2007 NSTI Nanotechnology Conference and Trade Show - Nanotech 2007 - 10th Annual

Characterization of Materials and Multilayer Structures of OLED by Spectroscopic Ellipsometry.

C. Defranoux, J.P. Piel, A. Bondaz and L. Kitzinger
SOPRA-SA, FR

Keywords:
OLED, Polymer, refractive indices, Ellipsometry

Abstract:
Spectroscopic Ellipsometry (S.E) is a well adapted optical technique widely used for the characterisation of all types of thin films for thickness and optical indices on glass or plastic substrates. It is now applied to the characterization of materials and multi-layer structures of organic light-emitting diodes (OLEDs); where all parameters of each layer are given in one single measurement. The main parameters of interest are the thickness and dopant values that are relatively small (lower than 50 nm and a few %). Dopant concentrations can be measured, monitored and controlled in these films. S.E allows this determination on the whole surface of the coated sample that Quartz balance can not afford. The determinations of the refractive indices by S.E. offer the possibility to optimize the micro cavities effect of the structure. S.E. and appropriate software allows to simulate and optimize for each type of pixel the thickness of any layers to obtain the best efficiency. As the OLED materials are sensitive to moisture and pollution, it is required to measure the materials optical properties and thickness values through an encapsulated layer. We will demonstrate how we can measure single layer and multi-layers through encapsulated samples from the front side or from the back side of the substrate. As demonstrated by our results, “Backside” measurements can also be applied for the determination of the ITO resistance, without contact, by using Near Infra Red Ellipsometry.

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