Direct Al cathode layer sputtering on LiF/Alq ₃ using facing target sputtering with a mixture of Ar and Kr

Using facing target sputtering (FTS) with a mixture of Ar and Kr, direct Al cathode sputtering on LiF Alq3 layers was accomplished without the need for a protective layer against plasma damage. Organic light emitting diodes (OLEDs) with a directly sputtered Al cathode in a mixture of Ar and Kr showed a much lower leakage current density (∼1× 10-5 mA cm2 at -6 V) than those (∼1× 10-1 mA cm2 at -6 V) of OLEDs with an Al cathode prepared by FTS or dc sputtering in a pure Ar ambient. This indicates that the bombardment of energetic particles is effectively restricted by mixing a heavy noble gas. Based on the current-voltage curve for the OLED, a possible mechanism is proposed to explain the effect of a heavy noble gas mixture on electrical properties of OLEDs for direct Al cathode sputtering by FTS.