bank structures hydrophobic. These manufacturing difficulties can easily be overcome by surface engineering using microwave (MW) plasma.

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