Organic light-emitting diode micro patterned with a silicon convex stamp

We report on 30-mu m-pitch organic light-emitting diode (OLED) stripes, whose cathode was patterned by lift-off method using a surface-unmodified silicon (Si) convex stamp. The OLED stripes consisted of ITO (120 nrn)-alpha-NPD (70 nm)-Alq(3) (70 nm)-Al (30 nm)-Au (approx. 1 nm) layers on a glass wafer (12 mm x 12 mm x 0.5 mm). A 0.7-mu m-wide convex stamp was formed on an Si wafer by plasma etching in CF4. and it was pressed on the unpatterned Al-Au surface of the OLED cathode layers. The unwanted metal was removed because the additive top Au layer adhered to the Si stamp, resulting in a fine cathode pattern. Because the surface of the stamp does not need to be modified or covered by any other layers when it is pressed, this stamp is more suitable for repeated use than ones in previously proposed lift-off methods. The stamp endured use for patterning six times. We calculated the shearing stresses in the metal layers using the finite element method and estimated the optimal thickness of the metal and organic layers. The experimental results fit well with the estimation: layer thicknesses of 20-30 nm for the metal layer and 100-150 nm for the organic layer were optimal. Some areas near the metal-removed areas were damaged, suggesting that the stamping lift-off method is limited to pattern scales larger than several microns. (c) 2006 Elsevier B.V. All rights reserved.