OLED substrate conditioning by low power density RF plasmas

Capacitively coupled radio-frequency discharges in oxygen and tetrafluoromethane were used for surface conditioning of indium tin oxide (anode) and ZPN1168-30 (bank material) thin films, respectively, prior to the inkjet printing during organic display device fabrication. The actual power density delivered to the plasmas was calculated by cancelling the stray impedance of the cell and taking into account the transmission function of the system. This calculation allowed the systematic study of the influence of the main process parameters to the wetting properties of the films. Hydrophilic indium tin oxide (min contact angle 12 deg) and hydrophobic ZPN1168-30 resist (max contact angle 112 deg) were obtained, while the power density was maintained lower than 15 mW/cm2 in both discharges. Positive-ion flux measurements were carried out, using an RF-biased single-sided planar probe, and values up to 1014 cm-2 s-1 were found at this low power density. Optical emission spectroscopy showed that oxygen plasma was rich in O2+ ions and tetrafluoromethane plasma in CF2+. Thus, the ion contribution to the treatment mechanism was discussed and the complementary role of other plasma particles, like excited neutrals and photons, in the treatment process remained a question in debate.