Recent progress on the vacuum deposition of OLEDs with feature sizes ≤ 20um using a contact shadow mask patterned in-situ by laser ablation

We report progress on the development of a new technique that has the potential to enable the vacuum deposition of OLEDs with feature sizes ≤ 20um, and hence high resolution OLED displays. An OLED device with 16um by 130um sub-pixel size has been successfully demonstrated utilizing the novel idea of the in-situ shadow mask patterning method showing the capability of this method to achieve high resolution OLED patterning. In the approach proposed here, two sheets of polyimide film are mounted on an electrode, and the top sheet of the two stacked sheets is patterned in-situ by laser ablation to create apertures. The protective under sheet is then removed, and OLED materials are deposited through the patterned slits. Since mask alignment is not required in this approach, the technique circumvents the resolution limitations imposed by the difficulty of aligning shadow masks in the conventional techniques, and allows achieving high resolution pixel patterning. Furthermore, shadow effects, another factor that limits resolution in conventional techniques, can be reduced due to the thin plastic shadow mask (~7.5um) that is directly held on the substrate by electrostatic force. In principle, by applying this technique to the standard three color side-by-side sub-pixel matrix scheme, a resolution and aperture ratio of 338ppi and 60%, respectively, can be expected, which is estimated based on the fact that the width of the deposited material is 25um for the 16um wide electrode. In addition, the OLED device fabricated using this technique shows uniform emission and reasonable I-V characteristics similar to those of the OLED fabricated through the standard technique, which indicates that this method does not compromise device quality.