T. Uchida

Study of low power deposition of ITO for top emission OLED with facing target and RF sputtering systems

Deposition of ITO as top transparent electrode was studied using two deposition systems with and without direct contact to working plasma; namely with conventional RF-magnetron planar (RSS) and pulsed-DC facing target sputtering systems (FTS). Test devices were made on glass substrates and consisted of (from bottom up) ITO/4 Organic Layers/ITO. Depositions were performed at low deposition powers; 30 and 60 watts, to reduce damages by energetic sputtered particles to underlying organic layers. Test devices from both sputtering systems were found to function well. Leakage current density at -5 V reverse bias were relatively constant from 0.3 and 0.4 mA/cm2 at 30 W and 60 W in FTS, while the values were found to increase from 0.001 to 0.2 mA/cm2 at 30 W and 60 W in RSS.

Investigation of Low-Damage Sputter-Deposition of ITO Films on Organic Emission Layer

The damage to the organic layer of aluminum (III) bis(2-methy1-8-quninolinato)-4-phenylphenolate (BAlq) film was investigated on the basis of the change in photoluminescence (PL) intensity. To suppress the bombardment of the substrate with high-energy particles such as γ-electrons and negative oxygen ions, we used a facing-target sputtering (FTS) system. A marked reduction, however, of the PL intensity of the organic layer was still observed upon the deposition of an indium tin oxide (ITO) film on the organic film. To reduce this reduction, we proposed the insertion of a sector-shaped metal shield near the target electrode, and we showed its effectiveness in reducing the damage. This reduction of the damage is thought to be caused by the elimination of γ-electrons incident to the organic film surface escaping from the target area near the substrate side. We confirmed that high-energy electron bombardment leads to a significant reduction of PL intensity of the organic layer. This indicates that high-energy electrons incident to the organic film surface play a key role in the damage of the organic layer during the sputtering process.

Good Conformability of Indium-Tin Oxide Thin Films Prepared by Spray Chemical Vapor Deposition

Tin-doped In 2 O 3 (indium-tin oxide, ITO) transparent conducting films were deposited between 200 and 400°C on stripe-patterned Si substrates by spray chemical vapor deposition. ITO films with a homogeneous tin composition and crystallinity were successfully fabricated. The step coverage increased as the deposition temperature decreased and reached 90% at 200°C. Postdeposition annealing lowered the resistivity to 3.3 × 10 -4 Ω cm, which is approximately homogeneous because the measured resistance agreed well with the calculated one assuming the resistivity value of the film deposited on a flat surface and considering the film thickness of various portions. These films should contribute to optoelectric devices.

Fabrication of Organic Light-Emitting Devices with Indium–Tin-Oxide Anode Prepared by Spray Chemical Vapor Deposition

Organic light-emitting devices (OLEDs) were fabricated using an indium–tin-oxide (ITO) anode and a small molecular light-emitting material, tris(8-hydroxyquinolinato) aluminum (Alq3). The ITO anode (thickness, 120 nm) was prepared inexpensively by spray chemical vapor deposition using ethanol solution consisting of indium chloride and tin chloride onto a glass substrate at 270 °C, which is 80 °C lower than the temperature previously reported by the present authors. The work function and lowest resistivity of the as-deposited anode containing 6.6 at. % Sn were respectively 4.7 V and 3.7×10-4 Ωcm. The luminance and turn-on threshold voltage of the OLED were respectively 6500 cd/m2 and 3.5 V. These values agreed with those of an OLED with the same layer structure but without the commercial ITO anode deposited by physical vapor deposition. The effects of tin concentration in the present ITO anode on the work function and device performance were also investigated.