Flexible Display Device with Organic Composite Film

Oktay Yarimaga

In this study we present a flexible organic polymer display device which consists of a thin substrate of Polyether Sulfone, multilayer serpentine type microheater array that is fabricated on the substrate, and a UV-sensitive polydiacetylene (PDA)-polyvinyl alcohol (PVA) composite film. The colors of the micro-pixels, blue, red and yellow, and their transition tones were successfully tuned with the embedded microheaters under the PDA-PVA layer. PCDA-EDEA(10,12-pentacosadiyonicacid-2-2´(ethylenedioxy)bis(ethylamine)) is an amine-ended monomer of the PDA liposome. Mixing the PDA with PVA and curing the mixed solution result in a UV-sensitive white-opaque film. This film can be polymerized by 254nm UV-light irradiation, and due to the polymerization, the color of the film shifts to blue. Following the polymerization, the blue PDA-PVA patterns dramatically change to red with thermal stress generated by external stimuli. We have succeeded in developing thermally actuated organic display device on Pyrex Glass substrate in our previous work. (Figure 1) That device included Ti-Au microheaters, a SU-8 layer and an organic polymer composite film. The SU-8 layer with a thickness of 100μm and with designed pattern sizes in the range of 200μm to 700μm was used both as a device-embedded photomask while polymerizing the film with 254nm UV-light from the back side of the substrate and as a thermal insulator between adjacent pixels during the thermal actuation.In the current work, we extended our investigations to flexible design which employs a flexible, thermally and chemically stable substrate, Polyether Sulfone (PES). Ti-Au-Ti-Au(10-50-10-200nm) multilayer serpentine-type microheaters were patterned on a PES substrate with a thickness of 200μm and preferentially, the top Au-Ti layer of the microheater-only regions were wet-etched in order to focus the generated heat on the microheaters rather than on the connection wires. Using this method, the ratio of the driving heat of the microheater to that of connection wire becomes 5 to 1.